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The physical oceanography of Bute Inlet Tabata, Susumu 1954

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THE PHYSICAL OCEANOGRAPHY OF , BUTE INLET by SUSUMU TABATA '  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of PHYSICS  We accept t h i s thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS.  Members of the Department of PHYSICS  THE UNIVERSITY OF BRITISH COLUMBIA March, 1954  ABSTRACT  Distributions of s a l i n i t y , temperature, and oxygen of Bute Inlet based on eleven oceanographic surveys between the period August 1950 to August 1952 have been examined.  The shallow salinity, structures  of the various seasons can be c l a s s i f i e d under two main groups, those occurring at periods of small r i v e r runoff and the others occurring at periods of large r i v e r runoff.  In general, the surface s a l i n i t y  increases to seaward and with depth during a l l seasons. The surface water along the western shore i s almost always observed to be less saline than along the eastern shore. The s a l i n i t y of the deep water i s 30,6 %> during both periods. The seasonal fluctuation of s a l i n i t i e s at the surface i s well-marked but below a depth of 60 feet no normal cycle exists.  The temperature distributions of both seasons can also  be grouped under two main seasons, namely, Winter-and Summer. During both seasons the surface temperature generally increases to seaward. The temperature gradients i n the upper layers during the Winter and Summer are positive (increasing v e r t i c a l l y downward) and negative (decreasing v e r t i c a l l y downward) respectively.  From the Spring Transitional  to the l a t e Autumn, a well-defined temperature minimum, which becomes indistinguishable at the mouth, i s evident i n the intermediate depths. The water i n the greater depths has a temperature of 8°C and. remains almost unchanged throughout the seasons. The seasonal temperature variation of the surface and sub-surface water down t o a depth of 150 feet i s i n phase  with the a i r temperature cycle but below t h i s i t i s less noticeable. Insolation and cold runoff water from the r i v e r s are predominant factors i n determining the fluctuation i n the temperature. The concentration of dissolved oxygen i s usually high i n the surface layer.  The water at the  greater depth i s not stagnant as evidenced by the oxygen concentration. The characteristic water types of t h i s i n l e t are: the Deep Water, Runoff Water, Intermediate Water and Winter Surface Water. The three d i s t i n c t layers i n the oceanographic structures are: the upper brackish layer, mixed layer, and lower layer.  The main circulation of  t h i s i n l e t i s estuarine. Eddy coefficient of d i f f u s i v i t y of values 0*65 and 0.5S g./cm./ s e c , have been determined for the water above and below the layer of minimum temperature respectively.  ACKNOWLEDGEMENTS  The author wishes to make acknowledgements to the Pacific Oceanographic Group, Pacific Biological Station, Nanaimo, B.C., and the Institute of Oceanography, University of B r i t i s h Columbia, Vancouver, B.C., for permission to use the f a c i l i t i e s and the oceanographic data; to the Meteorological Division, Department of Transport, Toronto, Canada, for the issuances of the current a i r temperature data; to the Water Resources Division, Department of Resources and Development, V i c t o r i a , B.C., for the issuances of the recent discharge data. The author i s also indebted to the Royal Canadian Navy who provided the ships and f a c i l i t i e s , and especially to the officers and men of H.M.C.S. Cedarwood and C.N.A.V. Ehkoli for their cooperation.  Acknowledgement  i s also made to Dr. J.P. Tully f o r h i s helpful c r i t i c i s m and encouragement and also to the Fisheries Research Board of Canada who provided financial assistances which permitted the completion of the task. F i n a l l y , the author wishes to express h i s thanks to Dr. G.L. Pickard who supervised the work for his continued interest, advice, c r i t i c i s m , and encouragement during the writing of t h i s thesis.  TABLE OF CONTENTS  P.age I. II.  III.  IV.  INTRODUCTION  1  GENERAL CHARACTER OF THE REGION  2  Physiography  2  Drainage  7  COLLECTION AND TREATMENT OF DATA  7  Collection of Data  7  Treatment of Data  9  Land Drainage Data  10  A i r Temperature Data  10  GENERAL CHARACTERISTICS OF THE WATER STRUCTURE  11  Salinity  11  Temperature  12  Oxygen  17  Density Anomaly ( Of )  20  V. DISCUSSION OF RESULTS AND POSSIBLE CIRCULATION PATTERNS  20  Winter (December - February)  25  Spring Transitional (March)  32  Spring ( A p r i l , May)  36  Summer (June - August)  39  Page  VI.  Autumn Transitional (September)  43  Autumn (October, November)  46  Summary of the General Circulation Pattern  50  SEASONAL VARIATION OF SALINITY AND TEMPERATURE Variation of S a l i n i t y  51  Runoff from Rivers and Precipitation  54  Variation of Temperature  55  Analysis of the Long Term Variation VII. VIII.  50  59  EDDY DIFFUSIVITY  60  SUMMARY AND CONCLUSIONS  65  REFERENCES  71  APPENDIX  75  DISTRIBUTION OF SALINITY, TEMPERATURE, AND OXYGEN Distribution of S a l i n i t y and Temperature Cruise I - August 2, 1950 Cruise I I - September 10, 1950  75 75 75 77  Cruise I I I - November 28, 29, 30, 1950  78  Cruise IV - January 11, 1951  81  Cruise V - February 20, 21, 22, 1951  83  Page Cruise 51-2-1 - May 17-26, 1951  83  Cruise 51-2-II - August 4, 1951  86  Cruise 51-3 - October 25, 26, 1951  89  Cruise 52-1 - March 30, 1952  93  Cruise 52-2 - May 29, 30, 31, June 7, 8, 1952  93  Cruise 52-3 - August 9-13, 1952  95  Distribution of Oxygen  95  LIST OF FIGURES  Page Figure  1.  Bute Inlet and adjacent regions.  3  Figure  2.  Chart of Bute Inlet showing adjacent channels, rapids, and peaks on both sides of the i n l e t .  4  Figure  3«  Plan of Bute Inlet showing station positions and longitudinal and transverse bottom p r o f i l e s of this inlet.  6  Figure  4.  Character of water i n Bute Inlet during the small runoff period i l l u s t r a t e d by (a) v e r t i c a l s a l i n i t y p r o f i l e s (%>) and (b) longitudinal v e r t i c a l section showing the d i s t r i b u t i o n of s a l i n i t y .  13  Figure  5.  Distribution of s a l i n i t y during the small runoff period i n a • . (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  13  Figure  6.  Character of water i n Bute Inlet during the large runo f f period i l l u s t r a t e d by (a) v e r t i c a l s a l i n i t y p r o f i l e s ($o) and (b) longitudinal v e r t i c a l section showing the d i s t r i b u t i o n of s a l i n i t y .  14  Figure  7.  Distribution of s a l i n i t y during the large runoff period i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  14  Figure  8.  Character of water i n Bute Inlet during the winter 15 i l l u s t r a t e d by (a) v e r t i c a l temperature profiles (°C) and (b) longitudinal v e r t i c a l sections showing the d i s - v ' . - y : \ tribution of temperature.  Figure  9»  Distribution of temperature during the winter i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  15  Page Figure 10. Character of water i n Bute Inlet during the summer i l l u s t r a t e d by (a) v e r t i c a l temperature profiles (°C) and (b) longitudinal v e r t i c a l sections showing the dist r i b u t i o n of temperature.  16  Figure 11, Distribution of temperature during the summer i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  16  Figure 12. Character of water i n Bute Inlet during the winter (small runoff period) i l l u s t r a t e d by (a) v e r t i c a l oxygen saturation profiles {%) and (b) longitudinal v e r t i c a l sections showing the distribution of oxygen.  18  Figure 13.  Character of water i n Bute Inlet during the summer (large runoff period) i l l u s t r a t e d by (a) v e r t i c a l oxygen saturation profiles (%) and (b) longitudinal v e r t i c a l section showing the distribution of oxygen.  19  Figure 14. Typical s a l i n i t y ($o), temperature (°C) and density (tft) - depth curves of Bute Inlet during (a) the winter (small runoff period) and (b) the summer (large runoff period), i l l u s t r a t i n g the s i m i l a r i t y between the s a l i n i t y and dens i t y curves.  21  Figure 15. Distribution of density ( ) of the water of Bute Inlet i n a v e r t i c a l section along the i n l e t (a) during the winter and (b) during the summer.  22  Figure 16. Temperature-salinity relation i n Bute I n l e t , Nodales Channel, and the Strait of Georgia i l l u s t r a t i n g the various water types.  24  Figure 17. Monthly mean discharges of (a) Homathko River near Tatla Lake (1930-1932) and (b) Fraser River at Hope (1930-1932, 1950-1952).  26  Note. Measurement of Homathko made at outlet of Tatlayako Lake, about 50 nautical miles from the mouth. Measurements made at mouth (May 18, 1951) indicate discharge to be about 10,000 ft.