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Late glacial ice margin fluctuations (~12.5-10.0 ¹⁴C KYR BP) in the Fraser lowland and adjacent Nooksack… Kovanen, Doris J. 2001

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L A T E GLACIAL ICE MARGIN FLUCTUATIONS (-12.5-10.0 1 4 C KYR BP) IN THE FRASER LOWLAND AND ADJACENT NOOKSACK V A L L E Y , SOUTHWESTERN BRITISH COLUMBIA, CANADA AND NORTHWESTERN WASHINGTON, U.S.A. By Doris J. Kovanen B.A. (Geology) University of North Carolina, 1989 M.S. (Geology) Western Washington University, 1996 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF EARTH AND OCEAN SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 2001 © Doris J. Kovanen, 2001 In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Earth and Ocean Sciences The University of British Columbia 129-2219 Main Mall Vancouver, Canada V6T 1Z4 Date: Abstract The last glacial/non-glacial transition has important implications for understanding how abrupt climate changes were transmitted throughout the Northern Hemisphere. The Younger Dryas cold period, for example, is believed to be linked to a reorganization of the thermohaline circulation in the North Atlantic Ocean. The late Wisconsin deglaciation of the Fraser Lowland (3500 km2) in southwestern British Columbia and northwestern Washington was reconstructed from multiple lines of evidence. Traditional mapping and field techniques were integrated with computer-generated digital images to visualize morphologic features. New terminal positions are recognized associated with fluctuations of a piedmont ice lobe that occupied the central Fraser Lowland during the late stages of the Fraser Glaciation. The start of deglaciation is recorded by glaciomarine and glaciofluvial sediments of the Fort Langley Formation (Everson Interstade). Marine shells from stony mud range in age from c. 12,500 to 11,400 1 4 C yr BP. Multiple ice readvances of the Sumas Stade, after c. 11,600 1 4 C yr BP deposited moraines, outwash, and ice contact sediments in the Fraser Lowland and adjacent valleys. Between c. 10,900 and 10,250 1 4 C yr BP, ice retreated an unknown distance and readvanced again, constructing moraines near the towns of Mission and Sumas. These ice fluctuations are bracketed by more than 70 radiocarbon dates, but the analytical uncertainties of c. ± 45-200 1 4 C yr BP indicate that more accurate dating of these rapid fluctuations will be difficult to achieve. However, constraining information provided at key localities by morphology, stratigraphy, and radiocarbon dating gives confidence in the broad evolving pattern proposed. A review of present-day glacier fluctuations on Mt. Baker (3285 m), 50 km southeast of the Fraser Lowland, indicates a linkage between alpine glaciers and Pacific Decadal Oscillation of sea surface temperatures. This link highlights the sensitivity and response of the glaciers to changes in the oceanic-atmospheric system. The emerging picture is that the glacier fluctuations in the Fraser Lowland and adjacent valleys may have ii responded to regional late-glacial climate oscillations similar to those of the North Atlantic and northeast Pacific, including the Allerad, Younger Dryas, Holocene transition. iii Table of Contents Abstract ii List of Tables viii List of Figures ix Preface x u * Acknowledgments xiii 1 Introduction 1 1.1 Study area 4 1.2 Previous work and stratigraphy 5 1.2.1 Changes in relative sea level during deglaciation 10 1.3 Research problem 13 1.4 Thesis overview 14 2 Methods 16 2.1 The use of multiple sources of evidence 16 2.2 Stratigraphy -. 16 2.3 Dating 17 2.3.1 Relative dating 17 2.3.2 Numerical dating 18 2.3.2.1 Radiocarbon dating 18 2.3.2.2 Tephrochronology 19 2.3.2.3 Sediment coring 19 2.4 Morphologic expression - hillshade generation and visualization 20 2.4.1 U.S. digital data 22 2.4.2 Canadian digital data 23 2.5 Statistics 24 3 Paleodeviations of radiocarbon marine reservoir values for the NE Pacific 25 3.1 Introduction 25 iv 3.2 Sample selection and radiocarbon measurements 27 3.2.1 Sample locations 27 3.2.2 Total marine reservoir value 29 3.2.3 Comparison with other reservoir values 31 3.2.4 Comparison of non-paired shell and wood dates 31 3.3 Discussion 33 3.4 Summary 35 4 Timing and extent of Altered and Younger Dryas age 38 (c. 12.5-10.0 " C kvr BP) oscillations of the Cordilleran Ice Sheet in the Fraser Lowland, Western North America 4.1 Introduction 38 4.2 Deglaciation in the Fraser Lowland 38 4.2.1 Previous work 41 4.3 Morphology and chronology of the Sumas phases 42 4.3.1 Oldest Sumas phase, SI 42 4.3.1.1 Age of SI 44 4.3.2 Second Sumas Phase, SII 45 4.3.2.1 Age of SII 46 4.3.3 Third Sumas Phase, SIII 50 4.3.3.1 Age of SIII 51 4.3.4 Four Sumas Phase, SIV 51 4.3.4.1 Age of SIV 53 4.4 Summary 55 5 Morphologic and stratigraphic evidence for Altered and Younger Dryas age 59 glacier fluctuations of the southwestern margin of the Cordilleran Ice Sheet, British Columbia, Canada and Northwestern Washington, U.S.A 5.1 Introduction 59 5.1.1 Terminology and stratigraphy 62 5.2 Moraines and drift deposits of the Sumas Stade 64 5.2.1 SI ice margin 67 5.2.2 SII ice margin 67 5.2.2.1 Stratigraphy ofthe Aldergrove moraine deposits 68 v 5.2.3 SHI ice margin 81 5.2.4 SIV ice margin 86 5.3 Discussion 87 6 Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack 97 drainage North Cascades, Washington 6.1 Introduction 97 6.1.1 Previous work 97 6.1.2 Regional glacial history 98 6.1.3 Climatic influences 103 6.1.4 Glacial setting 104 6.2 Evidence for late Pleistocene alpine glaciers in the Nooksack Valley 105 6.2.1 Glacial deposits in the Nooksack Middle Fork 106 6.2.1.1 Age of glacial deposits in the Nooksack Middle Fork 108 6.2.1.2 Evidence for readvance of the Middle Fork glacier 114 6.2.2 Glacial deposits in the Nooksack North Fork 116 6.2.2.1 Age of glacial deposits in the Nooksack North Fork 118 6.2.2.2 Evidence for readvance of the North Fork glacier 119 6.2.3 Glacial deposits in the Nooksack South Fork 119 6.2.3.1 Age of the glacial deposits in the Nooksack South Fork 120 6.3 Discussion 124 7 Decadal variability in climate and glacier fluctuations on Mt. Baker 128 7.1 Introduction 128 7.2 Approach, climate data, and seasonal dependence 130 7.3 Climate variations since 1891 131 7.3.1 Temperature 133 7.3.2 Precipitation 135 7.4 Glacier fluctuations on Mt. Baker 138 7.5 Climate indices 139 7.6 Discussion 141 8 Conclusions 144 8.1 Summary 144 vi 8.1.1 Deglaciation in the Fraser Lowland 147 8.1.2 Early Holocene 147 8.2 Possible correlations 150 8.2.1 Local correlations 150 8.2.2 Regional correlations 152 8.2.3 Extended correlations 153 8.3 Discussion 153 8.3.1 Future considerations 155 References 158 Appendix A - Radiocarbon dates 191 Appendix B - Radiocarbon sample descriptions 201 Appendix C - Oxygen and carbon isotopes 218 Appendix D - History of the Stade and Interstade terminology 239 of the Fraser Glaciation Appendix E - Section and coring log descriptions 249 Appendix F - Holocene eruptive history of Mount Baker, W A 263 Appendix G - Raw climate data 288 vii List of Tables Number Page 1-1 Contributions to the late glacial history in the Fraser Lowland 8 3-1 Radiocarbon measurements on paired shell and wood samples 30 3-2 Other paired dates 31 3-3 Summary reservoir values from the northeast Pacific Ocean 33 3-4 Selected Radiocarbon Ages from the Fraser Lowland 36 5- 1 Radiocarbon Dates from the Fraser Lowland 91 6- 1 Radiocarbon dates from the Nooksack Drainage 115 7- 1 Data sets and climate indexes used in this study 131 7-2 Comparison of monthly, annual, summer and winter temperatures 132 at weather stations surrounding Mt. Baker, Olga and Anacortes vii i List of Figures Number Page 1-1 GISP2 ice core climate transitions and European pollen zone boundaries 3 1-2 Formation of end moraines 3 1-3 Study area 4 1-4 (a) The distribution of surficial deposits and (b) late Wisconsin stratigraphy 7 1-5 Interpretation of deglaciation during the Sumas Stade by previous workers 9 1- 6 Relative sea level curves and sea level reconstructions 12 2- 1 Figure showing how effective shaded relief can be 22 3- 1 Location of study area 27 3- 2 Reservoir-corrected shell ages compared to wood dates 32 4- 1 Location of the Fraser Lowland 39 4-2 GISP2 ice core climate transitions, mean SST curve, and chronology 40 of the Fraser Lowland 4-3 Shaded digital topographic model of locations and extent of the Sumas phases. 43 4-4 Stacked histogram of wood and shell dates from glaciomarine sediments 45 4-5 (a) Map of SII moraine (b) Tenmile Creek meltwater channel 49 4-6 Hillshade of SIII moraine (a) and SHI meltwater channel (b) 52 4-7 Geologic cross-sections 53 4-8 Shaded digital topographic model of SIV moraine and outwash plain at Sumas. 55 4- 9 Comparison of Sumas phases and selected alpine glacial records 58 5- 1 Location map of the Fraser Lowland 60 5-2 Simplified surficial geologic map and stratigraphic framework 61 5-3 (a) Comparison of interpretations in the Bradner pit and (b) the Fraser Lowland 63 5-4 (a) Shaded digital topographic model of the Sumas phases 65 (b) Distribution of radiocarbon dates 66 5-5 (a) Map showing relation of Campbell River delta and meltwater channels 69 (b) Topographic map of the SII moraine 69 ix (c) Simplified stratigraphic sections from gravel pits in the SII moraine 70 5-6 Photographs of the Bradner pit. (a & b) Units 1,3, and 5 74 (c) Peat (unit 4) and stony mud (unit 5), (d) Close-up of massive stony mud 75 (e) Two subunits of unit 5, (f) Peat and laminated silt/clay 76 5-7 (a) Stony mud in the Steelhead pit, (b) Stony mud in the Little Rock pit 77 (c) Stony mud in Little Rock pit traced continuously to upland 77 5-8 Plot of 50 marine fossil elevations in the stony mud 78 5-9 (a & b) Schematic sections through the SII moraine 80 5-10 Plot of the INTCAL98 calibration curve between 9 500-13 000 1 4 C yr BP 81 5-11 (a) 3D shaded digital topographic model of SIII terminal area 84 (b) Moraine in Miracle Valley 84 5-12 (a) Ti l l exposed in road cut of SIII moraine, (b) SIII moraine segment 86 5-13 Plot of selected radiocarbon dates and sequence of glacial events 88 5- 14 Greenland ice-core chronologies, mean SST curve, and Marion Lake curve 89 6- 1 Shaded digital topographic model of the study area 100 6-2 Lithostratigraphic and geologic climate units in the Nooksack drainage 100 6-3 Reconstruction of the Cordilleran Ice Sheet at the Vashon maximum 101 6-4 Reconstruction of the Nooksack Valley glacier system 102 6-5 Bedrock geologic map of the Nooksack drainage 109 6-6 Shaded digital topographic model of Mosquito Lake area 109 6-7 Mosquito Lake ketfle-kame complex and lateral moraine 110 6-8 Comparison of lithologies I l l 6-9 Source area of the Middle Fork glacier 112 6-10 Cross section and radiocarbon dates 112 6-11 Stratigraphic section 113 6-12 Photo of the Kendall and Maple Falls moraines 121 6-13 Geologic map of the glacial deposits in the Kendall area 122 6-14 Ice-contact face at the head of the Columbia Valley outwash 123 6- 15 Geologic cross-section 123 7- 1 (a) Location and place names 129 x 7-2 Geographic distribution of weather stations (a) and glaciers on Mt. Baker (b) ..129 7-3 Temperature variations around Mt. Baker, Olga, and Anacortes 132 7-4 (a) Temperature variations around Mt. Baker and Anacortes 134 (b) Temperature variations at Olga compared to a composite 134 7-5 Yearly temporal trends means of temperatures at Olga 135 7-6 Annual precipitation variations at Olga and stations surrounding Mt. Baker 136 7-7 Yearly temporal trends means of precipitation at Olga 137 7-8 Annual winter precipitation and summer temperature at Olga 137 7-9 Terminus positions of glaciers on Mt. Baker for 1940-1990 period 139 7- 10 Stacked time-series of climatic records for the last 100 years 143 8- 1 GISP2 ice core with Sumas phase 148 8-2 Plot of calibrated radiocarbon dates 149 8-3 Correlation between glacial records 151 xi Preface In accordance with library specification, information on material published (or in press) by the author is provided below. Kovanen, D.J., and Easterbrook, D.J. (2001). Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack drainage, North Cascades, Washington: Geological Society of America Bulletin 113,274-288. Kovanen, D.J., Easterbrook, D.J., and Thomas, P.T. (2001). Holocene eruptive history of Mount Baker, Washington: Canadian Journal of Earth Science 38, 1355-1366. Kovanen, D.J. (in press). Morphologic and stratigraphic evidence for Altered and Younger Dryas age glacier fluctuations of the southwestern margin of the Cordilleran Ice Sheet, British Columbia, Canada and Northwestern Washington, U.S.A.: Boreas. Kovanen, D.J., and Easterbrook, D.J. (in press). Extent and timing of Altered and Younger Dryas age (c. 12,500-10,000 1 4 C yr BP) oscillations of the Cordilleran Ice Sheet in the Fraser Lowland, Western North America: Quaternary Research. Kovanen, D.J., and Easterbrook, D.J. (in press). Paleodeviations of radiocarbon marine reservoir values for the Northeast Pacific: Geological Society of America Geology. Evidence gathered and manuscript preparation was by the first author. The co-authors contributed a review of draft manuscripts, guidance and funding for radiocarbon dates. Because these chapters have been prepared as individual papers, some redundancy in introductory material was unavoidable. xii Acknowledgements The supervisory committee included Dr. Garry Clarke (research supervisor), Dr. Olav Slaymaker, and Dr. Tom Pedersen. I appreciate freedom in research activities granted by Dr. Clarke. I am deeply indebted to Dr. Slaymaker for his expertise, encouragement, and the contributions made during numerous discussions, critical input of written work, and several field visits. His guidance, patience, and support are greatly appreciated. The supervisory committee provided comments on a draft of the thesis and support during the "12-hour" for which I am thankful. I am very grateful to many people for their help and support without which this research would not have taken place; to gravel operators and owners for allowing access to the pits ~ including Garry Briggs of Fraser Valley Aggregates, West Coast Aggregates, LaFarge Central Aggregates, Steelhead Aggregates, Little Rock Quarries, and the McLean family of Valley Gravel Sales, Ltd.; to Brian Conrad, Aimee d'Andrea and Tracy Minick for assistance in obtaining bog cores; to Sheri Fritz for analysis of samples for diatoms; to the Department of Geology at Western Washington University for use of the wet lab during the summer of 2000; to the Ministry of Environment, Lands and Parks, Geographic Data B.C. for the loan of proprietary digital data; to Mike Price of Environmental Systems Research Institute, Inc. (ESRI) and Gene Heuroff for assistance with digital data formatting; to Stephanie Kienast and Jennifer McKay for sharing the latest sea surface temperature estimates from the northeast Pacific Ocean; and to Stacy Weber for companionship on several pit visits. The Faculty of Graduate Studies and the Faculty of Science provided a partial tuition scholarship in the form of a bursary award which was appreciated. Coring equipment and the analytical costs for all radiocarbon dates presented in this thesis were provided by a National Science Foundation grant to Dr. Don Easterbrook of Western Washington University. His innate enthusiasm, patience, and kindness were an inspiration. In formulating the research ideas, I benefited from discussions with Don Easterbrook and Olav Slaymaker. The sharing of their knowledge of the area provided impetus for the recognition of many glacial features. For more specific input regarding the determination of a marine reservoir value, I thank Dr. Paula Reimer. And to my immediate family; Kay (mom) & Archie (dad), David, Debbie & family, Danny & Megan, and Sadie, I can't thank them enough for their support and love. xiii Chapter 1 Introduction The stratigraphic record covering the transition from the last glacial to interglacial transition (c. 18-9 1 4 C kyr BP) is one of the most intensively studied because it provides the best-resolved archive of rapid climate change. Paleoenvironmental reconstructions for this period are dated with relatively high degree of accuracy and precision (for example, radiocarbon, varve sequences, ice-layer chronologies) and indicate the rapidity of high-amplitude climate modes and the short duration (millennial to century scale changes) of the events. In the North Atlantic region, northwest Europe, and eastern North America, these climate oscillations are known as the Oldest Dryas, B0 l l ing , Older Dryas, Allerod, Younger Dryas epochs (Fig. 1-1). The oscillations are thought to result from interactions between marine, terrestrial, cryospheric, and atmospheric processes as the earth adjusted from cold (glacial) to warm (interglacial) climate modes and have been linked to freshwater fluxes to the North Atlantic, which disrupt thermohaline circulation. Interest has increased in local environmental changes and what may be considered comparable events in the Greenland ice cores (GISP2 and GRIP) in order to test current ideas about the contemporaniety and causes of rapid environmental change. The question of their existence in the glacial record of the Pacific Northwest has until now not been resolved. However, with increased understanding of the climate system, feedbacks, and growing evidence of past abrupt temperature changes from deep sea cores (Kienast and McKay, 2001; Patterson et al, 1995), in the northeast Pacific, and in pollen records (Mathewes, 1993; Mathewes et al., 1993), a physical mechanism (i.e., temperature change) is now available to support the field observations of multiple glacial fluctuations caused by interruptions of the deglacial warming trend by cold reversals during the late Wisconsin. This thesis explores the nature of the last glacial to non-glacial transition (c. 12.5-10.0 1 4 C kyr BP) in the Fraser Lowland and adjacent alpine areas of the Pacific Northwest. 1 The abruptness and amplitude of the Younger Dryas cooling event (11.0-10.0 C kyr BP) is well documented in the North Atlantic region, but its existence in other parts of the world has been a point of controversy. In the Fraser Lowland, sediments that span the Allerod, Younger Dryas, Holocene transitions are now well dated. The timing of ice-front fluctuations illustrates cooling associated with the Younger Dryas and possibly the intra-Allerod cold period. The emerging picture is that the rapid oscillations were global (Kudrass et al, 1991; Rutter et al, 2000). These climate oscillations may have also extended into the Holocene. Multiple moraines on the flanks of Mt. Baker and in nearby cirques record glacier oscillations somewhat similar in nature, but of considerably smaller magnitude and scale, than those of the late Wisconsin. Present-day glaciers are sensitive to oceanic-atmospheric instabilities in the northeast Pacific (e.g., Hodge et al, 1998; McCabe et al, 2000). Presumably, the late Wisconsin glaciers were also sensitive to changes in the proximal Pacific Ocean. Glaciers and moraines are considered sensitive indicators of climatic variations because glaciers change shape and size in response to a combination of factors (Fig. 1-2). However, individual glaciers may respond differently due to variations in basin configuration (size, elevation, mass balance feedback and flow response to mass balance change); basal hydrology; nature of the climatic forcing; mechanics of glacier flow; and crustal movement and sea-level change. Moraines form during ice-front stillstands or advances and ice-front movements (ice-flux), may be more rapid than the resolution of radiocarbon dating. Therefore, recognition and comparison of local patterns of ice-front behavior are necessary in order to determine the regional climatic signal. The timing and extent of climate oscillations as recorded in glacial moraines is explored in this thesis to assist in investigation of their propagation throughout the Northern Hemisphere. 2 GSP2 8,000 9,000 10,000 11,000 ! 1£000 • 13,000 14,000 15,000 16,000 8™0(%<a Figure 1-1. 8 1 80 variations within GISP2 ice core indicating climate transitions (curve is a five-point (~100-yr) moving average) with European pollen zone boundaries. The termination of the Younger Dryas is at 11,640 ± 200 cal yr BP (Alley et al, 1993; Meese et al, 1994). Double vertical lines denote suggested periods of rapid sea level rise (Fairbanks et al., 1992). IACP is the intra-Allerad cold period. External factors Depositional environment, processes and mode of sediment supply Ice-front behavior Basin geometry Chrono-stratigraphic framework Regional history of ice-front movements Sedimentary facies analysis Morphology Lithostratigraphy Radiocarbon dating Construction of ice-front movement " I -rj z m o Figure 1-2. Formation of end moraines is controlled by a combination of factors and reflects ice-front behavior (modified from Lonne, 2001). 3 1.1 Study area The Fraser Lowland, (a large fraction of the Whatcom Basin) (Fig. 1-3) of southwestern British Columbia (B.C.) and northwest Washington is bounded on the north by the Coast Mountains, on the southeast by the Cascade Mountains, and on the west by the Strait of Georgia, covermg an area of c. 3500 km (Armstrong, 1960). Drainage of the area is accomplished by the Fraser and Nooksack Rivers. The Fraser River flows in a valley filled with up to several hundred meters of sediment during the late Pleistocene and Holocene. Locally, north and south of the Fraser River, the Fraser Lowland consists mainly of gently rolling terrain, with elevations lower than 175 m. 1.2 Previous work and stratigraphy During the Fraser Glaciation, between 17.0 and 14.5 1 4 C kyr BP (maximum), alpine glaciers expanded from the Coast Mountains, coalesced, and advanced c. 250 km into the Puget Lowland. These glaciers formed part of the Cordilleran Ice Sheet, which extended southward to the Strait of Juan de Fuca where it split into the Puget and the Juan de Fuca lobes. Deglaciation (c. 12.5-10.0 1 4 C kyr BP) of the area was rapid. Thinning and retreat of the ice from the Strait of Juan de Fuca allowed marine waters to transgress into the Puget Lowland, initiating glaciomarine conditions. This led to rapid retreat of ice during the late stages of deglaciation. The surface distribution and stratigraphic succession of late Wisconsin deposits in SW British Columbia are shown in Figure 1-4 (Armstrong, 1957, 1956, 1960, 1981, 1984). Lithostratigraphic (mappable) units were designated by Armstrong and Brown (1954), Armstrong (1981,1984), Armstrong et al. (1965), Easterbrook (1963, 1976a, b), Clague (1976), Hicock and Armstrong (1981, 1985) (also see discussion of nomenclature in Appendix D) who inferred some of the time limits for the sequence of events along the margins of the remnants of the Cordilleran Ice Sheet. The stratigraphic sequence of events during the transition from the glacial/non-glacial transition spans the Everson Interstade (glaciomarine and fluvial sediments) and the Sumas Stade (terrestrial deposits) as set out by Armstrong et al. (1965). Terminology of Armstrong et al. (1965) provides the framework that has been applied in this research. The last appearance of the drastically thinned Cordilleran Ice Sheet (technically a piedmont or outlet glacier - bounded by rock) in this area is represented by Sumas Drift of the Sumas Stade. Table 1-1 tabulates contributions to the late glacial history of the Fraser Lowland since the 1950's and 1960's when researchers made substantive observations on emerged glaciomarine deposits (Armstrong and Brown, 1954; Armstrong, 1957,1981,1884; Armstrong and Hicock, 1980, Easterbrook, 1963, 1969, 1992). Studies on glacial deposits, meltwater channels, and landforms have shown that multiple fluctuations of the terminal area of the glacier occurred during the Sumas Stade (Armstrong et al, 1965; Mark and Ojamaa, 1980; Cameron, 1989; Easterbrook, 1994; Clague et al, 1997; Kovanen and 5 Easterbrook, 1997). Figure 1-5 shows the different interpretations of deglaciation during the Sumas Stade by previous workers. Armstrong and Easterbrook recognized abandoned meltwater channels of Sumas age and alluded to multiple late glacial ice advances, but did not discuss the spatial distribution and temporal relationships because both workers used the international border as a boundary to their work. Late-glacial moraines were identified by these early workers, but the chronology was not defined in detail. In the Chilliwack drainage adjacent to the Fraser Lowland, Saunders et al. (1987) presented evidence for two ice marginal advances of ice c. 11.6 to 11.2 1 4 C kyr BP. Similarly, McCrumb and Swanson (1998) and Friele et al. (1999) presented evidence for moraines and kame deposits dated at c. 10.6 1 4 C kyr BP in Howe Sound and Squamish valley. Uncertainty arises as to whether these deposits/moraines represent stillstands induced by regional climate amelioration and whether they reflect cold/warm oscillations similar to those in the North Atlantic region (e.g., Hicock et al, 1999). This subject matter will be revisited in subsequent chapters. 6 Figure 1-4. (a) The distribution of surficial deposits on bedrock (modified from Armstrong 1984; also see Figures 5-2, 5-5a). 7 Time-Stratigraphic Units Geologic-Climatic Units Lithostratigraphic Units Age (1 4C kyr BP) Holocene Postglacial Salish and Fraser River Sediments -10.0 Late Wisconsin Slaciation Sumas Stade <C^Sumas < ^ > D r i f t -11.6 -12.5 Fraser < Everson Interstade Capilano and Fort Langley glaciomarine sediments Vashon Stade Vashon Drift Figure 1-4. (b) Late Wisconsin stratigraphic framework in the Fraser Lowland (after Armstrong, 1984). 7a Table 1-1 Contributions to the late glacial history in the Fraser Lowland Reference Contributions Armstrong and Brown (1954) Easterbrook (1963) Armstrong et al. (1965) Easterbrook (1969) Fulton (1971) Mathewes (1973) Easterbrook (1979) Clagueefa/. (1980) Mark and Ojamaa (1980) Clague(1981) Armstrong (1981) Hicock a/. (1982) Armstrong (1984) Easterbrook (1986) Saunders et al. (1987) Cameron (1989) Easterbrook (1992) Mathewes etal. (1993) Easterbrook (1994) Claguee/ al. (1997) Hicock et al. (1999) Evidence of glaciomarine drift and associated sediments; concepts influence subsequent surficial geology maps of the area (Armstrong 1957, 1960; Easterbrook, 1976a, b; Armstrong and Hicock, 1980a, 1980b). Widespread late Pleistocene glaciation and relative sea-level changes; developed criteria for recognition of glaciomarine deposits Established framework for late Pleistocene stratigraphy and chronology that is the basis for current usage. Pleistocene chronology of the Puget Lowland and San Juan Islands. Radiocarbon chronology of the Puget Lowland and San Juan Islands. Palynology of post-glacial vegetation changes in southwest B.C. The last glaciation of northwest Washington. Advance of the late Wisconsin Cordilleran Ice Sheet in southern B.C. Description of meltwater channels based on evidence of postglacial emergence, and they suggested that Sumas ice extended farther west than previously known. Summary and discussion of radiocarbon-dated Quaternary history. Post-Vashon Wisconsin glaciation, Fraser Lowland, B.C. Lag of the Fraser glacial maximum based on pollen and macrofossil evidence. Environmental and engineering applications of the surficial geology of the Fraser Lowland, B.C. Stratigraphy and chronology of Quaternary deposits of the Puget Lowland. Deglaciation of the Chilliwack valley. Late Quaternary geomorphic history of the Sumas Valley. Advance and retreat of Cordilleran Ice Sheets, U.S.A. Evidence for a Younger-Dryas-like cooling event on the B.C. coast based on pollen assemblages. Stratigraphy and chronology of early to late Pleistocene sediments in the Puget Lowland; recognition of multiple Sumas advances. Two "Sumas" pre-Younger Dryas resurgences of the Cordilleran Ice Sheet. "Bond cycles" recorded in terrestrial Pleistocene sediments; extended correlations based on nomenclature established by Armstrong. 8 > White Aktergrovp'» CultusLake Bellingham Figure 1-5. Interpretation of deglaciation during the Sumas Stade by previous workers, (a & b) Mark and Ojamaa (1980) recognized seven stages based on the positions of meltwater channels and "form lines", (c & d) Cameron (1989) suggested a sequence of ice retreat and sedimentation patterns between 11,300 and 11,000 yr BP based on drilling and water well records plus seven radiocarbon dates, (e) Clague et al. (1997) suggested two resurgences of ice; the younger one shown here at c. 11,400 BP (light stipple) and ice position several hundred years prior to readvance (dark stipple); an older readvance before c. 11,900 BP is not shown. 9 1.2.1 Changes in relative sea level during deglaciation After c. 14.5 1 4 C kyr BP, a significant and rapid retreat of glaciers marked the beginning of the Everson Interstadial. The lithostratigraphy is complicated by marine inundation of the Fraser Lowland during more than one highstand and subsequent isostatic rebound and emergence of the lowland. Easterbrook (1963,1992) defined the pattern of local relative sea level changes based on the interpretation of two fossiliferous massive stony clay units as being glaciomarine in origin at a large exposure along a river cutback of the Nooksack River (Fig. l-6a). Armstrong (1960, 1981) suggested a similar pattern in B.C. (Fig. l-6b) with emergence being interrupted by a short-lived (rapid) resubmergence. Mathews et al. (1970) summarized the regional relative sea level pattern inferred from Easterbrook and Armstrong curves (Figs. l-6a, b, respectively), and eastern Vancouver Island and found that the emergence may not have been uniform. Due to these complexities, Clague and Luternauer (1983) proposed an envelope of possible shoreline positions for the Fraser Lowland (Fig. l-6c) and suggested that asymmetric isostatic rebound may have left marine deposits higher in some places. The two transgressions are called the Fort Langley Fm. and Capilano Sediments in B.C. (Armstrong, 1984) and Kulshan and Bellingham of the Everson Interstade in Washington (Easterbrook, 1963). Difficulties arise in terms of process (e.g., developing relative sea level curves) because, generally, early Canadian workers have differentiated the Capilano and Fort Langley Fm. based on geographic location, rather than stratigraphic position. However, evidence exists for abrupt relative sea level changes that were regional in extent based on the radiocarbon dates from peat and rooted stumps beneath the younger glaciomarine sediments at several locations (Kovanen and Easterbrook, 2000a). Everson glaciomarine sediments form the lower boundary of the Sumas Drift; therefore, its recognition is critical because it relates to the original definition of the Sumas Drift (Appendix D). In this research, I have restricted interpretations and inferences to those emergent glaciomarine sediments that are surface-forming. The age of those sediments is discussed in Chapters 3,4, and 5, and generally fall within the envelope suggested by Clague and Luternauer (1983). Figure 1-6 provides an illustration of the minimum relative sea level reconstructions superimposed on present day topography. 10 A Sumas, emergent delta (Campbell River delta, Fig. l-4a) was deposited at a time when sea level was c. 30 m above present-day sea level (Fig. l-6e). A sea cliff developed at that time and separates the Capilano sediments to the west from the Fort Langley Fm. to the east. The channel that fed the delta is cut into Fort Langley glaciomarine sediments and heads at a Sumas age moraine (Armstrong, 1957,1960b; Armstrong and Hicock, 1980a). In the model of deglaciation presented in this thesis, the height of the Campbell River delta limits the height of sea level and the lower limit of meltwater channels during the Sumas Stade. The eustatic component of relative sea level change (Fig. l-6d) provides an indirect measure of the amount of water on the continents stored as ice and oceans during glacial cycles. This has been reconstructed from sites situated away from the margins of the large ice sheets based on corals submerged in New Guinea and off Barbados (Bard et ai, 1990; Fairbanks, 1990). During the last glacial maximum, eustatic sea level was c. 125 m lower than the present day due to ice build-up on the continents. As deglaciation set in, rise in eustatic sea level was not uniform, with an initial rise c. 20 m between 18 to 13 1 4 C kyr BP, followed by rapid rises centered on 12 1 4 C kyr BP (Meltwater Pulse LA, mwp-IA) and 9.5 1 4 C kyr BP (Meltwater Pulse LB, mwp-LB). Meltwater fluxes have been linked to changes in North Atlantic deep water production, which in turn has led to cooler climates in the North Atlantic basin (Broecker, 1990; Broecker et al., 1985). The existence of these rapid environmental changes in the Fraser Lowland and adjacent areas are the topic of this thesis and elucidation on them may help in understanding the propagation, leads and lags, and causes of these changes. A tempting suggestion is that, eustatic sea level rise could cause accelerated calving rates of the ice front and isostatic recovery could have allowed ice to advance thereby allowing for an alternative deglaciation model similar to the Laurentide Ice Sheet. However, we know that sea level was at c. 30 m above the modern level and as will be shown in subsequent chapters, Sumas ice margins were grounded (Sumas ice advanced over its own outwash); therefore sea level probably did not play a principal role in the formation of Sumas moraines. 11 J D 400' M « 300' 1 a 200' o m > _u 100' ( a ) , « Upper Ha r ln* L l « i t I i tL i Fraser Lowland, B.C. i i I 1 ' i J . \ . > L-A* w-Whatcom g l a c l o M r l n a d r i f t S - S U M S g l a c i a l d r i f t > 300' o j5 (b) - Uppar Marine L I a l t Whatcom County, WA. V Vashon t i l l n B S -K £ ~ K - Kulahan g lac io t t a r lo t d r i f t i y D • Dawlng sand J^ t B - B a l l l o g h a s g l ac ioaa r l a a d r i f t ! \ S - S U M « g l a c i a l d r i f t m 152 nT 12 11 IO 3 y a a r i B . P . i — r E 100-( c ) MATHEWS E T A L . 1 9 7 0 ARMSTRONG. J981 Lv .v .y .v i E N V E L O P E OF POSSIBLE V * .YJY IY .Y I SHORELINE POSITIONS 1 2 10 3 Y E A R S BP «•>:: \ Y -1 K \ • i \\ - 0 " 0 : \ " 0 * " 1 0 1 2 3 4 5 6 9 10 t1 12 13 14 15 16 17 18 19 20 Age (ka) 6 Figure 1-6. Relative sea level curves and sea level reconstructions, (a & b) from Mathews et al., 1970, after Armstrong, 1960b and Easterbrook, 1963. (c) from Clague and Luternauer (1983). (e) Present-day sea level, (f) Sea level at c. 30 m above present (g) Sea level at c. 180 m above present. 12 1.3 Research problem Between c. 11.6-10.0 1 4 C kyr BP, glaciers readvanced over emerged glaciomarine sediments, depositing scattered ice-marginal sediments that may have been coeval with the Allered and Younger Dryas intervals. Although the regional patterns of pre-maximum glacial advances are well established, the post-maximum advances were known only from a few sites and required closer investigation. The purpose of this research is to examine the stratigraphy and geomorphology along the margins of the former Cordilleran Ice Sheet and to test the hypothesis that glaciers here were highly sensitive to changes in the global climate system. This work also aims to link present day glacier fluctuations with synoptic climate to elucidate the sensitivity (e.g., response of glaciers to climate perturbations) of alpine glaciers to changes in the climate system. The research problem is summarized into two principal objectives: 1) What was the response of the Cordilleran Ice Sheet to abrupt changes in climate during the last glacial/non-glacial transition (c. 12.5-10.0 1 4 C kyr BP)? 2) If effects are detected, how do they compare with regional and global chronologies? The integration of surficial mapping, sedimentological, radiocarbon, palynological, oceanographic, and digital imagery data to document the spatial and temporal pattern of deglaciation is the distinctive feature of this research. Understanding how past abrupt climate changes affected the remnants of the Cordilleran Ice Sheet will provide a greater understanding of causal mechanisms for glacier fluctuations in this area. In order to investigate these changes, the following subset of objectives provided impetus. 1) Produce digital images that span the U.S.-Canadian border to allow more detailed analysis of the glacial morphology, which is necessary to determine the changing ice-sheet extent; 13 2) Conduct field studies to unify, extend, and confirm the early mapping of surficial sediments in the area; 3) Collect samples to determine radiocarbon ages that establish the bracketing dates of glacial events; 4) Derive a marine reservoir value to allow comparisons of marine shell dates with wood dates on late glacial sediments; and 5) Integrate the new geomorphic and stratigraphic evidence with the application of a new reservoir value to early dates obtained by Armstrong, Easterbrook, Clague and others. This work challenges the inference that the cold/warm oscillations known as the Billing (13.0-12.0 1 4CkyrBP), Oldest Dryas (12.0-11.8 1 4CkyrBP), Allerod (11.8-11.0 1 4 C kyr BP), and the Younger Dryas (11.0-10.0 1 4 C kyr BP) were confined to the North Atlantic region. 