-ysec.  Page Figure  18, Monthly mean a i r temperatures at Thurlow, Comox and Powell River (1950-1952).  26  Figure  19. Distribution of s a l i n i t y during the Winter i n the upper 150 feet i n a v e r t i c a l section along the inlet.  27  Figure  20, Distribution of temperature during the Winter i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  27  Figure  21, Temperature-salinity relations i n Bute Inlet for the Winter period. The depths i n feet for the values are also entered.  27  Figure  22, Schematic representation of the average currents during the Winter period as inferred from s a l i n i t y and temperature distributions.  31  Figure  23, Typical s a l i n i t y profiles (%) and their corresponding density p r o f i l e s ( cf£ ) for the Spring Transitional period.  33  Figure  24. Temperature-salinity relations i n Bute Inlet f o r the Spring Transitional period. The depths i n feet for the values are also entered.  33  Figure  25. Distribution of salinity, during the Spring Transi t i o n a l period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  35  26, Distribution of temperature during the Spring Transitional period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  35  Figure  27. Distribution of s a l i n i t y during the Spring i n the upper 150 feet i n a v e r t i c a l section along the inlet.  37  Figure  28« Distribution of temperature during the Spring i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  37  Figure  29, Temperature-salinity relations i n Bute Inlet for the Spring period. The Runoff Water (R) and the Intermediate Water (I) are shown. The depths i n feet for the values.are also shown.  37  •Figure  Figure  30. Temperature-salinity relations i n Bute Inlet f o r the Spring period. The depths i n feet for the values are also entered.  Figure  31.  Schematic representation of the average currents during the Spring period as inferred from s a l i n i t y and temperature distributions.  Figure  32.  Distribution of s a l i n i t y during the Summer period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  33. Distribution of temperature during the Summer period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  34. Temperature-salinity relations i n Bute Inlet for the Summer period. The depths i n feet f o r the values are also entered.  Figure  35.  Distribution of s a l i n i t y during the Autumn Transi t i o n a l period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  36.  Distribution of temperature during the Autumm Transitional period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  37. Temperature-salinity relations i n Bute Inlet f o r the Autumn Transitional period. The depths i n feet for the values are also entered.  Figure  38.  Figure  39. Distribution of s a l i n i t y during the Autumn period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  40.  Distribution of temperature during the Autumn period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure  41.  Distribution of temperature for the deeper section during the Autumn period.  Figure  42.  Temperature-salinity relations i n Bute Inlet for the Autumn period. The depths i n feet for the values are also entered.  Set of s a l i n i t y profiles ($0) for the Autumn period.  Page Figure 43a, Seasonal variation of s a l i n i t y at the surface and depths of 15 and 30 feet.  52  Figure 43b, Seasonal variation of s a l i n i t y at depths from 60 to 1,500 feet.  53  Figure 44a« Seasonal variation of temperature at the surface and depths of 15 and 30 feet.  56  Figure 44b, Seasonal variation of temperature at depths of 60 to 1,800 feet.  57  Figure  45. Character of water i n Bute Inlet (Cruise II-September 10, 1950) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 750 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature t o a depth of 750 feet. Note. Bathythermograph casts (750 feet) made at each station.  76  Figure  46, Character of water i n Bute Inlet (Cruise Ill-November 28, 29, 30, 1950) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 900 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature t o a depth of 900 feet. Note. Bathythermograph casts (840 feet) made at each station.  79  Figure  47• Character of water i n Bute Inlet (Cruise Ill-November 28, 29, 30, 1950) (a) transverse section of s a l i n i t y i n the upper 150 feet at Station 3, (b) transverse section of temperature i n the upper 150 feet at Station 3, (c) transverse section of s a l i n i t y i n the upper 150 feet at Station 5, (d) transverse section of temperature i n the upper 150feet at Station 5. Note. Bathythermograph casts (840 feet) made at each station.  80  Page Figure 48V' Character of water i n Bute Inlet (Cruise IV-January  11, 195D  82  (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 450 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 450 feet. Note. Bathythermograph casts (450 feet) made at each station. Figure 49. Character of water i n Bute Inlet (Cruise V-February  20, 21, 22, 1951)  (a) longitudinal section 150 feet, (b) longitudinal section 1,650 feet, (c) longitudinal section 150 feet, (d) longitudinal section of 1,650 feet.  84  of s a l i n i t y i n the upper of s a l i n i t y to a depth of of temperature i n the upper of temperature to a depth  Note. Bathythermograph casts (450 feet) made at each station. Figure 50,  Character of water i n Bute Inlet (Cruise V-February  20, 21, 22, 1951)  (a) transverse section of s a l i n i t y i n the upper 150 feet at Station 3, (b) transverse section of temperature i n the upper 150 feet at Station 3, (c) transverse section of s a l i n i t y i n the upper 150 feet at Station 5, (d) transverse section of s a l i n i t y i n the upper 150 feet at Station 5.  Note. Bathythermograph casts (450 feet) made at each station.  85  Page Figure 51. Character of water i n Bute Inlet (Cruise 51-2-I-May  17-26, 195D  (a) longitudinal 150 feet, (b) longitudinal 1,800 feet, (c) longitudinal 150 feet, (d) longitudinal 1,800 feet.  87  section of s a l i n i t y i n the upper section of s a l i n i t y to a depth of section of temperature i n the upper section of temperature to a depth of  Note. Bathythermograph casts (840 feet) made at each station. Figure 52. Character of water i n Bute Inlet (Cruise 51-2-I-May 17-26, 1951) . (a) transverse section of s a l i n i t y i n the upper 150 feet at Station 4, (b) transverse section of temperature i n the upper . 150 feet at Station 4.  88  Note: Bathythermograph casts (450 feet) made at each station. Figure 53. Character of water i n Bute Inlet (Cruise 51-2-II-August 4, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,250 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,250 feet.  90  Note. Bathythermograph casts (840 feet) made at each station. Figure 54. Character of water i n Bute Inlet (Cruise 51-3-October 25, 26, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,650 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,650 feet. Note. Bathythermograph casts (840 feet) made at each station.  91  Page Figure 55. Character of water i n Bute Inlet (Cruise 51-3-October 2 5 , 26, 1951) (a) transverse section of s a l i n i t y i n the upper 150 feet at Station 3, (b) transverse section of temperature i n the upper 150 feet at Station 3. Note.  92  Bathythermograph casts (840 feet) made at each station.  Figure 56. Character of water i n Bute Inlet (Cruise 52-1-March "30, 1952) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,800 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature t o a depth of 1,800 feet. Note.  Bathythermograph casts (840 feet) made at each station.  Figure 57. Character of water i n Bute Inlet (Cruise 52-2-May 2 9 , 3 0 , 31, June 7, 8, 1952) (a) longitudinal section-of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,500 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,500 feet. Note.  " 96  Bathythermograph casts (840 feet) made at each station.  Figure 58, Character of water i n Bute Inlet (Cruise 52-3-August 9-13, 1952) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,800 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,800 feet. Note.  94  Bathythermograph casts (840 feet) made at each station.  97  Page Figure 59a. Distribution of oxygen i n a longitudinal section along the i n l e t (September 10, 1950). Values from August 2, 1950 are also entered.  98  Figure 59b. Distribution of oxygen i n a longitudinal section along the i n l e t (January 11, 1951)•  98  Figure 60a, Distribution of oxygen i n a longitudinal section along the i n l e t (February 1951).  99  Figure 60b„ Distribution of oxygen i n a longitudinal section along the inlet (May 1951).  99  Figure 6la« Distribution of oxygen i n a longitudinal section along the i n l e t (August 3, 1951 and October 26,  100  195D.  Figure 6lb» Distribution of oxygen i n a longitudinal section along the i n l e t (May 29, 1952).  