1.4 Thesis overview The first two chapters are introductory and briefly explain the use of multiple sources of evidence. Central to this research are new radiocarbon dates that provide age control, which will allow local, regional, and continental-scale extended correlations of the deglaciation sequence. Chapter 3 contains the derivation of a marine reservoir value, which allows for more accurate calculation of radiocarbon ages for marine shells. This is necessary to compare shell with wood dates and to make use of shell dates for chronology. Chapter 4 contains morphologic, stratigraphic, and spatial evidence for oscillations of the late Wisconsin glacier that were grouped into four distinct phases (SI, SII, SIII, SIV) of ice retreat during the latest Pleistocene and early Holocene (Sumas Stade) transition in the Fraser Lowland. This includes documentation of previously unrecognized features (e.g., moraines and meltwater channels) that were constructed during the Younger Dryas period. Sumas phases were recognized on the basis of morphologic and stratigraphic features that provide relative age relationships needed for the subsequent discussions in Chapter 5. 14 This chapter also demonstrates the usefulness of digital imagery in the recognition of glacial features and allows the unification of previous work. Chapter 5 examines specific evidence for the origin of massive fossiliferous gravelly mud that has a bearing on the sequence of events and extent of ice during the Sumas interval. The results of chapters 4 and 5, linked with the sea surface temperature curve west of Vancouver Island (Kienast and McKay, 2001) and pollen records, suggest a response to abrupt climatic changes similar to those of the GISP2 ice core. Chapter 6 presents evidence for an alpine glacial system in the Nooksack drainage which heads on Mt. Baker, Mt. Shuksan and the Twin Sisters Range. The Nooksack valley is situated adjacent to the Fraser Lowland. Moraines found in the drainage document the extent of alpine ice at the glacial, non-glacial transition. This alpine system was independent of the Cordilleran Ice Sheet, which was positioned in the Fraser Lowland (and spilled over into the adjacent Chilliwack valley) at the time moraines were constructed in the Nooksack. While much of the geomorphic evidence was previously documented (Kovanen, 1996), ten new radiocarbon dates add to the evidence, as does a discussion on topographic and climatic factors that may have contributed to the development of the system as the accumulation centers shifted from the ice sheet (e.g., late glacial maximum) to the flanks of Mt. Baker during deglaciation. Chapter 7 presents observations on the influence of recent temperature and precipitation variations in the northeast Pacific on glacier fluctuations on Mt. Baker. The hypotheses here is that the margins of present day glaciers have been and will continue to be highly sensitive to changes in the climate system (e.g., oceanic and atmospheric processes). This data is useful to understand how local physical interactions may be link to climate, glaciers and glacier variability. While this chapter represents a temporal shift compared to previous chapters (millennial-scale versus decadal-scale superimposed on a centennial trend), I speculate that late Wisconsin glaciers may have had a similar relation to longer-term cycles. Therefore, the record of Holocene (the last c. 10.0 1 4 C kyr BP) glacier variations in this area may provide a proxy of pre-instrumental variations. 15 Chapter 2 Methods 2.1 The use of multiple sources of evidence The significance of glacial deposits in terms of data on climate change can be evaluated through a combination of numerical dates and constraints on the relative stratigraphic positions of isolated sections. 2.2 Stratigraphy Standard stratigraphic methods were used to identify the origin of sediments and their relation to one another (Chapters 3,4, and 5). Sedimentary facies were assessed using a combination of texture, composition, fabric, and degree of compaction. The chronology of stratigraphic units and geomorphic features was established using radiocarbon age-determination, tephrachronology, stratigraphic position, and geomorphic relations. Outwash deposits were traced upvalley (Chapters 4, 5, and 6) and their relation to moraines was established to help in the process of mapping and relative age assignment. A key to interpretation of late-glacial paleoenvironments is the genesis of sediments. Broadly, the basic terms below were employed. Glacial drift: all rock material transported or deposited by glacier ice or meltwater. Till: unsorted and unstratified drift, deposited directly by and underneath a glacier without subsequent reworking by meltwater, and consisting of a heterogeneous mixture of clay, silt, sand, gravel and boulders. Glaciomarine drift: material released by melting of ice into the sea, whether by continuous rain-out beneath a floating mass of glacier ice, or sporadically from icebergs. The material is delivered to the marine depositional site by floating ice. 16 Glaciofluvial drift: drift transported and deposited by running water emanating from a glacier. Glaciolacustrine: material derived from, or deposited in glacial lakes; deposits and landforms composed of suspended material brought by meltwater streams flowing into lakes bordering the glacier, such as varved sediments and deltas. Diamicton: a non-sorted or poorly sorted unlithified terrigenous sediment that contains a wide range of particle size The critical distinctions that this research deals with are the identification of glaciomarine drift (e.g., massive, fossiliferous, stony mud), lacustrine deposits, and glacial till. Glaciomarine, massive, stony mud, and lacustrine deposits often resemble glacial till. To distinguish between deposits, several characteristics were used in this study. Glaciomarine stony mud deposits contain scattered marine shells, foraminifera, and have higher void ratios and lower bulk densities than basal tills (Easterbrook, 1964) (discussed in chapter 5). In contrast, lacustrine deposits lack the marine evidence, but typically consist of varved clay, silt, and sand containing scattered dropstones (Armstrong, 1984). Mapping by Armstrong and Hicock (1980a, b) indicates that glaciolacustrine sediments have a limited distribution in the Fraser Lowland (Armstrong, 1981). 2.3 Dating 2.3.1 Relative dating Morainal topography, stratigraphy of drift sheets, boring logs, and high-resolution digital images provide evidence of late Pleistocene glacial advances. The most useful observations used in this investigation to determine the relative ages of features were cross-cutting and other morphologic and stratigraphic relations. Moraines were identified based on morphologic characteristics and grouped according to their relative positions with respect to other moraines (Chapter 4). Because all of the sediments studied are so young and radiocarbon dates are so plentiful, no attempts were made to establish ages based on degree of soil development. 17 2.3.2 Numerical dating 2.3.2.1 Radiocarbon dating Where wood, shells, or other organic matter was preserved in late Pleistocene to early-Holocene glacial or volcanic deposits, radiocarbon dating was employed to determine the age. All ages used in this research are presented in Appendix A, which supplements the results presented in the thesis chapters. In order to standardize the data and facilitate comparisons, the dates are reported in radiocarbon years and calibrated to calendar years using the radiocarbon CALEB software program (using INTCAL98, Stuiver and Reimer, 1993; Stuiver et al., 1998). Refer to Appendix B for sample descriptions. If dates are based on bulk sediment samples, the uncertainties may be so large as to render the results of rangefinder value only. Therefore, more weight has been given to accelerator mass spectrometer (AMS) dates. Since calibration age ranges are not symmetrical, the full probability (method B) range is given for each date, which best represents the full extent of the uncertainties. Up to c. 10.3 1 4 C kyr BP, the calibration curve is in close agreement with both GISP2 and GRIP chronologies. The calibration curve (INTCAL98), for dates older than 10.3 14C kyr BP is based on Cariaco (marine) dates, which are in agreement with the GISP2 reconstruction. Therefore, in this research, comparisons are made with the GISP2 ice core rather than GRIP. An age correction for the marine reservoir effect is applied to the reported dates on marine shells, using a correction of-1100 years (Chapter 3). When attempting to establish a chronology of events, one should be able to assess the accuracy and reliability of the dates, which can be biased in several ways. Refer to Appendix C for a detailed discussion of isotopic oxygen and carbon. Note that "old" dates reported in the Fraser Lowland were often obtained by conventional P-counting methods from a mixture of shells or bulk gyttja and hence, represent a blended age. AMS dates are preferred because they yield discrete ages. 18 The sampling strategy took heed of temporal and spatial relations of deposits, and considered the position of geomorphic features, surface geometry, and stratigraphic position relative to a radiocarbon sample. Because of possible contamination of samples from modern carbon, such as by invasion of rootlets, great care was taken to collect pristine samples and to prevent possible contamination during handling. Because radiocarbon ages from marine shells need to be corrected for 1 4 C marine reservoir effects, samples of wood and shells from the same site were dated and compared in Chapter 3. The wood ages reflect the atmospheric carbon reservoir and deviation from marine shell ages is a measure of the marine radiocarbon reservoir effect. Once this difference is established, marine shell ages must be corrected before comparisons can be made with wood and other terrestrial samples. In this study, a new radiocarbon reservoir value was determined for shells enclosed by late Wisconsin-age sediments (Chapter 3). 2.3.2.2 Tephrochronology The presence of distinct ash layers from Cascade volcanoes can be used as stratigraphic markers. Field classification based on color, composition, thickness, grain-size, and stratigraphic position is a common way to identify individual volcanic eruptions. Mazama ash (6700-6850 , 4 C yrs BP) is the most useful and widespread marker horizon in this region for dating the glacial features. In addition, the Schriebers Meadow scoria, Cathedral Crag ash, and Rocky Creek ash provide useful stratigraphic markers on the flanks of Mt. Baker and were identified based on textural, chemical, and optical properties (Appendix F). 2.3.2.3 Sediment coring To obtain bracketing dates for glacial features, undisturbed cores were obtained from lake and channel bogs. During this research, a non-motorized piston corer (Livingston corer) was utilized to collect continuous 1-meter cores. Twenty-five sediment cores were collected ranging from 9 m to 20 m in depth, totaling more than 220 linear meters of core (Appendix E contains core log descriptions). Multiple discrete basal samples from multiple cores provide bracketing information for the timing of the glacial events (Chapters 4,5, and 6). 19 2.3.2.3.1 Coring site selection In the study area, there exist many lakes or depressions, abandoned outwash channels, and meadows. Basal sediments from these features containing organic material provide useful limiting dates related to the nature of the stratigraphic problem or geomorphic feature being investigated. At every bog under investigation, coring site location was considered in detail as it was of primary importance to obtain organic matter from the deepest part of the bog. To determine the deepest section of sediment, cross-sections of the bog were obtained. This was accomplished by systematically pushing segmented probes (0.5 cm diameter iron rods) to the bottom of the organic matter to determine its depth and enable the construction of basin profiles. This served two useful purposes: to determine the depth of the organic matter for the most suitable site for the coring and once the core site had been selected, to check for any obstructions (e.g., logs or boulders) at depth. Sites near stream inlets were not considered, as they likely contained clastic material that interferes with coring. Wetlands are difficult to negotiate on foot and provide poor drilling platforms. Therefore, boardwalks and drilling platforms were constructed of plywood sheets to provide stable working surfaces. Core sections were extruded and packaged in the field, then transported to a laboratory for measurements and organic material extraction. These methods add validity to the sample age. 2.4 Morphologic expression - hillshade generation and visualization Glacial landforms were mapped in the field, on aerial photographs, and on digital computer images. Moraines were identified based on morphologic characteristics and grouped according to their relative positions with respect to other moraines. Landform/sediment associations identified in the Fraser Lowland and adjacent Nooksack drainage include the following elements: 20 (1) prominent hummocky moraines and moraine complexes (or belts) with associated till, which document the former existence of glacier lobes or ice streams during deglaciation; (2) abandoned meltwater channels that document the positions of subglacial and glacial meltwater around the receding/oscillating glacier ice; (3) outwash plains. Traditional field and contour map measurements were integrated with hillshade images, which are an effective way to represent terrain and morphologic expressions, revealing the landscape (Fig. 2-1). The relative relations of landforms provide an important line of evidence for interpretation of surficial features. Therefore, numerous digital shaded relief images were computer-generated as a tool for interpretation of the deglacial history of the study area. A unique feature of digital shaded relief imaging is the ability to adjust the azimuth and elevation of the illumination of topographic features. Depending on scale and resolution of a feature and the digital data, this enables and facilitates recognition of geomorphic features (i.e., glacial moraines, landslide scarps, outwash channels, etc.) that might otherwise be overlooked in the field, on a topographic map, or on an aerial photograph. These images proved to be of immense value in interpreting the Quaternary geology of the Fraser Lowland, allowing many features to be observed for the first time. Elevation data were used to interpolate elevations on a regular grid (with a spacing of 10, 25 or 30 m). Because elevations in the digital elevation model (DEM) consist of interpolated values, the geometrical accuracy is less than that of directly measured points. The error is dependent on the interpolation algorithm and the topography of the specific area. In the context of this study, the accuracy of the interpolation of the grid nodes is inversely related to the relative relief of the area. Within the Fraser Lowland, the relative relief is not high compared to the Coast Mountains or North Cascades, and therefore the accuracy of the DEM is considered to be high. This permits the construction of high-quality representations of the land surface that assists in the geomorphic interpretations. The hillshade images shown in this thesis were generated using proprietary software: Environmental Systems Research Institute, Inc. (ESRI) Arc View 3.1 or 3.2 with 21 the spatial analyst and 3D extensions; Golden Software, Inc. Surfer 6.04 or 7.0; Earth Resource Mapping, ERMapper 5.0; or the U.S.G.S. DEM3D Version 1.0. Figure 2-1. This figure illustrates how effective shaded relief can be when added to a contour map. (a) Lakes, rivers, and contours of the Mt. Baker area, (b) Same map with shaded relief added. 2.4.1 U.S. digital data The United States Geological Survey (USGS) produces two large-scale (1:24,000) digital data types: (1) Spatial Data Transfer System (SDTS) format-DLG vector data and (2) D E M grid models. A l l 1:24,000 scale data were developed using the USGS topographic quadrangle maps as a base. For this study, 1:24,000-scale, D E M , data sets were obtained. The data were registered using metric Universal Transverse Mercator (UTM) values according to the North American Datum of 1927 (NAD27). Elevation points are provided along north-south profile lines, generally with a 30-meter spacing between adjacent data points and profile lines. For a portion of Washington State, 7.5 minute Quadrangle DEMs are available on 10-by-10-meter data spacings, improving the resolution of shaded relief images. For this study, forty 7.5 x 7.5-minute USGS D E M 10 meter data sets were merged and some have been averaged to a cell size of 20 or 25 m (horizontal resolution). Before images can be generated, the D E M files must be converted to allow entry into the software packages mentioned above. Public domain utilities used to uncompress data were gzip, tar and WINZIP. Data conversions were accomplished using the DOS 22 version of Chop, sdtsldem, SDTSEDEM.EXE, Dem2dat, and Demlxyz. Each of the following data sets (i.e., 7.5 minute quadrangles) in Washington State was processed separately: Acme, Alger, Anacortes North, Anacortes South, Baker Pass, Bertrand Creek, Bellingham, Bellingham North, Bellingham South, Bearpaw Mountain, Birch Point, Blaine, Bow, Canyon Lake, Cavanaugh Creek, Damnation, Deming, Eliza Island, Ferndale, Glacier, Grandy Lake, Groat Mountain, Hamilton, Haystack, Kendall, La Conner, Lake Shannon, Lake Whatcom, Lawrence, Lumni Bay, Lumni Island, Lyman, Lynden, Maple Falls, Marblemont, Mount Baker, Mount Larrabee, Mount Sefrit, Mount Shuksan, Shuksan Arm, Twin Sisters, Sumas, and Welker. 2.4.2 Canadian digital data The B.C. Ministry of Environment, Lands and Parks (MELP), Geographic Data B.C. loaned its proprietary Terrain Resource Information Management (TRIM) GRIDDED DEM data files for this research. The following five TRIM gridded DEM digital data file were utilized: 92G, 92H, 92B, 92J, and 921. The digital map files in the B.C. Atlas series (1:20,000 TRIM) were in SAIF/ZLP compressed format. All TRIM data were referenced to the UTM Coordinate System based on the 1983 North American Datum. The raw TRIM data which were created using 70 m and 80 m point data, were converted by two-dimensional interpolation to a 25-m spacing. During the task of data processing, significant data quality issues arose in data tile 92G, but reprocessing of the mass point and breakline data contributed to additional smoothing (of the data). All mass point data were interpolated to 20 meters and converted to 32 bit floating point number for continuous representation. The accuracy of the interpolated DEM conforms to 1:20,000 TRIM data accuracy which states that ninety percent of all points interpolated from the TRIM DEM are accurate to within 10 meters of their true elevation. The horizontal resolution or cell size of 20 m was used in this research (unless stated elsewhere) is a reasonable compromise between loss of information on terrain characteristics because of the smoothing associated with larger grid cells and the generation of artifacts by the interpolation routines used in DEM generation as grid cells become smaller. 23 The TRIM data were converted to the NAD27 datum and, finally, the two large data sets were merged. The full data set includes 6100 rows and 7400 columns with data accuracy of points within 10 m of their true elevation. In order to eliminate shadows, the illumination of the individual hillshade images varies because emphasis was placed on the recognition of specific features. No topographic exaggeration is applied, except where noted. 2.5 Statistics Simple statistics were used to refine and interpret data, including the following determinations: mean, moving average, standard deviation, variance, skewness, kurtosis, standard error, root mean square, correlation coefficient, and probability. In this way, time-lags and feedback related processes between different parts of the climate system may be established. 24 Chapter 3 Paleodeviations of radiocarbon marine reservoir values for the Northeast Pacific 3.1 Introduction Rapid environmental changes are well known during the last glacial to interglacial transition (14-9 1 4 C kyr BP). Correlation of these rapid changes between marine and terrestrial sequences is difficult. Now, with the production of the detailed Greenland, Summit ice core records (GISP2 and GRIP) that span deglaciation (e.g., Stuiver and Grootes, 2000), increasing the level of precision between marine and terrestrial records is essential in attempting to evaluate the contemporaniety and causes of these changes. The marine reservoir effect is important because it gives marine organisms anomalously old radiocarbon (14C) ages in comparison to coeval terrestrial material, and while the current global reservoir value is known (410 yr), evidence exists that this value changes, thereby complicating correlations. As was recently recommended in the INTIMATE Workshop (the Integration of Ice-core, Marine and Terrestrial Records; a program of the International Quaternary Union Palaeoclimate Commission), "further work is urgently required to establish the magnitude and timing of temporal variations in marine reservoir effects for different sectors" (Lowe et al, 2001, p. 1177). In this chapter, a new marine reservoir value for the Fraser Lowland (Fig. 3-1) is presented, which should increase the precision of dating events and correlating them with global changes. Radiocarbon (14C), is produced in the upper atmosphere by cosmic radiation, is rapidly mixed throughout the stratosphere but mixing with ocean water lags by hundreds of years. The concentration of 1 4 C in surface ocean water is controlled by the amount of 1 4 C in the atmosphere (CO2), and oceanic circulation (e.g., rate of upwelling of 14C-deficient deep ocean water; Mangerud, 1972; Stuiver and Polach, 1977; Andree et al, 1986; Broecker et al, 1988b; Shackleton et al, 1988; Bard et al, 1994; Haflidason et al, 1995). The concentration of 1 4 C in deep ocean water is lower than surface water because of slow 25 vertical mixing and varies geographically, currently resulting in differences of c. 400 years in the tropics and c. 1200 yr in polar waters (Stuiver and Polach, 1977). Sikes et al. (2000) suggested that reservoir values were twice as large as those presently observed at c. 11.9 1 4 C kyr BP in the SW Pacific Ocean, and at c. 10.5 1 4 C kyr BP in the North Atlantic (Bard et al, 1994; Bondevik et al, 2001; Waelbroeck et al, 2001). In order to compare 1 4 C ages of shell and wood samples directly as well as to compare ages of shells from different regions the marine reservoir value must be established (Mangerud, 1972; Stuiver et al, 1986; Stuiver and Braziunas, 1993). The total 1 4 C marine reservoir correction, R, is Rt = Rgt+AR (3.1) where Rg, is the global value of c. 410 yr and AR is the regional component (Stuiver et al, 1986; Stuiver and Braziunas, 1993). Conventional age (Stuiver and Polach, 1977) is used for shell and wood dates that have been adjusted for the effects of isotopic fractionation (Broecker et al, 1960); measured 8 1 3 C values, 0%o shell, -25%o wood, are normalized to the same standard value, -25%o, which roughly cancels out the global reservoir value of 410 yr. The total reservoir age is then given by the conventional shell age minus the age of the paired wood sample. The reservoir-corrected age of the shell is the conventional shell age minus the reservoir value. Robinson and Thompson (1981) determined a reservoir age of c. -800 years for modern, pre-bomb shells. Southon et al. (1990) determined a similar value (mean 790 ± 3 5 1 4 C yr BP) for modern, Holocene, and Younger Dryas shells from coastal waters in Alaska, northern British Columbia, and Oregon. However, when this reservoir value is applied to marine shells from the Fraser Lowland, the results do not yield ages comparable to the paired wood ages. In the following, data is presented for a reservoir value of-1100 yr and the new value is compared with previously reported values. 26 Figure 3-1. Location of study area. Inset shows regional surface ocean currents prevailing in northeastern Pacific (after Sabin and Pisias, 1996). 3.2 Sample selection and radiocarbon measurements Modern 1 4 C marine reservoir values may be determined by dating shells and coral collected prior to the nuclear-testing-induced rise in global 1 4 C (e.g., Druffel and Linick, 1978; Druffel and Griffin, 1993). Ancient marine reservoir values may be established by determining the differences in ages of coeval pairs of shell and wood, which is the method applied in this study. 3.2.1 Sample locations Six pairs of shell and wood samples were collected from late Wisconsin emergent glaciomarine sediments in the Fraser Lowland (Fig. 3-1). Shells and wood are situated in 7-10 m of massive stony silty clay (mud) that can be traced throughout several large gravel pits (including the Bradner and Axton gravel pits, which are 15 km apart) and is continuous with the surface-forming fossiliferous stony mud for many kilometers. The upper and 27 lower contacts of the stony mud are sharp, indicating that the age limits of the unit are well defined without long transitions. Detailed descriptions and discussion of the origin and characteristics of the glaciomarine sediments were given by Armstrong and Brown (1954), Armstrong et al. (1965), Armstrong (1981,1984), and Easterbrook (1963,1969,1992), and are not repeated here. Because reworking of either shell or wood samples would lead to unreliable results, demonstration of contemporaneous deposition is essential. At the sample sites, paired shell and wood samples occurred within 1 m of each other. The following evidence demonstrates in situ deposition of the shells in marine water: (1) large proportion of articulated bivalves; (2) whole bivalves that still retain delicate nacreous layers, radula, delicate ornamentation, and growth rings; (3) articulated bivalves that are filled with the same silty clay that encloses them; (4) the uniform nature of the stony mud at the sample sites, and the lack of evidence of reworking (e.g., no stony mud clasts and no grain segregation); (5) the elevations of 100 other nearby fossil localities in the stony mud with similar radiocarbon ages (Armstrong, 1981), indicating that the sample sites were submerged beneath at least 100 m of marine water during the time of deposition; and (6) lack of freshwater organisms (e.g., diatoms). The questions of whether the wood could have come from the cores of old trees or could have been be reworked from older deposits are also essential to the evaluation of the paired samples. Wood in the glaciomarine stony mud is abundant at the sample sites. Many logs, branches, twigs, needles, and cones demonstrate that the trees were alive shortly before or during deposition. Needles on twigs still attached to branches that were connected to tree trunks were found, indicating little transport. The samples that were dated were from (1) branches and the outer rings of small bark-covered logs (to avoid the possibility of dating wood from an old tree), and (2) a cone, which represents a single year of growth with no inherent age history. This evidence demonstrates that the samples were derived primarily from in situ populations, providing an excellent opportunity for the determination of the marine reservoir effect. 28 3.2.2 Total marine reservoir value Paired shell and wood samples were accelerator mass spectrometer (AMS) dated on the same accelerator wheel to maximize laboratory precision to ±40-60 yr. Dates of three paired shell and wood samples from the Bradner and Axton pits indicate a mean reservoir value of-1247 ± 35 yr and -961 ± 36 yr, respectively (Table 3-1). Wood ages at both sites are statistically equivalent, but shell dates from the Axton pit are younger and somewhat more variable, so the differences in shell and wood ages from the two site do not overlap within two standard deviations. This has implications as to whether the two sites should be combined into the overall mean. But, because the wood ages at both sites are statistically equivalent, we have not treated them separately. The mean derived from both sites is -1102 ± 107 yr. Most of the shells from both pits are articulated Nuculana, although some samples also included Chlamys, Clinocardium, and Macoma shells. Therefore, the age differences are apparently not related to the shell species because some samples from both sites consisted only of Nuculana shells. The differences may be related to the time span of deposition of the sediments from which the samples were taken. Two paired shell and wood scintillation dates (Armstrong, 1981) yield a reservoir value of-1103 ± 591 (Table 3-2). The low laboratory precision (180^ 150 yr) of these samples makes them less useful than the AMS dates, and the results were therefore not included in the calculation of the reservoir value. 29 Table 3-1 Radiocarbon Measurements on Paired Shells and Wood Sample Material Dated Conventional Age (14C yr BP ± lo) Lab No. B-144094 B-144095 Site 2 Shells Wood 12,950 ± 40 11,680 ±50 = -1270 ± 64* B-144096 B-144097 Site 3 Shells Wood 5"C (%o) Bradner pit southwest British Columbia Site 1 Shells 12,950 ±40 Wood 11,770 ±40 -1180 ±56* -0.3 N.D.§ -0.2 N.D. -0.1 N.D. 12,970 ±40 B-144098 11,660 ±50 B-144099 fl, = -1310±64* Weighted mean R, = -1247 ± 35f Axton pit northwest Washington Site 4 Shells 12,680 ±40 B-145455 Wood 11,670 ±40 B-145458 J?,= -1010 ±64* Site 5 Shells 12,720 ±40 B-145456 Wood 11,830 ±50 B-145459 Rt= -890 ±64* Site 6 Shells 12,760 ±40 B-145457 -0.0 Wood 11,790 ±50 B-145460 -28.5 R< = -970 ±64* Weighted mean R, = -961 ± 36f Weighted mean of all 6 sites; R, = -1102 ± 107t * The uncertainty of the individual reservoir values was determined by Voi2 + o22-* The uncertainty of the mean reservoir values was determined by ECT;. § N.D. = no data. -0.3 -27.2 -0.0 -29.0 30 Table 3-2 Other Paired Dates Material Conventional Age Lab No. Dated ( 1 4 CyrBP±2o)* Shells 11,710 ±190 GSC-227 Wood 10,690 ± 180 GSC-185 Rt = -1020 ±262' Shells 13,035 ±450 I(GSC)-6 Wood 11,590 ±280 GSC-226 R,= -1445 ±530' Mean R, = -1103±591 § * Dates are from Armstrong (1981). * The uncertainty of the individual reservoir values was determined by VCM2 + a*-§ The uncertainty of the mean reservoir values was determined by £o~j. 3.2.3 Comparison with other marine reservoir values The mean regional reservoir value has been interpreted to be close to that of the modern reservoir correction (Table 3; -800 yr; Robinson and Thompson, 1981). Variance in their data is thought to result from the long time span of deposition of the sediments from which the samples were taken, as well as to possible sampling errors, or variations in oceanic upwelling or mixing (Southon et al, 1990). 3.2.4 Comparison of nonpaired shell and wood dates Published dates from the surface-forming glaciomarine stony mud (Armstrong, 1981; Easterbrook, 1963,1969,1992) range from c. 12.5-11.5 1 4 C kyr BP using a reservoir correction of -800 1 4 C yr (Table 3-4; Fig. 3-2). To test the hypothesis that a larger reservoir value is appropriate, 14 shell dates were compared with 18 wood dates from the stony mud. Figure 3-2a shows that the shell dates after a reservoir value of -800 yr is applied, are c. 400 yr older than the wood dates (mean reservoir-corrected age is 12,041 1 4 C yr BP, whereas the mean wood age is 11,641 1 4 C yr BP). The concordance of the dates is improved when a reservoir value of -1100 yr is applied (Figure 3-2b) (mean reservoir-31 corrected shell age is 11,741 C yr BP; mean wood age is 11,641 C yr BP; mean difference is 100 yr). Wood dates from the glaciomarine sediments range from c. 11.8 to 11.4 1 4 C kyr BP excluding one younger outlier (Fig. 3-2). The range of ages for shell dates is much greater (c. 1000 years), in part probably due to the lower laboratory precision of older dates. Three of the four shell dates (Fig. 3-2b) younger than 11.4 1 4 C kyr BP were scintillation-counted 40 years ago with laboratory precisions ranging from 180-450 yr. The shell dates older than 11.8 1 4 C kyr BP (Fig. 3-2b) are also early dates with laboratory precisions ranging from 170 to 210 years. 13,000 12,500 DL 12,000 CD o, 11,500 < 11,000 10,500 • • • • • • • • • C D O O O O o • Shells (Rt, -800) O Wood • • • • • • C O C Q % O o o O O • Shells (Rt,-1100) O Wood 13,000 12,500 12,000 °r co 11,500 o> < 11,000 10,500 Figure 3-2. Reservoir-corrected shell ages compared to wood ages using the reservoir values of -800 yr (a) and -1100 yr (b). 95% confidence interval for the wood samples is 11.7-11.5 1 4 C kyr BP. 32 Table 3-3 Summary of reservoir values from the northeast Pacific Ocean Location Radiocarbon Age ( 1 4CyrBP) Reservoir Value ( 1 4CyrBP) References Alaska to Oregon Modern -790 ± 3 5 Southon e/a/. (1990); Robinson and Thompson (1981) 2,600 ± 110 -670 ± 90 Southon etal. (1990) 4,990 ± 110 -720 ± 1 4 0 Southon etal. (1990) 6,360 ± 60 - 1 1 8 0 ± 1 1 0 Southon etal. (1990) Mary Point B* & 9,010 ± 4 0 -725 ± 5 0 Southon et al. (1990) Cook Bank 10,230 ± 160 - 6 8 0 ± 1 1 0 Southon etal. (1990) Fraser Lowland c. 12,500-11,500 -1102 ± 2 5 This chapter * The reservoir age for Mary Point B and Cape Ball is a pooled mean age. Cape Ball is c. 50 km southeast of Mary Point B locality (see text for discussion of data) 33 Discussion Radiocarbon age differences on paired shell and wood samples indicate that the radiocarbon reservoir value for the northeast Pacific was ca. -1100 yr during the Allerad. This is 300 yr older than the reservoir value for the late-Younger Dryas and for the present day in this area (Table 3-3). This is due partly to variations in both deep ocean and surface ocean conditions (Bjrjrck et al., 1996; Hughen et al., 1998) and partly to variations in concentration of radiocarbon in the atmosphere (Goslar et al., 2000). Among the possibilities for the higher reservoir value in the northeast Pacific are: (1) Pacific coastal upwelling transports water from a depth of 100-300 m to the surface, which may fed the inland waterways with old water; (2) the production rates of 1 4 C in the upper atmosphere may have varied; (3) melting of the Cordilleran ice sheet may have added 14C-deficient water to the sea; (4) the effects of rapid eustatic sea level rise during deglaciation may have altered oceanic circulation patterns; and (5) uptake of detrital carbon may have been enhanced. The dominant bedrock in this region is siliceous, so variations in the amount of dissolved old carbon did not contribute to the higher reservoir value. The preceding five points are briefly discussed in the following. 33 Surface ocean circulation in the northeast Pacific can be divided into three main regions: the Alaskan Current, the Transition Zone, and the California Current, and the position of these may have varied during deglaciation (Fig. 3-1 inset; Zahn et al, 1991; Sabin and Pisias, 1996). In addition, the West Wind Drift, a surface current, presently crosses the Pacific between 40° and 50°N. Little is known about the relative strength of these currents, but decreases in sea-surface temperature (SST) in the Santa Barbara Basin have been attributed to an intensified California Current during stadial events, which increased the influence of Sub-arctic water (Hendy and Kennett, 2000). Alkenone SST estimates west of Vancouver Island also suggest rapid rates of temperature change during deglaciation (1 °C/40-80 yr; Kienast and McKay, 2001). Cool temperatures (c. 6-7 °C) during stadial events may suggest an increase in the advection of Subarctic water or perhaps in situ top down cooling (e.g., reduced radiative warming due to fog or cloud cover). These rapid changes suggest ocean-atmosphere coupling (e.g., de Vernal and Pedersen, 1997). Strong, stationary, low-pressure systems are associated with the Subarctic Front (Kutzbach, 1987; CLIMAP Project Memebers, 1981) and may have migrated southward to c. 40°N at the last glacial maximum (LGM; Fig. 3-1, inset; Zahn et al, 1991). If the location of the ocean currents and large-scale pressure systems changed, those processes would have affected wind gradients and upwelling patterns. Therefore, the paleodeviations in the reservoir value may reflect a link to ocean-atmosphere interactions over the Pacific Ocean, but more work is necessary to unravel the system feedbacks. Variations in the 1 4 C production rate are thought to be responsible for A 1 4 C plateaus (centered at 11.7,11.4,10.6, and 9.6 1 4 C kyr BP; Becker et al, 1991; Becker, 1993; Kromer and Becker, 1993; Goslar et al, 1995; Hughen et al, 1998). The variations in production rate can affect the relative age difference between coeval wood and shells and consequently the marine reservoir value (e.g., to increase only the production rate is to increase the difference between shell and wood dates until ocean comes into equilibrium with changed values). A comparison of changes in the concentrations of A 1 4 C and 1 0 Be estimated in ice cores (Muscheler et al, 2000), implies that a fundamental change in oceanic ventilation played a main role in modulating global 1 4 C content during deglaciation. 34 Meltwater contributions to the sea may also affect the relative proportions of C in marine shells by contributing old carbon originally trapped as C O 2 in the ice. Similarly, the uptake of carbon by marine organisms (detrital versus filter feeders) complicates interpretation. But is not critical because shells are of various feeding types (Table 3-4). The age range of the new data (c. 12.5-11.5 1 4 C kyr BP) overlaps the global meltwater record of Fairbanks et al. (1992), which places the peak of meltwater pulse IA at c. 11.8 i 4 C kyr BP. Eustatic sea level rose rapidly; 8 1 80 values of-0. l%o, -0.5%o, and -0.8%o obtained from shell samples (Table 3-1) suggest that meltwater dilution had little effect on the marine waters in the ancestral Fraser Lowland at this time. This is confirmed by the faunal assemblages in the stony mud, which reflect normal salinities without brackish-water forms (Wagner, 1959). Effects attributable to restriction of flow during eustatic low sea level are unknown. 3.4 Summary Identifying paleodeviations in the marine reservoir value is crucial for a wide range of paleoenvironmental studies (e.g., rates of change). The application of the mean -1100 yr reservoir value (or -1247 ± 35 yr and -961 + 36 yr for two sites) for sediments older than c. 11.5 1 4 C kyr BP may improve correlation of environmental changes in the Fraser Lowland with environmental changes elsewhere. This marine reservoir value determination builds upon the work of Southon et al. (1990), and Robinson and Thompson (1981) (Table 3-4), and illustrates the need to establish the magnitude, timing, and causes of temporal variations in the reservoir effect. (Visit http://www.calib.org/marine/ for the global marine reservoir correction database). 35 Table 3-4 Selected* Radiocarbon Ages from the Fraser Lowland Conventional Age Reservoir-corrected Lab No. Locality/Material Location Ref. No." ( 1 4 CyrBP) Shell Ages dated JLat Long ( 1 4 CyrBP) t (°N) (°W) Shells 12,090 ±180 10,990 ±208 GSC-186 County Line overpass/ 49°06' 122°30' 1 pelecypods and Serpula 12,310 ±300 11,210 ±318 L-391C Burnaby 49° 16' 122°56' 2 12,340 ± 190 11,240 ±217 GSC-168 SE of Fort Langley/ 49° 10' 122°35' 3 Macoma 12,520 ± 80 11,420 ± 132 TO-4089 Bradner gravel pit 4 9 o 0 l ' 125°26' 4 12,640 ± 200 11,540 ±226 GSC-74 Burnaby, Piper Ave./ 49° 15' 122°56' 5 Serpula 12,870 ± 170 11,770 ±200 GSC-64 North Delta 49°08' 122°55' 5 12,950 ± 40 11,850 ±113 B-144094 Bradner pit 49°01' 122°26' 6 12,950 + 40 11,850 ± 113 B-144096 Bradner pit 49°01' 122°26' 6 12,970 ± 40 11,870 ± 113 B-144098 Bradner pit 49°01' 122°26' 6 13,010 ± 120 11,910 ± 160 GSC-2612 Port Moody/ Fusitron 49° 16' 122°49' 1 13,010 ± 170 11,910 ±200 GSC-37 Boundary Bay/ 49°01' 123°04' 5 pelecypods 13,210 ± 170 12,110 ±200 I(GSC)-248 Boundary Bay 49°01' 123°04' 11 13,035 ±450 11,935 ±462 I(GSC)-6 White Rock 49°01* 122°50' 7 13,100 ± 190 12,000 ±217 1-5959 6 km SW of Marion 49° 17' 122°35' 8 13,110 ± 150 12,010 ± 183 GSC-2604 East Delta/ 49°08' 122°54' 1 Clinocardium 13,010 ± 175 11,910 ±204 I(GSC)-248r Boundary Bay 49°01' 123°04' 9 13,250 ±210 12,150 ±235 B-135695 Bellingham Bay 48°48' 122°32' 12 13,310 ±170 12,210 ±200 GSC-2193 Gravel pit 6.5 km 49°18' 122°47' 10 Websters Corner/ Mya truncata 12,680 ± 40 11,580 ± 115 B-145455 Axton pit/ Nuculana 48°51' 122°28' 6 12,720 ± 40 11,620 ±115 B-145456 Axton pit/ Nuculana 48°51' 122°28' 6 12,760 ± 40 11,660 ±115 B-145457 Axton pit/ Nuculana 48°51' 122°28' 6 Wood 11,450 ± 150 N . A . § L-331A Norrish Crk. NE of 49°12' 122°10' 11 Mission 11,700 ±150 N.A. L-331B Norrish Crk. NE of 49°11' 122°9' 11 Mission 10,950 ±200 N.A. L-331C Small Crk. north of 49°01' 122°16' 13 the Monastery near Mission. 11,400 ±170 N.A. GSC-1695 Draper Crk., north of 49°01' 122° 16' 14 Mission 11,600 ± 100 N.A. GSC-5770 Bradner pit 49°01' 122°26' 4 11,800 ± 100 N.A. GSC-5860 Bradner pit 49°01' 122°26' 4 11,800 ±50 N.A. GSC-5862 Bradner pit 49°01' 122°26' 4 11,600 ±70 N.A. TO-4087 Bradner pit 49°01' 122°26' 4 11,740 ±70 N.A. B-120446 Bradner pit 49°01' 122°26' 6 11,590 ± 140 N.A. GSC-226 Near White Rock 49°02' 122°47' 11 11,700 ±120 N.A. GSC-2842 Aldergrove 49°04' 122°28' 15 11,800 ±400 N.A. 1-1037 Everson type locality 48°50' 122°19' 36 11,770 ±40 11,680 ±50 11,660 ±50 11,670 ±40 11,830 ±40 11,790 ±40 N.A. N.A. N.A. N.A. N.A. N.A. B-144095 B-144097 B-144099 B-145458 B-145459 B-145460 Bradner pit Bradner pit Bradner pit Axton pit Axton pit Axton pit 49°01' 49°01' 49°01' 48°51' 48°51' 48°51' 122°27' 122°26' 122°26' 122°27' 122°27' 122°27' 6 6 6 6 6 6 * "Selected" radiocarbon dates mean that ages were included in this data set i f samples were from the surface-forming Fort Langley, Capilano, or Everson glaciomarine sediments. Other dates exist, but they were either located at depth or the unit description of the collector was inadequate to determine the stratigraphic position of the sample. * The reservoir-corrected age uncertainty is ((ka s) 2 + ar2)m where k is 1.6 for GSC dates and 1 for all other dates; a s is laboratory precision of the sample; crr is the uncertainty of the reservoir value. Note that in accordance with laboratory protocol, the uncertainty for GSC dates was reported with 2cr errors. For comparison with lrj age ranges reported by other labs, the error should be reduced to lcr by a division of 2 (R. McNeely, personal communication, 2000) but has not been done in this chapter. § N . A . = Not applicable * References: (1) Dyck et al. (1965); (2) Mathews et al. (1970); (3) Dyck and Fyles (1964); (4) Clague et al (1997); (5) Dyck and Fyles (1963); (6) This report; (7) Walton et al. (1961); (8) Mathewes (1973); (9) Trautman and Walton (1962); (10) Lowdon and Blake (1977); (11) Armstrong (1981); (12) Weber and Kovanen (2000); (13) Broecker and Kulp (1957); (14) Lowdon and Blake (1975); (15) Lowdon and Blake (1981). 37 Chapter 4 Timing and extent of Altered and Younger Dryas age (c. 12.5-10.014C kyr BP) oscillations of the Cordilleran Ice Sheet in the Fraser Lowland, Western North America 4.1 Introduction Abrupt, late-Wisconsin, millennial-to-centennial-scale, climate oscillations are well documented. In order to understand the causal mechanisms for abrupt climate change, a more complete picture of the geographic extent of these changes is needed. This chapter explores the nature of the late Wisconsin-to-Holocene transition in the Fraser Lowland in an attempt to evaluate the hemispheric linkage of these abrupt climate episodes (Figs. 4-1, 4-2). This region is well suited for the study of rapid environmental changes because: (1) it is located on the windward side of the maritime Coast Mountains and North Cascades, making it highly sensitive to climatic variability; and (2) abundant material for radiocarbon dating is available in the deposits. Increased understanding of the climate systems, direct evidence of past climate changes from deep sea cores west of Vancouver Island (JT96-09, Figs. 4-1,4-2, Kienast and McKay, 2001; Sabin and Pisias, 1996), and from pollen records (Mathewes, 1993; Mathews et al., 1993) provide a mechanism (i.e., temperature changes) in support of the field observations of multiple glacier margin oscillations. 4.2 Deglaciation in the Fraser Lowland During the late stages of deglaciation (c. 12.5-10.0 1 4 C kyr BP), the Cordilleran Ice Sheet thinned rapidly and retreated northward. When ice vacated the Strait of Juan de Fuca, marine waters entered the Puget Lowland and led to rapid retreat of the ice sheet c. 12.5 1 4 C kyr BP (Easterbrook, 1963,1992). This roughly coincides with major meltwater pulses in 38 Figure 4-1. Location of the Fraser Lowland in southern British Columbia, Canada and northwest Washington State, U.S.A JT96-09 is the location of a deep sea core which yielded SST estimates (Kienast and McKay, 2001). Inset shows location of GISP2 ice core and selected sites where indications of Younger Dryas cooling have been documented and are shown approximately: 1-Gosse et al, 1995; 2-Reasoner and Jodry, 2000; 3-Grigg and Whitlock, 1998; 4-Mathewes et al, 1993; 5-Mathewes, 1993; 6-Patterson et al, 1995; 7-Engstrom et al, 1990; 8-Kennett and Ingram, 1995; 9-Reasoner et al, 1994; Osborn et al, 1995. (Also see Rutter et al, 2000, their Fig. 1) The eustatic sea level record resulting from warming as reflected in the SST record (Kienast and McKay, 2001) and Greenland ice core (GISP2, Fig. 4-2). The retreat continued until grounding positions were established in the Fraser Valley. Topographically controlled, low-gradient, piedmont ice lobes formed between the Coast Mountains on the north and the North Cascade foothills on the southeast (Fig. 4-3). Early studies considered deglaciation (c. 14.5-10.0 1 4 C kyr BP) to reflect a single, late-glacial interruption (the 39 Sumas Stade) of the deglacial warming trend after the late Wisconsin maximum (the Vashon Stade). The combination of rapid climate change, isostatic rebound and eustatic sea-level adjustments created a complex glacial history (Fig. 4-2). Figure 4-2. 8 1 80 variations within GISP2 ice core indicating climate transitions (curve is a five-point (100-yr) moving average) with European pollen zone boundaries, the mean SST curve (Kienast and McKay, 2001) west of Vancouver Island in the NE Pacific, and chronology of the Fraser Lowland. GISP2 curve based on Stuiver and Grootes (2000) (Meese/Sowers Timescale: Alley et al., 1993; Meese et al., 1994; Meese et al., 1994; Grootes and Stuiver, 1997). Data from the Quaternary Isotope Laboratory Web site (http://depts. Washington.edu/qil/). Greenland Summit Ice Core data may also be obtained from the National Snow and Ice Data Center, University of Colorado at Boulder, and the World Data Center-A for Paleoclimatology, National Geophysical Data Center, Boulder, Colorado (U.S.A.). SST data was provided by S. Kienast. The SST age model is based on a reservoir value of-800 yr BP between 8-12 kyr (Southon et al. 1990) and -1100 yr for dates older than 12 kyr (Chapter 3). IACP is the intra-Allerad cold period (Lehman and Keigwin, 1992). Double vertical lines denote suggested periods of rapid sea-level rise (Fairbanks et al., 1992). 40 4.2.1 Previous work Table 1-1 lists contributions to the late glacial history of the Fraser Lowland since the 1950s and '60s when Armstrong and Easterbrook independently made substantive observations on emerged glaciomarine deposits and readvance of the remnants of the Cordilleran Ice Sheet (Armstrong and Brown, 1954; Armstrong, 1957,1981; Easterbrook, 1963, 1969, 1992). Later work on glacial deposits and landforms has shown that multiple fluctuations of a piedmont ice lobe occurred during the Sumas Stade (Armstrong 1957; Mark and Ojamaa, 1980; Saunders et al, 1987; Cameron, 1989; Easterbrook, 1994; Clague et al, 1997). The Sumas Stade is defined as beginning with emergence of the lowland following deposition of glaciomarine sediments and readvance of the Cordilleran Ice Sheet (Armstrong et al, 1965; Fig. 4-2), technically a piedmont lobe at that time. A critical observation to retain for the following discussions is that relative sea level during the Sumas interval was close to that of the present, whereas sea level prior to that was up to 180 m higher, during deposition of the glaciomarine drift (Armstrong, 1957, 1960; Easterbrook, 1963). Sea level during the early Sumas was c. 30 m or less, and during the late Sumas was close to modern sea level. Therefore, at the sites discussed below, the Sumas is not coeval with the glaciomarine deposits. The range of interpretations of the Sumas has recently diverged (Clague et al, 1997; Easterbrook and Kovanen, 1998a, b). At issue is whether or not massive stony mud containing articulated marine shells and foraminifera (6-30 species, Armstrong 1981; Clague et al, 1997) represents in situ deposition (making any underlying sediments pre-Sumas by definition). Clague et al (1997) contended that the fossils were eroded from older sediments and redeposited into an ice-marginal lake. Easterbrook and Kovanen (1998b) contented that the fossils were not reworked and presented evidence that the stony mud is glaciomarine in origin, which corroborates the findings of the early workers. The ramification of the differences in interpretation lie in the number, extent and timing of glacial advances recognized during the Sumas interval. In this chapter, the geomorphic features of the Sumas interval are clarified (some of which were not recognized by Clague et al, 1997,1998) and provide evidence for the timing of glacier oscillations. 41 4.3 Morphology and chronology of the Sumas phases Figure 4-3 illustrates four separate phases (SI, SII, SIII, and SIV) of the piedmont ice lobe during the Sumas Stade based upon morphologic, stratigraphic, and temporal relations. Each phase represents a time of glacier readvance or stillstand following ice retreat. Radiocarbon ages from the Everson glaciomarine deposits define the lower (older) age limit of Sumas Drift throughout the Fraser Lowland (Armstrong et al., 1965; Armstrong, 1981; Easterbrook, 1963, 1969, 1992). The chronology of the Sumas phases is based on 70 radiocarbon dates presented in Appendix A, but not discussed individually. This list includes new atomic mass spectrometer (AMS) and old scintillation dates (dates based on bulk sediment samples or blended from a mixture of shells), and more weight is given to AMS dates at critical localities (also see Chapter 5). In order to compare marine shell ages with wood ages, a total marine reservoir value of -1100 ± 100 1 4 C yr BP is applied to the shell dates. This value was determined from the difference of six paired shell and wood samples from glaciomarine sediment (Chapter 3). Since calibration ranges are not symmetrical, the full 2-sigma age range is given to best represent the full uncertainties, but note that many of the limiting dates fall within steep sectors of the calibration curve (INTCAL98), which limits the range of possible calendar ages. 4.3.1 Oldest Sumas Phase, SI The northern and western maximum limits of Sumas ice (SI, Fig. 4-3) are marked by scattered till, ice-contact deposits, and outwash that rest on glaciomarine sediment over broad areas, rather than a single ice-marginal position (Armstrong, 1957; Armstrong and Hicock, 1980a). The SI ice limit (Fig. 4-3) is drawn at the western margin of these deposits. A lobate embankment of poorly stratified, sandy till, 1-10 m thick fills the Miracle Valley near Stave Lake (Fig. 4-3) and rises c. 120 m above the valley floor as a subdued, convex-upvalley moraine that blocked drainage from the valley to the north to form a lake (Armstrong, 1960b, 1980a). Three topographically lower, arcuate, depositional features may indicate successive stands of glacier recession. These features have been mapped as 42 Fort Langley glaciomarine stony silt or Sumas sandy till (Armstrong, 1980a), but based on their morphology we consider them moraines. The southern SI margin is recognized by the head of a deeply incised meltwater channel at Squalicum Creek (Fig. 4-3), which is graded to a sea level close to the present. Because the channel is incised into glaciomarine stony mud (see Chapter 5), it must post-date them. Figure 4-3. Shaded digital topographic model showing the extent of the Sumas phases discussed in text. B-gravel pit off Bradner Road; LJ-Laxton and Judson Lakes; P-Pangborn Lake; F-Fazon Lake. Horizontal resolution, 25 m; scale is c. 1:600,000. 43 4.3.1.1 Age of SI The lower age limit (i.e., maximum age) of SI is based on 21 dates on shells (reservoir-corrected age 12,210-10,990 1 4 C yr BP, mean is 11,750 1 4 C yr BP; Appendix A) and 18 dates on wood (11,830-10,950 1 4 C yr BP, mean is 11,641 1 4 C yr BP) from glaciomarine deposits underlying SI drift. The dates cluster between a 11,800-11,600 1 4 C yr BP. (Fig. 4-4). Because many of the new dates on wood were determined by AMS, a higher degree of reliance is placed on them than on earlier, scintillation-counted dates. The weighted mean of five AMS dates on wood is 11,707 1 4 C yr BP, of which, three dates cluster between 11,660 and 11,680 1 4 C yr BP. In addition, a basal bog date of 11,413± 75 1 4 C yr BP (Appendix A, Chapter 5, site 54) from an outwash channel cut into glaciomarine sediments (Figs. 5a, 7a) indicates that the glaciomarine sediments must be older than c. 11,400 1 4 C yr BP. Prior to this date, a few hundred years must have elapse during building of a large moraine and cutting of the outwash channel. Therefore, the lower limiting age of SI is placed at c. 11,600 1 4 C yr BP based on the sequence of events and the youngest reproducible dates. The upper limiting age (i.e., minimum age) of SI is the 11,400 1 4 Cyr BP age of the Sumas SII moraine to the east (Appendix A, Table A-l). 44 12,400 12,200 12,000 11,800 11,600 11,400 11,200 1 4 C yr BP Fig. 4-4 Stacked histogram of wood and shell dates from glaciomarine sediments. The deposition of glaciomarine drift ended at c. 11,600 1 4 C yr BP. 4.3.2 Second Sumas Phase, SII Moraines, terraces, kettles, and abandoned meltwater channels record the extent of SII. A prominent, 9 km long and 0.5-1.5 km wide, hummocky moraine (Armstrong, 1957, 1960b, 1980a, 1981,1984; Armstrong and Hicock, 1980a) marks the SII ice margin southeast of Aldergrove and southwest of Abbotsford (Figs. 4-3, 4-4a). Abandoned, ice-marginal, meltwater channels run parallel to the moraine against the adjacent upland of glaciomarine sediment and extend away from the moraine to the west and south where outwash built a delta c. 30 m above modern sea level (Figs. 4-5a, 4-6a, 4-7a; Armstrong, 1957, 1960b; Mark and Ojamaa, 1980). Gravel pits in the moraine expose glaciomarine stony mud of the Fort Langley Formation and the overlying Sumas ice-contact sand and gravel. Till and deltaic deposits beneath the glaciomarine sediment represent a pre-Sumas ice stand within the Fort Langley Formation (Armstrong, 1981,1984). Clague et al. (1997) contended that the stony mud is lacustrine and included this till as part of their Sumas. In this model, the i t 12 10 3 8 IS Shell dates • Wood dates 45 fossiliferous stony mud is glaciomarine; therefore, the till is pre-Sumas and not included in the Sumas because it would violate the definition of the Sumas Stade. The southern SII margin is marked by the c. 30-m-deep, 305-m-wide, Tenmile Creek meltwater channel cut into glaciomarine stony mud (Fig. 4-5b). The channel is graded to a relative sea level close to the present and c. 180-210 m lower than that during deposition of the glaciomarine sediment, based on the maximum elevation of marine sediments. Lake Fazon (Fig. 4-5b), a kettle c. 2 km north of Tenmile Creek, is surrounded by a c. 10-m-deep peat bog. The relation of the kettle and outwash channels to the glaciomarine' sediment demonstrates the Sumas age of these features. At this elevation, Sumas ice had to be thick enough to send meltwater across an upland of glaciomarine drift at 60 m and remain long enough for meltwater to incise a 30-m-deep outwash channel system. The area between Lake Fazon and the large moraine in British Columbia is covered by younger outwash and the modern Nooksack River floodplain. 4.3.2.1 Age of SII In British Columbia, the SII moraine is younger than four reservoir-corrected marine shell ages from glaciomarine stony mud (11,870 ± 40-11,420 ± 80 1 4 C yr BP; Appendix A, sites 5,11-13; statistically equivalent at the 95% confidence level) and eight dates on wood (11,800 ± 50-11,600 ± 50 1 4 C yr BP; Appendix A, sites 25-28, 31-34). Dates from two rooted stumps (11,900 ± 50 and 11,750 ± 80 1 4 C yr BP; Appendix A, sites 23,43) beneath the fossiliferous stony mud provide supporting evidence for the age of the glaciomarine sediments. Reworking of this stony mud has been suggested by Clague et al. (1997), but that does not seem plausible because branches with twigs that contain needles and cones suggest that trees were alive shortly before deposition and could not have been appreciably reworked. Reworking of shell material is also considered implausible because: (1) no reworked clasts occur in the stony mud; (2) articulated shells are abundant; (3) there is a diverse foraminifera content (6-30 species); (4) whole bivalves still retain delicate ornamentation; and (5) the elevations of 100 (positively identified localities) other fossil 46 localities in the glaciomarine sediment (with similar C age, Armstrong, 1981) show that this area was submerged more than 100 m during this time interval. The SII moraine in British Columbia is also younger than twenty-one dates from marine shells in glaciomarine stony mud which yielded reservoir corrected ages ranging from 12,210 to 10,990 1 4 C yr BP (mean is 11,750 1 4 C yr BP; Appendix A, sites 1-21; Chapter 5) and 18 dates on wood (11,830-10,950 1 4 C yrs BP; mean is 11,641 1 4 C yr BP; Appendix A, sites 22-39). The age of SII is younger than at c. 11,600 1 4 C yr BP based on the youngest reproducible dates. In northwest Washington, the SII ice margin is younger than dates on wood and shells from the same stony mud. Nine dates from glaciomarine stony mud range from c. 12,150-11,455 1 4 C yr BP (Appendix A, sites 21,35, 44-50; Chapter 5). Because the glacier was banked against an older upland of glaciomarine sediment, meltwater from the ice margin was forced southward, cutting three channels up to c. 7 km long (Armstrong, 1957,1980a; Mark and Ojamaa, 1980) between the ice margin at the SII moraine and the upland to the west (Figs. 4-5a, 4-7a). When ice pulled back from the moraine, meltwater was cut off from the channels and reestablished inside the moraine. The age of ice retreat from its morainal margin must be older than the age of basal peat in the abandoned channel. Multiple cores taken with a Livingston corer reveal c. 10 m of peat in the channels. Wood in the basal peat of the oldest abandoned outwash channels (Figs. 4-5a, 4-7a) yielded AMS dates of 11,413 ± 75,11,037 ± 72, and 10,595 ± 80 1 4 C yr BP (Easterbrook and Kovanen, 1998a,b; Appendix A, sites 51, 53, 54). The oldest age (11,413 1 4 C yr BP) is the date by which time ice must have pulled back from the moraine and meltwater from the nearby ice ceased to flow (Fig. 4-7a). The deposition of peat must have begun shortly after the cessation of meltwater flow because the water table in the enclosing outwash sand and gravel then must have been within a meter of the surface and the channel could not remain dry for any appreciable length of time. The age of the SII moraine is younger than underlying stony mud, c. 11,600 1 4 C yr BP and older than the basal date from the outwash channel, 11,413 1 4 C yr BP (Fig. 4-4a; Appendix A, site 54). 47 In northwest Washington, the deeply incised outwash channels at the Sumas II position at Tenmile Creek (Fig. 4-5b) were abandoned when meltwater was cut off by ice recession and peat began to accumulate in the bogs. Basal peat from cores in the abandoned channel yielded AMS dates of 11,080 ± 100 and 11,113 ± 77 1 4 C yr BP (Appendix A, sites 57-58). These dates indicate that meltwater ceased to flow in Tenmile Creek channel by c. 11,000 1 4 C yr BP, about the same time as meltwater channels were abandoned at the northern ice margin. Two dates from basal peat at Fazon Lake are 9,770 ± 75 and 10,400 ± 85 1 4 C yr BP (Appendix A, sites 60-61). These dates suggest an upper limit for the melting of ice from the kettle somewhat younger than the dates from Tenmile Creek channel. 48 Figure 4-5. (a) Map of the SII moraine and ice-marginal meltwater channel. B-gravel pit off Bradner Road, (b) Tenmile Creek meltwater channel and Fazon Lake. Contours are in meters above sea level and the ages are 1 4 C basal bog dates referred to in the text. 49 4.3.3 Third Sumas Phase, S i l l As ice retreated from the SII maximum, it thinned until Sumas Mt., a 883-m-high, elongate bedrock knob in mid-valley, stood as a nunatak (Fig. 4-6a) between two remnant ice tongues. Stillstands of the two ice tongues produced a suite of moraines and ice-contact features that suggest a complex interaction, with multiple marginal fluctuations. Four subdued recessional SII moraines at c. 150 m a.s.l. at Mission (Fig. 4-6a) are cut across by a prominent SIII moraine which indicates a readvance of ice (Fig. 4-6a). Only with retreat of ice from the SII moraine c. 11,400 1 4 C yr BP did the Abbotsford outwash plain (Figs. 4-3,4-5,4-6a) to the east become activated. Outwash that forms a broad (up to 12 km wide), south-sloping surface (Fig. 4-7b) is dissected by younger meltwater channels. Fishtrap Creek (Figs. 4-3, 4-7a), which occupies a meltwater channel, incises the western margin of this plain and can be traced to the morainal system of the northern lobe, SIII morainal complex. The elevation of the head of the channel is c. 60 m and was abandoned when the source of water fell below this elevation. The significance of the geomorphic position of the broad Abbotsford outwash plain, which lies inside the SII moraine and heads at the SIII moraines (ice margin), is that it demonstrates that ice must have retreated from the area of Abbotsford outwash plain prior to its deposition. The ice margin must have retreated at least 20 km from the SII terminal position prior to readvance and deposition of the SIII moraines and the Abbotsford outwash plain. Therefore, the SIII morainal complex must be younger than the SII moraine. These geomorphic relations between SII and SIII are apparent on our hillshade images, but have not been considered in earlier interpretations of Sumas ice marginal positions. A deep meltwater channel incised c. 25 m into older drift originating from the SIII margin establishes that the ice must have been stable at its margin long enough to allow meltwater to carve the channel (Figs. 4-6). The distal end of this channel issues into Sumas Prairie (Fig. 4-6), but the position the ice front in the valley is uncertain. 50 4.3.3.1 Age of SIII Radiocarbon dates on SIII (undifferentiated) deposits from the upland north of Mission (Fig. 4-6a, Appendix A) were originally reported as coming from glaciomarine sediment, but were later listed as Sumas ice contact deposits (Armstrong, 1981). Because wood is so plentiful in glaciomarine drift in this area and because none has been reported elsewhere from the ice-contact deposits, we believe that the wood most likely comes from glaciomarine drift as originally reported and only represents a lower limiting ages for SIII (i.e., pre-SEI). The dates are 11,600 ± 140, 11,000 ± 900, 11,400 ± 85 and 10,950 ± 200 1 4 C yr BP (Appendix A, site 22-23, 62, 64). A date of 11,500 ± 1100 1 4 C yr BP (Appendix A, site 63) was obtained by Armstrong (1981) on Sumas deposits from Sumas Mt. Basal peat from a core in Fishtrap Creek channel behind the SII moraine (Figs. 4-5a, 4-7a) yielded a date of 10,980 ± 250 1 4 C yr BP (Easterbrook and Kovanen, 1998a, b; Appendix A, site 52). As the ice continued to thin and retreat, meltwater drainage shifted eastward and flowed southward from several SIII morainal ridges, abandoning the channels on the west side of the outwash plain. Therefore, ice must have retreated back from the SII moraine and the meltwater drainage shifted eastward by 10,980 ± 250 1 4 C yr BP (Fig. 4-3). 4.3.4 Fourth Sumas Phase, SIV Phase SIV of the Sumas Stade is represented by a well-defined moraine (Figs. 4-3,4-8) about 15 km east of the SII moraine. It consists of interbedded till, sand, and gravel making a hummocky, ridge that is concave eastward across the valley near Sumas and bends northeastward along the Cascade margin for about 3 km as a hummocky kame terrace (Fig. 4-8). An outwash terrace about 10 m above the present floodplain slopes southward away from the eastern portion of the moraine (Fig. 4-8), but most of the original outwash plain to the west has been removed by subsequent meltwater erosion that breached the moraine as the glacier retreated upvalley. Till resting on outwash in exposures at Sumas indicates that the ice advanced over a subaerial surface and therefore represents a readvance. 51 Figure 4-6. (a) Shaded relief image of Abbotsford area showing SIII moraine and associated Abbotsford outwash plain (black arrows show direction of meltwater flow), SII Miracle Valley moraine, and SII and SIV ice margins. Profiles A - A ' , B - B 1 , are shown in Figure 4-7. Refer to Figure 4-3 for the relation of the SHI and SIV margin with SII. L , J, P-Laxton, Judson, Pangborn Lakes, (b) SIII (Abbotsford) outwash channel. 52 (b) B Sill moraine North « 10 km . South Figur 4-7. Geologic cross-sections, (a) When ice pulled back from the SII moraine, the meltwater channel to the west was immediately abandoned (c. 11,413 ± 75 1 4 C yr BP); (b) Termination of the head of the Abbotsford outwash plain is against an SIII moraine. Large kettles at Pangbora bog, Laxton and Judson Lakes must have been filled with ice until deposition of outwash from SIII ceased at c. 10,250 1 4 C yr BP. Dates on figure are 1 4 CyrBP. Furthermore, till and ice-contact deposits of the SIV moraine block the southern end of the incised outwash channel (Fig. 4-8), indicating a readvance after the channel was abandoned. Meltwater from ice at this moraine and/or meltwater flowing marginally along the ice front, spread outwash sands and gravels westward that buried evidence of the older phases. 4.3.4.1 Age of SIV The SIV phase post-dates the SII and SIII ice-stands and peat deposition in Northwood bog (10,980 ± 250 1 4 C yr BP; Appendix A, site 52) and Pangborn Lake (10,245 ± 90 and 10,265 ± 65 1 4 C yr BP; Appendix A, sites 68-69). Outwash buried two large blocks of ice 53 c. 1 km in diameter left during SII glacier recession at the eastern side of the outwash plain, forming kettles at Pangborn bog and Laxton-Judson Lakes (Figs. 4-3,4-7b). Two cores in a 10-m-thick peat yielded AMS dates of 10,245 ± 90 and 10,265 ± 65 1 4 C yr BP (Easterbrook and Kovanen, 1998b; Appendix A, sites 68-69), which indicate the time of cessation of meltwater from the SIV ice margin because outwash would otherwise have filled in the kettle. A southward-extending, meltwater channel incised c. 15 m into the SIII outwash plain (Fig. 4-8) east of the SIV moraine was overridden by the SIV advance and the distal end of the channel is blocked by the SIV moraine. The SIV moraine must therefore be younger than this SIII outwash channel. Based on the limiting date from Fishtrap Creek (Figs. 4-3, 4-5a, 4-7a) and those from Pangborn bog (Fig. 4-7b), the age of the Abbottsford outwash plain is between c. 10,980 and 10,250 1 4 C yr BP. The readvance that deposited the SIV moraine occurred between before 10,250 1 4 C yr BP, but unfortunately, cores have not been obtained to establish a minimum age for the ice margin. Coring of a bog situated in a younger channel of SIV yielded a basal date of 8050 ± 65 1 4 C yr BP (Appendix A, site 65). Although this is a minimum constraining age, the oldest part of the bog was probably not reached. 54 122°22'W SIII outwash channel 122015'W Figure 4-8. 3D shaded digital topographic model of the SIV moraine and outwash plain at Sumas. Note that the northern margin of the moraine blocks the distal end of the SIII outwash channel and must therefore represent a readvance of the ice margin. Outwash from the SIV ice margin filled topographic troughs to the southwest and buried SI and SII moraines (Fig. 4-3). Scale is variable and changes with position on the diagram. 4.4 Summary The general deglacial history of the Sumas Stade between c. 11.6 and c. <10.0 1 4 C kyr BP includes at least three readvances (and possibly more) that interrupted the overall retreat of the remnants of the Cordilleran Ice Sheet. Phases SI and SII both occurred after c. 11.6-11.4 1 4 C kyr BP, and SII occurred before 11.4 l 4 C kyr BP, approximately equivalent to the Allerad (Fig. 4-2). Phase SIII occurred between 11.40 and 10.25 1 4 C kyr BP and phase SIV occurred c. 10.25 and <10.0 (?) 1 4 C kyr BP, falling within the Younger Dryas cold interval (Fig. 4-2). The timing and pattern of deglaciation presented in our ice-retreat model is constrained by 70 radiocarbon dates. Based on the comparison of the time span of glacial events in the Fraser Lowland to those established in the SST curves of the N E Pacific and the GISP2 ice-core record in Greenland, the extended correlations as shown 55 in Figure 4-2 are suggested, which are in general agreement with the extended correlations of Hicock et al. (1999). The short duration (i.e., submillennial scale) of the ice oscillations are difficult to extract from the SST curve, the oxygen isotope profile, and pollen records, but appear to be coincident within the resolution of the data. Uncertainties of the chronology caused by radiocarbon plateaus are recognized, but note that morphologic and stratigraphic evidence constrains the relative age of the phases. Therefore, this model is as accurate as present dating methods allow, although it probably represents a simplification of a complex natural system. As to whether or not the Sumas phases were triggered by climate changes or by other processes, we considered evidence from other climate proxies (e.g., nearby glacial, pollen, and oceanic records, see below). It is difficult to attribute these glacier oscillations to soft bed mechanics because no glacial deformation features in the underlying glaciomarine stony mud have been observed and most Sumas tills rest upon undeformed outwash. Moreover, no evidence of glacial surging (e.g., broad belts of ice-stagnation deposits), perhaps caused by sudden release of water from ice-dammed lakes that could have changed the basal hydrology, has been found in the study area. Even though these glacier oscillations might be more widespread, they have not been observed in this detail, possibly because physical conditions elsewhere were not sensitive enough and insufficient dating has been available. For instance, Figure 4-9 illustrates some possible regional and extended correlations with alpine moraines, but many are constrained only by minimum ages, so could date from any time following the last glacial maximum. Dates on moraine sequences from within the region (Chilliwack Valley - Saunders et al, 1987; Icicle Creek - Swanson and Porter, 1997; Mt. Rainier - Heine, 1998; Squamish Valley - Friele et al, 1999; Nooksack Valley - Kovanen and Easterbrook, 2001) provide some age control for ice expansion, which may suggest a common climatic causal mechanism, but more work is needed to determine correlations with the individual Sumas phases. For example, Saunders et al. (1987) described two diamictons that dated between 11.8 and 11.2 1 4 C kyr BP in the Chilliwack Valley adjacent to the Fraser Lowland. These tills mark the position of the lateral margin of the valley glacier that flowed into the 56 Chilliwack Valley from the lowland (Fig. 4-3). A 'younger' till resting on an organic-rich layer dated at 11.2-11.3 1 4 C kyr BP may correspond to the SIII advance, however, 4 out of 6 radiocarbon dates (Saunders et al, 1987) are in inverted stratigraphic position. Therefore, the ages are too equivocal for specific assignment to the Sumas fluctuations in the glacier terminal area. Other work in western North America documents Younger Dryas-type cold events in the Wind River Mts. of Wyoming and in the Colorado and Canadian Rocky Mts. (Fig. 4-1). Alkenone SST estimates from cores west of Vancouver Island (Fig. 4-1) indicate a drop of 3°C during the Younger Dryas following a period of c. 1400 years when temperatures rose c. 7°C (Fig. 4-2) (Kienast and McKay, 2001). Cool-water foraminifera suggesting Younger Dryas cooling have been found on the British Columbia shelf and in the Santa Barbara Basin (Fig. 4-1). These temperature changes are consistent with estimates from pollen records in southwestern British Columbia, northwestern Washington, western Oregon, and southeastern Alaska (Fig. 4-1) many of which show cooling during the Younger Dryas. Mathewes et al. (1993) suggested a summer air-temperature decline of 2-3°C between 11.1— c. 10.2 1 4 C kyr BP inferred from pollen records (ages that are essentially equivalent to the SIII advance), which is similar to the SST record. In eastern North America, at about the same latitude (46°N) as the Fraser Lowland (49°N), deglaciation in Northern Nova Scotia (Fig. 1) was nearly complete by 11.0 1 4 C kyr BP, followed shortly thereafter by pronounced re-growth of local ice centers that expanded from the highlands to the sea coast more than 50 km away (Stea and Mott, 1989,1998). With growing evidence of broadly synchronous global cooling (e.g., Lowell et al, 1995; Rutter et al, 2000), the timing of these events is critical in evaluating the role of interruptions in the North Atlantic thermohaline circulation (e.g., Lehman and Keigwin, 1992; Manabe and Stouffer, 1997; Ganopolski et al, 1998) as a trigger or amplifier in rapid climatic change. This evidence supports the abundant oceanic, and pollen records that show cooler climates prevailed during times of glacial readvance and stillstand in the Fraser Lowland. Because this evidence is far removed from the direct influence of the North Atlantic Ocean 57 thermohaline circulation at the same latitude (49°N), it adds to the growing body of evidence that rapid climatic episodes were at least hemispheric i f not interhemispheric. This work also illustrates the spatial complexities of millennial to centennial-scale climate oscillations, the sensitivity of climate proxies, which may or may not archive the complete climate history, and the need for more secure age control of morainal sequences for syntheses. SI & SII sill SIV Piper Lake moraine «=> j] I Minimum age from Glacier Peak ash G. 11.200 (Osbom and Gertotf, 199?) u Recess Peak moraine i > II I Minimum age, 11.190 ± 70 (Clark and GMIespie, 1997) Crowfoot advance n >—trr^^n -(Reasoner et al.. 1994; [] U U H H I M'""™" 1 ^ 1 °°20 ± TO Osbom efaf.,1996) Maximum age, 11.330 + 330 [ ] S >* Younger McNeeley moraine [ J Minimum age. 9140+ 100 (Heine, 1998) ^ Maximum age, 10.080 ±60 L E H H I I Okter McNeetey moraine = > [ ] \^MU Minimum age, 11.320 ± 60 (Heine, 1998) L ^ ^ " L J Squamish Valley kame, B.C. *—>J ] Minimum age. 10.650 ± 70 (Friele etal. 1999) i^^miim-> Howe Sound moraine. B.C. " = ^ [ [ M ll Minimum age, 10.690 ±180 (McCnjmb and Swanson, 1998) I I l I l I l I l l I l l l l i l i l i I i i i i i i i i i i i < i i I i t i l i i i . t i i . i l 15,000 14,000 13.000 12.000 11,000 10,000 9000 I , Age {cal yr B.P.) , 12,000 11,000 10,000 Aoe{ 1 4 CyTB.P.) Figure 4-9. Comparison of Sumas phases and selected alpine glacial records spanning the last glacial to non-glacial transition. 