100  LIST OF TABLES  Page TABLE  I.  Catalogue of the surveys during the period August 1950 to August 1952 showing cruise details.  8  TABLE I I . Coefficients of v e r t i c a l eddy d i f f u s i v i t y (A ) above and below the minimum temperature layer.  64  TABLE I I I .  66  z  Numerical values of eddy d i f f u s i v i t y as derived from observed time and space variations of s a l i n i t y at Schultz*s Grund (Jacobsen, 1913).  I. INTRODUCTION  The f i e l d of physical oceanography has, i n the past, been centered around the study of physical structures and circulations of the open ocean. However, due mainly to demands from f i s h e r i e s , industries, defence, and health authorities, increased attention has been given i n recent years to the study of inshore waters.  Relatively l i t t l e oceano-  graphic study has been made i n the i n l e t s of the coast of B r i t i s h Columbia, but i t i s noteworthy to remark that the f i r s t of these oceanographic observations was made i n Bute, Toba, and Jervis Inlets i n 1928 (Hutchinson and Lucas, 1931). Later Carter (1933) reported on "The Physiography and, Oceanography o£ some B r i t i s h Columbia Fiords". Following t h i s , Tully (1937a) described the oceanography of Nootka Sound and i t s v i c i n i t y .  These studies are b r i e f and descriptive.  A notable  advance was made, however, i n the study of a fjord estuary by Tully i  (1949) who made a quantitative analysis of Alberni Inlet.  Two mathematical  treatments on the dynamics of i n l e t circulation have been attempted by Cameron (1951a) and Stommel (1951) both of whom described the circulation in a v e r t i c a l plane through the length of the i n l e t .  More recently^  Pritchard (1952) has reported on "The Physical Structure. Circulation and Mixing i n a Coastal Plain Estuary" and "A Review of Our Present Knowledge QL the. Dynamics and. Flushing p_f Estuaries". Among the other contributors i n the study of estuaries are Ketchum, Arons, and Redfield, whose works and discussions have been l i s t e d i n the "Proceedings of the Colloquium on "Ifce. Flushing of Estuaries" (September 1950).  -2-  Bute I n l e t , t y p i c a l of the many i n l e t s of B r i t i s h Columbia, may be termed an i n l e t estuary i n the sense of the d e f i n i t i o n that the fresh water from land drainage i s i n contact with the more saline coastal water which i s not necessarily that of the open sea.  I t d i f f e r s from  Alberni Inlet i n two respects: there i s no s i l l at the mouth, and i t i s not i n contact with the open sea. During 1950, 1951 and 1952 eleven oceanographic cruises were conducted i n Bute Inlet under the direction of the P a c i f i c Oceanographic Group, or of the Institute of Oceanography of the University of B r i t i s h Columbia. The data available at present are s u f f i c i e n t for examination and i t i s believed that a preliminary analysis for the general oceanographic features can be made from these. The present thesis constitutes a study of the s a l i n i t y and temperature structures, the circulations and t h e i r seasonal variations, and of the heat transfer i n Bute I n l e t .  II.  GENERAL CHARACTER OF THE REGION  Physiography Bute Inlet i s a deep i n l e t , situated about 100 nautical miles northwest of Vancouver, B r i t i s h Columbia. The general features of Bute Inlet and i t s adjacent regions are shown i n Figures 1 and 2. This i n l e t , l i k e the other i n l e t s of B r i t i s h Columbia and  -3-  j  Figure 1*  Bute Inlet and adjacent regions.  Figure 2.  Chart of Bute Inlet showing adjacent channels, rapids, and peaks on both sides of the i n l e t .  -5-  southern Alaska, represents a pre-glacial valley which has been subsequently modified by glacial erosion (Bancroft, 1913)• From the head, which i s fronted by sandbanks, the inlet extends seaward i n three reaches, for AO nautical miles.  The width varies from  1 1/4 to 2 1/2 nautical miles. The sides are precipitous and rocky, with rugged mountains rising abruptly from the water as high as 8,000 feet (Figure 2). The higher summits are usually snow-capped a l l year round, and i n the upper reaches of the inlet, glaciers and patches of ice occupy the hollows of some of the lofty mountains. The sides of the inlet are as steep below the sea level as they are above, and the inlet s t i l l possesses the U-shaped cross sections (Figure 3) which are similar to those of the large land valleys within this d i s t r i c t , and are the result of glacial erosion (Bancroft, 1913). The bottom i s covered with a heavy deposit of grey s i l t and i s f a i r l y level and smooth, except near the head where peaks and sudden depressions are found.  From the mouth, regarded as the region i n the vicinity  of Stuart Island, the depth increases from 2,000 feet to a maximum of 2,200 feet at"Station 3, between Fawn Bluff and Clipper Point, and then decreases toward the head (Figure 3)o The waters of Bute Inlet are i n contact with the well-mixed waters of the Nodales and Cordero Channels (Saur, 1950) through Yuculta and Arran Rapids, and also with the waters of the Strait of Georgia through Calm Channel and Pryce to Homfray Channels (Figure 1).  -6-  LONGITUDINAL  BOTTOM  PROFILE  DISTANCE  STATION 2  TRANSVERSE  STATION  BOTTOM  IN N A U T I C A L  MILES  6  PROFILES  Figure 3. Plan of Bute Inlet showing station positions and longitudinal and trans verse bottom profiles of this i n l e t .  •7-  Pxajnage At the head are two muddy r i v e r s , the Homathko emptying into the i n l e t from the north, and the Southgate from the southeast. The former has i t s head water i n the i n t e r i o r plateau of B r i t i s h Columbia and flows through the Coast Range, where i t i s joined by many t r i b u t a r i e s which flow from the glaciers.  The Southgate on the other hand has less  contribution from these t r i b u t a r i e s . Another smaller r i v e r enters the i n l e t at Orford Bay.  Besides these principal r i v e r s , the i n l e t receives  many cascading streams which are dry or negligible i n August and September, but are well developed during heavy precipitation of winter, and especially i n late spring and early summer when the stored winter snow at higher levels i s melting.  III.  COLLECTION AND TREATMENT OF DATA  The thesis i s based on eleven separate oceanographic surveys between the period August 1950 to August 1952 inclusive.  The f i r s t  five surveys were conducted by the P a c i f i c Oceanographic Group of Nanaimo, B.C., and the remainder by the Institute of Oceanography of the University of B r i t i s h Columbia. A catalogue of the surveys i s shown i n Table I . Collection  Data-  Surface water samples were obtained by using an ordinary bucket  TABLE I . Catalogue of the surveys during the period August 1950 to August 1952 showing cruise details.  Cruise No. I II III IV V.  Cruise From 2 Aug 10 Sept 28 Nov 11 Jan 20 Feb  51-2-1 17 51-2-II 4 51-3 25 52-1 30 52-2 29 52-3 9  +  BT Salinity No. of Hydrographic Stns. Lowerings Det erminat ion s Authority  Date To  50 50 50 - 30 Nov 51 51 - 22 Feb  May 51 - 26 May Aug 51 Oct 51 - 26 Oct Mar 52 - 31 Mar May 52 - 11 June Aug 52 - 13 Aug  50 51 51 51 52 52 52  2 7 18 6 22  4 7 17 11  a  22 77 196 66 241  44 4 13 3 3 14  57 11 16 21 61 134  494 54 156 28 72 242  P P P P P I I I I I I  0 0 0 0 0  G* G G G G  0 U B C+ 0 U B C 0 U B C 0 U B C OUBC 0 U B C  Pacific Oceanographic Group, Nanaimo, B.C. Institute of Oceanography, University of B r i t i s h Columbia, Vancouver, B.C.  -9-  while a l l subsurface samples were collected by Atlas, Nansen, Ekman or F j a r l i e water sampling bottles secured to a hydrographic wire at desired intervals. The sea surface temperatures were obtained by a chemical thermometer immersed i n a sample of water draxm from the surface i n a bucket. Subsurface temperatures were obtained by reversing thermometers attached to sampling bottles and also by bathythermographs (Spilhaus, 1938), Temperatures from the reversing thermometers were also used to calibrate and check the bathythermograph readings. Measurements for both the s a l i n i t y and dissolved oxygen were made by t i t r a t i o n s , the former using the Mohr method and the l a t t e r using the Winkler method (Manual pX Oceanographic Methods. A p r i l 1950), The oxygen content of the water i s expressed as a percentage of the s o l u b i l i t y (% saturation) at the temperature and s e l i n i t y in, s i t u rather than i n absolute measure (mgms./cc.) since the former method gives the better indication of the a v a i l a b i l i t y of the oxygen for biol o g i c a l demand. Treatment of Data The s a l i n i t y , temperature, oxygen saturation, and density ( V£  )  data from each station were plotted as functions of depth, and T-S diagrams were constructed. y2  ( 0~t i s defined by  where  i s the density of a sea water sample at the temperature at which i t  was collected.  