1 4 C dates are provided with calibrated age ranges (black and white fills are 1-sigma and 2-sigma age ranges, respectively). Note that all calibrated dates in Appendix A are given in 2-sigma age ranges (95% confidence interval). 58 Chapter 5 Morphologic and stratigraphic evidence for Altered and Younger Dryas age glacier fluctuations of the Cordilleran Ice Sheet, British Columbia, Canada and Northwestern Washington, U.S.A. 5.1 Introduction The focus of this chapter is morphologic and stratigraphic evidence for fluctuations of the remnants of the Cordilleran Ice Sheet in the Fraser Lowland (Fig. 5-1; c. 12-10 1 4 C kyr BP). At its late Wisconsin maximum c. 14.5 1 4 C kyr BP, the Cordilleran Ice Sheet was c. 1800 m thick over the Fraser Lowland (Easterbrook, 1963) and extended c. 80 km south of Seattle (Fig. 5-1). During deglaciation, the ice sheet thinned and backwasted to the Strait of Juan de Fuca (Fig. 5-1) where invasion of seawater beneath the glacier c. 12.5 I 4 C kyr BP triggered rapid breakup of the ice (Easterbrook, 1992). Melting of debris-laden ice, floating in marine water up to c. 180 m above modern sea level, deposited glaciomarine sediments over a wide area (c. 18,000 km2; Armstrong and Brown, 1954; Armstrong, 1957, 1980a; Armstrong and Hicock, 1980a, 1980b; Easterbrook, 1963,1969,1976a, b, 1992). Following emergence of the lowland at c. 11.6 1 4 C kyr BP, the remnant of the ice sheet readvanced several times. These rapid environmental changes took place during the Everson Interstade and Sumas Stade (Fig. 5-2), which span the Allerad and Younger Dryas periods. More details for the extent and timing of grounded ice during the Sumas Stade are given in (Chapter 4, Appendix B, D, E) and pertinent site-specific stratigraphic and morphologic evidence are summarized here. Clague et al. (1997: 261-277) interpreted pre-Younger Dryas resurgences of the southwestern margin of the Cordilleran Ice Sheet based on three stratigraphic sections from selected localities in a large gravel pit in the Fraser Lowland (Figs. 5-1, 5-2). Easterbrook and Kovanen (1998b: p. 225) pointed out evidence for the origin of massive stony mud as 59 glaciomarine (i.e., Armstrong 1981, 1984). The discrimination of the origin of these sediments has ramifications for their assignment to recognized stratigraphic units; specifically, those related to the Fort Langley Formation (Everson Interstade) and Sumas Drift (Sumas Stade) of the Fraser Glaciation (Fig. 5-2). A sound interpretation of these sediments is critical as it carries implications for the extent of ice during the Sumas Stade and its correlation with records elsewhere (e.g. Hicock et al, 1999). British Columbia CANADA aser wland JT96-09 ® •49°N Strait of Juan de Fuca PACIFIC OCEAN #^f^f%_GISP2|-^\^h Nova Scotia PACIFIC OCEAN < Washington U.S.A. ^-Seattle Puget Lowland 300 Kilometers w 125°W I Figure 5-1. Location map of the Fraser Lowland in southern British Columbia, Canada and northwestern Washington State. JT96-09 is the location of a deep sea core discussed later in the text. 60 L E G E N D Alluvium Peat • £ 1 Sum is Drift So Sumas outwash: Includes recessional and advance glaciofluvial, glaciolacustrine deposits Sumas silt & clay of uncertain origin, but of about the same age as Sumas outwash Sumas till & ice-contact deposits | Fort L a n g l e y F m . / E v e r s o n G l a c i o m a r i n c D e p o s i t s H H B H B F o r t Langley stony mud: Includes j l j j c j j g i wave-washed surface mantling sand & gravel, and marine terrace deposits Undifferentiated glacial deposits Note: For detailed surficial geology see Armstrong 1957, 1960, 1980; Armstrong 8. Hicock 1980a; Easterbrook 1976. Other Fort Langley and Sumas deposits occur in the upland areas within the view, but are not shown Refer to Fig. 4A for place names, topography and Sumas ice-marginal positions B-Bradner pit; LJ-Laxton and Judson Lakes; P-Pangborn Lake, ML-Marion Lake. F R A S E R L O W L A N D S T R A T I G R A P H I C F R A M E W O R K Time-Strati graphic Units Holocene Late Wisconsin Geologic-Climatic Units Postglacial Sumas Stade Everson nterstadel Vashon Stade Litho-stratigraphic Units Salish and Fraser River Sediments Sumas Drift Fort Langley glaciomarine sediments Vashon Drift Age 1 4 C y r B P ) | | -10 000 -11 600 -12 500 Fig. 5-2. Simplified surficial geologic map and stratigraphic framework in the Fraser Lowland (map units taken from Armstrong 1980a; Armstrong and Hicock, 1980a; Easterbrook, 1976b). 61 5.1.1 Terminology and stratigraphy The Sumas Stade was formally defined by Armstrong et al. (1965). It began with emergence of the lowland following deposition of Everson glaciomarine sediments and ended with the disappearance of the Cordilleran Ice Sheet from the area. Sumas Drift includes lodgement till, minor flow till, ice-contact sand, gravel, till, proglacial deltaic sand and gravel, glaciofluvial channel and floodplain sand and gravel, which cover a large part of the Fraser Lowland (Fig. 5-2; Armstrong, 1957, 1960b, 1980a, 1981, 1984; Mark and Ojamaa, 1980; Easterbrook, 1963,1969,1976b, 1994; Clague, 1981; Cameron, 1989; Clague et al, 1997; Easterbrook and Kovanen, 1997, 1998a, b). The emerged, surface-mantling, glaciomarine sediment provides the lower bounding surface for the Sumas interval and therefore, its recognition is critical. Bracketing ages for Sumas Drift in the Fraser Lowland were discussed by Clague et al. (1997) at one gravel pit in the Fraser Lowland (Figs. 5-1, 5-2). In fact, Sumas Drift is much more extensive and temporal relations are more complex. Figure 5-3 illustrates the differences of interpretation between Clague et al. (1997) and those in this chapter: (1) Clague et al. (1997) interpreted all sediments in the Bradner pit as Sumas Drift, including fossiliferous stony mud mapped nearby as Fort Langley (Everson) glaciomarine drift (Armstrong, 1980a). (2) Clague et al. (1997,1998) consider marine shells in the massive stony mud (unit 5) to have been disseminated from older marine sediment and redeposited into an active ice-marginal lake. (3) Easterbrook and Kovanen (1998b) interpreted the fossiliferous stony mud as glaciomarine in origin based on criteria established by earlier investigations (Armstrong and Brown, 1954; Armstrong et al, 1965; Armstrong, 1981, 1984; Armstrong and Hicock, 1980a; Easterbrook, 1963,1976a, b, 1992). The importance of this interpretation is that, by definition, the Sumas includes only glacial sediments younger than Everson glaciomarine sediment. (4) Easterbrook and Kovanen (Easterbrook, 1976b, 1994; Easterbrook and Kovanen, 1998b) recognized other Sumas moraines and diamictons 62 (e.g., landforms and sediments) that have not been included by Clague et al. (1997,1998) in their interpretation of the sequence of events during the Sumas interval. These four points are the main pillars of the subsequent discussion and suggest that Clague et al. (1997,1998) have not presented compelling evidence to demonstrate that the Sumas is strictly pre-Younger Dryas in age. Easterbrook & Kovanen(1998b) Clague etal. (1997, 1998) •Older Sumas (SII) Sumas Di •Younger* Sumas . O • » © « e o e * o • • o "» o • © o o o • nation Fort Langley glaciomarine sediment Sumas Drift Lake deposits c o Pre-Sumas 'Older" >t till Sumas « • • • o • o • o o o o o o o Marine deltaic °o o \ ° t deposits © o \^^  u. \ o \ ° Depth (m) 0 MO 20 Unit 7 Diamicton Unit 6 Stratified, sand and gravel Unit 5 Fossiliferous stony mud * — Unit 4 Peat layer '3° Unit 3 Diamicton 40 h50 Unit 2 Silt Sand and gravel (topset beds) Unitl Dipping sand and gravel (forset beds) Massive sand ( 1 4CyrBP) This study * Easterbrook & Kovanen (1998b) Clague etal. (1997) c. 10,000 to c. 11,600 SIV SIII SII SI Younger Sumas Not distinguished Older Sumas Not distinguished Denied Not recognized Younger Sumas Not recognized s11,600 Glaciomarine sediments Pre-Sumas Older Sumas * Sumas phases are based on morainal morphology and stratigraphy b Figure 5-3. (a) Comparison of stratigraphic interpretations in the Bradner pit. (b) Comparison of interpretations for the Fraser Lowland. 63 5.2 Moraines and drift deposits of the Sumas Stade Figure 5-4a shows reconstructed ice margins from c. 12.5 to 10.0 1 4 C kyr BP. The distribution of seventy radiocarbon dates on marine shells, wood, and peat (Table 5-1, at end of chapter) are shown in Figure 5-4b. Radiocarbon dates in Table 5-1 are grouped in three general categories: (a) those that permit a definable relation to retreating ice, providing upper limits; (b) those related to the intervals of earlier marine submergence, providing lower limiting ages; and (c) undifferentiated. Because of large uncertainties associated with many of the scintillation-counted dates (Table 5-1), they are considered as rangefinder values and more weight is given to new atomic mass spectrometer (AMS) dates at critical localities. Therefore, not all of the dates are discussed individually in the text. In order to compare marine shell ages with wood ages, a total marine reservoir value of-1100 ± 100 1 4 C yr BP is applied to the shell dates (Chapter 3). The term 'phase' is used to mean a stillstand or readvance of the ice margin. The basis for delimiting each of the Sumas phases is on morphologic and stratigraphic evidence. The radiocarbon dates provide the ages of the phase and permits correlations, but are not the basis for their definition. Meltwater channels incise the stony mud (Fig. 5-2) and record the limits of Sumas ice (Armstrong and Hicock, 1980a, b; Easterbrook, 1976b; Mark and Ojamaa, 1980). Note that the level to which these channels are graded was c. 30 m above present sea level. This means that, in general, deposition of Sumas drift was not contemporaneous with Fort Langley glaciomarine deposits. 64 Figure 5-4. (a) Shaded digital topographic model of the Sumas phases based on position of scattered ice marginal deposits, prominent moraines and configuration of meltwater channels. B-Bradner pit; LJ-Laxton and Judson Lakes; P-Pangborn Lake; F-Fazon Lake. Horizontal resolution is 20 m. 65 • 11.2(2) •11.6(6) • 12.2 (19) *11.9 (14) FRASER RIVER • 11.7 (10) • 13 (17) • 12 (18) LEGEND # Conventional shell dates © AMS shell dates A Conventional or unknown wood and peat dates A AMS weed and peat dates N 11.2(3)* 11.6(27,28) 11.7(32) I > / (si 11.4(6) . 11.8 (11-13>a 11.4 (54 10.9 (52) 10 10 Kilometers sAIOi (68, » SII v A 8 (66) 11.5(7) ^ 1 11.6(8 9) ^ ^ ' 10.7(56) 11.6(36) 10.8(66) 116(48) 'ft 1 1 7 <M> 1 1 f 5 7) 11.7(49)/ - ^ 1 - 8 ( 3 7 » "•1<5 8> 12.2 (601 \ 12.1 (21) 11.4(44) H11.5(45) 11.6(46) 11.8(35, 47) Figure 5-4. (b) Distribution of radiocarbon dates. Dates are shown in thousands of year ( 1 4 C kyr BP) with the corresponding site number in parentheses from Table 5-1. Dates are from bog bottoms in front of and behind moraines, underlying glaciomarine stony mud, and stratigraphic sections. Note that dates from glaciomarine stony mud provide the limiting dates for SI and SII. 66 5.2.1 SI ice margin The SI ice margin (Fig. 5-4a) is drawn on the basis of the western-most limits of Sumas till, ice-contact deposits, and related drift. These deposits do not define a simple, single ice margin, but the glacier terminus must have reached at least to the western extent of the deposits. Therefore, in contrast to the other ice margins, the SI glacier margin is only a hypothetical ice limit, not a well-defined, single, terminal zone. Whether the SI drift represents readvances of the ice sheet or a grounding of floating ice from the previous period of glaciomarine deposition is unknown. The southern SI margin is marked by the head of a deeply incised, meltwater channel at Squalicum Creek (Fig. 5-4a; Easterbrook, 1963,1976b). The channel is graded to a sea level close to the present and must post-date Everson glaciomarine stony mud because the channel is incised into it (Fig. 5-2). The age of the SI ice margin is younger than the underlying glaciomarine sediments (c. 11.6 1 4 C kyr BP) and older than the 11.4 1 4 C kyr BP basal bog age of the younger SII margin to the east (Fig. 5-5b) (see later discussion). 5.2.2 SH ice margin A prominent moraine and incised meltwater channels record the SII ice margin in southwestern British Columbia (Figs. 5-4a, 5-5a, b). The northern SII ice margin is marked by a hummocky moraine, 9 km long and 0.5-1.5 km wide (Armstrong, 1957,1960b, 1980a, 1981, 1984; Clague et al, 1997) (Figs. 5-4a, 5-5A, B). Abandoned ice-marginal meltwater channels occur parallel to the moraine between it and the adjacent upland and lead away from the moraine to the west and south (Fig. 5-5a; Armstrong, 1957,1960b, 1980a; Armstrong and Hicock, 1980a; Mark and Ojamaa, 1980). As shown by a marine delta at the western, distal margin of the channel (Fig. 5-5a), sea level at this time was c. 30 m above modern sea level. The southern SII margin is marked by the head of the c. 30-m-deep, 305-m-wide, Tenmile Creek meltwater channel (Fig. 5-4a) cut into glaciomarine stony mud (Easterbrook, 1976b). The channel is graded to a relative sea level close to the present and 67 c. 180-210 m lower than during deposition of the glaciomarine sediment. Lake Fazon (Fig. 5-4a), a semicircular kettle 2 km north of Tenmile Creek, is surrounded by a c. 10-m-deep peat bog. The Sumas age of Fazon Lake kettle and Tenmile outwash channel is demonstrated by their relation to the glaciomarine drift. At this position, Sumas ice had to be thick enough to send meltwater across the upland of glaciomarine drift at 60 m and remain long enough for meltwater to incise a 30 m deep outwash channel into the glaciomarine sediment. 5.2.2.1 Stratigraphy of the SII moraine deposits The SII (Aldergrove) moraine (Fig. 5-5b) was constructed of ice-contact sand, gravel, and till deposits by remnants of the Cordilleran Ice Sheet upon massive stony mud that makes up the adjacent upland to the west (Armstrong, 1981,1984). Several issues revolve around the stratigraphy of drift units exposed in gravel pits in the core of the moraine. Deposits in the Bradner pit (Figs. 5-3, 5-5b, c) are the only Sumas units recognized by Clague et al. (1997, 1998) in the lowland and they interpret the massive stony mud containing articulated shells and foraminifera to be glaciolacustrine in origin (Fig. 5-3a), rather than glaciomarine as mapped by Armstrong (1960b, 1981). Beneath the glaciomarine stony mud, Armstrong recognized pre-Sumas till overlying deltaic sand and gravel (Figs. 5-3a, 5-5c, 5-6a,b, c, d) that he included in the Fort Langley Fm. However, Clague et al. (1997) contend that the overlying stony mud is lacustrine, rather than glaciomarine, and interpreted this till as their "Older Sumas" (Fig. 5-3a). The ramification of this difference in interpretation is that the glaciomarine origin of the stony mud means that the till beneath it must be pre-Sumas by definition and the overlying ice-contact deposits are the only true Sumas sediments that they recognize. The basis for the glaciomarine interpretation of the stony mud is discussed below. 68 Figure 5-5. (a) Map showing relation of Campbell River delta and meltwater channels to SII moraine (modified from Clague and Luternauer, 1983). (b) Topographic map of SII moraine showing the location of gravel pits examined in this study. Gravel pit site designations: 1-Valley Gravel Sales Ltd. pit off Lefeuvre Road; 2-Fraser Valley, West Coast Aggregates, and LaFarge Central Aggregates, pit off Bradner Road; 3-Imperial pit off Bradner Road; 4-Steelhead Aggregates pit off Ross Road; 5—Little Rock Quarries pit off Ross Road; 6-Valley Gravel Sales Ltd. pit off Marshall Hi l l Road; 7-exposure that reveals stony mud "inside" of SII moraine; 8-Valley Gravel Sales Ltd. pit west of Peardonville Road. 69 Llthofacies codes DIAMICT Dmm Dms Dcs Matrix-supported, massive Matrix-supported, stratified Clast-supported, stratified GRAVEL Gmm Gms Gcs Matrix-supported, massive Matrix-supported, stratified Clast-supported, stratified SAND Sm/Fm Sh/Sc/Sr Sd/Fd Massive / fines Horizontally bedded / cross stratified / rippled Sand / fines with dropstones SILT/CLAY Sim/Sid/Sir Sitty-clay, massive / laminated with dropstones / rippted Symbols « Shells Rooted stump IV Unit number 11,770±40 1 4 C v r B P s 100 90 o 80 Wood 11,770 ±40 11,750 ±80 11,740 1 70 Shells 11,850 ±40 11,850±40 11,870 ±40 excavated Peat layer 2A Sumas ice-contact 4 drift Dmm Dms.''' Unit 5 S h " '£='Ftg.5-7a Sid ="Figs. 5-6c, d, e J Sid. Sir |' -Peat layer covered Fig. 5-5f covered Figs. 5-6a, b * <r l Fort Langely Dmm glaciomarine sediments Peat layer Omm < = i Fig. 5-7b covered S/i Sc \ Fig. 5-7c Fig. 5-5 continued, (c) Simplified stratigraphic sections from gravel pits in the SII moraine. The location of logs (2A, 2B, 4, and 5) is shown approximately on Figure 5-5b. 70 Massive stony mud (unit 5; Figs. 5-5c, 5-6d) up to 10 m thick overlies peat (unit 4) (Figs. 5-6c, 5-7b). The stony mud is divided into two subunits; basal laminated silt/clay up to 2 m thick (Fig. 5-6e) and massive stony mud (Fig. 5-6e; Clague et al, 1997). The laminated silt sharply overlies the peat (unit 4) and contains abundant woody material. Although laminated silt is commonly lacustrine, laminated marine sediments have been widely reported in the literature (Powell, 1983; Eyles et ah, 1985; Domack, 1990; Andrews et al, 1994; Jennings, 1993; Dowdeswell and Dowdeswell, 1989; Dowdeswell et al, 2000). Therefore, the laminated sediments could be either marine or lacustrine, based solely on the laminations themselves. The massive stony mud contains abundant marine mollusk shells and foraminifera and has been previously interpreted as a product of floating ice delivering heterogeneous debris to a marine environment (Armstrong and Brown, 1954; Armstrong, 1981,1984; Easterbrook, 1963,1992). Clague et al (1997,1998) interpreted the stony mud as glaciolacustrine and postulated that shells and foraminifera were reworked. The basis for their interpretation is the sharpness of the contacts (e.g. no transgressional deposits). However, such sharp contacts bounding the glaciomarine stony mud are typical in the region (Easterbrook, 1969,1992; Armstrong, 1981,1984; Weber, 2000). The absence of transgressional sediments is not unusual and indicates a very rapid drowning of the area. Even if the glaciolacustrine hypothesis of Clague et al (1997) were to be accepted for the Bradner site, its extension to the whole region presents insurmountable obstacles. The massive stony mud contains many well-preserved, articulated, mollusk shells (many show no signs of abrasion, retaining delicate radula and nacreous layers), foraminifera, and numerous logs and branches with attached needles. Within the articulated shells is a silty clayey material identical to the surrounding matrix. The integrity of the shells and the presence of needles on twigs and branches indicate that neither has undergone significant transport. Shells are scattered, but occur with concentrations up to 12 shells per square meter of exposed surface in some places. All shell species are marine and 8 O values for three bivalve shells were -O.896o, -0.5%o, and -0. l%o, which shows that they lived in water of normal marine salinity. These observations 71 are not compatible with the reworking hypothesis. Observations by Clague et al. (1998) inferring the lack of articulated shells suggests that they overlooked shell-rich sites. Furthermore, the reworking hypothesis requires dissemination of shells and foraminifera from a previously deposited glaciomarine sediment, followed by transportation and redeposition into different enclosing material (Easterbrook and Kovanen, 1998), at the same time maintaining species assemblages similar to in-situ assemblages in the primary glaciomarine drift. The absence of clasts of reworked glaciomarine sediments is also incompatible with the reworking hypothesis. Bulk samples of unit 5 were analyzed for fresh-water diatoms or ostracodes, the presence of which would prove a lacustrine origin for either the stony mud or the laminated silt. However, none was found (S. Fritz, personal communication, 1999) and because freshwater diatoms are common in lacustrine deposits, their absence suggests (but does not prove conclusively) that the laminated sediment is not lacustrine. Whether the laminated sediment is lacustrine or marine is not critical because in either case the sediments may be regarded as transitional, between the deposition of the peat layer (unit 4) and the massive fossiliferous stony mud. The claim that Armstrong was unaware of unit 5 and that the stony mud falls within Armstrong's Sumas Drift (Clague et al, 1997) is misleading. Armstrong did indeed recognize the "glaciomarine stony silt to clay loam " to be the uppermost unit in the Fort Langley Fm., and he interpreted only the overlying lodgement till and glaciofluvial sand and gravel as Sumas Drift (Armstrong, 1984: section number 37 and 38, p. 20). This is in agreement with the stratigraphy exposed in the Bradner pit (Fig. 5-5c). A review of proprietary information provided by pit owners indicates that the massive stony mud laps up onto the uplands and is continuous many kilometers to the east, north, and northeast where it emerges to form the surface and near-surface material (Figs. 5-5C, 5-7) positively identified by Armstrong (1980). This is in the immediate vicinity of Steelhead and Little Rock pits where the massive stony mud can be observed less than 2 km from the Bradner pit (Figs. 5-5b, 5-5c, 5-7). Its upper limit is c. 93 m above present-day sea level (Fig. 5-5c) and can be traced continuously to the upland (Figs. 5-7b, 5-7c) and beyond where it is not lacustrine. 72 Other stratigraphic sections shown by Armstrong (1981,1984) indicate the stratigraphic sequence and elevations of the Fort Langley and Sumas deposits in the area. The elevation of the bottom of unit 5 ranges from c. 75-90 m (Clague et al, 1997), which is well within the range of elevations that Armstrong shows for the Fort Langley sediments (Fig. 5-8). The age of these sediments is consistent with the Fort Langley Fm., so a widespread lake at the same time that the Fort Langley glaciomarine stony mud was being deposited is unrealistic. Upland areas occur to the north and west, the area to the southwest is low-lying and open to the sea, providing no opportunity to impound a lake (Fig. 5-4a). Considering the documented observations of more than four decades by Armstrong and Easterbrook; the lack of unequivocal evidence for a physical mechanism that could have impounded a widespread lake during the time that Fort Langley glaciomarine sediments were being deposited; and the lack of positive evidence for the interpretation of a lacustrine origin for the massive fossiliferous stony mud, the glaciomarine origin of the stony mud must be preferred on the balance of the evidence. Clague et al (1997: p. 268-9) argued against the glaciomarine origin of the stony mud (Unit 5) on the grounds that shells in the unit might be reworked, based largely on the 12,520 ± 80 1 4 C yr BP age of a shell (Table 5-1) was interpreted as being too old. They reduced the shell age by a regional reservoir value of -800 years (Southon et al, 1990), which gives a reservoir-corrected age of 11,720 1 4 C yr BP. Six paired, shell and wood dates, including three from the Bradner pit (Table 5-1), indicate a local marine reservoir value of-1100 ± 100 1 4 C yr BP (Chapter 3). Reducing the above shell date by -1100 years yields a reservoir-corrected age of 11,420 1 4 C yr BP. Three dates from other shells in the stony mud yielded reservoir-corrected ages of 11,870 ± 40,11,850 ± 40, and 11,850 ± 40 1 4 C yr BP, while three dates on wood yielded ages of 11,770 ± 40,11,750 ± 80, and 11,740 ± 70, 1 4C yr BP (Table 5-1; Figs. 5-4b, 5-9). These dates suggest that the 'old' shell date above is c. 400 years younger than in-situ wood and shells in the stony mud. 73 Figure 5-6. Photographs of the Bradner pit. (a & b) Units 1,3, and 5. The approximate thicknesses of the units are shown. 74 Figure 5-6, continued. Photographs of the Bradner pit. (c) Peat (unit 4) and stony mud (unit 5). The stump is rooted in till (unit 3) and was one of 12 found. The inset is an articulated Nucalana enclosed by stony mud. Peat and laminated silt/clay drape onto the trunk of the stump, (d) Close-up of the massive stony mud (unit 5). 75 Figure 5-6, continued. Photographs of the Bradner pit. (e) Laminated clay and silt, (f) Rooted stump. Shovel is 54 cm long. 76 Figure 5-7. (a) Stony mud in the Steelhead pit, previously mapped as part of the Fort Langley Fm. (Armstrong, 1980a). (b) Stony mud in the Little Rock pit. (c) Little Rock pit: stony mud is traced continuously to the upland where it emerges and has previously been mapped as Fort Langley glaciomarine stony mud (Armstrong, 1980a). Refer to Figure 5-5b for pit locations. 77 Figure 5-8. Plot of 50 marine fossil elevations in the stony mud relative to present-day sea level (based on Armstrong 1981; p. 19) from the Fraser Lowland. The minimum elevation of the stony mud within the Bradner pit is added to the plot. Twenty-one radiocarbon dates on shells between 11.8-11.6 1 4 C kyr BP indicate a marine transgression at that time. Figure 5-9 illustrates how important stratigraphy and morphology are to proper interpretation of 1 4 C dates. The sequence of depositional events is as follows: (i) deposition of pre-Sumas till under subaerial conditions; (ii) ice retreat, growth of forest (now rooted stumps, Figs. 5-6c, f) dated at 11,750 ± 80 and 11,900 ± 50 1 4 C yr BP; (iii) deposition of peat (Fig. 5-6f) that laps up onto the stumps and contains wood dated at 11,680 + 80 1 4 C yr BP (site 27); (iv) rapid marine submergence and deposition of glaciomarine stony mud on the peat (Figs. 5-6c, 5-7b); ten 1 4 C dates on wood, branches, cones average 11,702 1 4 C yr BP (six AMS dates range between 11,660 and 11,770 1 4 C yr BP); (v) emergence and readvance of ice, building of the SII moraine (Fig. 5-5b); (vi) incision of ice marginal meltwater channels between the moraine and the upland to the northeast (Figs. 5-2, 5-5); 78 (vii) retreat of ice from SII moraine, abandonment of the channel, and deposition of peat in the channel began 11,413 ± 75 1 4 C yr BP (AMS date, site 54); and (viii) establishment of meltwater channels inside (east) of the SII moraine that head at the S i n morainal complex. Clague et al. (1997) obtained dates of 11,300 ± 80 (site 40) and 11,410 + 110 (site 41) 1 4 C yr BP from the peat and concluded that the overlying ice-contact drift was younger than 11,300. Based on 1 4 C dates and the sequence of events described above, the 11,300 and 11,410 dates are considered anomalously young (400-500 years). Acceptance of the young dates implies that the peat below the glaciomarine stony mud and basal peat in the outwash channel are the same age and would require the following: (/') the sequence of events i-vi to occur simultaneously; (ii) dismiss the 10 dates in the overlying stony mud; and (iii) dismiss many other dates from the same, regionally extensive stratigraphic unit (Fig. 5-2). The anomalously young 1 4 C dates cannot be reconciled by age uncertainties from plateaus in the radiocarbon calibration curve (Fig. 5-10). These dates fall on steep sectors of the calibration curve and the possible range of ages does not overlap. Clearly, resolving these site-specific differences is important in order to produce a solid stratigraphic and chronologic framework. From the above discussion, the age of the SII moraine is bracketed between c. 11.6 and 11.4 1 4 C kyr BP, not younger than 11.3 1 4 C kyr BP (Clague et al, 1997) and both Sumas phases SI and SII are Allerad in age. 79 ioo -r c g *.*-» co > 111 A SII A ' outwash channel (Peat) I SII moraine 1 / Fishtrap outwash channel (Peat) 10,980 504. NW ~3 km ? Abbotsford (SIII) outwash plain SE Incised outwash channel SII ice-contact gravel, sand and till / 10 1 4C dates avg. 11,702 Wood in peat (11,680) Needle (11,300) Charcoal (11,410) Fig. 5-9. (a & b) Schematic sections through the SII moraine showing stratigraphic position of the radiocarbon dates. 80 INTCAL98 11,000 12,000 13,000 14,000 15,000 13,000 13,500 14,000 14,500 CalyrBP CalyrBP Figure 5-10. Plot of the INTCAL98 calibration curve between 9,500-13,000 1 4 C yr BP (based on Stuiver et al., 1998a) and dates from peat and overlying stony mud in the Bradner pit. 5.2.3 SIII ice margin The glacier retreated c. 20 km to the northeast following the construction of the SII moraine before readvancing again over portions of the northern end of the SII moraine and building of a complex of SIII moraines (Figs. 5-4a, 5-11). An upland ridge c. 125 m asl west of Mount Lehman is interpreted as the maximum limit of SIII ice (a northern lobe of ice relative to ice filling Sumas Prairie during development of SIV moraine; Fig. 5-11; see later discussion), which was restricted between Sumas Mt. and the upland above Mission and c. 14 km wide in its terminal area. The upland area formed a buttress to advancing ice: to the west of the ridge is a gentle slope composed of Fort Langley stony mud; to the east are Sumas ice stagnation features composed of sandy till up to 10 m thick and ice-contact deposits (Figs. 5-2, 5-4a, 5-11; Armstrong, 1980a). Distinct ice-marginal belts, each separated by intervening meltwater channels at successively lower elevations, suggest time-transgressive decay of the ice. The highest 81 106 m); another relatively broad hummocky moraine may be traced between c. 90-75 m for c. 5.5 km and contains small, isolated, steep-sided, water-filled depressions. The material exposed in road cuts is substratified to stratified sandy silt with gravel. Erratics composed Of granodiorite and Jackass Mt. conglomerate lie on this surface showing that the source of the ice was the Fraser Valley to the east. Several intervening, trough-like valleys 6-15 m deep and up to 100 m wide trace the margins of the moraines. These troughs are interpreted as channels that were cut by meltwater flowing between the ice margin and the moraines while the lower reaches of the valley were filled with ice. The channels developed on this surface roughly mark the ice front position at different times in the ice retreat, are visible on the shaded digital topographic model (Fig. 5-11), and are easily recognized in the field. A plateau area between bedrock spurs north of Mission (c. 150 m asl) contains at least three subdued asymmetric ridges transverse to the direction of ice flow and are arcuate in the downvalley direction (Figs. 5-2, 5-4a, 5-11). Several of these ridges are composed of substratified silt, sand, and gravel, which are interpreted as moraines that document the position of ice during its retreat. Peat bogs filling intervening abandoned channels have maximum depths of 3 m. These features are cut across by a larger prominent moraine, which indicates a readvance of ice. Along the valley side, ice-marginal channels are associated with ice contact deposits, kame terraces, and moraines that were constructed by this ice lobe. Drainage was diagonally across the slope toward ice-free areas to the west. More work is needed to determine numerical age constraints of events in this area. Near Stave Lake, a subdued, convex-upvalley moraine composed of substratified till 1-10 m thick fills the Miracle Valley near Stave Lake (Figs. 5-2, 5-4a, 5-1 lb; Armstrong, 1960b, 1980) to c. 120 m above the valley floor and blocks drainage from the lake. Three topographically-lower, arcuate depositional features may indicate successive stands of glacier recession. Against Sumas Mt. southeast of Mission, several ridges composed of till-like, substratified, silty, gravelly diamicton interbedded with water-sorted gravel and sand containing pebbles, cobbles, and boulders, are interpreted as lateral moraines (Figs. 5-11, 5-12). Several undulating sharp-crested morainal segments rise c. 30 m above the 82 surrounding topography. The highest ridge (124 m asl) has a 0.6-km-long profile and slopes downvalley. On the distal side of the moraine is a flat surface composed of sand and gravel interpreted as outwash. The steep-sided proximal slope evolves into undulating topography about 20 m below the ridge crest. This topography may be traced c. 0.5 km downvalley where it merges into a segmented, sharp-crest moraine. Three segments are roughly asymmetric at 75-85 m asl and c. 10-20 m above the surrounding topography (Fig. 5-12b). Narrow outwash aprons on the distal side of the moraine are restricted between the valley side on the east and the moraine on the west. These features may represent ice activity at progressively lower and younger phases. The height of the moraines indicates the minimum thickness of ice at time of their deposition. Based on elevation and morphologic similarities, the morainal segment at c. 75 m is associated with moraines on the Mt. Lehman upland. Proximal to the lower morainal segment is a prominent narrow terrace (up to 365 m wide and 2.5 km long) exhibiting an arcuate form. The slope of this surface is in the opposite direction to that of the proximal side of the moraine (toward the Fraser River), 60-50 m asl. The origin of what resembles meander scarps (?) is not clear, but may be an overprint of ice-marginal drainage or post-glacial Fraser River activity. The terrace has been incised by younger drainage flowing off Sumas Mountain. Because these moraines are closely spaced and have parallel apexes, this suggests superposition of several episodes of moraine building, but suitable exposures revealing the stratigraphic structure have not been discovered to support this assertion. Therefore, whether or not all of these moraines or parts of them represent a major readvance of ice or minor oscillations is unclear, although, from cross-cutting relations of moraines, at least one significant readvance did occur with a minimum ice thickness of c. 120-150 m. A low-gradient, meltwater channel incised the Sumas drift in Abbotsford (Figs. 5-2, 5-4b, 5-11; Chapter 4, Fig. 4-6b). The channel is c. 10 m deep, 150 m wide, and c. 1.5 km long and provides Abbotsford a main throughway across the undulating Sumas surface from Sumas Prairie to the modern Fraser River floodplain. This abandoned channel, referred to as the Abbotsford meltwater channel, developed as ice retreat opened up a lower pathway late in deglaciation. Remnants of the initial phase of entrenchment may be seen 83 along the inner channel in the form of a terrace, which may be traced to the morainal segments mentioned above (Chapter 4, Fig. 4-6b). Figure 5-11. (a) 3D shaded digital topographic model of SIII terminal area. Scale is approximate, (b) Miracle Valley moraine. 