A T-S diagram i s simply a plot of s a l i n i t y with temperature.  -10-  On each cruise longitudinal and transverse sections of salinity., temperature, and density ( (JT ) were drawn. Additional sections, were drawn to show the details above the depth of 150 feet. Land Drainage Data Since the discharge data for the Homathko River are only available for the years 1930, 1931 and 1932, and since data are unavailable f o r the Southgate River, the actual volume of fresh water emptying into the i n l e t i s not known. However, on comparing the discharge of the Homathko River with that of the Fraser River, i t i s apparent that the curves of the monthly mean discharges plotted against time of both are similar i n shape except that the peak discharge of the Homathko occurs one month l a t e r than that of the Fraser» The discharge data f o r the Homathko have then been estimated by assuming them to have the same ratio to those of the Fraser i n 1950-52 . as they had i n 1930-32,  Discharge data were obtained from the Pacific  Drainage (1941) and data from unpublished records (Water Resources Division, B.C. Department of Resources and Development, V i c t o r i a , August 1952), A i r Temperature Data The meteorological station at Thurlow on Thurlow Island was o r i g i n a l l y selected as a reference station because of i t s proximity to Bute Inlet, but since the observations at t h i s station were discontinued i n May  1951,  Comox and Powell River have been selected. The monthly mean temperatures at these stations to June 1950 were obtained from the Monthly Records gJi Meteorological Observations (Department of Transport) and current data  -11-  from the unpublished reports of this Department (Air Services, Meteorological Division, Department of Transport, Canada, July 1952),  IV.  GENERAL CHARACTERISTICS OF THE WATER STRUCTURE  The data on the distribution of s a l i n i t y , temperature and oxygen are presented i n the Appendix and are i l l u s t r a t e d i n series of v e r t i c a l sections accompanied by brief comments, A discussion of the general characteristics of the structures Of s a l i n i t y , temperature, density anomaly ( <Jf ) and oxygen i s given here and w i l l be followed by a more detailed discussion. Salinity The s a l i n i t y distribution for the different seasons may be c l a s s i f i e d under two main groups: one occurring at periods of small r i v e r runoff (October t o A p r i l ) and the other at periods of large r i v e r runoff (May to September). During both periods the s a l i n i t y i n the i n l e t increases, i n general, with depth and to seaward. The horizontal s a l i n i t y ranges during the large and small runoff periods are about 20 %o and 3 %° respectively and at mid-inlet the values of the v e r t i c a l ranges are similar t o those of the horizontal ranges i n their respective periods.  Typical v e r t i c a l s a l i n i t y  profiles f o r periods of small and large runoff are shown i n Figures 4a and 6a  #  As i l l u s t r a t e d i n these -figures, the s a l i n i t y gradients are smaller  during the low runoff period than those during the large runoff period,  -12-  which usually has well-develcped haloclines.  Typical s a l i n i t y distributions  for the period of small runoff are shown i n Figures 4b and 5 and those for the periods of large runoff i n Figures 6b and 7, The regular slopes of the isohalines i n the shallower depths during large runoff (Figure 7a) i l l u s t r a t e the gradual mixing of the fresh water as i t progresses down-inlet.  As shown  i n the transverse sections for both periods (Figures 5b and 7b) the surface water along the western shore of the i n l e t i s less saline than along the other shore.  The deep water during both periods has a s a l i n i t y of 30.6 %o .  The most marked feature i n the s a l i n i t y variations i s that while the s a l i n i t y of the surface layer shows wide variations, these are less marked'; below the depth of 60 feet and are almost negligible below the.depth o f 300 feet throughout the seasons. Temperature The temperature distributions f o r the different seasons may be grouped generally under those of the winter and summer. As i l l u s t r a t e d i n Figures 8a and 10a, the temperature profiles of the upper 500 feet for both periods are less regular than those of the s a l i n i t y (Figures 4a and 6a). The less simple pattern i n the temperature distributions as compared to that of the s a l i n i t y i s again evident i n the longitudinal sections (Figures 8b and 10b) although the transverse distributions of both the s a l i n i t y and temperature i n the upper 150 feet are of the same character. (Compare Figure 5b with Figure 9b and Figure 7b with Figure l i b ) . In general, the temperature i n the upper layer and also at the intermediate depths increases  -13-  0  10  20  30  0  \  " \  2 100 u "2O0  L  1  '  '  '  10  20  '  4  2  30  ' \  " '' I 7  SB  ^300  ^400 500.  (o) VERTICAL SALINITY PROFILES 11U 6  2000 -,  NAUTICAL  7 8  MILES  LONGITUDINAL SECTION OF SALINITY (%.)  Figure 4, Character of water i n Bute Inlet during the small runoff period i l l u s t r a t e d by (a) v e r t i c a l s a l i n i t y p r o f i l e s (%) and (b) longitudinal v e r t i c a l section showing the distribution of salinity. STATIONS  (a) LONGITUDINAL SECTION OF SALINITY <%.)  1  (t>) TRANSVERSE SECTION OF SALINITY (%.)  Figure 5, Distribution of s a l i n i t y during the small runoff period i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  -14-  UJ Id  100  ^200 1300 S400  1  3  5  7  8  (a)  900STATIONS 0  VERTICAL SALINITY PROFILES t%.) 45 I  2  3  NAUTICAL MILES  LONGITUDINAL SECTION OF SALINITY (%.) Figure 6*  Character of water i n Bute Inlet during the large runoff period i l l u s t r a t e d by (a) v e r t i c a l s a l i n i t y p r o f i l e s ($o) and (b) longitudinal v e r t i c a l section showing the distribution of salinity.  Figure 7#  Distribution of s a l i n i t y during the large runoff period i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  -15-  STATIONS  0  10  NAUTICAL J l L E S  2000 .  LONGITUDINAL SECTION OF TEMPERATURE PC)  Figure 8,  Character of water i n Bute Inlet during the winter i l l u s t r a t e d by (a) v e r t i c a l temperature p r o f i l e s (°C) and (b) longitudinal v e r t i c a l sections showing the d i s t r i b u t i o n of temperature.  DEPTH  - 0 FEET  NAUTICAL  MILES  (0) LONGITUDINAL SECTION OF TEMPERATURE PC) (b) TRANSVERSE SECTION OF TEMPERATURE PC) AT  i  Figure 9«  STATION  5  Distribution of temperature during the winter i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  -16-  VERTICAL TEMPERATURE  PROFILES  CC)  LONGITUDINAL SECTION OF TEMPERATURE PC)  .  :  .  ;  I-  Figure 10* Character of water i n Bute Inlet during the summer illustrated by (a) vertical temperature profiles (°G) and (b) longitudinal vertical sections showing the distribution of temperature,  Figure 11  #  Distribution of temperature during the summer i n a (a) longitudinal section and a (b) transverse section i n the upper 150 feet.  -17-  progressively from the head seaward (Figures 9a and 11a), During the winter the temperature increases with depth to a maximum at a depth of  ,  several hundred feet and then decreases gradually to the bottom. The vertical temperature gradients in the upper water during this period are smaller than those during the summer (Figures 8a and 10a). During the summer, the temperature a l l along the inlet except at the mouth decreases with depth to a well-defined minimum at a depth of a few hundred feet, then increases to a maximum, similar to that evident during the winter, and then decreases slowly to the bottom.  Note that there i s a well-defined minimum  in the temperature-depth curves for the summer (Figure 10a)»  The salient  feature i n the seasonal variations of the temperature i s that the variations which are large at the surface and progressively decreasing with depth are i n phase with those of the a i r temperatures to a depth of 150 feet and possibly to 300 feet, but are less evident below the latter depth and the water remains almost constant i n temperature (8°C) throughout the year.  Oxygen In general, the concentrations of dissolved oxygen, expressed as percent saturation, are very high i n the surface layer with maxima of 90$ to 130/6 occurring hear the halocline but not necessarily coinciding with it.  As shown i n Figures 12 and 13, the concentration drops from the above  maxima to 70$ i n the summer and 80$ i n the winter at a depth of 60 feet, and from this depth i t decreases gradually to 50 to 35$ in the deeper water.  The high oxygen values above 100$ i n the surface layer are  -18-  VERTICAL OXYGEN SATURATION PROFILES  (%)  LONGITUDINAL SECTION OF OXYGEN SATURATION (•/.)  Figure 12.  Character of water i n Bute Inlet during the winter (small runoff period) i l l u s t r a t e d by (a) v e r t i c a l oxygen saturation profiles . {%) and (b) longitudinal v e r t i c a l sections showing the distribution of oxygen.  Figure 13»  Character of water i n But© Inlet during the summer (large runoff period) illustrated by (a) vertical oxygen saturation profiles (%) and (b) longitudinal vertical section showing the distribution of oxygen.  -20-  associated with phytoplankton blooms (Gran and Thompson, 1931)  and i n  the summer months they are higher than those i n the winter months, due primarily to the seasonal increase i n plankton a c t i v i t i e s .  Since the  concentration of oxygen i n the deeper water of Bute Inlet i s not low i t may be presumed that an inflow of water must be present to maintain t h i s oxygen l e v e l , PeasityAnQmaly ( J g L ) The density anomaly ( 0^ ) curves for the water of t h i s i n l e t generally follow those of the s a l i n i t y more closely than those of the temperature, as?; i l l u s t r a t e d i n Figure 14,  Consequently, the comments on  s a l i n i t y w i l l apply except i n special cases. Longitudinal sections of density ( Q£ ) for winter and summer are shown i n Figure 15; these may be compared with those of s a l i n i t y (see Figures 4b and 6b) and contrasted with those of temperature (see Figures 8b and 10b).  During both periods, the  density ( <JtT ) of the deep water has tft values between 23.8 and  V.  23.9.  DISCUSSION OF RESULTS AND POSSIBLE CIRCULATION PATTERNS  The distribution of s a l i n i t y and temperature w i l l now be discussed and proposals f o r the circulation patterns made on the basis of seasons, rather than of individual cruises, to f a c i l i t a t e the presentation of the sequence of events that occur during the year.  -21-  f  ~  ~  ~  D E N S j T Y .Iff, ) S A L I N I T Y IV..)  I'c)  TEMPERATURE D E N S I T Y 117,1  0  25  SALINITY  IV..I  D  5.  10  15  20  25  30  1  -  -  SALINITY J /  75  (b)  DENSITYj  TEMPERATURE/ l  1  IOO' TEMPERATURE  CCI  i  Figure 14,  Typical s a l i n i t y ($o), temperature (°C) and density ( <T£ ) - depth curves of Bute Inlet during (a) the winter (small runoff period) and (b) the summer (large runoff period), i l l u s t r a t i n g the s i m i l a r i t y between the s a l i n i t y and dens i t y curves.  -22-  DISTRIBUTION (O)  OF  DENSITY (<r,)  DURING THE WINTER  NAUTICAL MILES  <t» DURING THE SUMMER  N A U T I C A L MILES  Figure 15.  Distribution of density ( Gtf ) of the water of Bute Inlet i n a v e r t i c a l section along the i n l e t (a) during the winter and (b) during the summer.  -23The water types have been grouped into four characteristic classes according t o t h e i r T -S relationships, a technique which was originallyintroduced by Helland Hansen (Sverdrup, eji a l , 1942) and which has been used successfully i n identifying oceanic water masses. In physical oceanography the T-S diagrams are frequently used to study the various mixing processes that occur i n the sea, but i n the present discussion they are used primarily to identify the water types at different depths and to study the seasonal changes of the water structures.  The water types of  t h i s i n l e t are indicated i n the T-S diagram of Figure 16 as follows: (a) the Runoff Water (R), characterized bjy temperatures of 6°C to 7°C and by very low s a l i n i t y , (b) the Intermediate Water ( I ) , water lying between the Deep Water and the modified Runoff Water, (c) the Winter Surface Water (W), characterized by temperatures of 5°C to 6°C and s a l i n i t i e s of 2? <&> t o 29  , and  (d) the Deep Water (D), characterized by temperature of about 8°C and s a l i n i t y of 30 %o or over. In the T-S diagram of Figure 16 the water types of Nodales Channel (N) and S t r a i t of Georgia (G) (below a depth of 70 feet) are also shown. Seasons are divided into Winter (December, January and February), Spring ( A p r i l and May), Summer (June, July and August), and Autumn (October and November), March and September are classed as Spring Transitional and Autumn Transitional respectively.  -24-  i i  11 0 10 9  1• 1 5 10 -----  SALINITY (V..I 1 1 1 1 1 5 20 25 30 35 NO O A L E S— n S u m m e r BUTE —==-n •>Mi i e rmediaG tE eO —TZJ* STRAITInt O F R G I A 1.11' M "D BUTE STRAIT O FG E O R G I A /g/-J f "' Winter NWin 0 ALES——^ J nnj t0 er 1  8  0  7 6  —B E RU uT no ff  Li  n i i U» Tr E .!1'•Wr*——BMn 1  j j Suifaca  5 1 1 1  .  1 1  1 •  Figure 16• Temperature-salinity relation i n Bute Inlet, - Nodales Channel, and the Strait of Georgia i l l u s t r a t i n g the various water types.  -25-  The seasonal distribution of salinity and temperature w i l l now be discussed and comments made upon the possible circulation patterns.  As  only relatively small changes i n the distribution of properties and i n the circulations occur during any one season, i t i s sufficient to present a single set of diagrams which describe the conditions that exist throughout that particular season. Winter  (December - February) During the Winter the runoff from river discharges i s low (see  Figure 17) and consequently the salinity of the surface water of the inlet reaches a relatively high value i n most of the places (Figure 19)« There i s , however, some evidence of fresh water near the head where surface water of salinity 18.4 %o has been observed (January 1951). However,* the fact that the lowest value of surface salinity was 18.4 %o indicates that what l i t t l e volume of fresh water enters the inlet soon undergoes mixing with the more saline water of the i n l e t .  This mixed water at the  head occurs i n the upper zone whose boundary can be "located from the halocline (usually accompanied by the thermocline) at about 5 feet.  By  February, the water i n the upper 20 to 30 feet reaches near homogeneity and associated with this the boundary of the upper zone generally occurs at about 20 feet i n the upper reaches of the inlet and reaches about 30 feet at mid-inlet, becoming less evident toward the mouth. Water of lower salinity than that at the head has been observed at Station 7, several miles from the head; this occurrence i s probably due to the eddies formed  -26-  MONTHS'  -  J  1000  «  800  -  6001-  0  4001-  (E 1  u y) O  to) MONTHLY MEAN DISCHARGE HOMATHKO RIVER 0  F  N  E  A  R  TATLA  LAKE  200 0  300,000  5 100,000 50P00  Figure 17, Monthly mean discharges of , (a) Homathko River near Tatla Lake (1930-1932) arid (b) Fraser River at Hope (1930-1932, 1950-1952). Note. Measurement of Homathko made at outlet of Tatlayako Lake, about 50 nautical miles from the mouth. Measurements made at mouth (May 18, 1951) indicate discharge to be about 10,000 ft.3/sec.  MONTHS  Figure 18. Monthly mean a i r temperatures at Thurlow, Comox and Powell River (1950-1952),  -27-  Figure 19.  Figure 20,  Distribution of s a l i n i t y during the Winter i n the • upper 150 feet i n a vert i c a l section along the inlet.  SALINITY  24.0 I 1.0 |  250 1  1  1  26.0  1  270 1  1  1  Distribution of temperature during the Winter i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  (K..I  28.0  29.0  n  L_J*__J  A  HE  o  MID-INLET  • . n  _i  Figure 21,  L  J  L  30.0  J  31.0  r  T  AO  MOUTH STATION 2  I  L  1_  Temperature-salinity relations i n Bute Inlet for the Winter period. The depths i n feet for the values are also entered.  -28-  by the surface current or from the cloud of fresh water from t i d a l release. Along the western shore the surface water was observed to be less saline than along the other side. Associated with t h i s , the transverse isohalines, as shown i n Figure 5b, slope downward from the east to the western shore. This fact i s attributed to the effect of Coriolis force. There appears then that there i s a p a r t i a l balance between the C o r i o l i s force and the force caused by the transverse pressure gradient. The a i r temperature also reaches a minimum during the Winter (Figure 18) and consequently the surface water temperature i s expected to be low at t h i s time.  The general relationship that exists between the  a i r temperature and the sea surface temperature of the B r i t i s h Columbia coast has already been remarked by Pickard and McLeod (1952) who established a strong correlation between the long term averages of the a i r and the sea surface temperatures i n the sheltered regions such as Georgia Strait.  In a much enclosed region such as Bute I n l e t , t h i s relationship  should also hold and the data indicate that t h i s i s the case. Only the essential facts w i l l be discussed here, but later i n the thesis under "Seasonal Variation of. Temperature" a more detailed discussion on t h i s relationship w i l l be given. Owing to the cold a i r mass i n the i n l e t , the surface water i s subject to cooling and during January the annual minimum sea surface temperature (4°C) i s reached. As i l l u s t r a t e d i n the longitudinal v e r t i c a l section of temperature (Figure 20) the surface temperature along the i n l e t i s generally around 5°C i n the upper reaches and 6°C i n the lower reaches of the i n l e t .  