84 Only with ice retreat from SII moraine did the Abbotsford outwash plain become activated. The earliest outwash was deposited along the western part of the outwash plain. As ice retreat continued, younger outwash was deposited over the expanding outwash plain to the east. Basal peat from an early outwash channel that heads at the SIII moraine and situated behind the SII moraine (Figs. 5-4a, 5-9b) yielded a date of 10,980 ± 250 1 4 C yr BP (Table 5-1, Fig. 5-4b). As ice continued to thin and retreat, meltwater drainage shifted eastward and flowed southward behind a series of morainal ridges, abandoning the channels on the west side of the outwash plain. Gravel pits reveal stratified, coarse grained, sand, and gravel overlain by a substratified, compact, gravelly diamicton about 5-7 m thick that is interpreted as lodgement till, mantled by a thin veneer of outwash. This till resembles that described by Armstrong (1981, 1984) for his type section of the Sumas Drift, 4 km to the east. Outwash buried large blocks of ice c. 1 km in diameter at the eastern side of the outwash plain during glacier recession. Melting of the ice blocks left large kettles at Pangborn bog, Laxton, and Judson Lakes (Figs. 5-2, 5-4a, 5-11). Basal bog dates of 10,245 + 90 and 10,265 + 65 1 4 C yr BP (Figs. 5-4a, 5-4b, Table 5-1) limit the time of cessation of meltwater from the SIII ice margin because outwash would otherwise have filled in the kettle. Therefore, the SIH phase spans the time from 10,980 to c. 10,250 1 4 C yr BP, within the Younger Dryas period. These features are not incorporated in the interpretations of Clague etal. (1997,1998; Fig. 5-3b). 85 a b Figure 5-12. (a) Till (c. 8 m) exposed in road cut of moraine, (b) Arrow points to one of several moraine segments that rise above surrounding topography along Sumas Mt. 5.2.4 SIV ice margin A readvance of the southern ice lobe near Sumas left an arcuate, hummocky, ridge of till, interbedded with sand and gravel overlooking a south-sloping outwash terrace (Fig. 5-2). At its western margin, the moraine extends across and blocks the distal end of a SIII outwash channel and till rests on subaerial outwash, both indicating that the ice readvanced. Pangborn bog kettle just west of the SIV moraine (Figs. 5-2, 5-4) must have been occupied with ice when the moraine was constructed, otherwise the kettle would have been filled in by outwash. Therefore, the SIV readvance must slightly predate the basal bog dates of 10,245 ± 90 and 10,265 ± 65 L 4 C yr BP mentioned above. A broad outwash plain southwest of Sumas (Figs. 5-2, 5-4a) contains many peat-filled bogs. The oldest date obtained from basal peat is 8050 ± 65 1 4 C yr BP (Fig. 5-4b), but the oldest part of the bog 86 was probably not reached so the termination of Sumas IV is not yet adequately dated. Clague et al. (1998) do not recognize the SIV moraine (Fig. 5-3b). 5.3 Discussion Reconstruction of the late Wisconsin deglaciation is based on the integration of morphologic and stratigraphic evidence, surficial mapping, visualization of features produced from digital elevation data, and radiocarbon dating. An attempt has been made to view the Sumas interval in a broad context by combining previous observations (e.g. Armstrong 1981, 1984; Easterbrook 1976b, 1994; Clague et al, 1997) with new data. The glaciomarine origin of fossiliferous, massive, stony mud (Unit 5), discussed by Clague et al. (1997, 1998) and Easterbrook and Kovanen (1998b) is preferred, corroborating Armstrong's (1981, 1984) conclusion of the glaciomarine origin of this unit and mapping of it in the area (Armstrong, 1980a; Armstrong and Hicock, 1980a; Easterbrook, 1976a, b). The glaciolacustrine hypothesis for the origin of the massive stony mud (Clague et al, 1997) can be discarded on the basis of field evidence and radiocarbon dating. The massive fossiliferous stony mud is traceable continuously to broad uplands where it is positively identified as glaciomarine in origin (Armstrong 1981,1984; Armstrong and Hicock, 1980a). Figure 5-13 shows a plot of radiocarbon dates and an overview of glacial events during the Sumas interval. Estimates in Figure 5-14 provide a basis for time-parallel correlations between ice-core, marine, and terrestrial records, but caution must be exercised, as we know that different proxies respond at different rates to climate changes. However, the concurrence with other records suggests that the Sumas ice fluctuations may represent responses to changes of climate (whether direct or indirect influence of local factors). The SST estimates from the northeast Pacific west of Vancouver Island (Figs. 5-1, 5-14) indicate a drop of c. 3°C during the Younger Dryas. Pollen records suggest a 2°C change in average July temperature from c. 11.5-9.5 1 4 C kyr BP on the Olympic Peninsula (Heusser, 1973; Fig 5-1). From Marion Lake bog (Figs. 5-2, 5-4a), just beyond the Sumas ice margin, a decrease in summer air temperature of 2 - 3 ° C between 11.1-10.2 kyr BP was inferred from pollen transfer functions (Fig. 5-14; Mathewes et al, 1993; see 87 Fig. 5 in Mathewes, 1993). The pollen records (e.g., Mathewes and Heusser, 1981) seem to manifest the large-magnitude events, but not the rapid events (i.e., Gl-lb, intra-Allerod cold period), possibly because the vegetation was amply robust to survive short-lived climatic oscillations. And even though the pollen records are not highly resolved, they do provide strong evidence for the Younger Dryas event in this region (i.e., Mathewes, 1993; Mathewes et al, 1993). Radiocarbon Dates 11,500 10,000 12,500 10,500 13,000 11,000 a. a. m I o 13,500 ii,soon 14,200 12,000 14,400 12,500 Sites 68, 69, Pangborn bog siv X -o SI • SII lower limit D SII upper limit • SIII maximum • SIV lower limit SIII Site 52, Fishtrap Crk. bog -Sequence of Glacial Events Building of SIV moraine Readvance of ice Building of SIII moraine complex Deposition of Abbotsford outwash plain Readvance of ice -Retreat of ice Building of SII moraine Readvance of ice Emergence and scattered SI drift Oepositon of Fort Langley sediments (glaciomarine stony mud) Figure 5-13. Selected radiocarbon dates (with site numbers from Table 5-1) and sequence of glacial events during the Sumas interval. Dashed lines when timing of events is approximate, but confined by morphologic and stratigraphic evidence. Shaded band delimits the deposition of Fort Langley-Everson glaciomarine sediments. The upper limit is placed at 11,600 1 4 C yr B P , based on the discussion in text. 88 GISP2 GRIPS809 NE Pacific Marion event (JT96-09) Lake -42 -40 -38 -36 -42 -40 -38 -36 6 8 10 2 4 , n « • , Mean Temp. Terrestrial Fig. 5-14. Bidecadal Greenland ice-core chronologies (based on 8 1 8 0 variations; Alley et al, 1993; Grootes et al, 1993; Meese et al, 1994; Stuiver and Grootes, 2000), mean SST curve (based on C37 alkenone variations) in the N E Pacific (Kienast and McKay, 2001), and Marion Lake curve for mountain hemlock pollen percentages (after Mathewes, 1993). Shaded areas are the colder episodes of the INTIMATE Event Stratigraphy (Bjorck et al, 1998; Walker et al, 1999; Lowe et al, 2001). The European pollen zones are provided for comparison (Mangerud et al, 1974). IACP is the intra-Allerod cold period (Lehman and Keigwin, 1992). GRIP data provided by the National Snow and Ice Data Center, University of Colorado at Boulder, and W D C - A for Palaeoclimatology, National Geophysical Data Center, Boulder, Colorado. GISP2 data was obtained from the Quaternary Isotope Laboratory Web site (htt://depts. Washington.edu/qil/). SST data was provided by S. Kienast. The SST age model is based on a reservoir value of -800 yr between 8-12 kyr (Southon et al, 1990) and -1100 yr for dates older than 12 kyr (Chapter 3). 89 Based on the local morphology and stratigraphy, if the above time-parallel correlations are valid, then large-scale (synoptic) oceanic-atmospheric circulation system changes have occurred (e.g., Trenberth, 1990). These changes are similar to those observed around the Atlantic basin at about the same latitude (e.g., Norwegian Sea, 49°N; Koc-Karpuz and Jansen, 1992; Lehman and Keigwin, 1992) and (e.g., maritime Nova Scotia, 45°N; Mott et al, 1986; Stea and Mott, 1989; Keigwin and Jones, 1995). Temperatures in northwestern Europe decreased to near full-glacial levels (Goslar et al, 1993). Along the maritime coasts of Nova Scotia and British Columbia, cold and moist conditions prevailed after c. 11.0 1 4 C kyr BP (Mott et al, 1986; Stea and Mott, 1989; Mathewes et al, 1993; Kienast and McKay, 2001). The glacier fluctuations (retreat followed by significant readvances) of the terminal zone of the glacier overlap several recognized climatic changes in Europe. Phases SI and SII correlate with the Allerad. Dating resolution is not adequate to assign either SI or SII to the inter-Allerad cold period, but the possibility exists. Phases SIII and SIV lie within the time span of the Younger Dryas. This work relates the terrestrial stratigraphy with the marine and ice-core records to better understand rapid regional and global environmental change. Notwithstanding issues of chronology details, which will no doubt be further resolved as new evidence emerges, the Sumas events may now be reliably related to other terrestrial, ice-core, and marine isotopic sequences at a scale within the precision and accuracy of 1 4 C dating (e.g., Hicock et al, 1999). 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SO_ cn ftftT —H I—1 ft—. .—( so CN CN fN oo CN SO tn <N co °ft OSft ,—T CN CN ft-T -Hft^  m so tn cn «/"> SO so CN" CN" < z SO + 1 oo so < Z o Os -H OS SO a o o 96 Chapter 6 Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack Drainage, North Cascades, Washington 6.1 Introduction This chapter discusses the geology, climatic implications, and chronology of eight late Pleistocene moraines in the Nooksack drainage of the North Cascades of Washington (Fig. 6-1). Following the last retreat of the Cordilleran Ice Sheet from this area, glaciers 23-45 km long occupied each of the three forks of the Nooksack Valley (Fig. 6-1). Present herein is morphologic, lithologic, stratigraphic, and chronologic evidence to demonstrate that the glaciers that built these moraines were alpine glaciers not connected to the Cordilleran Ice Sheet, including a period of moraine building that overlapped the Younger Dryas. The readvances of long, alpine glaciers in the North Cascades during the late Pleistocene carries implications with respect to our understanding local, regional, and global climatic changes. 6.1.1 Previous work The earliest observations of Pleistocene glaciation in the northwest Cascades were reconnaissance surveys made by Dawson (1877-1878) in southwestern British Columbia and by Smith and Calkins (1904) and Daly (1912) in northwest Washington. Smith and Calkins observed gravel terraces above the Nooksack River, and Daly recognized that an ice sheet covered the Nooksack drainage. Easterbrook (1963,1969) reported erratics northeast of Mt. Baker and confirmed the north-south flow of the Cordilleran Ice Sheet in this area on the basis of north-south glacial grooves on ridge crests and the complete absence of Cascade rocks in glacial drift in the adjacent lowland. Heller (1980) suggested that the Cordilleran Ice Sheet in its early advance flowed from the lowland eastward up ice-free valleys in the northwest Cascades and observed that glacial grooves on ridges east of Mt. Baker confirmed north-south flow 97 of the Cordilleran Ice Sheet at its maximum. About 64 km southeast of the map area, Vance (1957) also found that the Puget lobe moved up the Cascade stream valleys to within 27 km of the Cascade crest. Quaternary deposits of six 1VJ quadrangles in the area were mapped and dated (Kovanen, 1996). 6.1.2 Regional glacial history During the late Wisconsin maximum of the Fraser Glaciation (Fig. 6-2), the Cordilleran Ice Sheet flowed southward from British Columbia, covering the northern Puget Lowland and the northwestern Cascades except for peaks higher than c. 2100 m that rose above the ice surface as nunataks. At the glacial maximum, the ice sheet extended across the entire North Cascades from the Puget Lowland to the Columbia Plateau. Reconstruction of minimum ice-surface altitudes and ice-flow directions for the Cordilleran Ice Sheet is shown in Figure 6-3 based on altitudes of ice-marginal features, drumlins, and glacial grooves. In the Nooksack Valley, glacial grooves occur on ridge crests at altitudes to 2000 m and erratics were deposited by ice that must have crossed divides as high as 1800 m (Daley, 1912; Ragan, 1962; Easterbrook, 1963, 1969; Heller, 1980). Ice flow directions and ice-surface elevations are important to later discussions of the source of ice for glaciers in the Nooksack Valley. Daly (1912) recognized granitic erratics from Canada at elevations to 1400 m on ridge crests and concluded that the ice sheet had completely covered mountains just west of Kendall and must have been at least 900 m thick, perhaps more than 1200 m thick. He suggested that in the higher Cascades to the east, the ice sheet must have reached the 2100 m contour and must have been 1200-1500 m thick. In the late 1930s, Coombs recognized north-south-trending glacial grooves across ridge crests 2000 m above sea level north of Mt. Baker, and in the late1950s and early 1960s, Misch and Moen (summarized in Easterbrook, 1963,1969) reported erratics in the study area that must have crossed divides of 1400 m and higher near the Canadian boundary. Granitic erratics on dunite bedrock of the Twin Sisters Range (Fig. 6-1) at elevations of 1600 m were observed by Ragan (1962), who concluded that only peaks above 2100 m were above the Cordilleran Ice Sheet at its maximum. 98 Independent confirmation of north-south flow of the Cordilleran Ice Sheet in the Nooksack drainage is found in erratics on a 1700 m ridge crest that could only have come from an area immediately to the north, and in the lithology of Vashon till and Everson glaciomarine drift of the Cordilleran Ice Sheet. Vashon till and outwash, Everson glaciomarine drift, and Sumas till and outwash completely lack Mt. Baker andesite, Twin Sisters dunite, and other typical northwest Cascade lithologies, showing that the Cordilleran Ice Sheet had no significant westerly component of flow (Easterbrook, 1963, 1969). Retreat of the ice sheet began abruptly c. 14,500 1 4 C yr BP (Mullineaux et al., 1965; Easterbrook, 1992; Porter and Swanson, 1998), and by c. 13,000 1 4 C yr BP, the Cordilleran Ice Sheet had retreated and thinned sufficiently to allow the remaining ice to float, initiating glaciomarine conditions over the region during the Everson Interstade (Fig. 6-2) (Armstrong and Brown, 1954; Armstrong, 1981, Easterbrook, 1963, 1969, 1992). The Nooksack Valley was inundated by rise of marine water relative to the land, and glaciomarine drift was deposited from floating ice of the Cordilleran Ice Sheet at least 10 km upvalley from the lowland to elevations as much as 200 m above present sea level (Easterbrook, 1963, 1969,1992; Kovanen and Easterbrook, 1998). Following emergence of the area, glaciomarine sediments were buried by outwash in the Nooksack Valley. Thus, the Cordilleran Ice Sheet must have disappeared from the study area before deposition of moraines in the Nooksack drainage (Kovanen, 1996). The glaciomarine drift 10 km upvalley is significant because it provides limiting 1 4 C ages for the overlying Nooksack Valley outwash and demonstrates that the Cordilleran Ice Sheet had completely withdrawn from the lower Nooksack Valley. Once the Cordilleran Ice Sheet had melted below drainage divides in the area, the ice became topographically controlled, and glaciers in the Nooksack Valley became isolated from the main ice sheet (Fig. 6-4). The deterioration of the Cordilleran Ice Sheet remaining in the Fraser Lowland to the northwest was interrupted several times by readvances or stillstands of the ice sheet during the Sumas Stade between c. 10,000 and 11,600 1 4 C yr BP (Fig. 6-2) (Kovanen and Easterbrook, 1997). 99 Figure 6-1. Shaded digital topographic model of the study area generated by merging digital data from 36 71/2' quadrangles originally produced by the U.S. Geological Survey. ML-Mosquito Lake Valley; CL-Cranberry Lake; SL-Silver Lake. Glacier Extent Through Time (Drifts Deposited by the CIS Flowing from North (Canada) to South (U.S.) Time (14C kyrs B.P.) Geologic Climate Units of the Fraser Glaciation Lithostratlgraphlc Units of the Nooksack 10.0 11.0 13.0 18.0 Middle Fork North Fork Resurgences Of the Ice Sheets _---— * ^ - -Sumas Stade Drift of Lateral Moraine Ice-Contact Drift Drift of Maple Falls Moraine Kendall Moraine 14.0 14.5 Catastrophic Collapse of the Ice Sheet Everson Interstade Everson Gaciomarlne Drift Vashon Stade Vashon Drift South North < - 250 Km Olympia US/Canadian Border Figure 6-2. Lithostratigraphic and geologic climate units in the Nooksack drainage. 100 Figure 6-3. Reconstruction of the Cordilleran Ice Sheet at the Vashon (late Wisconsin) maximum. Surface contours (shown in meters above sea level) were drawn on the basis of the altitude of ice marginal features against the Cascade Range and Olympic Mountains. Arrows (blue) are ice-flow directions from drumlin topography on Vashon drift (modified from Easterbrook, 1979). The ice-flow directions (red arrows) on ridges near Mt. Baker in the Cascade Range are based on glacial grooves on ridge crests and show a consistent north-south direction of flow. 101 Figure 6-4. Reconstruction of the Nooksack Valley glacier system on a hillshade image showing its relation to the remnant Cordilleran Ice Sheet following the Vashon maximum. The North Fork glacier originated from the north-facing cirque on Mt. Shuksan and was fed by large tributary glaciers flowing north from broad ice fields on Mt. Baker. The Middle Fork glacier originated from a broad ice field on the southwest flank of Mt. Baker and from glaciers on the western flank of the Twin Sisters Range. The South Fork glacier originated from both sides of the Twin Sisters Range, extended into the east end of Lake Whatcom, and filled the valley to the south. A remnant of the Cordilleran Ice Sheet is situated in the lowland northwest of the Nooksack Valley, 1500 m below intervening ridge crests. Reconstruction of the Nooksack glacial system was made on detailed images at scales of 1:4,000 based on geomorphic features and assuming minimum ice thicknesses required for glacial flow. 102 6.1.3 Climatic influences The climate of the North Cascades is a function of the interaction between local topographic features and meteorological conditions produced by atmospheric pressure patterns over the North Pacific Ocean. In winter, storms are generated by a quasipermanent, low-pressure cell (Aleutian Low) that extends over much of the North Pacific from late fall to spring and a high-pressure cell (North Pacific High) to the south. The size and intensity of the Aleutian Low may show substantial intraseasonal, interannual, and interdecadal variability (Mantua et al., 1997; Hodge et al., 1998). The positioning of the low and high off the North American coast directs the marine-dominated storm tracks toward the North Cascades. Topographic features that influence the meteorological conditions of the North Cascades include the Olympic Mountains, the Coastal Mountains of Vancouver Island, and the Cascade Mountains of Washington and British Columbia. Peaks reaching 1500-2000 m in the Olympic Mountains and Vancouver Island form a partial barrier to incoming storms. However, the Strait of Juan de Fuca is a prominent east-west-trending trough that offers direct avenue for storms to enter the study region. Eastward-moving frontal systems pass over the foothills, converging in a narrow corridor about 20-30 km wide in which the precipitation is about twice as much as on either side before reaching Mt. Baker (3285 m) and the Twin Sisters Range (2113 m) (Fig. 6-1), which provide the first significant barrier to storm tracks. Paleoclimatic conditions distinctive to the northwest Cascades may have been responsible for long alpine glaciers in the Nooksack drainage. The close proximity of the Cordilleran Ice Sheet may provide a plausible explanation for the long alpine glaciers in the Nooksack, and the following hypotheses are presented. (1) The Cordilleran Ice Sheet may have altered the typical low pressure storm systems coming from the north Pacific that dominate local weather patterns. (2) Southward-flowing, cold, katabatic air off the ice sheet may have reduced air temperatures and increased snowfall. (Although moisture content in cold air may be low, snow accumulation would increase). (3) The terminus behavior may be explained by accumulation areas at high elevations above late Pleistocene equilibrium-line altitudes 103 (ELAs). Therefore, climatic conditions near the Cordilleran Ice Sheet, coupled with the large size of the alpine source area, may set this area apart from areas to the south. 6.1.4 Glacial setting Mt. Baker (Fig. 6-1) is a large Quaternary stratovolcano that is the highest peak in the North Cascades (3285 m), and is c. 50 km east of the Strait of Georgia in a maritime climatic zone. At present, Mt. Baker has broad ice fields and 12 large valley glaciers extending to elevations of 1200 m, a result of high snow accumulation areas that provide abundant nourishment. Glaciers radiate from the volcano into the Nooksack Middle and North Forks. Today, high elevation, heavy winter precipitation, and northerly latitude combine to form a 49 km2 ice field covering the summit and all sides of the mountain. The large size of the local accumulation areas on the flanks of Mt. Baker, the Twin Sisters Range, and Mt. Shuksan permitted the development of long Pleistocene valley glaciers in the North Cascades similar to those in Alaska today. Because the Nooksack Valley glaciers were constructed of confluent ice streams from multiple sources at different elevations, and had relatively low gradients for much of their extent, reconstructing ELAs is complex (see Porter, 2001 for a discussion of inherent errors that limit the accuracy of five primary methods of ELA reconstruction). Therefore, changes in ELAs that may have affected the spatial and temporal histories of these glaciers have not been calculated. Heine (1998, p. 1140) interpreted the "required lowering of ELA required for this advance is more than 1500 m," in contrast to only 900-1000 m for the Vashon maximum of the Cordilleran Ice Sheet (Porter, 1977). Heine's interpretation does not seem plausible, because if a lowering of the ELA by 1000 m resulted in an ice sheet c. 2000 m thick, why would an ELA lowering of 1500 m produce only relatively minor alpine glaciers? This illustrates that the use of standard techniques for calculating ELAs of the late Pleistocene Nooksack complex alpine glaciers system does not yield meaningful results. 104 6.2 Evidence for late Pleistocene alpine glaciers in the Nooksack Valley Glacial drift deposited from the Cordilleran Ice Sheet during the last glacial maximum contains material derived from sources to the north in Canada that are distinctly different from the local bedrock of the northwestern Cascades. Distinctive bedrock types that produce glacial deposits with unique pebble, boulder, and heavy mineral suites underlie the upper reaches of each principal fork of the Nooksack drainage (Fig. 6-5). Therefore, distinguishing deposits of the Cordilleran Ice Sheet from locally derived sediments is not difficult. However, a secondary question here is whether the ice in the Nooksack Valley that deposited these locally derived sediments was connected to the Cordilleran Ice Sheet. Fortunately, several lines of evidence are available to answer this question and all indicate that the Cordilleran Ice Sheet was not connected to the Nooksack valley glaciers during building of the Nooksack moraines. The following evidence demonstrates that the lower Nooksack glaciers were alpine glaciers not connected to the Cordilleran Ice Sheet. 1. Glaciomarine drift found 10 km up the Nooksack drainage from the lowland shows that grounded Cordilleran ice had vacated the valleys prior to 12,000 1 4 CyrBP. 2. The lithology of the glaciomarine drift in the Nooksack Valley is totally of Canadian provenance and lacks any key, up-valley rock types (such as Mt. Baker andesite and Twin Sisters dunite). This indicates that the source of sediment in the glaciomarine drift was not from the northwestern Cascades, but rather from the thinning Cordilleran Ice Sheet in the lowland to the northwest. 3. During retreat of the Cordilleran Ice Sheet, when the ice surface dropped below the level of ridge crests in the northwestern Cascades, the ice must have become topographically controlled. Because north-south flow of the Cordilleran Ice Sheet in this part of the Cascades has long been well established, no connection with Cordilleran ice east of Mt. Baker existed at this stage. The Cordilleran Ice Sheet could not have reoccupied the upper Nooksack drainage thereafter without topping drainage divides more than 105 1500 m above the valley floors (Fig. 7-4). Had this happened, the lithology of the drift in Nooksack moraines would have been very different. 4. The margin of the Cordilleran Ice Sheet during deposition of the Nooksack moraines is well known from moraines in the adjacent lowland and a 200 m ice-contact face 10 km north of the northernmost Nooksack moraines (Fig. 6-4). The Cordilleran Ice Sheet in the lowland was reduced to a piedmont tongue in the lowland and the Chilliwack Valley (Fig. 6-4), a long, east-west trending valley just north of the Nooksack drainage in Canada, was ice free except for a small tongue of ice from the piedmont tongue. Hence, the position of the Cordilleran Ice Sheet margin was well north of the Nooksack drainage at this time and well below intervening drainage divides. However, summit ice-fields and large cirque glaciers continued to exist on Mt. Baker, Mt. Shuksan, and the Twin Sisters Range. 6.2.1 Glacial deposits in the Nooksack Middle Fork The Nooksack Middle Fork (Figs. 6-1,6-4) originates from the Deming Glacier on the southwest flank of Mt. Baker and flows westward through bedrock dominated by distinctive Mt. Baker andesite, dunite from the Twin Sisters Range, arkosic sandstone of the Chuckanut Formation, and Darrington phyllite (Fig. 6-5) (Ragan, 1963; Brown et al., 1986; Tabor et al., 1994). The Twin Sisters dunite and Mount Baker andesite are exceptionally useful as unique source indicator clasts and are easily identified in the field. Mosquito Lake Valley, a dry tributary valley to the Middle Fork, is 23 km downvalley from Mt. Baker; it is deeply kettled, and filled with ice-contact drift fills, (Figs. 6-1,6-6, 6-7), forming a kettle-kame complex (Kovanen, 1996). The preservation of the complex may be attributed to its position in a former tributary valley that has not been reoccupied by postglacial streams. Ice-contact drift of the kettle-kame complex is composed mostly of sand and gravel that contains numerous glacially faceted and striated boulders and cobbles, the lithologies of which are dominated by Chuckanut sandstone (45%), andesite from Mt. Baker (17%), and dunite from the Twin Sisters Range (17%) (Fig. 6-8b). The Mt. Baker andesite must have entered the glacial load directly in the headwaters of the Middle Fork, whereas the 106 Twin Sisters dunite entered from several tributary valleys along the south side of the valley (Figs. 6-5, 6-9). Chuckanut sandstone is not very durable and entered the glacial load along the north side of the valley within 8 km of the terminal area. A few granitic and quartzite clasts occur in the deposits, but in minor quantities (l%-2%) compared to much larger amounts (30%-40%) found in sediments of the Cordilleran Ice Sheet (Fig 6-8b). These lithologies indicate that the glacier that transported them must have originated in the headwaters of the Middle Fork (Figs. 6-4, 6-5). From the evidence discussed earlier, these glaciers must have been alpine glaciers heading on Mt. Baker and the Twin Sisters Range. Very deep kettles in the ice-contact drift indicate that the ice that pushed up into the Mosquito Lake valley (Fig. 6-6) from the Middle Fork must have stagnated. Deep Kettle Bog (Figs. 6-6, 6-7, 6-10a) is about 35 m deep to the surface of a peat bog and the base of the peat is 20 m below that, totaling 55 m for the total depth of the kettle. At the base of the bog in this kettle, a thin layer of organic material beneath deep-water diatomite (Fig. 6-10b) could apparently only have formed on stagnant ice before the kettle formed and was filled with deep water. The sand and gravel of the ice-contact drift have been tilted and offset by small faults from collapse of the sediments as the supporting stagnant ice melted away. A sharp-crested, lateral moraine composed of 10 m of till containing many glacially faceted and striated cobbles and boulders, derived almost entirely from Mt. Baker and the Twin Sisters Range (Figs. 6-5, 6-9), is preserved on top of the ice-contact drift (Figs. 6-6, 6-7,6-11). The lateral moraine is several kilometers long and tapers in elevation downvalley (Figs. 6-6, 6-7). Erratic boulders greater than 1 m that litter the surface of the left lateral moraine consist predominantly of Mt. Baker andesite (83%), with smaller amounts of Twin Sisters dunite (9%), and granodiorite (9%) (Fig. 6-8b). Most of the cobbles consist of dunite; together with the dominance of Mount Baker andesite boulders, this indicates a source in the Middle Fork headwaters (Kovanen, 1996). The lack of Chuckanut sandstone erratics is probably due to its low durability. No granitic plutons are known in the headwaters of the Middle Fork, so the few granitic erratics must be reworked from earlier Cordilleran Ice Sheet deposits. Granitic boulders are almost completely absent from lateral moraines just upvalley, suggesting that by the time they were deposited, virtually all of the lag granitic boulders had been cleaned out of the valley by earlier ice. The absence of garnet, a Cordilleran Ice Sheet Canadian source indicator, in the sand 107 The absence of garnet, a Cordilleran Ice Sheet Canadian source indicator, in the sand fraction in both the till of the lateral moraine and in the underlying ice-contact sediments confirm the source of ice as the upper Middle Fork valley, not the Cordilleran Ice Sheet (Kovanen, 1996). 6.2.1.1 Age of glacial deposits in the Nooksack Middle Fork Two 20 m cores from Deep Kettle Bog terminated in gray, pebbly sand. The thirteen 1 4 C dates (Fig. 6-10b; Table 6-1) on wood and other organic matter from the base of the core closely date the time of ice stagnation and hence limit the age of the kettle-kame complex (Kovanen, 1996; Kovanen et al., 1996). Four accelerator mass spectrometer (AMS) radiocarbon dates from wood immediately on the basal sand/gravel average 12,280 1 4 C yr BP, and six AMS dates from wood in overlying peat average 12,070 1 4 C yr BP (Fig. 6-5c; Table 6-1). Three AMS dates from rootlets in the basal sand/gravel average 11,870 1 4 C yr BP. The reason for the younger dates in the basal sand and gravel probably reflects root growth of vegetation in the overlying material. Pure diatomite just above the dated organic material includes species indicative of a deep lake that formed in the kettle immediately following melting out of the ice. The deep water level of the lake is controlled by groundwater in the highly permeable sand and gravel of the ice-contact drift, so water in the kettle could not have been shallow enough to allow peat formation until well after the ice had melted out of the kettle. Therefore, the rootlets in sand/gravel and overlying organic material at the base of the bog had been growing in rock debris on stagnant ice before the underlying ice melted out to make the kettle. Therefore, the basal AMS dates closely date the time of ice stagnation. The lateral moraine overlying the kettle-kame complex and a younger lateral moraine upvalley have not yet been directly dated, but must be younger than the dates from the base of Deep Kettle Bog (c. 12,00014C yr BP). Logs in a lateral moraine in the upper Middle Fork were dated at 10,680 ± 70 and 10,500 ± 70 1 4 C yr BP. 108 Figure 6-5. Bedrock geologic map of the Nooksack drainage showing distribution of principal lithologic units that contributed to alpine glacial deposits in the area (modified from Tabor et al, 1994). The most significant contributors of clastic material to Nooksack moraines are Mt. Baker andesite, Twin Sisters dunite, Chuckanut sandstone, and Darrington phyllite. Figure 6-6. Shaded digital topographic model of Mosquito Lake kettle-kame complex and lateral moraines of the Nooksack Middle Fork. The glacier stagnated in the valley south of the river, then later readvanced over the ice-contact deposits to form the lateral moraine. 109 Twin Sisters Figure 6-7. Mosquito Lake kettle-kame complex and lateral moraine looking up the Nooksack Middle Fork. Cores of Deep Kettle bog are shown in Figure 6-10. The source of the glacier was a broad ice field on Mt. Baker just off the upper left side of the photo and an ice field on the west flank of the Twin Sisters Range. 110 LITHOLOGY OF CORDILLERAN ICE SHEET DRIFT Figure 6-8. Comparison of lithologies of glacial drift from the Cordilleran Ice Sheet (a) with glacial drift in the Nooksack Valley (b). The Cordilleran Ice Sheet is strongly dominated by granitic clasts with smaller but significant amounts of quartzite. It lacks Mt. Baker andesite and Twin Sisters dunite. Drift in the Nooksack Valley is composed mostly of Mt. Baker andesite, Twin Sisters dunite, and Chuckanut sandstone with only a few lag granitic clasts and rare quartzite. The Kendall moraine has granitic clasts derived from its headwaters on Mount Shuksan and Mt. Baker andesite, but has no Twin Sisters dunite. It has significant amounts of Mt. Baker andesite brought in from tributaries on the north side of the mountain. I l l Figure 6-9. Source area of the Middle Fork glacier from broad ice fields on the flank of Mt. Baker and the Twin Sisters Range (photo by U.S. Forest Service). a 20 m 1 6,850 ± 6 5 Mazama Ash Peat Diatomite 20 cm I Sand and Gravel \ I Figure 6-10. (a) Cross section of deeply kettled, stagnant-ice deposits and overlying lateral moraine at Deep Kettle Bog in the Mosquito Lake Valley of the Nooksack Middle Fork, (b) Radiocarbon dates from the base of Deep Kettle Bog core. The diatomite overlying the basal peat contains deep-water diatoms, indicating the filling of the kettle with water soon after it was free of ice. This suggests that the basal peat may have formed on the stagnating ice and dropped onto the floor of the kettle upon melting. 12,150 + 95 12,035 ± 9 0 12,120 ± 9 0 12,045 ± 8 5 11,945 ±85 12,145 ±90 12.360 ± 9 0 12,165 ± 9 5 12,365 ±115 12,230 ± 8 0 11,520 ±190 11,940 ±180 12,160 ± 9 0 112 Meters Feel 28.9 95 27.4 90 24.4 80 21.3 70 18.3 60 15.2 50 H 12.2 40 4 9.1 30 - i 6.1 3.0 Tilt with many striated and faceted boulders of Mt. Baker andesite, Twin Sisters dunite, Chuckanut sandstone, and Darrington phylite Coarse, pebbly sand Bedding offset - 1 m along small faults Sand and gravel containing many Suartz pebbles derived from larrington phyllite Sand and gravel. Mostly Mt Baker andesite with Chuckanut sandstone, Darrington phyllite and Twin Sisters dunite Well-sorted sand Sand and gravel; interbedded silt dips 55° upvalley. Sand and gravel. Matrix supported fine to coarse gravel consisting of - 50% Mt. Baker andesite and - 50% Chuckanut sandstone Slide debris and S IO D B wash Figure 6-11. Stratigraphic section in a landslide is along the north side of the lateral moraine overlying ice-contact sediments of the kettle-kame complex in cross section in Figure 6-10a. The upper till makes up the lateral moraine, and lower sand and gravel make up the kettle-kame complex. Both consist almost entirely of Mt. Baker andesite, Twin Sisters dunite, Chuckanut sandstone, and Darrington phyllite. 113 6.2.1.2 Evidence for readvance of the Middle Fork glacier Following disappearance of the Cordilleran Ice Sheet, the late Pleistocene Middle Fork glacier, fed by extensive snowfields on Mt. Baker and the Twin Sisters Range, extended c. 23 km downvalley from its source; but how much of this represents a readvance after the retreat of the Cordilleran Ice Sheet? The transition from the ice sheet to an alpine glacier system occurred when the surface of the ice sheet thinned below c. 1500 m and dropped below the elevation of the ridges that separate the Middle Fork from the area to the north (Fig. 6-4), cutting off connections to the Cordilleran Ice Sheet. Once that happened, the ice accumulation center shifted to local areas on Mt. Baker and the Twin Sisters Range (Fig. 6-4) and new glacial equilibrium systems were established. Exactly where the terminus of the Middle Fork glacier stabilized immediately after this transition is difficult to determine. Because the lithology of the kettle-kame deposits strongly reflects the local source area upvalley and lacks lithologies found in Cordilleran Ice Sheet drift, the Middle Fork glacier must have existed for some period of time after its disconnection from the Cordilleran Ice Sheet and prior to stagnation and deposition of the ice-contact drift. The sharp-crested lateral moraine that drapes across the ice-contact deposits (Figs. 6-6, 6-7,6-10) shows no evidence of ice-contact deposits or ice collapse features so prominent in the kettle-kame complex, suggesting that the moraine was deposited later by a glacier that was not stagnant. The reinvigorated glacier advanced over the ice-contact drift for a distance of at least 2 km, but because we do not know how far upvalley the glacier retreated from the kettle-kame complex before it readvanced, we can only measure the minimum distance that it must have advanced. Several smaller lateral moraines occur upvalley from the outermost lateral moraine, indicating that retreat of the glacier took place by alternating terminus recession and short stillstands in contrast to the stagnation of the older kettle-kame complex. Whether any of these nested laterals represent readvances or just short stillstands during overall recession is unknown. 114 Table 6-1 Radiocarbon dates from the Nooksack drainage Radiocarbon age* Calibrated ageT ( 1 4 CyrBP) (cal.yrBP) Sample no./ Lab no. § Dated material Comments Middle Fork - Deep Kettle Bop 6850 ±65 7791 -7577 12,145 ±90 15,395-13,828 12,045 ±85 15,344- 13,661 12,120 ±90 15,383- 13,684 12,035 ±95 15,341 -13,656 12,150 ±90 15,394- 13,829 12,230 ±80 15,433- 13,843 12,380 ±90 15,506- 14,110 12,365 ± 115 15,508- 13,869 12,165 ±95 15,407- 13,830 11,945 ±85 15,289- 13,633 11,520 ±190 14,028-13,031 11,940 ± 180 15,326- 13,463 12,160 ±90 15,403- 13,831 Middle Fork 10,680 ±70 12,965-12,359 North Fork 10,788 ±77 13,098- 12,631 DKB1-6/ AA22201 DKB1-8/ AA-22203 DBK2-3/ AA-22205 DBK2-4/ AA-22206 DBK2-5/ AA-22207 DBK2-6/ AA-22208 DKB1-4/ AA22199 DKB1-3/ AA22198 DKB1-2/ AA-20750 DKB1-1/ AA-20749 DKB2-1/ AA-22204 DBK2-8/ AA-22210 DBK2-7/ AA-22209 DKB1-7/ AA-22202 RC-1/ B-124911 RH2-4/ AA-27079 1- cm diameter wood, 3 cm below contact with Mazama ash 2- cm diameter wood in dark peat with many <lmm white interbeds; 4.5 cm from base of core Small piece of wood in basal peat 0.5 cm below contact with diatom layer Small piece of wood in basal peat ~1 cm below contact with diatom layer Small piece of wood in basal peat at contact with diatom layer. Small piece of wood in basal peat at contact below contact with diatom 2.5 cm long twig (2 mm diameter) at top of basal peat at contact with overlying diatomite ~1 cm long branch at top of basal peat at contact with overlying diatomite. Half of a 1-cm piece of wood resting on the material in DKB1-1 Rootlets in lower 2 cm of core 2 small pieces of wood 1 cm up from the base of the core Small piece of wood in basal sand at contact with overlying basal peat Small piece of wood in basal sand at contact with overlying basal peat 2.5-cm-long, twig (4-6 branches) in basal sand (1 cm thick) at core bottom Wood in lateral moraine. Max. age of Mazama ash Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Dates deposition of lateral moraine. Uppermost charcoal in sand Minimum age of outwash 115 10,603 ± 69 12,944 - 12,192 RH2-1/ AA-27078 Lowermost charcoal in sand Minimum age of outw 11,910 ±80 15,265 - 13,618 WG-1/ ~1 cm diameter wood in clay, Maximum age of two B-1220447 Welcome gulch stillstands South Fork - Cranberry Lake Bog 12,733 ± 75 15,788 -14,333 BB5-2/ AA-27076 Peat Minimum age of ice stagnation 12,596 ±80 15,627 -14,204 BB3-2/ AA-27075 Peat Minimum age of ice stagnation 12,425 + 90 15,526 - 14,123 BB3-1/ AA-27065 Plant fragments Minimum age of ice stagnation 13,750 ± 127 17,062 -15,980 BB3-2/ AA-27074 Plant fragments Minimum age of ice stagnation 12,255 ±84 15,446 - 13,846 CB5-3/ AA-27077 Plant fragments Minimum age of ice stagnation 12,215 ± 85 15,428 - 13,840 CB5-1/ AA-27064 Plant fragments Minimum age of ice stagnation 14,167 ±82 17,518 -16,491 CB1-1 AA-27073 Peat Minimum age of ice stagnation * Laboratory error precession is 1 sigma. + 2 sigma age range calibrated years before AD 1950 using the CALIB 4.0 program of Stuiver and Reimer (1993). 8 Laboratory designation: AA - Univ. of Arizona AMS Facility; B - Beta Analytic Inc. 6.2.2 Glacial deposits in the Nooksack North Fork The Nooksack North Fork originates from a 3.5-km-wide cirque on the northwest flank of Mt. Shuksan, and extends westward in a broad, U-shaped valley (Figs. 6-1, 6-4). Bedrock in the cirque consists mostly of granodiorite, and smaller amounts of greenschist, blueschist, and phyllite (Misch, 1966). Remnants of two end moraines are preserved along the north side of the valley, 43 km downvalley from the cirque (Figs. 6-12, 6-13). The outermost of the two moraines, the Kendall moraine, is a distinct ridge of till several hundred meters long, the axis of which is transverse to the valley. The Maple Falls moraine is 1.5 km upvalley from the outer moraine, and its axis is also transverse to the valley. The cobble lithology of the Kendall moraine shows a strong, local, upvalley provenance. Chuckanut sandstone makes up 54% of the cobbles, and Mt. Baker andesite makes up 12% (Fig. 6-8b). The high percentage of Chuckanut sandstone is explained by extensive outcrops upvalley. The incidence of many clasts of Mt. Baker andesite is significant because it means that ice must have flowed northward from Mt. Baker into the North Fork valley in the opposite direction as earlier flow of the Cordilleran Ice Sheet. 116 This confirms that the Cordilleran Ice Sheet could not have been responsible for deposition of the Kendall moraine. Granodiorite makes up 3% of the cobbles and is probably derived from exposures in Nooksack Cirque on Mt. Shuksan, although it is indistinguishable from Canadian granodiorite. A few cobbles from a unique outcrop of Paleozoic volcanic rock that occurs only in the upper North Fork drainage were found. An unusually large number of pebbles and cobbles in the till making up the Kendall moraine are faceted, striated, and polished, many more than we have observed at any other locality in the Pacific Northwest. The reason for so many glacially abraded stones appears to be the long transport distance from the glacial source 45 km upvalley at Nooksack Cirque on Mt. Shuksan. A second moraine, the Maple Falls moraine, occurs about 1 km upvalley from the Kendall moraine. Abundant erratic boulders on the Maple Falls moraine consist mostly of granodiorite (41%) (Fig. 6-8b), which appears to have been derived upvalley from granodiorite in Nooksack Cirque. However, like the cobbles of the Kendall moraine, the granodiorite is indistinguishable from Canadian granodiorite. Erratics of Mt. Baker andesite (4%) indicate a contribution of ice from Mt. Baker, most likely from three tributary valleys that head on Mt. Baker (Figs. 6-1,6-4). Local Chuckanut sandstone makes up 10% of the erratics. The relative percentage of various lithologies of erratics on the Maple Falls moraine is somewhat different from that of cobbles in the till of the Kendall moraine, but that is probably due to the difference is clast size and durability; e.g., Chuckanut sandstone is abundant (54%) among cobbles but makes up only 10% of erratics. Three end moraines in the Silver Lake valley, a north-south tributary 6 km north of the North Fork (Figs. 6-1,6-13), were built by ice that did not reach the North Fork (Kovanen, 1996). Their lithologies are quite different from those of the Kendall and Maple Falls moraines, and more resemble those of the Cordilleran Ice Sheet, suggesting that they were made by a tongue of the ice sheet from the Fraser Valley just to the north in Canada (Figs. 6-4,6-14). Glaciomarine drift is exposed at elevations of 200 m a few kilometers downvalley from the Kendall and Maple Falls moraines (Figs. 6-13,6-15), attesting that the Cordilleran Ice Sheet had previously vacated the Nooksack Valley. The lithology of clasts in the glaciomarine drift is typical of the Cordilleran Ice Sheet (Fig. 6-8a) and contains no 117 lithologies typical of the Nooksack Valley. This confirms that Nooksack Valley ice did not contribute to the glaciomarine drift and that the very different, upvalley-derived lithologies of the Kendall and Maple Falls moraines came from alpine ice, not the Cordilleran Ice Sheet. Outwash from the Cordilleran Ice Sheet to the north at the head of Columbia Valley merges with outwash from the Kendall and Maple Falls moraines near Kendall (Figs. 6-12, 6-13) and overlies glaciomarine drift (Easterbrook and Kovanen, 1996a, 1996b). This, together with the locally derived lithology of the moraines indicates that the long valley glacier that built the moraine originated in Nooksack Cirque on Mt. Shuksan and was fed by ice from Mt. Baker (Fig. 6-4) at a time when the margin of the Cordilleran Ice Sheet was to the north. 6.2.2.1 Age of the glacial deposits in the Nooksack North Fork Outwash from the alpine moraines in the North Fork merges smoothly with Cordilleran Ice Sheet outwash in the Columbia Valley near Kendall (Figs. 6-12, 6-13). The Columbia Valley outwash extends continuously 10 km northward up the Columbia Valley to an ice-contact face of the Cordilleran Ice Sheet in Canada (Fig. 6-14). The Cordilleran Ice Sheet margin at this time is well known. Wood from the ice-contact face at Cultus Lake has been dated at 11,300 ± 100 1 4 C yr BP (Lowden and Blake, 1978). The outwash terrace 9 km south of the Kendall and Maple Falls moraines is at an elevation of 120 m, 12 m above the present floodplain, and overlies glaciomarine drift (Fig. 6-13). Wood in the glaciomarine drift is dated at 11,910 ± 80 1 4 C yr BP (Table 6-1; Kovanen and Easterbrook, 1998). The surface of the outwash terminates against the Maple Falls moraine and does not extend upvalley from the moraine. The outwash contains several 1-3 cm layers of interbedded charcoal exposed in a river terrace c. 3.6 km downvalley from the Kendall moraine. The uppermost charcoal layer e l m below the surface of the terrace was radiocarbon dated at 10,788 ± 77 1 4 C yr BP and another charcoal layer near river level was dated at 10,603 ± 69 1 4 C yr BP (Fig. 6-15; Table 6-1). Therefore, the age of the outwash lies within the Younger Dryas interval. 118 6.2.2.2 Evidence for readvance of the North Fork glacier As in the case of the outer kettle-kame complex in the Middle Fork, no way exists to assess the transition from the Cordilleran Ice Sheet to the subsequent alpine glacier system. Hence, whether the entire 45-km-long alpine glacier represents the initial, newly stabilized descendent of the Cordilleran Ice Sheet or if some of it represents a readvance of alpine ice is not known. After building the Kendall moraine, the glacier receded to or beyond the position of the Maple Falls moraine, then stabilized long enough to build the Maple Falls moraine. However, unlike the two moraines in the Middle Fork, evidence for readvance of the glacier that made the younger moraine is lacking here. Regardless of whether or not either moraine is related to glacier advancement, the younger moraine clearly represents recession from the older terminal position followed by a glacial stillstand. 6.2.3 Glacial deposits in the Nooksack South Fork The late Pleistocene South Fork glacier split into three topographically controlled lobes at the junction of the South Fork valley, the upper Samish River valley, and the valley just east of Lake Whatcom (Figs. 6-1, 6-4). The northern lobe flowed northward in the South Fork for an unknown distance. The middle lobe flowed through the valley that reaches to the southeast arm of Lake Whatcom, forming a lateral moraine that makes a ridge along the south shore of the lake and terminates as a peninsula into the present lake (Fig. 6-4) (Kovanen and Easterbrook, 1996). The southern lobe extended down the upper Samish River valley, depositing kame terraces against the valley side, and terminated in kettled topography near Cranberry Lake (Figs. 6-1,6-4). A long alpine valley glacier flowed down the Nooksack South Fork and into the south end of the valley occupied by Lake Whatcom (Figs. 6-1, 6-4). A lateral moraine that extends along the southern shoreline of the lake contains large, faceted, and striated dunite erratics derived from the Twin Sisters Range 42 km to the east, and till there consists almost entirely of phyllite from the valley to the east. The lithologies of erratics and till indicate that the Nooksack South Fork was also part of the Nooksack alpine glacial system. 119 6.2.3.1 Age of the glacial deposits in the Nooksack South Fork Five cores were obtained from a deep bog that surrounds Cranberry Lake at the terminus of the South Fork glacier (Figs. 6-1, 6-4). Basal bog dates (Table 6-1) are generally equivalent to those at Deep Kettle bog in the Middle Fork (12,215-12,733 1 4 C yr BP), but two cores yielded somewhat older dates. The significance of the older dates is not clear. One date (13,750 ±127 1 4 C yr BP) is suspiciously sandwiched between dates of 12,596 ± 80 and 12,425 ± 90 1 4 C yr BP and the other (14,167 ± 82 1 4 C yr BP) is from a core with no other supporting dates. Whether or not these dates might be related to an early phase of transition from the Cordilleran Ice Sheet to the Nooksack alpine glacial system remains unknown. Meltwater from the southern lobe of the South Fork glacier drained southward rather than northward, as does the present drainage (Fig. 6-1). The lower part of the valley inherited river meanders that are many times larger than those of the present stream (Fig. 6-1), suggesting that it is underfit relative to the late Pleistocene meltwater of the South Fork glacier 33 km upvalley. These meanders are incised 60 m into Everson glaciomarine drift, Vashon till, and Vashon advance outwash, and cut across post-glaciomarine-drift beach ridges at a marine limit of 65 m before terminating at a marine delta a 30 m above sea level (Easterbrook, 1979, 1992,1994). The age of the South Fork outwash is younger than the glaciomarine drift (c. 11,500 1 4 C yr BP) and younger than the marine shorelines (11,700 ± 110 1 4 C yr BP; Siegfried, 1978) cut by the incised valley. Therefore, the age of the outwash channel must be younger than c. 11,500 1 4 C yr BP (Easterbrook, 1994). At this time the Cordilleran Ice Sheet was reduced to a piedmont tongue in the Fraser Lowland of British Columbia. 120 Figure 6-12. Photo of the Kendall and Maple Falls moraines deposited by the North Fork alpine glacier, which flowed from the right side of the photo. The Columbia Valley outwash of the Cordilleran Ice Sheet merges with outwash of the North Fork alpine glacier at the left center of the photo. Columbia Valley extends northward from this junction to the Sumas ice-contact face in British Columbia (Fig. 6-14). 121 Figure 6-13. Geologic map of the glacial deposits in the Kendall area of the North Fork and Columbia Valleys. The geologic cross-section is drawn along line A-A'. 122 Figure 6-14. Ice-contact face (c. 3 km wide) at the head of the Columbia Valley outwash, marking the terminus of that spilled into the Chilliwack Valley when the North Fork moraines were deposited. The outwash terminates abruptly 242 m above Cultus Lake (left side of photo). Figure 6-15. Geologic cross-section transverse to the axis of the Nooksack North Fork near the distal end of the outwash terrace in Figure 6-13, showing stratigraphic and chronologic relations of radiocarbon dates from charcoal layers in the outwash south of Kendall. Qev - Everson glaciomarine drift; So4 - Sumas outwash terrace. 123 6.3 Discussion During deglaciation of the Nooksack drainage, the transition from the remnants of the Cordilleran Ice Sheet to alpine glaciers occurred when the surface of the ice sheet fell below the elevation of the ridges that separate the Nooksack Valley from the area to the north. Once that occurred, the source area of the ice changed from the Cordilleran Ice Sheet to local areas of accumulation on Mt. Baker, Mt. Shuksan, and the Twin Sisters Range, a new glacial equilibrium was established, and the flow direction became topographically controlled. Thus, an unknown period of time ensued during which the load of glacial debris changed from the typical granitic-dominated lithology of the Cordilleran Ice Sheet to debris dominated by local rock types. Where the terminus stabilized immediately after this transition of source areas is unknown, but may be important in evaluating the lengths of the confluent glaciers that built the moraines. Consequently, whether the Middle Fork kettle-kame complex and the Kendall moraine represent glacier advances or merely the position of the newly stabilized alpine glacier terminus is unknown. Therefore, although the period of outermost moraine building lacks evidence to demonstrate a readvance of ice, it does represent a period of terminus stability that interrupted deglaciation. The Middle Fork lateral moraine indicates a resurgence of ice over the kettle-kame complex. The glacier that built the prominent lateral moraine readvanced at least 2 km over stagnant ice deposits, then deposited several small lateral moraines upvalley, the last one containing wood dated at 10,680 ± 70 and 10,500 ± 70 1 4 C yr BP. The glacier that deposited the Maple Falls moraine in the North Fork receded from the Kendall moraine downvalley, then stabilized long enough to construct the moraine. Whether it receded upvalley and readvanced to the Maple Falls moraine is unclear, but the moraine does indicate an interruption in the overall recession of the glacier. Outwash downvalley contains several charcoal layers, the uppermost dated at 10,788 ± 77 1 4 C yr BP and the lowermost dated at 10,603 ± 69 1 4 C yr BP. These dates lie within the Younger Dryas interval. The presence of two phases of moraine building in the Nooksack Middle and North Forks invites possible regional correlation with two prominent Sumas moraines of the Cordilleran Ice Sheet to the north near the Canada-United States boundary (Fig. 6-4). 124 Radiocarbon ages of the inner Nooksack moraines overlap radiocarbon ages of the inner Sumas moraine in the northern Puget Lowland (Kovanen and Easterbrook, 1976,1996b, 1997; Easterbrook and Kovanen, 1998a,b) and both fall within the Younger Dryas. The apparent absence of similar alpine glacial deposits in the South Cascades may result from (1) differences in proximity to the Cordilleran Ice Sheet, (2) substantial differences in the size of accumulation areas, (3) different climatic regimes to the south, or (4) lack of recognition of existing glacial deposits. We believe that the Nooksack alpine moraines have more in common with moraines (some now submerged) in fjords along the British Columbia coast to the north. McCrumb and Swanson (1998) dated a prominent, partially submerged moraine in Howe Sound north of Vancouver, British Columbia, at 11,500 cal yr BP and correlated it with the Sumas Stade. Mathewes (1993) and Mathewes et al. (1993) found paleoecological evidence for Younger Dryas cooling between 10,700 and 10,000 1 4 C yr BP on the British Columbia coast to the north. Pollen of mountain hemlock (Tsuga mertensiana), increased relative to pollen of other tree species at low-elevation sites in southwestern British Columbia during this period. Crandell and Miller (1974) interpreted McNeeley moraines in small cirques near Mt. Rainier to be late Pleistocene, but their age was not well constrained. Heine (1998) found two moraine-building phases in small cirques near Mt. Rainier, the older beneath organic material dated at 11,320 ± 60 and 11,120 ± 200 1 4 C yr BP and the younger beneath organic material dated at 10,080 ± 60,9840 ± 70, and 9140 ± 100 1 4 C yr BP. However, outwash dated between 10,000 and 11,000 1 4 C yr BP is not considered by Heine, so his interpretation remains controversial. Swanson and Porter (1997) dated (36C1 ± 20%) end moraines of alpine valley glaciers in the eastern North Cascade Range and suggested that two late-Pleistocene ice advances there correlated with the Sumas Stade. These moraines appear to be similar in age to the Nooksack moraines. At the maximum extent of the Okanogan lobe of the Cordilleran Ice Sheet on the Columbia Plateau east of the Cascades, the glacier built the prominent Withrow moraine. During deglaciation, a short stillstand of the glacier deposited a smaller end moraine, where numerous eskers terminated (Easterbrook, 1979). A later stillstand deposited more 125 morainal material in the Okanogan Valley to the north (Pine, 1985). Although none of these moraines have been dated and no direct correlations can be made, the glacial pattern is similar. Gosse et al. (1995) 10Be dated the Titcomb Lakes moraines in the Wind River Range, western United States. The cirque glaciers deposited two moraines 4 km from the cirque between 12,300 and 10,600 10Be yr BP. Of 10 boulder exposure ages, 9 averaged 11,300 1 0Beyr BP. These moraines have been correlated with the Temple Lake moraines (Zielinski and Davis, 1987). Reasoner et al. (1994) recognized a Younger Dryas age advance of the Crowfoot Glacier in the Rocky Mountains of Canada, and Younger Dryas glacial events have been found in Alaska (Hajdas et al, 1998) and the Santa Barbara basin of California (Hendy and Kennett, 1999). Late Pleistocene moraines 20-40 km upvalley from terminal moraines of the last glaciation have been reported from several localities in the Southern Alps of New Zealand. The best-known of these moraines is the Waiho Loop moraine deposited by the Franz Josef Glacier about 20 km upvalley from the late glacial maximum moraine (Mercer, 1976,1982, 1988; Wardle, 1978; Lowell et al, 1995; McGlone, 1996). The forty three 1 4 C dates from wood in the Waiho Loop moraine average 11,200 1 4 C yr BP, (Denton and Hendy, 1994). On the east side of the Southern Alps, the late Pleistocene Birch Hill and Prospect Peak moraines occur c. 40 km upvalley from the late Wisconsin maximum positions (Burrows, 1975, 1983, 1984, 1988). Erratics on two Prospect Peak moraines have yielded 10Be dates of 12,700 and 12,800 10Be yr BP well within the Younger Dryas. Thus, Younger Dryas moraines are present not only here in the northeastern Pacific, but also in the Southern Hemisphere. Perhaps one of the most interesting aspects of this work is the multiple nature of the late Pleistocene glacial events in the Nooksack Valley that seem to have counterparts elsewhere in the North America. The outer Nooksack moraines are pre-Younger Dryas and represent a more extensive stillstand of alpine ice than the Younger Dryas moraines, mirroring the pattern seen in the adjacent Cordilleran Ice Sheet Sumas moraines. The consistency of the pattern argues for a climatic origin. 126 Strong evidence of early Holocene glaciation occurs in the upper Nooksack drainage, but on a much reduced scale (Easterbrook, 1975,1999; Easterbrook and Kovanen, 1999; Thomas, 1997). The overall picture of deglaciation in this region is one of multiple, short, glacial events that extended into the early Holocene. 127 Chapter 7 Decadal variability in climate and glacier fluctuations on Mt. Baker 7.1 Introduction At decadal time scales, the link between glacier fluctuations and climate is relevant to the reconstruction of climatic history. In the Pacific Northwest, researchers have recognized climatic trends associated with atmospheric forcing caused by sea surface temperature (SST) and sea level pressure variations (SLP) (Namias, 1978; Peterson, 1989; Trenberth, 1990; Graham, 1994; Hare and Francis, 1995; Trenberth and Hurrell, 1994; Mantua et al, 1997; Minobe, 1997; Zhang et al, 1997; McCabe et al., 2000). They find that recurring patterns of interdecadal climate variability are widespread in the Pacific basin (Fig. 7-1) and call this climate pattern the Pacific Decadal Oscillation (PDO). The PDO is similar to El Nino events, but the 20 century PDO events persist for 20-30 years, whereas El Nino events persist for 6-18 months (Mantua et al, 1997). These patterns have been correlated with changes in salmon production and terrestrial ecological variables between Alaska and the Pacific Northwest (Brodeur and Ware, 1992; Beamish, 1993; Mantua et al, 1997). In this chapter, instrumental and historical temperature and precipitation records combine with the record of glacier terminus fluctuations on Mt. Baker (Fig. 7-2) are compared to Pacific SST modes and provide insights about their interrelations. No attempt is made to cover all questions of decadal variability in the Pacific Ocean. Only the PDO variability that concerns glaciers on Mt. Baker is described. Mt. Baker (3285 m), a stratavolcano, covered by a 35 km2 ice cap is situated in a maritime climatic zone c. 50 km east of the Strait of Georgia (Figs. 7-1, 7-2). The northerly latitude and high-altitude distribution area combine to form a sensitive glacio-climate relation. The altitude of the equilibrium line often glaciers that radiate from Mt. Baker is presently c. 2000 m, + 100 m (Thomas, 1997). Glaciers terminate between 1200 128 and 1800 m. Six glaciers (Fig. 7-2) vary in surface slope (c. 18-25°), thickness (39.2-51.3 m), length (3.26-5.41 km), and total area (1.9-5.9 km2) (Harper, 1992). Figure 7-2. (a) Geographic distribution of the weather stations. Olga and Anacortes weather stations is located on Fig. 7-1. (b) Glaciers on Mt. Baker. 129 7.2 Approach, climate data, and seasonal dependence The meteorological data from six National Ocean Atmospheric Administration (NOAA) stations used in this study are listed in Table 7-1 and shown on Figure 7-2. Data around the Mt. Baker area extend back to c. 1931. Continuous historical records at Olga on Orcas Island, c. 75 km west of Mt. Baker, extend back to 1891 (Fig. 7-1). The dominant modes of atmospheric forcing at Mt. Baker are taken to be winter precipitation and summer temperature; accumulation and ablation are respectively dominant in these seasons. The winter accumulation season is defined as October 1 through April 30. The summer ablation season is defined as May 1 to September 30. Some gaps in the weather station records exist: individual months were not used for annual or monthly statistics if more than 5 days were missing from the dataset; individual years were not used for annual statistics if any month in that year had more than 5 days missing. The daily, monthly, and yearly missing data were filled by linear interpolation. Climate trends are recognized in smoothed time-series (2-year moving averages of the two previous points), which were composed of long-term aggregates of monthly and yearly values. These methods were applied to data from individual stations and to the composite of stations surrounding Mt. Baker. Data transformations include only a conversion to metric units and normalization of values determined from the distribution characterized by mean and standard deviation. No correction for the inference of the standard error has been applied. Because the weather stations are well distributed in a topographically diverse area, an area-weighted average has not been applied. The PDO and North Pacific (NP) indexes were derived from the Reynolds and Smith (1995) Optimally Interpolated SST dataset for 1900-93 of the U.K. Meteorological Office. The PDO index is based on departures from monthly means of SST in the Pacific Ocean, poleward of 20°N (Fig. 7-1; Mantua et al, 1997). The monthly mean global average SST anomalies were "removed" to separate the pattern of variability from any "global warming" signal that may be present in the raw data (Mantua et al, 1997). The NP index is based on sea level pressures (Ziooo) and is a good indication of the intensity and variability of the Aleutian Low, a quasi-permanent low-pressure cell that lies over much of the North Pacific from late fall to spring. Detailed discussions related to dominant modeled 130 circulation features of synoptic climate are provided by Ware (1995), Namias (1978), Peterson (1989), Trenberth (1990), Trenberth and Hurrell (1994), Mantua et al. (1997), Minobe (1997), Zhang et al. (1997), Cayan et al. (1998). Table 7-1 Data sets and climate indexes used in this study Data set Location Elevation Recording Source (m) Period Weather Stations Latitude (N) Longitude (W) Upper Baker Dam 48°39' 121°41' 210 1965-2000 N O A A Bellingham 48°47' 122°29' 34 1948-1985 N O A A Clearbrook 48°58' 122°20' 20 1931-2000 N O A A Sedro Woolley 48°30' 122°13' 17 1931-2000 N O A A Glacier Ranger Station 48°53' 121°57' 285 1949-1983 N O A A Concrete 48°42' 12F49' 82 1931-2000 N O A A Olga 48°7' 122°48' 8 1891-2000 N O A A Anacortes 48°31' 120°37' 3 1931-2000 N O A A Glacier Boulder Coleman Deming Easton Rainbow Roosevelt Mt. Baker 3230-1175 3230-1180 3230-1175 2960-1585 2280-1205 2280-1205 1940-1990 1940-1990 1940-1990 1940-1990 1940-1990 1940-1990 Harper, 1992 Harper, 1992 Harper, 1992 Harper, 1992 Harper, 1992 Harper, 1992 Climate Indices PDO Index: The PDO index is based on departures from monthly means of SST in the Pacific Ocean, poleward of 20°N (data from Mantua et al., 1997). NP Index: an area-weighted sea level pressure (Zi 0oo) over the region 30N—65N, 160E-140W, Jan. 1899 - March 1999 (data from Trenberth, and Hurrell, 1994). Fraser River flow: mean discharge (m 3 s"1) for an annual year from Hope, B.C. measuring station (data from Beamish et al, 1994). 7.3 Climate variations since 1891 The typical pattern of annual temperature variations at Mt. Baker, Anacortes, and Olga is shown in Figure 7-3. The nature of the annual temperature curve and the monthly means (± standard deviations) of all the stations are similar and indicates that climatic variations affect the stations in this area similarly (Fig. 7-3). High standard deviations (Table 7-2) 131 may reflect biasing toward local meteorological conditions, and/or inconsistent data collection techniques (e.g., daily means verses hourly means, etc.). Although this area and location of stations encompasses a wide range of topographical settings and elevations, which could produce disparate data, the consistency of the data indicates they are a reliable source of proxy records. Upper Baker Dam (1965-2000) —•— Bellingham (1948-1985) —A—Clearbrook (1931-2000) - B - Sedro Wolley (1931-2000) X Glacier (1949-1983) Concrete (1931-2000) —f— Olga (1891-2000) —A— Anacortes (1931-2000) Month Figure 7-3. Annual temperature variations at weather stations around Mt. Baker, Olga, and Anacortes Table 7-2 Comparison of monthly, annual, summer and winter temperatures (°C) at weather stations surrounding Mt. Baker, Olga and Anacortes (standard deviation shown in parenthesis) Weather station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Sura Win Upper Baker Dam 0.8 (1.9) 2.5 (1.7) 4.8 (1-5) 7.7 (4.5) 11.4 (1.2) 14.2 (1.3) 16.6 (1.1) 17.1 (1.2) 14.5 (1.4) 9.6 (1.2) 4.6 (1.5) 1.4 (1.6) 8.7 (0.7) 14.8 (1-8) 4.5 (1.9) Bellingham 2.6 (2.7) 5.1 (1.6) 6.3 (11.3) 8.8 (0.9) 12.1 (1.1) 14.8 (1.2) 16.7 (1.2) 16.6 (1.1) 14.3 (1.0) 10.1 (1.5) 6.4 (1.9) 4.0 (0.7) 9.8 (1.0) 14.9 (1.9) 6.2 (2.6) Clearbrook 2.2 (2.9) 4.3 (2.0) 6.5 (1.3) 9.4 (1.2) 12.5 (1.2) 15.1 (1.1) 17.0 (1.1) 16.8 (1.1) 14.4 (1.1) 10.1 (1.0) 5.8 (1.8) 3.2 (1.8) 9.8 (0.7) 15.2 (1.9) 5.9 (3.0) Sedro Woolley 3.6 (2.9) 5.4 (2.0) 7.2 (1.3) 9.8 (1.2) 12.7 (1.2) 15.2 (l.D 16.9 (1.1) 17.1 (1.2) 14.7 (1.1) 10.8 (1.0) 6.7 (1.8) 4.4 (1.8) 10.4 (0.7) 15.3 (1.9) 6.9 (3.0) Glacier -0.5 (4.0) 2.6 (1.6) 4.3 (1.4) 7.6 (1.3) 11.3 (1.8) 14.6 (1.7) 17.0 (1.5) 16.8 (1.5) 13.6 (1.3) 8.5 (1.3) 3.7 (1.7) 1.45 (1.5) 8.8 (2.2) 14.7 (2.4) 4.0 (3.2) Concrete 2.7 (2.2) 4.6 (1.9) 6.8 (1.5) 10.0 (1.5) 13.3 (1-5) 15.7 (1.4) 18.0 (1.3) 18.2 (1.0) 15.7 (1.4) 11.3 (1.2) 6.3 (1.7) 3.5 (1.6) 10.4 (0.9) 16.4 (1.3) 6.4 (0.9) Olga 4.0 (2.1) 5.3 (1-6) 6.8 (1.3) 9.2 (1.1) 11.8 (1.0) 13.9 (0.8) 15.4 (0.8) 15.5 (0.8) 13.7 (0.8) 10.4 (0.9) 6.9 (1.4) 4.9 (1.4) 9.8 (0.6) 14.0 (1.5) 6.8 (2.3) Anacortes 4.4 (2.1) 5.8 (1.7) 7.4 (1.2) 9.9 (1.1) 12.7 (1.0) 15.1 (0.9) 16.7 (0.9) 16.7 (0.9) 14.7 (0.9) 11.1 (1.0) 7.3 (1.6) 5.2 (1.6) 10.6 (0.7) 15 (1.7) 7.3 (2.4) 132 7.3.1 Temperature Although changes of the recording technique have probably occurred, the homogeneous, long-term, temperature record can be used to investigate temperature variations since the late-19th century. The overall annual mean temperature is 9.7°C, with diurnal temperature variations generally smaller than the annual amplitude. With somewhat milder winters and cooler summers, the Olga and Anacortes records are more controlled by oceanic influences. The period of record is shorter for weather stations surrounding Mt. Baker compared to that at Olga, where continuous recordings started in July 1891. A strong correlation between Mt. Baker (mean composite temperature of all stations surrounding Mt. Baker for a 68 year period) and Olga (Figure 7-4a, b; R2= 0.86, r = 0.93,/? < 0.001,1931-1999) allow the Olga temperature record to be used as the representative temperature data in this study. This extends the Mt. Baker temperature data another 40 years and is useful in subsequent studies of glacier terminus fluctuations. Annual and five-year running averages of the Olga temperature data reveal four general features (Fig. 7-5), which are also coincident with PDO regimes (see discussion below). (i) Toe. 1923: the first four decades show a relatively low temperature level with winter minima in the 1909, 1916, and 1922, that are also visible in the summer and annual records. The 1916 minimum is coincident with c. a 66 cm snowfall in the lowland areas. (ii) 1923-1947: a 2.5°C rapid increase in annual temperature from 1922 to 1926 (3.3°C temperature increase during winter months). An abrupt reversal from this warming trend occurs between 1932-1937, separated by a one year warm period which may be attributed to short-term El Nino events. The variations of winter temperature may control the annual temperature record (R2 = 0.90, r = 0.95,/? < 0.0001) for 2-yr running means of Olga winter (October-April) 1895-1997, compared to R2 = 0.84, r = 0.91,/? < 0.0001 for 2-yr running means of summer (May-September) and annual temperatures). 133 (iii) 1947-1977: a 30 year cool period. Although, warm excursions occurred in 1953 and 1958. (iv) 1977 to present: a warming trend, but temperature drops in 1985 to levels comparable to lows of 1890s, 1916, and 1955. 3 2 I E o 12 11 10 (b) ml ——Olga — Composite 8 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Figure 7-4. (a) Mean annual temperature variations at Anacortes and weather stations surrounding Mt. Baker, (b) Mean annual temperature variations at Olga compared to the composite of annual means of Anacortes and five other stations surrounding Mt. Baker. 134 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Y e a r Figure 7-5. Yearly temporal trend of means for summer (May-September; mean, 14.1 °C; SD = 0.406), annual (mean, 9.8 °C; SD = 0.408) and winter (October-April; mean, 6.8 °C; SD = 0.452) temperatures at Olga (1981-2000). The superimposed curves represent 2-yr running means. Because maximum ablation occurs during summer months the means are shown; 13.8 (1893-1922), 14.3 (1923-1947), 13.8 (1948-1977), 14.6 (1978-2000). 7.3.2 Precipitation Because of the lack of long-term precipitation recordings in the North Cascades, the Olga data set was used to investigate the relation between temperature, precipitation, and glacier fluctuations. Figure 7-6 illustrates the pattern of annual variations in precipitation, with an early summer minimum (July) and a winter maximum in December. Compared to the transition of the temperature record in the 1920s, 1940s, (Fig. 7-5), the precipitation pattern exhibits similar characteristics (Fig. 7-7), although the summer precipitation pattern is not pronounced. After a period of relatively high precipitation to c. 1923, precipitation decreased to c. 1944. The dry episode in 1930 was associated with a bad fire year in 135 Washington State with (532 km2) of timber burned. Between 1944 and 1976, precipitation increased. A rapid reduction in winter and annual precipitation is noted at 1976, with a relative decreased level until 1995. A comparison between temperature and precipitation indicate that they are inversely correlated (e.g., significant negative slopes). Figure 7-8 illustrates the annual and 2-yr running means of ablation-season temperature and accumulation-season precipitation climate trends. This means that higher precipitation is linked to cooler temperatures and lower precipitation to higher temperatures and suggests that accumulation and ablation seasons cannot be treated independently (Tangborn, 1980). 