Because of the r e l a t i v e l y warm December of 1950  -29(5°C) the subsurface water below the depth of 10 feet did not cool as much as usual and remained., almost unchanged from November to January. However, between January and February there was a general drop i n temperature (from 0.5 to 1,0 C°) i n the subsurface waters and even at a depth of 150 feet the temperature dropped by 0.5 G°, from 7.3 to 6.8°G during t h i s interval. •In January and February as the runoff approaches the minimum, and as the water near the surface i s cooled under the influence of the cold northerly wind that has been observed i n t h i s i n l e t during the Winter, an almost homogeneous water i s formed which i s presumed to be the  consequence of wind mixing. A distinct water type of s a l i n i t y 27  to 29 %o and temperature of 5 to 6°C forms i n the upper 20 or 30 feet (Figure 21).  This i s designated Winter Surface Water (W).  The s a l i n i t y i n the greater depth i s 30.6 %o (Figure 4b). A tongue-like body of warm water with a maximum temperature of 8.3°C occurs below the depth of 300 feet and above the depth of 1,000 feet and intrudes well into the i n l e t (see Figure 8b). This Deep Water (D) at a depth below 300 feet i s very similar i n character to that of the water at a similar depth i n the northern part of the Strait of Georgia. This i s best seen from the T-S diagrams of both regions as shown i n Figure 21,  The process of exchange of deep water i s l i t t l e understood at the  present time, but i t may be possible that the Deep Water flows i n over the  s i l l s from the S t r a i t of Georgia to Bute Inlet (depths at Baker  Passage and i n the passage between Savary Island and the mainland are both about 450 f e e t ) .  The well-mixed water through the Yuculta Rapids  -30-  (water at Arran Rapids i s assumed to be similar to that at Yuculta Rapids) i s characteristically the same as the water at a depth of 150 feet i n Bute Inlet.  Therefore, i t i s unlikely that the water from these  rapids would influence the motion of water i n the greater depths. The cold surface water flows to seaward and as i t progresses i t mixes with the warmer and more saline water of the i n l e t as evidenced from the increase i n s a l i n i t y and temperature towards the mouth. This surface flow i s confirmed by current measurements with d r i f t buoys which indicate a net seaward flow during the t i d a l cycle (Cruise V, February 1951). In order to compensate the salt transported out of the i n l e t through the upper layer a counter flow below t h i s layer must be postulated to maintain the continuity, Tully (1949) has shown that i n Alberni Inlet the mixing depth not only separates the upper and lower layers i n structural patterns, but alSo divides the current system.  I t appears that this  i s also true i n the current system of Bute I n l e t .  The depth of no motion,  as inferred from the s a l i n i t y distribution i s at a depth of about Z>5' feet at Station 5.  A possible circulation proposed for t h i s period i s shown  by the schematic representation i n Figure 22. As mentioned e a r l i e r , there appears to be an intrusion of warm water below the depth of 300 feet extending w e l l into the i n l e t (see Figure 8b), Wust (Sverdrup s£ a l , 1942) has successfully applied h i s core method (Kernschicht methode) to ocean c i r c u l a t i o n by following some s a l i n i t y or temperature extremes, and since the tongue of warm water i n t h i s i n l e t may be treated as a temperature extreme, t h i s method has  -31-  Flgure 22.  Schematic representation of the average currents during the Winter period as inferred from s a l i n i t y and temperature distributions.  -32-  been considered. This warm water which appears as a tongue at about mid-depths i n Bute Inlet then, i s believed to be the water from the S t r a i t of Georgia. Since the concentration of dissolved oxygen i n the deeper water . i s r e l a t i v e l y high (40$ to 50% at 1,300  feet depth) i t may be assumed  that the water i n the greater depth i s not stagnant and thus a deep water circulation i s l i k e l y to be present i n t h i s i n l e t . Spring Transitional (March) The runoff due to r i v e r discharges reaches a minimum i n March or A p r i l i n Bute Inlet; consequently, the amount of fresh water present i n the i n l e t w i l l be at a minimum also.  This i s exactly the condition  which i s observed i n March 1952 when the surface zone shows l i t t l e evidence of fresh water i n the upper layer except near the head where an upper zone of above a depth of about 15 feet i s recognized; below t h i s depth the s a l i n i t y increases steadily with depth. Typical s a l i n i t y and density ( Of ) profiles for t h i s period are shown i n Figure 23.  I t i s readily  seen from t h i s that the water i n the upper 50 feet i s almost homogeneous except at the head. By t h i s time the a i r temperature has risen a few degrees since the Winter and surface warming of the water i s taking place as evidenced by the small negative temperature gradients i n the upper layer. The T-S diagrams for t h i s period are shown i n Figure 24.  On  examining t h i s , a surface water which i s s l i g h t l y warmer (7°C) and more  -33-  DENSITY to-,) SALINITY (%.) 30.0 20 0 „ 25.0 30.0 15.  20.0 . 25.0 0  ' '  50  DENSITY SALINITY]  STATION  Figure 2 3 ,  30.0  STATION 5  3  I  Typical s a l i n i t y profiles ($0) and their corresponding density p r o f i l e s ( Of ) f o r the Spring Transitional period.  SALINITY 240  °l 10.0  250  '  1  260  I  1  27 0  1  (%.> 28 0  1 ' 1  29 0  1  1  30 0  1  1  31 0 1  1  -  9 0 -  290  5.0 -  A  HEAD  o .MID-INLET 1952 •  Figure 24.  STATION 3  Temperature-salinity relations i n Bute Inlet f o r the Spring Transitional period. The depths i n feet f o r the values are also entered.  •34-  saline (29.0 %o ) than that of February 1951 i s evident i n the upper layer.  From the appearances of these water types i n the T-S diagram,  i t i s suggested that a more clearly defined Winter Surface Water than that found during the cruises and of s a l i n i t y greater than 29.0 %o and temperature of 5 to 6°C i s formed sometime during the Winter. The minimum temperature layer can be recognized at 250 feet i n the T-S diagram (Figure 24).  As evident i n the T-S diagram, the deep water has not changed  since the previous period (Figure 21).  In view of the fact that there i s  a marked departure i n the s a l i n i t y and temperature structures i n the upper 150 feet from those for the Winter (Figures 19 and 20) a different pattern of c i r c u l a t i o n i s to be anticipated.  In the upper reaches of the  i n l e t the slopes of the isohalines and isopycnals are steeper to a depth of 40 feet i n the upper reaches of the i n l e t than i n the lower reaches and similarly the isotherms are also steeper, though irregular to a greater depth (Figures 25 and 26).  Homogeneity i s reached i n the upper layer and  at Station 5 water of neutral s t a b i l i t y occurs i n the upper layer. Cruise 52-1 a convergence was observed near Purcell Point.  During  I t seems l i k e l y  that these steep isolines are associated with t h i s convergence.  The  neutral s t a b i l i t y may possibly be the end of an i n s t a b i l i t y period and an intermittent v e r t i c a l current may have been present. . Between the depths of 200 and 300 feet there exists a layer of water of minimum temperature (6°C) which appears to have formed sometime during the Winter of during the Transitional period.  -35-  Figure 25.  Distribution of s a l i n i t y during the Spring Transi t i o n a l period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure 26,  Distribution of temperature during the Spring Transitiona l period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  -36-  Sjariag (April,  May)  Since the maximum monthly discharges of the Fraser River during 1951 and 1952 are reached i n May and June respectively, i t w i l l be assumed that the peak discharges of the Homathko and Southgate Rivers during  1951  and 1952 are reached i n June and July respectively. In the latter part of May and i n the early part of June the runoff due to river discharges i s close to or at a maximum level and therefore a large volume of fresh water i s being transported into the i n l e t . This cold fresh water (temperature of about 7°C and salinity less than 1 $ 0 ) designated R (Figure 29), undergoes mixing with the warmer and more saline water and soon reaches a salinity greater than 1 %o and temperature greater than 8°G,  The temperature increase must also be augmented  by insolation and heat obtained from the atmosphere. This mixing results in the formation of an upper brackish layer which, i n general, increases in salinity and temperature as i t progresses seaward (Figures 27 and 28), This progressive mixing i s illustrated in a set of salinity profiles and vertical sections as shown earlier i n Figures 6a and 7a respectively. The mixing zone which i s defined to be the zone lying between the upper brackish layer and the more saline lower layer, occurs on the average between the depths of 10 feet (upper limit) and 24 feet (lower limit) and appears to occupy the same depth along the inlet except near the mouth, where i t i s shallower.  Tully has already remarked on the constancy of the  depth of this zone at any particular time and at any particular stage of tide in Alberni Inlet (Tully, 1949)  and i t i s believed this i s also  -37-  STATIONS 1 2 3  4  5  6  7  Figure 27. Distribution of s a l i n i t y during the Spring i n the upper 150 feet i n a vert i c a l section along the inlet.  SALINITY 10  15  8  STATIONS 1 2 3  4  5  6  7  8  Figure 28, Distribution of temperature during the Spring i n the upper 150 feet i n a vertical section along the i n l e t .  (•/..) 20  25 24 0  "•oi  4  HEAD  5  MID- INLET  o  MOUTH  25.0  1  1  SALINITY l-A.I  260 1  1  270 1  1  28 0  1  1  29.0  r  1951 If*!, 1951  Figure 29• Temperature-salinity relations i n Bute Inlet for the Spring period. The Runoff Water (R) and the Intermediate Water (I) are shown. The depths i n feet for the values are also shown.  J  Figure 30,  l_  I  I  '  30.0  31.0  1 n—-]  r-  A  HEAD  1991 _  S  MID - I N L E T  o  MOUTH  I  I  liu 1951 -  I  I  Temperature-salinity relations i n Bute Inlet for the Spring period. The depths i n feet for the values are also entered.  -38-  characteristic of t h i s i n l e t .  The s a l i n i t y structure below the mixing  zone remains almost unchanged from that of the Transitional period (compare Figures 4b and 6 b ) . Since the Transitional period there has been a substantial surface warming (from 6°c to 12°C) from insolation and t h i s i s shown by the development of a thermocline i n the shallower layer followed by a slower decrease to the minimum at intermediate depths. The isotherms (Figure 28) of the upper 50 feet are now more nearly horizontal and more regular as compared to the confused steep ones present during the Transitional period. The minimum temperature layer remains at the same depth as i t did i n the Transitional period and increases very l i t t l e i n temperature (0.2C° to 0 . 3 C ° ) ,  Obviously, the insolation has not influenced t h i s  layer much, nor has the warmer water below.  Although the temperatures  of the minimum temperature layer of the two years (1951 and 1952) are the same, the average depth at which t h i s layer occurs i n 1951 i s shallower by about 80 feet from that of 1952 (see Figure 3 0 ) , A tongue of warm water similar to that found during the Transitional period i s again evident i n the greater depths (see Figure 1 0 b ) , but at t h i s time the intrusion i s s l i g h t l y more into the i n l e t . For convenience a water type of s a l i n i t y of 29 %o and temperature of 8°C and designated Intermediate Water (I) i s introduced.  This water  l i e s i n a layer between the Runoff Water (R) and the water above the minimum temperature layer.  1  I t i s this water which mixes with the Runoff  -39-  Water to form a mixed water. The T-S diagram f o r the mouth of the i n l e t i s modified and t h i s i s believed to be the result of mixing with the waters from Yuculta and Arran Rapids and from Calm Channel (Figure 30)o The" fresh water which i s continually supplied at the.head,-and which subsequently mixes with the more saline .water of the i n l e t , flows seaward i n the upper zone. Current observations at mid-inlet indicate a general seaward flow i n the upper zone during the entire t i d a l cycle, the velocities being larger, during the ebb than during the f l o o d  e  The  fact that the brackish water i s carried seaward indicates that some salt i s transported out of the i n l e t i n the upper zone. Assuming conservation of s a l t , then, there must be a replenishment of salt for that lost through the upper zone. This replenishment i s believed to occur i n the middle zone and also below this zone. A possible circulation pattern proposed f o r t h i s period i s shown i n Figure 31.  In view of the fact that the water on the western shore o f . the i n l e t has more fresh water than along the eastern side, i t i s probable that more fresh water i s transported out of the i n l e t along the western shore. Since the minimum temperature layer remains constant i n depth and changes very l i t t l e during the interval between the two periods, the net v e r t i c a l motion near t h i s layer must be very small. Summer (June - August) The runoff from r i v e r discharges for the month of August i s  -AO-  STATIONS I 2  -  5 0  H  l±J  a  100 -  150  Figure 31• Schematic representation of the average currents during the Spring period as inferred from s a l i n i t y and temperature distributions.  -41-  s l i g h t l y less than the peak flow, which i s usually reached i n July, but i s greater than that i n May,  Consequently during the Summer period  a greater volume of fresh water i s being discharged into the i n l e t than during the Spring periodl  The surface d i l u t i o n i s greater than during  the Spring period (compare Figures 27 and 32),  I t may be noted that the  10.0 %o isohaline reaches the mouth, whereas the same isohaline reaches "only to mid-inlet during the Spring period. The upper zone i n the summer of 1950 i s deeper than that of the succeeding summers. This can be explained from the fact that during the summer of 1950 the r i v e r d i s charge i s much greater than that of any of the other summers. Tully (1949) has remarked that the upper zone decreases i n depth with increasing discharge up to a c r i t i c a l value of the discharge.  This situation i s  not observed and i t may be that the discharges have exceeded t h i s c r i t i c a l value beyond which the upper zone increases with the r i v e r d i s charge. The s a l i n i t y structure for the greater depths i s again the same as that of the Spring period.  .  In phase with the a i r tempsrature which reaches a maximum i n July or August, the surface temperature increases considerably (3C°) since the Spring period and reaches i t s annual maximum. The subsurface layer i s also influenced by t h i s heating as evidenced i n the temperature pattern (compare Figures 28 and 33) which shows a general warming up of t h i s layer to a depth of about 150 feet.  The minimum temperature  increases by about 0,5C° during the intervening period. Below this depth the water remains almost constant i n temperature during the  -42-  Figure 32. Distribution of s a l i n i t y during the Summer period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  Figure 33. Distribution of temperature during the Summer period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  SALINITY (•/..) 24.0 I 1.0  25.0 r  -  I  26.0 1  27.0  1 ?  1  28.0  <~-—I  29 0 1  1  30.0 1  r  6.0  10  I  1  J  I  I  I  o • ©  MID- INLET  •  MOUTH  1  1931 1992 , „ „  MID - INLET  I  I  I9SI I  Figure 34. Temperature-salinity relations i n Bute Inlet for the Summer period. The depths i n feet f o r the values are also entered.  -43-  interval between the Spring and Summer periods. As shown i n the T-S diagrams of Figure 34, there i s a modification i n the structure of the water at the rninimum temperature layer, where both the temperature and s a l i n i t y have increased moderately. From Figure 34, i t i s evident that the water at the minimum temperature layer i s about one Centigrade degree colder i n 1950 than that of 1951 and 1952, and this difference i s attributed to the severe winter of 19491950 when the water at the minimum temperature layer was formed.  