1-2 i g. 0.8 -» | 0.6-J Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 7-6. Monthly precipitation variations (by rank) at Olga (solid bars) and stations surrounding Mt. Baker (empty bars). 136 100 80 E o c o 60 0 40 20 h • i • • • • i • • • • i -r • • t • • • i • •' • E • • • • t • • • 1 1 • •1 • r • • •' i' • 1 i 1 ' •' i • • • • i • • • • r •1 • •; •'1 * f11 • * i • 1 1 • i • • • • i' • 1 • i 1 • • • i - * • 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Figure 7-7. Yearly temporal trend of means for annual, winter (October-April), and summer (May-September) precipitation at Olga (1891-2000). The superimposed curves represent 2-yr running means. Because maximum accumulation occurs during winter months, the means are shown; 60.6 (1893-1922), 53.4 (1923-1947), 59.3 (1948-1977), 52.6 (1978-1999). 90 80 70 o q> 60 a> c 50 40 30 S u m m e r Tern p e r a t u r e C o o l & w e t W a r m & dry C o o l & w e t ' W a r m & dry 1 5 1 4 1 3 W c 3 3 (D H 12 -° a O 1890 , . . . . I . . . . . . . . . I . . . . I . . . . I . . . . . . . . . I . . . . I . . . . . . . . . t . r I . . . . I . . . . . . . . . . . . . . t I . . . . I . . . . { . . . . I. 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Y e a r 10 Figure 7-8. Annual winter precipitation and summer temperature at Olga with superimposed 2-yr running means. 137 7.4 Glacier fluctuations on Mt. Baker Ten major glaciers flow down the flanks of Mt. Baker (Figs. 7-1 and 7-2) and terminate between 1200 m and 1800 m above sea level. Mapping and dating of moraines have identified multiple episodes of glacier advance and retreat between the 15th and 20th centuries on six glaciers (Burke, 1972; Easterbrook and Burke, 1972; Fuller, 1980, Hiekkinen, 1984; Harper, 1992). Based on detailed photogrammetry, fluctuations in the glacier terminus positions for six glaciers between 1940-1990 were reconstructed by Harper (1992) (Fig. 7-9). In 1940, retreat phase had been in progress since the mid 1920s. A run-off-precipitation model compared to balance predicted by a precipitation-temperature model for Thunder Creek and South Cascade glaciers to the south of Mt. Baker suggests a recession during the early 1900s (Tangborn, 1980) and ended between 1945-1950. At Mt. Baker, the retreat between 1940 to about the early 1950s ranged from 182-520 m on the Roosevelt and Boulder glaciers respectively, with minimum rates of retreat ranging from c. 26-35 m/yr. From c. 1945-1955 all glaciers began to advance. Four glaciers advanced vigorously (Boulder, Deming, Rainbow, and Easton), while two (Roosevelt and Coleman) only moderately, with overall increases in length ranging from 13-24% (Harper, 1992). All glaciers accelerated their advance between 1974-1978 to climax c. 1978, followed by a reversal to a retreat phase from 1978 to present. The last reversal in glacier terminus position began c. 1978 with ice thinning and moraine building. The Easton glacier was the last to begin this retreat and last to commence a readvance owing to its response time of 10-12 years (Harper, 1992). The response-times of the glaciers range from 3—12 years for an advance phase and 3-11 for retreat phases, as determined by Harper, (1992) using methods after Johannesson et al. (1989a, 1989b). However, these response times are provisional because data points may be separated by 4-9 year gaps that affect the accuracy of precisely dating glacial responses. 138 c- 600 •> ro E a) o o rr a> 400 200 r - 0 I t -200 ro .» -400 -600 - Boulder - Co leman -o — Deming - • - - Easton - Rainbow - Roosevelt Retreat 1930 1940 1950 1960 1970 Year 1980 1 ' I ' ' ' 1990 2000 Figure 7-9. Terminus positions of glaciers on Mt. Baker for 1940-1990 period based on 1940 positions (data taken from Harper, 1992). 7.5 Climate indices Several independent studies find evidence for PDO-like cycles that alternate between positive (warm and dry) and negative (cool and wet) phases every 20-30 years in the past century (Graham, 1994; Trenberth and Hurrell, 1994; Mantua et ai, 1997; Cayan et al., 1998; Bitz and Battisti, 1999). Figure 7-10 illustrates the PDO index compared to the continental signature at Olga, flow of the Fraser River, and glacier fluctuations. The 2-year smoothed indices exhibit similar frequency variability with the patterns or transitions from cool and wet to warm and dry arbitrarily chosen based on when the PDO changes modes. (i) "cool" PDO regimes prevailed from 1890- c. 1923 and from c. 1944-1976. (ii) "warm" PDO events dominated from c. 1923-1944 and from 1976 through at least the mid-1990's. Note the variability within the PDO regimes in which the trend is reversed (e.g. the positive PDO values in 1958-61 within the generally cool and wet regime). The PDO has been linked to El Nino-Southern Oscillation (ENSO), which is believed to be fundamentally derived from coupled processes within the tropical Pacific. Since the late 1950's, seven El Nino events have occurred: 1957-58,1965-55,1968-69,1972-73,1976-77,1982-83, 1986-87,1991-92, and 1994-95, some of which appear to be recorded in the variability of 139 the annual records. Although climate signatures correlate well with the PDO index, causes for the PDO are not yet known. Because the precipitation and temperature over this region is determined by the synoptic activity associated with the atmospheric configuration and oceanic regime the NP Index is shown. Although at the 1000 mb level is generally above the 2000-3000 m level where the glaciers lie on Mt. Baker. Both the PDO and NP index have been linked to drought occurrences and stream flow signatures (Namias, 1966; Beamish etal, 1994). In the past century, changes in the PDO seem responsible for the glacier fluctuations. Bitz and Battisti (1999) studied the net winter and net annual mass balance anomalies for several maritime glaciers in Washington State and British Columbia. They showed a positive correlation with local precipitation anomalies and storminess and a negative correlation with local temperature anomalies (Bitz and Battisti, 1999). As shown on Figure 7-9, the timing of initiation and close of these events varied between glaciers. The retreat events were generally reactions to precipitation minima of the warm and dry PDO regimes (Fig. 7-10), while glacier advances were associated with a cool and wet PDO cycle. The associated climate changes preceded changes in glacier response c. 3-5 years. Based on these climate-glacier observations, inferences of glacier fluctuations may be extended back as far as the climate records. Since 1925, marine ecosystems in the northeast Pacific correlate with changes in the PDO; warm periods have enhanced coastal ocean biological productivity, while cold PDO eras have the opposite effect (Hare and Francis, 1995). 140 7.6 Discussion The PDO shows a strong relation to indices for El Nino-Southern Oscillation (ENSO) and the Aleutian Low (AL). Mantua et al. (1997) suggested that ENSO and the PDO affected the North Pacific through associated changes in the large-scale windstress field over the Pacific. The Northeast Pacific, ENSO, and PDO windstress signatures are similar, and much of the atmospheric variability is identified in an AL index. The AL and ENSO, however, both show more interannual variability than the PDO which operates under an interdecadal timescale. ENSO events typically occur every 2-7 years and last 12-18 months (Wallace andGutzler, 1981; Mantua et al., 1997). The relation between meterological data and glacier responses on Mt. Baker f h provides a climate-glacier proxy that extends back at least to the late 19 Century. Notwithstanding non-climatic geological processes (i.e., geothermal activity and landslides), when glacier fluctuations are cc^ npared to the PDO record, a linkage is apparent. The PDO affects the terminus position of six, maritime glaciers on Mt. Baker, producing precipitation anomalies in the seasonally averaged circulation patterns thereby affecting the balance of the glaciers. Because of the large distribution area at high elevations and high accumulation gradients on Mt. Baker, these glaciers are especially sensitive to perturbations in climate. The magnitudes of winter precipitation and summer temperature required to initiate a change in a glacier advance or retreat phase are dependent on the size and elevation range of the glacier. Therefore, the climate perturbation necessary to cause an advance of a glacier in a retreat state is different than that required to advance the same glacier in an extended position. This suggests that changes in terminus position are exceptionally sensitive to changes in climate trends. A limitation of the climate variability in this area may be the lack of sufficient data at high altitude locations. For instance, winter precipitation occurs as rain at low elevations, but snowfall is dominant above 1500 m (Tangborn, 1980). Lag times of glaciers on Mt. Baker vary, but this study and that of Harper (1992) indicate that the Coleman Glacier is the most responsive to changes in the trend of climate, with 3-5 year 141 response times. A cursory review of the modern glacial record on Mt. Rainier suggests that those glaciers may be experiencing similar fluctuation patterns and lags in response to the PDO. This work is consistent with the findings of others (Hodge et al. 1998; Bitz and Battisti, 1999; McCabe et al, 2000) An interdecadal climate signal that is evident in the oceanic-atmospheric climate and glacier record has been identified. Major glacier fluctuations are attributed to changes in PDO regimes. During this century, compared to the PDO (North Pacific SST pattern time series) and other climate indices, all six glaciers experienced the same general advance and retreat phases. Although the timing of initiation and conclusion of each event varied between glaciers, they are linked to the PDO index with a lag of c. 3-5 years. In view of the short-term sensitivity of these maritime glaciers to oceanic fluctuations (e.g., amount of precipitation, PDO), the record of Holocene glacier variations on Mt. Baker is a proxy of pre-instrumental PDO variations. 142 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 I " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! " " ! I ' 1 1 '11'1' I ' 1 1 ' I'11' I 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Figure 7-10. Stacked time-series of climatic records for the last 100 years. The datums are the mean of monthly data. OWP and OST are Olga's winter precipitation and summer temperature, respectively, the Fraser River annual flow is (FR), North Pacific index is (NP), and Mt. Baker glaciers is (MBG). Superimposed heavy curves are 2-yr running means with data normalized by the standard deviation, s, as given. 143 Chapter 8 Conclusions 8.1 Summary This thesis represents the first attempt to unify glacial geomorphology across the U.S.-Canadian border. This was enabled by the use of multiple lines of evidence, including: traditional mapping and field techniques, the use of computer-generated digital images that help to visualize morphologic features, and the use of many radiocarbon date to provide constraints on the ordering of events. This work revealed the timing of new terminal ice positions associated with fluctuations of a piedmont ice lobe that occupied the Fraser Lowland following drastic thinning of the ice sheet during the late stages of the Fraser Glaciation. These ice terminal fluctuations occurred at the last glacial to non-glacial transition, and have important implications for understanding how abrupt climate changes (e.g., the Younger Dryas cold period) may have been transmitted throughout the Northern Hemisphere. Glaciomarine and glaciofluvial sediments of the Fort Langley Formation (Everson Interstade) provide constraining stratigraphic and radiocarbon dated material for the overlying Sumas Drift (Sumas Stade), the youngest subaerial glacial deposit in the Fraser Lowland. Shells from the surface-mantling stony mud of the Fort Langley Formation range in age from c. 12,500 to 11,400 1 4 C yr BP, after a reservoir correction is applied. A 1 4 C marine reservoir value of c. -800 years has commonly been used to correct the ages of both modern and late Pleistocene marine shells in western North America. However, in this study, differences in 1 4 C ages of late Pleistocene, coeval, shell and wood samples from the same stratigraphic unit indicate a total marine 1 4 C reservoir value in the Fraser Lowland of c. -1100 years between 12,000 and 11,000 1 4 C yrs BP. Previously reported 1 4 C dates from marine shells in the region have not corresponded well with coeval wood. Shell dates using a total reservoir value of-800 years are consistently c. 400 years older than dates from 144 coeval wood. However, when a -1100 year total marine reservoir correction is applied, shells dates correspond much better with the wood dates. The ramifications of the -1100 year total marine reservoir value, 300 years more than that previously used, are that all previously published 1 4 C dates of shells between c. 12,500 and 11,500 1 4 C yr BP in the region are too old and must be recalculated, and the greater marine reservoir value suggests changes in oceanic-atmospheric circulation in the NE Pacific. When ice thinned below topographic divides, the locations of ice centers migrated to the Coast Mountains and Mt. Baker, which produced autonomous ice centers. Long valley glaciers constructed moraines in the Nooksack drainage, 25-^ 45 km downvalley from their sources (Chapter 6) at a time that a piedmont glacier lay 30 km to the northwest in the Fraser Lowland. The Middle Fork glacier stagnated c. 12,300 1 4 C years ago and deposited ice-contact drift that was later overridden when ice readvanced. Logs in a lateral moraine in the upper Middle Fork were dated at 10,680 ± 70 and 10,500 ± 70 1 4 C yr BP. The North Fork glacier, which originated at a large cirque on Mt. Shuksan and fed by glaciers from Mt. Baker, extended to Kendall where two moraines were deposited. Outwash from the moraines in the North Fork valley rests on glaciomarine stony mud dated at 11,910 ± 80 1 4 C yr BP and contains charcoal layers dated at 10,603 ± 69 and 10,788 ± 77 1 4 C yr BP. The South Fork glacier at its maximum was joined by ice from the Middle Fork and extended downvalley to Lake Whatcom and to Cranberry Lake. It retreated from its terminal position prior to c. 12,700 , 4 C yr BP. The emerging picture is that cool and moist conditions, which are evident in sea surface temperature and pollen records, may have caused these readvances. To better understand climatic-glacier response, a review of the present-day glacier fluctuations on Mt. Baker revealed a link to the PDO sea surface temperature modes (Chapter 7). Fluctuations in terminus positions of six high-altitude, maritime glaciers correlate with several climate signals. The advance-retreat phases lasted 20-30 years over the last 100 years, which correspond to climatic variability related to large-scale circulation anomalies associated with ENSO and PDO. The time of transition from warm and dry to cool and wet modes of the PDO and glacier response is roughly 3-5 years (with some uncertainty given the interval of data collection). This highlights the sensitivity and response of glaciers on 145 Mt. Baker to variability in climate and suggests that similar responses may have occurred during the last glacial/non-glacial transition. 8.1.1 Deglaciation in the Fraser Lowland At the glacial maximum in the Fraser Lowland, ice was ca. 1800 m thick and at c. 14.5 1 4 C kyr BP, climatic warming (and subsequent fluctuating sea levels) caused drastic ice retreat that was generally twice as fast as the advance (Porter and Swanson, 1998). As ice melted, rising seawater inundated the Fraser Lowland and adjacent areas, depositing glaciomarine sediments that are now up to c. 200 m above present sea level. In the lowland, a series of ice margins was established (Chapters 4, 5). This thesis determined that changing ice-extent between c. 13.0 and 10.0 1 4 C kyr BP appears to correspond with other proxy records (Fig. 8-1; Chapters 4, 5). Armstrong (1981) suggested that ice readvanced several times into the Fraser Lowland, based on interbedded tills within the Fort Langley Fm. Since then, several people have suggested multiple readvance scenarios. Integrating surficial mapping, palynological, oceanographic (from previous studies), sedimentological, radiocarbon, and digital imagery data that span the U.S.-Canada border, revealed multiple moraines and new terminal positions associated with oscillations of the piedmont remnants of the Cordilleran Ice Sheet during the late stages of the Fraser Glaciation. Following emergence of the lowland ate. 11.6 1 4 C kyr BP, two periods of glacier advance occurred 11.6-11.4 and 10.9— 10.2 1 4 C kyr BP during the Sumas interval. The spatial and temporal relations of Sumas Drift indicate four recognizable Sumas phases (SI, SII, SIII, and SIV) including three readvances of ice. Between c. 11.4-10.9 1 4 C kyr BP recession of ice from SII margin was followed by a significant readvance. Figure 8-2 shows the calibrated age ranges for the Sumas phases. 146 Sumas Phase Age Range ( 1 4 CyrBP) Characteristic SIV >10,250- ? 10,900-10,250 Readvance of ice and construction of a moraine Sffl Construction of SIII moraine complex and activation of Abbotsford outwash plain. Ice readvance, and building of prominent moraine. Outermost drift and meltwater channels, substrate same as SII SII 11,600-11,400 11,600-11,400 SI The deglaciation model is bracketed by 70 radiocarbon dates on marine shells, wood, peat, outwash, and raised marine deposits (28 on marine shells, 42 on wood and peat) and constrained by morphologic and stratigraphic evidence. A 1 4 C marine reservoir value of-1100 years was used to correct the ages of late Pleistocene marine shells. Calibrated radiocarbon dates are shown in Figure 8-2. The radiocarbon ages for each Sumas phase cluster, although the 1 and 2a age ranges overlap in places due to uncertainties that are inherent in radiocarbon dating. 8.1.2 Early Holocene During the early Holocene, changes in temperature can be inferred from an estimate of the ELA depression. On the southeast flank of Mt. Baker, three advances and retreats are recorded prior to the thermal maximum of the Hypsithermal interval. The modern ELA is c. 2095 m. During the Little Ice Age (LIA) and early Holocene the ELA declined to c. 1815 and 1730 m (Thomas, 1997), which translates to an ELA depression of 280 and 365 m, respectively. 147 (A « (A Q-« E £ o •i= OS OJ c E E o S. a. D E o S e w a. oo g « JE i so S <o 13 ~ -3 OJ k_ k. OJ w-C OJ tn £ E i f s | S I E OJ 5 * S u IE . a. OJ o 11 03 « £ o OJ I a * — .2 w !K *s In £ c » «3 OJ c c CO i & | « I 2 E l i OD £ <U i-n 2 ? .? OJ "55 *5 E -g o | .2 > c o> -ji 5 5 B Dl S £ .£ -fc o OJ g 2 •» E c 3 OJ £ » OJ 04 O '?= Si w •o o «2 o§ is E w £ i l l •8 if S o o DI l/l E CO to w rn i c 1 >s i I | = W o < 1 Til CD 1 Q Of 1 i & CD • i C 3 • vt Yo 3 Oldt o 9> o (da Jepuaieo) 96v 148 1 0 O O O 1 6 Q D O 1 4 0 0 0 1 3 0 0 0 1 2 0 0 0 1 1 o o o c a l B R Oldest Dryas I I Boiling a Allerod & 1 II M II Younger Dryas Holocene Figure 8-2. Plot of calibrated age ranges for radiocarbon dates. Black fill is la age range, white is 2a age range. Numbers on left are locality numbers keyed to radiocarbon tables (Chapter 5, Appendix A, Table A-l). See Appendix E for basal peat dates from cores obtained during this study. 149 8.2 Possible correlations In the following discussion, whether the reported dates are based on la or 2a standard deviations (lab precision) is not always possible to determine. The calibrated age ranges shown below are the reported radiocarbon ages that have been converted to la and 2a ages (68% and 95% confidence interval, respectively). Figure 8-3 illustrated some possible regional and extended correlations with late glacial cirque moraines. These cirque glaciers may or may not have responded similarly to the remnants of the Cordilleran Ice Sheet and Nooksack alpine system because of differences in size, internal ice dynamics, and responsiveness to perturbations in climatic changes. 8.2.1 Local correlations Saunders et al (1987) described two diamictons (till), dated between 11.8 and 11.2 1 4 C kyr BP at the Tamihi Slide site in the Chilliwack Valley adjacent to the Fraser Lowland. These tills mark the position of the lateral margin of the valley glacier that flowed into the Chilliwack Valley from the Fraser Lowland. These tills may or may not correspond to fluctuations in the glacier terminus in the Fraser Lowland. The lateral position of these tills indicates the minimal thickness of the ice needed to top the divide between the two drainages and therefore is a measure of ice thickness at that point. The possibility exists that significant fluctuations of the terminus of the glacier could have occurred without enough change in ice thickness to cause changes in till deposition here. At the Tamihi Slide site, Saunders et al. (1987) show a diamicton with dates of 11.8-11.2 1 4 C kyr BP resting on silt and gravel. This suggests that the glacier had retreated and thinned enough to allow the site to be free of ice prior to 11.6 and in that case, the Sumas readvance to SII must have been a substantial readvance, not just a local, minor oscillation. An upper till resting on an organic-rich layer dated at 11.2-11.3 1 4 C kyr BP may correspond to the SIII advance in the Fraser Lowland. However, 4 out of 6 radiocarbon dates (Saunders et al, 1987) are in inverted stratigraphic position. Therefore, the ages are too equivocal for specific assignment to the Sumas fluctuations in the glacier terminal area. 150 A resurgence of ice in Howe Sound following its initial rapid retreat deposited a moraine dated at about 10,690 ± 180 1 4 C yr BP (Armstrong, 1981; McCrumb and Swanson, 1998) (Figure 8-3). Half Moon Lake Lobe Mean = 16.0 ka Coef.Var. = 4.1% Titcomb Basin Inner Moraine Mean = 11.0 ka Coef. Var. = 4.1% 20 15 B e yr B.P. 10 SI & SII SIII SIV Piper Lake moraine « = > ( ] 1 Minimum age from Glacier Peak ash G. 11.200 (Osborn and Gertoff, 199/) u « - » " • Recess Peak moraine i j>U If! Minimum age. 11,190 + 70 (Clark aid Gillespie. 19S7) Crowfoot advance - r ^ ^ » (Rewoner e< al.. 1994; t=> I I! Minimum age. 10,020 ± 70 Osborn o( a/.. 1995) Maximum age, 11,330 ± 330 Younger McNeeley moraine [ [| Minimum age, 9140 ± 100 (Heine. 1998) ^ « ^ Maximum age, 10,080 ± 60 [ Older McNeetey moraine =^>[] [] Minimum age, 11,320 ± 60 (Heine, 1998) Squamish VaNey kame, B C. «—>j j Minimum age. 10.650 ± 70 (Friele etal,. 1999) Howe Sound moraine. B.C. e= > Q H ^ Z ^ Z l l Minimum age. 10,690 ± 180 (McCrumb and Swanson, 1998) I • * ' t I i i > i > i . i . I . i I i i i i I t i < l i t . i i 15.000 14.000 13.000 12.000 11,000 10,000 9000 , , Age (cal yr B.P.) , 12,000 11.000 10.000 A g e t 1 4 C y r B P . ) Figure 8-3. Comparison of Sumas phases and selected alpine glacial records spanning the last glacial to non-glacial transition. 1 4 C dates are shown in calibrated age ranges (black and white fills are la and 2a age ranges, respectively). Half Moon and Titcomb Basin dates from Gosse et al. (1995, 1999). 151 8.2.2 Regional correlations A variety of climatic proxies from the Cascade Range correlate with multiple late glacial fluctuations. The Hyak moraines at Snoqualmie Pass are limited by a date on wood above till behind the outermost Hyak moraine at 11,050 + 50 1 4 C yr BP (Porter, 1976) permit correlation with the SII advance. Mt. Baker (3285 m) is situated more than 300 km north of Mt. Rainier (4392 m), which makes comparison of the climatic factors responsible for the glacier advances difficult. Mt. Baker is the first prominent barrier to incoming storm tracks that converge and travel through the Strait of Juan de Fuca. In contrast, Mt. Rainer is positioned west of the Olympic Mountains in the Cascade Range. Heine (1997,1998) has suggested two advances (McNeeley 1 and 2) of cirque glaciers near Mt. Rainier based on the interpretation of lake sediment. The McNeely 1 advance occurred prior to 11,300 1 4 C yr BP. The McNeeley 2 advance occurred 9800-8950 1 4 C yr BP. Heine suggested that the McNeely 1 advance precedes the Younger Dryas. Because dates are minimum ages, the McNeely 1 may correlate with the Older Dryas (Fig. 8-3). Pollen records in British Columbia indicate a cool period during the Younger Dryas. Mathewes et al. (1993) calculated summer air temperatures of 2-3°C between 11,000-10,200 yr BP. Kienast and McKay (2001) documented three distinct cold phases (6-7°C) that interrupt two warmer periods (9-10°C) between 16,000-11,000 yr BP in sea surface temperatures for the northeast Pacific. If these correlations are accepted, this indicates a shift in regional climate that may be responsible for the Sumas interval readvances. The asynchronous response of cirque glaciers may be caused by the inherent differences between ice sheets and cirque glaciers. 152 8.2.3 Extended correlations In the Canadian Rockies, moraines have been correlated with the Crowfoot advance between 11,330 ± 330 and 10,020 ± 70 1 4 C yr BP (Reasoner et al, 1994). The Temple Lake moraine in the Wind River Range, Wyoming was constructed prior to c. 11,770 ± 770 1 4 C yr BP (± 2a, Zielinski and Davis, 1987). Gosse et al (1995,1999) has documented the late Pleistocene/Holocene glacial and paleoclimatic history of Titcomb Basin constrained by cosmogenic and radiocarbon dates. The dates correlate with the Temple Lake till (Zielinski and Davis, 1987). A moraine of the Recess Peak advance in Sierra Nevada was built prior to 11,190 + 70 1 4 C yr BP (Clark and Gillespie, 1997). The Piper Lake moraine in the Mission Mountains, Montana was constructed prior to the deposition of Glacier Peak ash G, 11,200 1 4 C yr BP (Osborn and Gerloff, 1997) which permits correlations to SII, although these correlations are permitted by minimum dates and further studies are needed to better constrain these correlations (Fig. 8-3). While the above correlations are from cirque glaciers, these changes are similar to those observed around the Atlantic basin at about the same latitude (e.g., Norwegian Sea, 49°N; Koc-Karpuz and Jansen, 1992; Lehman and Keigwin, 1992) and (e.g., maritime Nova Scotia, 45°N; Mott et al, 1986; Stea and Mott, 1989). The ice sheet terminus retreat, followed by renewed glacial activity 12,000-10,500 BP of Nova Scotia seems to mirror events in the Fraser Lowland. 8.3 Discussion A model of deglaciation for the Fraser Lowland has been proposed for contemplation which is based upon our current understanding of the geomorphic reconstructions, stratigraphy, oceanographic, and radiocarbon dating that determine changing ice-extent. An attempt has been made to view the Sumas interval in a broad context by combining previous observations (e.g. Armstrong, 1981,1984; Easterbrook, 1976b, 1994; Mark and Ojamaa, 1980; Clague et al, 1997) with new data. The primary style of deglaciation is frontal retreat with multiple readvances and stillstands during deglaciation. This is an improvement in the context of the deglaciation sequence in the Fraser Lowland and 153 provides a framework for local, regional and extended correlations (e.g., Hicock et al, 1999). Multiple ice readvances occurred during the late Wisconsin, before and after c. 11,600 1 4 C yr BP and deposited moraines, outwash, and ice contact sediments in the Fraser Lowland. Between c. 10,900 and 10,250 1 4 C yr BP, ice retreated an unknown distance and readvanced again, constructing moraines near the towns of Mission and Sumas. These ice fluctuations are bracketed by more than 70 radiocarbon dates, but the analytical uncertainties of c. ± 45-200 1 4 C yr BP indicate that radiocarbon dating of these rapid fluctuations will be difficult to completely resolve. However, constraining information at key localities provided by morphology, stratigraphy, and radiocarbon dating yields meaningful results. This research indicates that the high elevation alpine areas are highly sensitivity to changes in climate. The behavior of the linked ocean-atmosphere system at this latitude exerts substantial influence on the environment of this region. Chapter 7 provided needed context for understanding contemporary high elevation alpine glacial responses to decadal variability in climate. Glaciers on Mt. Baker appear to respond to PDO phase changes within 3-5 years. Identification of such lags may illuminate processes that control climate change and/or the marine versus continental responses to climate change. The available evidence suggests a sequence of glacial events in the North Cascades that does parallel those in northwestern Europe; if true, climatic changes of possible hemispheric proportions occurred roughly between 13,000-10,000 1 4 C yr BP, including cold periods separated by warm periods. Since glacier advances in the North Cascades are affected by available moisture from the northeast Pacific these sequences may not always be precisely in phase. Within the resolution of radiocarbon dating, we cannot exclude the possibility that these climatic event were driven by the same mechanisms. These late-glacial climate oscillations were probably influenced by events in the northeast Pacific Ocean, as suggested by the SST curves off Vancouver Island. Locally, those signals may be picked up differently, which may lead to apparent dissimilarities. 154 8.3.1 Future considerations The record of ice-front behavior may not reflect a single controlling factor; its deciphering is essential for a correct interpretation of the glacier dynamics and regional paleoclimate signal and glacier dynamics. While internal oscillations triggered by basal meltwater feedbacks are a possibility, modeling experiments have not yet been attempted on the Fraser or Nooksack systems. Abrupt temperature changes (external trigger) are known from paleoclimate records (e.g., Mathewes, 1993; Mathewes et al., 1993; Kienast and McKay, 2001). This has led me to postulate abrupt climatic shifts that drove the response of these glaciers. However, significant time lags exist for surface temperature perturbations to penetrate to the ice bed, so thermally-regulated events may not be triggered by high-frequency climate change alone. During the Everson Interstade when relative sea level was high, the glacier lost significant mass rapidly through calving of icebergs into the ancestral Fraser inlet, resulting in deposition of fossiliferous stony mud. Armstrong (1957) suggested many advances of ice during the Everson Interstade. The rapid retreats (or disintegration) and readvances are not necessarily related to climate fluctuations. Krimmel and Meier (1989) point out that tidewater glacier fluctuations may be related to the drainage basin geometry, glacier mass balance distribution, and the availability of erodible material, all of which are transmissible to the glacier history. However, thirty-nine radiocarbon dates from the marine sediment that blanket the Fraser Lowland correlate with the Billing and Allerod warm periods. In contrast, during the Sumas Stade, following emergence of the Fraser Lowland, I speculate that the ice was in a vulnerable state and hydrologically controlled, which would have more direct communication with climatic changes. A simplified formula that relates ice thickness and thermal diffusivity of pure ice to time (t~h I \Q m s ; where t is time, h is ice thickness in meters, and lO^m 2 s - 1 is thermal diffusivity) indicates that for a surface temperature change to penetrate 100 m of ice, time lags are c. 103 - 104 years (with very large attenuation with depth). In reality, climate-ice feedbacks are more complicated and require coupling with subglacial hydrologic processes. The rapidity of the advances suggests internal instability of the ice or a non-linear response to climate. Although, note 155 that ice streams and outlet glaciers typically exhibit fast flow. The regional correlations, albeit crude in some cases because of the lack of good dating control, suggest a climatic trigger. From understanding of the timing and extent of Sumas ice, the following questions arise: Was the Cordilleran Ice Sheet (and individual ice lobes) synchronous with other ice sheets, or other factors? How did the Cordilleran Ice Sheets respond to changes in ocean-atmospheric circulation in the Pacific Ocean and/or North Atlantic Ocean? Did warm intervals trigger rapid ice sheet collapse? Hydrogeologic model studies would provide characterization of bed and basal processes that are key to understanding ice fluctuating behavior (e.g., ice positioning and activation). Since up-ice conditions were situated in valleys, which were conduits for meltwater (both subsurface and surface meltwater inputs), a hydrological model that tracks the drainage of water at the bed and the evolution of subglacial drainage regimes would be useful. This work shows the heed for modification of the existing late Pleistocene glacial sequence in the Fraser Lowland (e.g. redefinition of the Sumas to include multiple readvances). The climate oscillations during deglaciation need not be restricted to the North Atlantic region. Causes of these changes and their propagation will require hemispheric and global analysis to attempt to explain local forcing and amplifiers. The leading hypothesis of these high-amplitude millennial-scale climate fluctuations seem to be linked to the rate of formation of North Atlantic Deep Water (NADW) as a causal mechanism through altering the oceanic heat transport to high latitudes (Broecker et al, 1985). This hypothesis has led to the development of many large-scale numerical models (e.g., climate models, ice sheet thermomechanic models, oceanic models) that seek parameterization of the processes. Perhaps, the most promising models are those that incorporate freshwater fluxes from ice sheets (e.g., Marshall and Clarke, 1999). Increased glacial meltwater flux to the North Atlantic reduces NADW formation, thereby reducing heat transport and subsequently, causing cooling. Clark et al. (2001) have proposed that the fluctuating southern margin of the Laurentide Ice Sheet caused multiple meltwater 156 routing changes. The reconstruction of changes in meltwater routing between southern and eastern outlets appear to be coincident with the abrupt climate flickers in the North Atlantic region during the last deglaciation. If this is true, then we are moved to ask how the freshwater flux to the North Atlantic, that may be the primary cause of climate variation, is propagated globally and apparently, synchronously? 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Zhang, Y., Wallace, J.M., and Battisti, D.S., 1997. ENSO-like interdecadal variability: 1900-93: Journal of Climate 10, 1004-1020. Zielinski, G.A., and Davis, P.T., 1987. Late Pleistocene age of the type Temple Lake moraine, Wind River Range, Wyoming, U.S.A.: Geographic Physique et Quaternaire 41, 397-401. 190 Appendix A Radiocarbon dates 191 Appendix A Radiocarbon dates Compiled are radiocarbon dates used in this study. New and old radiocarbon dates from the Fraser Lowland and Nooksack drainage are given and repeat those dates provided in the preceding chapters. Because this list includes new atomic mass spectrometer (AMS) and old scintillation dates from various laboratories, which reported dates differently, several details must be considered for accurate comparison of dates. GSC began measurements of 81 3C and reported normalized ages for most samples in the late 1960s. The ages of organic materials were normalized to -25 parts per mil (%o), whereas marine shells were corrected to 0%o. Since 1992, the GSC lab reports all of its ages adjusted to a 8 1 3C value of-25%o (for marine shells that is equivalent to adding c. 400 years to the measured age), but provides a corrected age for marine shells with all errors of ± 2 sigma range. The age errors include counting errors of sample, background, and standard, and the error in the half-life of 1 4 C. Prior to 1974, the GSC errors also included a term to account for variations in the 1 4 C concentration of the atmosphere, and the error assigned to an age was a minimum of ±100 years (Lowdon et al., 1972; Lowdon and Blake, 1973). GSC's lab multiplier is 1.6, which is applied to a 1 sigma error (R. McNeely, personal communication, 2000). In accordance with lab protocol, the laboratory precision for GSC dates was originally reported with 2 sigma errors. In order to compare dates from other laboratories, the lab multiplier should be the same. Therefore, the laboratory uncertainty for GSC dates was reduced to 1 sigma by a division of 2 (R. McNeely, personal communication, 2000). For shell dates listed here a reservoir correction off 100 ± 100 years was applied (Chapter 3). 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CN Os 0 £ IC ^ o o r- r-CN CN Os O OS cn SO so m O o o r> r-CN CN CN r-CN cn OO CN rr so 00 cn CN I t « Os g * CN os - H .T °^ ** in m oo CN rT ^ OS 0 -cn rt rt < < < z z z o so 00 o 00 CN < z 00 +1 o o rr o" rt CN m so so m so so m m CN CN rr SO \q cn rt" rt" rt" rt rt <—i / • ^ SO SO CN CN CN 00 CN SO in CN co O °\ 0\ CN CN" rt" rt" w S ' cn SO in m cn in SO^  so, rt" CN" CN" rt z o m Cm CN m o m +| SO r^  r~ o +1 +1 +1 00 o o o OS m Os m o" o o 00 oo Os Os r^  so < Z so +1 SO CN 00 SO < z o Os +1 rr CN Os so 3 1 "a © II K Table A-2 Radiocarbon dates from the Nooksack Drainage Radiocarbon Age ( l 4 CyrBP) Calibrated Age* Sample no./ 2 a yrBP Lab no.§ Dated material Comments Middle Fork - Deep Kettle Bog 6850 + 65 7577 - 7791 11,945 + 85 13,633- 15,289 11,520 ± 190 13,031- 14,028 11,940 ± 180 13,463- 15,326 12,160 + 90 13,831 - 15,403 7674 12,145 ±90 13,828- 15,395 14,114 12,045 ± 85 13,661 - 15,344 14,081 12,120 + 90 13,684- 15,383 14,106 12,035 ±95 13,656- 15,341 14,078 12,150 ±90 13,829- 15,398 14,116 12,230 ± 80 13,843- 15,433 14,149 12,380 ±90 14,110- 15,506 14,328 12,365 ± 115 13,869- 15,508 14,321 12,165 ±95 13,830- 15,407 14,121 14,040 13927 13,856 13,463 14,037 13,930 13,854 14,119 DKB1-6/ AA22201 DKB1-8/ AA-22203 DKB2-3/ AA-22205 DKB2-4/ AA-22206 DKB2-5/ AA-22207 DKB2-6/ AA-22208 DKB1-4/ AA22199 DKB1-3/ AA22198 DKB1-2/ AA-20750 DKB1-1/ AA-20749 DKB2-1/ AA-22204 DKB2-8/ AA-22210 DKB2-7/ AA-22209 DKB1-7/ AA-22202 1- cm diameter wood, 3 cm below contact with Mazama ash 2- cm diameter wood in peat 4.5 cm from base of core Small piece of wood in basal peat 0.5 cm below contact with diatom layer Small piece of wood in basal peat ~1 cm below contact with diatom layer Small piece of wood in basal peat at contact with diatom layer Small piece of wood in basal peat at contact with diatom layer 2.5 cm long twig at top of basal peat at contact with overlying diatomite ~1 cm long branch at top of basal peat at contact with overlying diatomite 1-cm piece of wood resting on the material in DKB1-1 Rootlets in lower 2 cm of core 2 small pieces of wood 1 cm from base of the core Wood in basal sand at contact with overlying basal peat Wood in basal sand at contact with overlying basal peat 2.5-cm-long, twig in basal sand at core bottom Maximum age of Mazama ash Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation Age of ice stagnation 199 Middle Fork 10,500 ±70 11,965-12,912 12,622 RC-2 Log in lateral moraine. Dates deposition of lateral 12,472 m O T a i n e 12,390 10,680 ±70 12,359-15,965 12,828 RC-1/ Log in lateral moraine. Dates deposition of lateral B-124911 moraine North Fork 10,788 + 77 12,631-13,098 12,886 RH2-4/ Uppermost charcoal in sand Minimum age of outwash AA-27079 10,603 + 69 12,192-12,994 12,653 RH2-1/ Lowermost charcoal in sand Minimum age of outwash 12,730 AA-27078 12,801 11,910 ± 80 13,618-15,267 13,845 WG-1/ Wood in glaciomarine drift Maximum age of two 1 3 9 5 1 B-1220447 at Welcome stillstands 14,017 South Fork - Cranberry Lake Bog 12,733 ±75 14,333 - 15,788 15,375 BB5-2/ AA-27076 Basal peat 1 m above bottom of core Minimum age of ice stagnation 12,596 + 80 14,204- 15,627 14,445 14,611 15,226 BB3-3/ AA-27075 Basal peat on thin clay and gravel Minimum age of ice stagnation 13,750 ± 127 15,980- 17,062 16,502 BB3-2/ AA-27074 Plant fragments in basal clay Minimum age of ice stagnation 12,425 ± 90 14,123 - 15,526 14,347 BB3-1/ AA-27065 Plant fragments in basal gravel Minimum age of ice stagnation 12,255 ± 84 13,846- 15,446 14,172 14,194 14,258 CB5-3/ AA-27077 Plant fragments in clay at very base of core, 1 m below basal peat Minimum age of ice stagnation 12,215 + 85 13,840- 15,428 14,142 CB5-1/ AA-27064 Plant fragments in sand 1 m above base of core Minimum age of ice stagnation 14,167 ±82 16,491- 17,518 16,982 CB1-1 AA-27073 Basal peat above thin clay and gravel Minimum age of ice stagnation Laboratory error precision is 1 sigma. * 2 a age range calibrated years before AD 1950 using the CALIB 4.1 program of Stuiver and Reimer (1993). 8 Laboratory designation: AA - Univ. of Arizona AMS facility. B - Beta Analytic Inc. 200 Appendix B Description of samples analyzed for radiocarbon age determinations 201 Appendix B Description of samples analyzed for radiocarbon age determinations Compiled for this appendice are descriptions of samples used for age determinations in this thesis. Since the initial collection of sample material, many of the sites have been disturbed or excavated. Therefore, original sample descriptions are meaningful and have direct implications for interpretations. Sample numbers correspond to Table A- l and A-2 in Appendix A. Note that all 'AA' dates were determined by AMS and 'rca' is the reservoir corrected age (Chapter 3). Fraser Lowland dates 1. 11,680 ± 90 (rca), GSC-186: County Line Overpass Description: Shells (several species of marine pelecypods and Serpula) from stony, silty clay at 95 m asl, in excavation from Trans-Canada Highway near County-Line Overpass, lower Fraser Valley (Dyck et al, 1965). Collector/date collected: J. Armstrong, 1963. Comment: Armstrong noted that" shells accumulated during post-Vashon marine submergence, and probably prior to advance of Sumas ice (Dyck et al., 1965). • Marine shell date blended from several species; lower limiting date of the oldest Sumas. 2. 11,210 + 150 (rca), GSC-391C: Burnaby, Lower Fraser Valley Description: Marine shells at elevation 134 m. Collector/date collected: Mathews et al, 1970 3. 11,240 ± 95, GSC-168: Fort Langley, Lower Fraser Valley Description: Marine shells (macoma calcarea) in marine clay, at excavation for Trans-Canada Highway southeast of Fort Langley (Dyck and Fyles, 1964). Collector/date collected: J. Armstrong, 1963. Comment: elevation 12 m 7.7 m below land surface Age of Fort Langley glaciomarine sediment. 4. 12,000 ± 95 (rca), 1-5959: Marion Description: Marine shells in glaciomarine sediment at 107 m asl northwest of Webster Corner. Collector/date collected: R. Mathews Comment: age of marine sediment 202 5. 12,520 ± 80 (rca), TO-4089: Bradner pit Description: Marine shells Collector/date collected: Clague etal, 1997 6. 11,540 ± 1 0 0 (rca), GSC-74: Burnaby Description: Marine shells (Chlamys selected from mixed shells, identified by W.H. Mathews) in stony marine mud beneath nonmarine sand, and peaty sand and gravel north of the Great Northern Railway, a few hundred meters west of Piper Avenue, Burnaby Collector/date collected: W. Mathews, G. Rouse and L. Hills Comment: age of glaciomarine sediment 7. 11,580 ± 40 (rca), B-145455: Axton Pit Description: marine shells; articulated Nuculana enclosed by glaciomarine stony mud from the county gravel pit off Axton Road. Shells are from massive stony mud previously mapped as Bellingham glaciomarine drift (the emerged glaciomarine sediment of the Everson Interstade) by Easterbrook (1976). The Bellingham is up to ca. 15 m thick and has a sharp contact with underlying sediments. The unit is identical with the glaciomarine sediment seen ca 15 km to the north exposed in the Bradner pit. The matrix within the shells is identical to the surrounding material indicating in-situ deposition. Collector/date collected: D. Kovanen and D. Easterbrook Comment: Two other shell samples were collected to determine a total marine reservoir value. Shells were sampled paired with wood from the immediate sample vicinity. Date provide the age of the glaciomarine sediment. 8. 11,620 ± 4 0 (rca), B-145456: Axton Pit Description: same as above Collector/date collected: D. Kovanen and D. Easterbrook Comment: same as above 9. 11,660 ± 4 0 (rca), B-145457: Axton Pit Description: same as above Collector/date collected: D. Kovanen and D. Easterbrook Comment: same as above 10. 11,770 ± 170, GSC-64: North Delta, Lower Fraser Valley Description: Marine shells of Serpula and of various marine pelecypods from Linton gravel pit, North Delta. Shells from stony, silty sand overlain by till-like material, glaciomarine stony, clayey silt, and beach gravel. The shell-bearing layer rests on the eroded surface of thick horizontal sand similar to the sub-till Quadra sediments level (Dyck and Fyles, 1963). Collector/date collected: J. Armstrong, 1961. Comment: "the shell-bearing material is interpreted as being glaciomarine, accumulated during wastage of the last (Vashon?) ice sheet. The date is compatible with this 203 interpretation and compares favorably with I(GSC)-248,12,800 ± 175 (Trautman and Walton, 1962). • Age of Fort Langley Fm. 11. 11,850 ± 4 0 (rca), B-144096: Bradner pit Description: marine shells; several articulated nuculana enclosed by glaciomarine stony mud from the Bradner pit. Matrix within shells is identical to the surrounding material indicating in-situ deposition. Massive stony mud ranges in thickness between 5-25 m in the pit and is laterally continuous. Collector/date collected: D. Kovanen Comment: Stony mud is log bearing, so these shells were collected with paired wood samples to determine a local reservoir value. This date provides the age of the glaciomarine sediment and lower limiting age of Sumas (SII) moraine. See chapter 3 for marine reservoir value determination. 12. 11,850 ± 4 0 (rca), B-144094: Bradner pit Description: marine shells; same as above. Collector/date collected: D. Kovanen Comment: same as above. 13.11,870 ± 40 (rca), B-144098: Bradner pit Description: marine shells; same as above. Collector/date collected: D. Kovanen Comment: same as above. 14. 11,910 ± 6 0 (rca), GSC-2612 : Port Moody Description: Marine shells (Fusitron oregonensis, a single large gastropod) in stony clayey silt resting on Vashon till and overlain by Capilano beach gravel on hill lying south and east of Port Moody at an elevation of 91.5 m (Lowdon and Blake, 1978). Collector/date collected: J. Armstrong, 1974. Comment: offshore bar deposit exposed near the surface Armstrong noted that "dates GSC-2604 and GSC-2612 help to establish the deglaciation pattern in relation to relative sea level changes in the Fraser Lowland. Since the Vashon ice retreated, the area apparently has undergone tow major submergences and subsequent emergences in relation to the sea. Both samples are found in material that formed part of the first emergence and that is Capilano in age. Because of the small size of the samples, only the outer 10% of shell was removed by HCL leach" (Lowden and Blake, 1978). 15. 121,910 ± 85 (rca), G S C - 3 7 : Boundary Bay Description: marine shells (pelecypod) Collector/date collected: J. Armstrong, 1960. Comment: Marine shells in diamicton; underlain by gravel and overlain by beach gravel and sand exposed at Delta municapal gravel pit, 0.2 km north of US border in upland near Boundary Bay (Dyck and Fyles, 1963). Sample from middle of layer of till-like material, 204 2-3 m thick interpreted as glaciomarine at 46 m asl. Shells dated as 12,625 ± 450 (I(GSC)-6) and 11,900 ± 360 (L-391 C) are assigned by Armstrong to the same event, whereas several dates ranging from 10,950 to 11,70 BP (L-221 D E; L-331 A, B, C) relate to the Sumas glacial advance. 16. 11,910 ± 8 8 (rca), I(GSC)-248: Boundary Bay Description: marine shells (pelecypod) ca. 46 m asl (150 ft), in till-like deposit, exposed in a gravel pit, 200 m. north of US-Canadian border in upland near Boundary Bay. Sample taken from middle layer of till-like material, 6 to 10 ft thick, resting on gravel and overlain by 3-5ft. of beach gravel and sand (Trautman and Walton, 1962). Collector/date collected: J. Armstrong, 1960. Comment: Armstrong noted that "till-like material inclosing the dated shells is interpreted as glaciomarine, accumulated during a glacial advance within the period of wastage of the last (Vashon) ice sheet. Shells dated as 12,625 ± 450, (I(GSC)-6) and 11,900 ± 360 (L-391C, unpublished) are assigned by Armstrong to the same event, whereas several dates ranging from 10,950 to 11,700 B.P. (L-221D, and E; L-331 A, B and C) relate to the Sumas glacial advance which may be later" (Trautman and Walton, 1962). 17. 11,935 ± 225,1(GSC)-6: Whiterock, Lower Fraser Valley Description: Marine shells (pelecypods) collected from drainage ditch on E side of King George Highway, Sunny side, near Whiterock. Shells enclosed in stony clay beneath ca. 1.5 m of marine sand at an elevation of ca. 39 m asl (260 ft) (Walton et al, 1961). Collector/date collected: J. Armstrong, 1957. Comments: age of Fort Langley sediments 18. 12,010 ± 150 (rca), GSC-2604 : East Delta, Lower Fraser Valley Description: marine shells (Clinocardium nuttalli-smgle intact pair) in stony clayey silt overlying Vashon till and overlain by Capilano beach gravel from gravel pit in East Delta at 70 m asl (260 ft) (Lowdon and Blake, 1978). Collector/date collected: J. Armstrong, 1957. Comments: age of Fort Langley sediments 19. 12,210 ± 85 (rca), GSC-2193 : Websters Corner Description: marine shells (Mya truncata L. and Mya) fragments from a gravel pit 6.5 km north-northwest of Whonnock, at an elevation of 154 m. The sample is from stony clayey silt of raised marine delta deposited against ice (Lowdon et al, 1977). Collector/date collected: J. Armstrong, 1975 from a fresh exposure. Comment: Armstrong noted that "the sample is from the highest elevation at which preserved shells have been found in the Fraser Lowland, and it dates an early stage in the first emergence of the area above the sea. At this site a probable marine terrace is found at approximately 195 m asl, and it is believed to represent the maximum post-Vashon ice. This raised delta was deposited against drumlinized Vashon ground moraine, (GSC-2177 12,000 ± 100), which is believed to represent a later stage in the first emergence of the 205 land" (Lowdon etal., 1977). Hiatella arctica, Serripes groenlandicus, Macoma, Balanus also present from surface of fresh exposures. • Age of Fort Langley Fm.; lower limiting date of SI 20. 12,110 ± 8 5 (rca), I(GSC)-248r: Boundary Bay Description: marine shells Collector/date collected: J. Armstrong Comment: age of glaciomarine sediment 21. 12,150 ± 210 (rca), B-135695: Bellingham Bay Description: marine shells Collector/date collected: D. Kovanen Comment: 22. 10,950 ± 200, L-331C: Norrish Creek, Near Mission Description: wood (driftwood?) from Whatcom glaciomarine, stony, clayey silt along a small creek north of the monastery near Mission, at an elevation of 98 m (Broecker and Kulp, 1957). Wood from same diamicton as GSC-1695. Collector/date collected: W.H.M. Comment: "the deposit is overlain by Sumas till" (Lowdon et al, 1967). • Lower limiting date of Sumas northern lobe; limiting date for SI & SII 23a. 11,400 ± 85, GSC-1695: Draper Crk. Description: wood from diamicton in a road cut 4.8 km northeast of Mission, on Draper Creek at an elevation of ca. 99 m (near Armstrong's Monastery, sample) (Lowden and Blake, 1975). Collector/date collected: G. Rouse and R. Blunden, 1972 Comment: Lower limiting date for SII and SI 24. 11,450 ± 150, L-331 A: Norrish Creek, near Mission Description: wood in Sumas ice-contact drift exposed along Norrish Creek at elevation 160 m (Broecker and Kulp, 1957). Collector/date collected: J. Armstrong. Comment: wood from ice-contact deposits, maximum age for SI and SIII 25 11,600 ± 50, GSC-5770: Branderpit Description: wood (branch) in stony mud (Clague et al., 1997) Collector/date collected: J. Clague Comment: provides age for stony mud 26. 11,600 ± 70, TO-4087: Branderpit Description: conifer needles from stony mud (Clague et al, 1997) Collector/date collected: J. Clague Comment: provides age for stony mud 206 27. 11,680 ± 50, B-144097: Branderpit Description: wood in stony mud from the Bradner pit. Collector/date collected: D. Kovanen Comment: collected with paired shell sample to determine total marine reservoir value (see chapter 3); date provides lower limiting age for SII 28. 11,660 ± 50, B-144099: Branderpit Description: wood in stony mud from the Bradner pit. Collector/date collected: D. Kovanen Comment: same as above 29 11,700 ± 150, L-331B: Norrish Creek Description: wood from till-like Whatcom glaciomarine deposits near the mouth of Norrish Creek (Broecker and Kulp, 1957). Collector/date collected: J. Armstrong. Comment: wood from ice-contact deposits, maximum age of Sumas Drift. • lower limiting date of SI, SII, SIII. 30. 11,700 ± 60, GSC-2842: Aldergrove Description: wood (Pinus contorta) in glaciomarine sediments from borehole 700 m north of Fraser Highway at Aldergrove, near 272nd at 87 m (surface elevation is 104 m) (Broecker, and Kulp, 1957). Shells from the same unit 4 km to the northwest were dated at 11,68 ± 180 1 4 C yrs. BP (GSC-186; Dyck et al, 1965) Collector/date collected: E. Halstead, 1978. Comment: sea level at time of deposition >87 m. • Lower limiting for SII 31. 11,740 + 70,6-120446: VGS pit Description: Wood (Cedar log) in glaciomarine sediment beneath ice-contact sand and gravel, from VGS gravel pit off Lefeuvre Road. Collector/date collected: D. Kovanen, 1998 Comment: Age of Fort Langley glaciomarine sediment 32. 11,740 ± 40,8-144095: BranderPit Description: Wood in glaciomarine sediment beneath ice-contact sand and gravel, from VGS gravel pit off Bradner Road. Collector/date collected: D. Kovanen, 1998 Comment: Age of Fort Langley glaciomarine sediment 33. 11,800±50,GSC-5860: Branderpit Description: log from stony mud (Clague etal, 1997) Collector/date collected: J. Clague Comment: maximum age of Sumas advance; age of stony mud 207 34. 11,800±50,GSC-5862: Branderpit Description: log (branch) from stony mud (Clague et al, 1997) Collector/date collected: J. Clague Comment: maximum age of Sumas advance; age of stony mud 35. 11,800 ± 400,1-1037: Everson Type Locality, Near Deming Description: wood in Bellingham glaciomarine sediment Collector/date collected: D. Easterbrook, 1963 Comment: age of glaciomarine sediment 36. 11,670 ± 50, B-145455: Axton Pit Description: wood in glaciomarine stony mud. Collector/date collected: D. Kovanen Comment: refer to sample description no. 7. 37. 11,830 + 50,8-145459: Axton Pit Description: wood in glaciomarine stony mud. Collector/date collected: D. Kovanen Comment: refer to sample description no. 7. 38. 11,790 ±50,8-145460: Axton Pit Description: wood in glaciomarine stony mud. Collector/date collected: D. Kovanen Comment: refer to sample description no. 7. 39. 11,590 ± 140, GSC-226: Surrey Description: wood (coniferous) in stony, silty clay with marine shells beneath marine sands of along ditch bordering Deas Island Highway, Surrey (GSC-186; Dyck et al, 1965). Collector/date collected: J. Armstrong, 1963. Comment: Armstrong noted that "deposit dates from post-Vashon marine submergence, probably prior to the advance of Sumas ice in the area to the east. Shells from stony clay (presumed to be same deposit) nearby dates 12,625 ± 450 (I(GSC)-6. 40. 11,300 ± 80, TO-4056: Bradner Pit, Aldergrove Description: conifer needles in peat (Clague et al, 1997). Collector/date collected: J. Clague Comment: peat layer between stony clay and underlying till. Age of Fort Langley glaciomarine sediment and maximum age of Sumas advance. 41 11,410 ± 1100, TO-4088: Bradner Pit, Aldergrove Description: charcoal from "burned soil" in the large gravel pit off Bradner Road near Aldergrove (Clague et al, 1997). Collector/date collected: J. Clague 208 Comment: charcoal beneath stony clay and underlying foreset beds. Maximum Age of Fort Langley glaciomarine sediment. 42. 11,680 ± 80, B-124905: Bradner Pit, Aldergrove Description: wood from peat in the large gravel pit off Bradner Road near Aldergrove. Collector/date collected: D. Kovanen, 1998 Comment: a piece of wood from peat at base of log-bearing glaciomarine sediment, Bradner gravel pit. Maximum age of Fort Langley glaciomarine sediment. 43 11,750 ± 80, B-124904: Bradner Pit, Aldergrove Description: wood Collector/date collected: D. Kovanen, 1998 Comment: Rooted stump at base of log-bearing glaciomarine sediment, Bradner gravel pit. Age of subaerial phase beneath Fort Langley glaciomarine sediment. 44. 11,450 ± 125, B-1324: Everson Type Locality, Near Deming Description: rooted stump Collector/date collected: D. Easterbrook, 1963 Comment: age of subaerial Deming sand 45. 11,500 ± 200, WW-1: Everson Type Locality, Near Deming Description: rooted stump Collector/date collected: D. Easterbrook, 1963 Comment: age of subaerial Deming sand 46. 11,640 ± 275, W-940: Everson Type Locality, Near Deming Description: wood in peat Collector/date collected: D. Easterbrook, 1963 Comment: age of subaerial Deming sand 47. 11,810 ± 60, B-135696: Everson Type Locality, Near Deming Description: rooted stump Collector/date collected: D. Kovanen Comment: age of subaerial Deming sand (Kovanen and Easterbrook, 2000) 48. 11,685 ± 86 (rca), AA-25747: Bellingham Bay - Cliffside Description: marine shells Collector/date collected: D. Kovanen, 1997 Comment: Cliffside2, highest shell in interbedded clay within Deming sand below Bellingham glaciomarine sediment along a cliff exposure at Bellingham Bay. 209 49. 12,860 ± 85 (rca), AA-25746: Bellingham Bay - Cliffside Description: marine shells Collector/date collected: Kovanen and Easterbrook, 1997 Comment: lowest shells in interbedded clay/sand mix within the Deming sand below Bellingham glaciomarine sediment along a cliff exposure at Bellingham Bay. 50. 12,900 ± 80, B-109852: Bellingham Bay - Cliffside Description: marine shells Collector/date collected: Kovanen and Easterbrook, 1997 Comment: marine shells (mostly Chlamys) in Kulshan glaciomarine sediment exposed at low tide in beach below Cliffside localities. 51. 10,595 ± 80, AA-25743: DeHann bog Description: basal peat Collector/date collected: Kovanen and Easterbrook, 1998. Comment: basal peat above sharp contact at 5.48 m, core #1 (DH1-2). Minimum age of Sumas II outwash. The DeHaan cores samples were extract with a Livingston corer obtained from a peat bog filling Sumas outwash channel just east of the Jackman Road a few hundred feet south of the border. This channel cuts through a Sumas moraine and the dates provide the uppers limits of time that meltwaters ceased to flow through this channel which is related to the SII ice position. Core # 1 is about half way between the residential house and the border and 230 ft. east of the drainage ditch beside the road. Core #2 is about halfway between the house and the border and a few meters east of the drainage ditch along jackman Road. Refer to appendices E for core log descriptions. 52. 10,980 ± 250, AA-27062: Northwood bog Description: plant fiber in basal organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fibers from core sample NW-1. The core samples were extract with a Livingston corer obtained from an abandoned outwash channel that is cut into the Abbottsford outwash plain. These dates provide the upper limit for the time meltwaters ceased to flow from Sumas ice. Refer to appendices E for core log descriptions. 53. 11,037 ± 72, AA-27071: DeHann bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1998. Comment: Small bits of organic material at base of core #2 (DH2-2). Minimum age of Sumas II outwash 210 54. 11,413 ± 75, AA-27072: DeHann bog Description: basal peat Collector/date collected: Kovanen and Easterbrook, 1998. Comment: 1 cm3 of peat, 1 cm up from basal contact in core # 2 (DH2-3). Minimum age of Sumas II outwash 55. 10,765 ± 70, AA-27067: Tenmile Creek bog Description: peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal cm of peat in core #2 (TM2-2). Minimum age of Tenmile Creek outwash channel. The core samples were extracted with a Livingston corer obtained from an abandoned outwash channel cut into Bellingham glaciomarine sediment. These dates provide the upper limits for the time meltwaters ceased to flow. The position of this channel also provides the marginal position of SII ice. The ice must have been nearby in order to provide meltwaters to carve this channel. Refer to appendix E for core log descriptions. 56. 10,815 ± 75, AA-27068: Tenmile Creek bog Description: basal peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal cm of peat from core #3 (TM3-2). Minimum age of Tenmile Ceek outwash channel. 57. 11,080 ± 100, AA-27056: Tenmile Creek bog Description: Organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fibers in clay below basal peat from core #1 (TM1-1). Minimum age of Tenmile Creek outwash channel. 58. 11,113 ± 77, AA-27066: Tenmile Creek bog Description: peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal 0.5 cm of peat from core #1 (TM1-2). Minimum age of Tenmile Creek outwash channel. 59. 12,950 ± 424, AA-27060: Tenmile Creek bog Description: organic material Collector/date collected: Kovanen & Easterbrook, 1997 Comment: plant fragments in sand below basal peat from core #2 (TM2-1). Minimum age of Tenmile Creek outwash channel. 211 60. 9,770 ± 75, AA-25745 : Fazon Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: organic material from 8-cm-thick, peaty, organic clay at 8.95 m, 15 cm below basal peat. Minimum age of Sumas II phase kettle. The core samples were extract with a Livingston corer obtained from a bog surrounding a kettle that formed in Sumas outwash. The date provides the upper limits for the time that a block of ice melted and peat began to form. Refer to appendices E for core log descriptions. 61. 10,400 ± 85, AA-25744: Fazon Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: organic material from 15-cm-thick, gray-brown, organic clay under 42 cm of clay below basal peat in core # 1 at 9 m. Minimum age of Sumas II phase kettle 62. 11,000 ± 900, L -221E: Mount Lehman Road Description: wood from station 252A (elevation of 78 m), Mount Lehman Road (Broecker et al, 1956; Lowdon et al., 1967). Wood from same diamicton as GSC-1675 (basal Sumas till) Collector/date collected: J. Armstrong. Comment: Armstrong noted that "material was taken from base of Sumas till, which is believed to represent the last advance of the ice in the lower Fraser Valley" (Broecker et al, 1956). 63. 11,500 ± 1100, L -221D: Sumas Mountain Description: small stems and rootlets from Richmix Quarry (Broecker et al, 1956) Collector/date collected: J. Armstrong, 1956 Comment: Armstrong noted that "material was taken from base of Sumas till, which is believed to represent the last advance of the ice in the lower Fraser Valley" (Broecker et al, 1956). Maximum age of Sumas Drift. 64. 11,600 ± 1 4 0 , GSC-1675 : Mt. Lehman Road Description: basal wood in Sumas ice-contact drift; overlies shell-bearing glaciomarine sediment. Road cut on east side of Mt. Lehman Road, 8.8 km northwest of Abbotsford (Lowdon and Blake, 1973). Age of Sumas II phase drift. Collector/date collected: J. Armstrong, 1953 212 65. 8050 ± 65, AA-27059: Fountain Lake bog Description: plant fragments in peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fragments from basal peat in core sample FL1-1. Minimum age of late Sumas outwash. The core samples were extract with a Livingston corer obtained from a bog surrounding a kettle that formed in Sumas outwash. The date provides the upper limits for the time that a block of ice melted and peat began to form. Refer to appendices E for core log descriptions. 66. 9090 ± 70, B-109850: Pangborn bog Description: Wood Collector/date collected: Kovanen and Easterbrook, 1997 Comment: wood from below peat/clay contact in core (PB2-3). Minimum age of Sumas II phase kettle. The core samples were extract with a Livingston corer obtained from bog surrounding a lake interpreted as a kettle. These dates provide the upper limits to when ice melted. The position of this kettle also suggests that ice was in close proximity and hence, provides a marginal position of SIII ice. 67. 9850 ± 75, AA-27069: Pangborn bog Description: Seed pod Collector/date collected: Kovanen and Easterbrook, 1997 Comment: seed pod from below peat/clay contact in core sample (PB2-2). Minimum age of Sumas II phase kettle 68. 10,265 ± 65, AA-27063: Pangborn bog Description: Organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: Plant fragments from core sample. Minimum age of Sumas II phase kettle 69. 10,245 + 90, AA-27057: Pangborn bog Description: Plant fibers Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fibers from base of core sample PB 1-1-2. Minimum age of Sumas II phase kettle Nooksack dates Mosquito Lake Road - Nooksack Middle Fork The following core samples were extract with a Livingston corer obtained from a deep glacial kettle filled with peat off of Mosquito Lake Road, near the Middle Fork road of the Nooksack River. These dates limit the time of alpine ice stagnation in the valley (Easterbrook, Kovanen, Evenson, Olsen, 1996). 213 Modern, AA-20751: Mosquito Lake Road Description: Organic material Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Tiny root hairs in sand/granules in lower 1 cm of the core (DKB2-2) 6,850 ± 65, AA-22201: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 1-cm diameter "rosebud" wood, 3 mm below contact with Mazama ash from core DKB1-6. Close to age of Mazama eruption. 11,520 ± 190, AA-22210: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small piece of wood in basal sand at contact with overlying basal peat from core DKB2-8. 11,940 ± 180, AA-22209: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small piece of wood in basal sand at contact with overlying basal peat from core DKB2-7. 11,945 ± 85, AA-22204: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 2 small pieces of wood 1 cm up from the base of the core (DKB2-1). 12,035 ± 95, AA-22207: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small piece of wood in basal peat at contact with diatom layer from core DKB2-5. 12,045 + 85, AA-22205: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small piece of wood in basal peat 0.5 cm below contact with diatom layer from core DKB2-3. 214 12,120 ± 90, AA-22206: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook & Kovanen, 1996. Comment: Small piece of wood in basal peat ~1 cm below contact with diatom layer from core DKB2-4. 12,145 ± 90, AA-22203: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 2-cm diameter wood in dark peat with many <lmm white interbeds; 4.5 cm from base of core (19.524 m). It's the base of the next core above the lower white diatomite (DKB1-8). 12,150 + 90, AA-22208: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small piece of wood in basal peat at contact below contact with diatom layer (DKB2-6). 12,160 ± 90, AA-22202: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 2.5-cm-long, branching twig (4-6 branches) in basal sand (11 thick) at very bottom of core (DKB1-7). 12,165 ± 95, AA-20749: Mosquito Lake Road Description: rootless Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small rootlets in lower 2 cm of core (DKBl-1). 12,230 ± 80, AA-22199: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 2.5 cm long twig (2 mm diameter) at top of basal peat at contact with overlying diatomite (DKB1-4). 12,365 ± 115, AA-20750: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: 0.5-cm piece of wood resting on the material in DKBl-1 (DKB1-2). 215 12,380 ± 90, AA-22198: Mosquito Lake Road Description: Wood Collector/date collected: Easterbrook and Kovanen, 1996. Comment: Small, Y-shaped branch (~1 cm long) at top of basal peat at contact with overlying diatomite (DKB1-3). 10,680 ± 70, Beta 124911: Nooksack Middle Fork Description: Wood Collector/date collected: D. Kovanen, 1998 Comment: Wood in lateral moraine along Ridley Creek 11,910 ± 80, B-1220447: Welcome gulch Description: wood Collector/date collected: Kovanen and Easterbrook, 1997 Comment: ~lcm diameter piece of wood in clay, Welcome gulch Cranberry Lake bog - South Fork The following core samples were extract with a Livingston corer obtained from a situated in a glacial kettle on the floor of the Nooksack South Fork. 14,167 ± 82, AA-27073: Cranberry Lake Bog Description: basal peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal peat from core #1 (CB1-1). 12,596 + 80, AA-27075: Cranberry Lake bog Description: basal peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal peat from core #3 (BB3-3). 13,750 ± 127, AA-27074: Cranberry Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fragments in clay at base of core #3 (BB3-2). 12,425 ± 90, AA-27065: Cranberry Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fragments in gravel at base of core #3 (BB3-1). 216 11,733 ± 75, AA-27076: Cranberry Lake bog Description: peat Collector/date collected: Kovanen and Easterbrook, 1997 Comment: basal 0.5 cm of peat from core #5 (CB5-2). 12,215 ± 85, AA-27064: Cranberry Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fragments in lower 2 cm of 3-cm thick sand below basal peat from core #5 (CB5-1). 12,255 ± 84, AA-27077: Cranberry Lake bog Description: organic material Collector/date collected: Kovanen and Easterbrook, 1997 Comment: plant fragments in lower 3 cm of sand from core #5 (CB5-3). 10,603 + 69, AA-27078: Racehorse Creek Description: Charcoal Collector/date collected: Kovanen and Easterbrook, 1997 Comment: Charcoal in the lowest discrete layer (soil horizon?) of an outwash terrace along the south side of the Nooksack North Fork. Noted 5 layers. The terrace is covered with large Chuckanut sandstone boulders of the Racehorse Creek landslide. 10,788 ± 77, AA-27079: Racehorse Creek Description: Charcoal Collector/date collected: Kovanen and Easterbrook, 1997 Comment: Charcoal in the highest discrete layer (soil horizon?) of an outwash terrace along the south side of the Nooksack North Fork. The terrace is covered with large Chuckanut sandstone boulders of the Racehorse Creek landslide. 217 Appendix C Oxygen and carbon isotopes 2 1 8 Appendix C Oxygen and carbon isotopes Appendix C focuses on the use of oxygen and carbon isotopes as a tool for investigating past climatic changes and their chronologies. This is an overview of the oxygen and carbon isotope systematics and is included to augment the main body of the text, but is limited in that, other tools used by researchers to interpret the earth's climatic history (e.g., pollen records, lake sediments, coral data) are not discussed. The chronology of the last glacial cycle plays an important role in understanding global climatic changes. Relative chronologies have become elaborate and some are based on isotopic analyses, which allow correlation between widely separated areas and are fundamental to the development of a coherent global picture of climatic change. Climate signatures in ice cores match those recorded in deep-sea cores (Bond et al, 1993). Based on various methods, other convincing correlations suggest that most Pleistocene climatic fluctuations were coeval in different regions (Kudrass et al, 1991). Many records lack calendar time scales, but there is a view that changes in climate took place synchronously (Broecker, 1992; Bender etal, 1994). Radiocarbon dating has been used extensively in this research and allows for a broader appreciation of the local terrestrial record during deglaciation. Once the local chronologies are more accurately established, comparisons with other records and clocks will provide a link to regional and hemispheric climate changes. Definition - Isotopes result from variations in mass of an atom. The nucleus is made up of protons and neutrons. The number of neutrons may vary, resulting in different isotopes of the same element, but the number of protons in the nucleus is the same. Thus, isotopes have different masses and behave differently from other isotopes having the 219 same atomic number. In general, light molecules are transported easier and/or react more quickly (Table C-l). Oxygen isotope systematics I S 1 ft Basic principles - atmospheric O and O Oxygen has nine isotopes but most oxygen is a mixture of three stable isotopes, O, O, 1 80. The relative abundance of oxygen isotopes is easier to measure than absolute amounts, so ratios of abundance of oxygen isotopes are generally used for interpretative purposes. Isotopic composition of water responds to evaporation and precipitation (Dole, 1934). In general, during evaporation of 1 8 0 and 1 60, water molecules composed of light isotopes (160) turn to vapor more easily than those composed of heavy isotopes (180) because of the higher vapor pressure of H2160. This allows 1 6 0 to evaporate more readily from the ocean surface and the resulting vapor is then depleted in 1 8 0 compared with the initial water. Conversely, as water vapor condenses to form clouds, the first precipitation is heavier isotopically and tends to pass from the vapor to liquid state more readily than light molecules, leaving lighter water vapor behind (Dalton's law of partial pressure). The resulting precipitation is then enriched in 1 8 0 compared with the remaining vapor (Dansgaard, 1961). These properties give rise to differences in 1 80 concentrations in water in various parts of the hydrologic cycle. Table C- l Natural isotopes of oxygen, carbon and hydrogen Isotope Relative Abundance (%) Type 1 6 0 oxygen 99.76 Stable n O oxygen 0.04 Stable l s O oxygen 0.20 Stable 1 4 C carbon <0.001 Radioactive (half-life is 5730 yrs) *H proteum 99.984 Stable 2 H deuterium 0.016 Stable 3 H tritium 0 - 10"15 Radioactive (half-life is 12.3 yrs) 220 The process whereby the isotope content of a substance c