In  1951, the increase i n temperature of t h i s layer was 0,5C° during the periods from Spring to Summer, but i n 1952 i t was only 0,2C°, This i s believed to be due to the greater proximity to the surface (by about 80 feet) of the minimum temperature layer i n 1951 at which time the a i r temperature between the periods from Spring to Summer was also higher than that of the year 1952,  As i l l u s t r a t e d i n Figure 34, the Deep  Ylater of Bute Inlet i s similar i n character to that of the S t r a i t of Georgia. The circulation pattern proposed for the Summer i s essentially the same as that f o r the Spring (see Figure 31)• Autumn Transitional (September) By this time the runoff i s reduced to half the peak flow of the year, and i s almost the same as that of the Spring. Concurrently with this drop i n the runoff, the a i r temperature drops by 2C° to 3C° from the maximum attained during the Summer, and i s  -44-  almost the same as that of the Spring, The conditions, as expected, are therefore similar to those of the characteristic Spring patterns, both i n the temperature and s a l i n i t y structures as seen from the comparisons of the v e r t i c a l sections of t h i s period (Figures 35 and 36), with the corresponding sections for the Spring (Figures 27 and 28). The upper zone i s seen to be shallower than that during the Summer, and i n the upper 30 feet the temperature structure i s the same as that of the Spring, but below this i t i s i d e n t i c a l with that of the Summer, Apparently, the surface cooling has not yet penetrated beyond the depth of 30 feet. The T-S diagrams also indicate that the Intermediate Water has almost the same characteristics as during the Summer period. The Deep Water has undergone no major changes since the Summer period, and as seen from comparing Figures 34 and 37, the water at the minimum temperature layer has increased i n temperature by 0.5°G and increased i n s a l i n i t y by 0,3 %o , The T-S relationships for the water of the S t r a i t of Georgia are also shown i n Figure 37, which show that the deep water i n Bute Inlet i s similar i n character to that of the Strait of Georgia. The circulation pattern proposed for this period i s similar to that for Spring and also Summer, and i n view of the fact that the minimum temperature s t i l l remains well-defined, i t i s evident that net v e r t i c a l motion i s again absent at and near this depth of minimum temperature layer.  45-  STATIONS I 2  STATIONS  3  SALINITY  DEPTH • 0 • FEET  (%.)  0 I i — NAUTICAL  S  TEMPERATURE l»C1 •  MILES  Figure 35. Distribution of s a l i n i t y during the Autumn Transi t i o n a l period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  •1  2  •  •  10 1  NAUTICAL MILES  Figure 36. Distribution of temperature during the Autumn Transitiona l period i n the upper 150 feet i n a v e r t i c a l section . along the i n l e t .  Figure 37. Temperature-salinity relations i n Bute Inlet for the Autumn Transitional period. The depths i n feet for the values are also entered.  -46Autumn (October, November) As Autumn approaches, the runoff due to r i v e r discharge decreases substantially and as a result the volume of fresh water emptying into the i n l e t decreases to a value which i s about twice the minimum discharge. At the same time, the a i r temperature decreases rapidly from a maximum value of 17°C attained during the Summer, to about 6°C at t h i s time. The s a l i n i t y structure i n the upper layer (Figures 38 and 39) shows a marked departure from that of the preceding periods and approaches a structure which i s similar t o the one for the Winter, During t h i s period, the fresh water that enters the i n l e t forms a w e l l defined upper zone near the head, but as i t progresses down the i n l e t i t becomes less sharply defined due to mixing and results i n an elimination of t h i s shallow layer.  This i s best i l l u s t r a t e d by the set of s a l i n i t y -  depth profiles as shown i n Figure 38, The 10,0 %o isohaline f o r the Autumn Transitional period i s now replaced by a more saline 25.0 %o isohaline and the surface layer i s generally much more saline than during the Transitional period.  In the  Deep Water, however, the s a l i n i t y structure i s the same as during the Transitional period. The drop i n the a i r temperature i s also accompanied by a similar drop i n the sea surface temperature, and'a corresponding, though less pronounced, drop i n the subsurface temperature. At the surface t h i s drop i s of the order of 4 to ?C° and less than 10° at a depth of 100  -47  LOCATION OF STATION S T.... i... .'f NAUTICAL MILES  SALINITY (%.) 300  20.0  250  30.0  20.0  25.0  30.0  100  Figure 38«  Set of s a l i n i t y profiles (%o) for the Autumn period  NAUTICAL  Figure 39* Distribution of s a l i n i t y during the Autumn period i n the upper 150 feet i n a v e r t i c a l section along the i n l e t .  MILES  Figure 40» Distribution of temperature during the Autumn period i n the upper 150 feet i n a v e r t i c a l sect i o n along the i n l e t .  -48-  feet (Figure 40), Compare the temperature distribution of t h i s period with that of the previous period (Figure 37)•  The water l y i n g between  the depths of 150 feet and 200 feet has been cooled and as a consequence c e l l s of warm water are formed, sandwiched between the surface cold water and the cold water at the minimum temperature layer." The l o n g i tudinal v e r t i c a l section of temperature of Figure 41 indicates these c e l l s of warm water occurring between these two layers.  Thus a reversal  i n the temperature gradients has taken place (negative t o positive) i n the upper layer.  On comparing the T-S diagrams f o r t h i s period  (Figure 42) with those for the Transitional period, i t i s seen that the water at the minimum temperature layer has increased i n temperature by 0.6 to 0«8C° from the preceding period. The minimum temperature layer has increased i n density since the Autumn Transitional period and t h i s i s accompanied by the descending of t h i s layer, which i s more pronounced near the mouth than at the head of the i n l e t . The circulation patterns are similar to those proposed fort the Winter (see Figure 22). The shallow transverse s a l i n i t y structures again exhibit the isohalines sloping downward from the western shore to the eastern shore of the i n l e t except during the flood at Station 5. This i s again, as i n previous occasions, the result of the C o r i o l i s force. The seasonal cycle of events i s completed at t h i s stage and from here, with further cooling and reduced runoff, a t y p i c a l Winter scene again re-appears.  -49-  STATIONS 1 2  3  4  5  6  7  8  Figure 41, Distribution of temperature f o r the deeper section during the Autumn period. .  24.0 11.01  "1  SALINITY  27.0  25 0  n—i  1  (»~>  28.0  1  r  29.0 '  y§  Figure 42. A  I  1_  -1  I  L.  I  31.0  MID-INLET O  —1  30.0  .1  I  I  MOUTH  I  ™ 1991  I  I  Temperature-salinity relations i n Bute Inlet f o r the Autumn period. The depths i n feet for the values are also entered.  -50-  Summary o£ ihe. General, Circulation Pattern From the preceding discussion of the circulatory patterns i t i s suggested that there i s only one main pattern, namely, the estuarine circulation, i n Bute Inlet during the course of the year. During the periods from Spring to Autumn Transitional large volumes of fresh water are transported into the i n l e t by the r i v e r s . On entering, the fresh water mixes with the more saline waters of the i n l e t and forms a brackish water i n the upper layer which flows seaward entraining the salt toward the mouth. A compensating counter-current i s suggested which carries the underlying water toward the head to maintain the continuity of s a l t .  The boundary that marks t h i s two-current system  i s believed to occur i n and below the mixing zone. The s i m i l a r i t y i n the structures of the water at mid-depths near the mouth of t h i s i n l e t and those at corresponding depths i n the northern section of the Strait of Georgia indicates that the abovementioned water i n the lower reaches of Bute Inlet may be an intrusion of Georgia S t r a i t Deep Water. . In the above discussion tides have been omitted, since only the average currents are considered.  VI.  SEASONAL VARIATION OF SALINITY AND TEMPERATURE  The seasonal fluctuation of temperature and s a l i n i t y of the  -51-  waters i n Georgia S t r a i t has been studied by Hutchinson, Lucas, and McPhail (1929) and more recently the seasonal variation of temperature and s a l i n i t y of the surface waters of the B r i t i s h Columbia Coast has been analysed by Pickard and McLeod (1952). On the Atlantic Coast similar studies have been made by Hachey (1939), Hachey and McLellan (1948) and recently by Lauzier (1952)« Most of the above studies are based on consistent data which are collected regularly.  The data available for Bute Inlet are irregular,  but an attempt has been made t o examine them i n t h i s i n l e t for periodic trends of temperatures and s a l i n i t i e s . For the purpose of t h i s discussion the i n l e t i s divided into three regions: the head, the middle (mid-inlet) and the mouth. Variation, of S a l i n i t y In Figure 43 are shown the seasonal variations of the' s a l i n i t y of the surface and subsurface waters of Bute I n l e t .  The most marked  feature i s that the seasonal fluctuations, while very marked at the surface throughout the i n l e t , are only noticeable at the head and at midi n l e t at a depth of 15 feet. They are less marked below the depth of 60 feet and almost negligible below 300 feet. The deeper water appears to have no significant difference i n s a l i n i t y from that of the adjacent waters such as Pryce and Homfray Channels and Toba Inlet. The water between the depths of 60 feet and 300 feet i s about 0.6 % ,  -52-  J  Figure 43b.  Seasonal variation of s a l i n i t y at depths from 60 to 1,500 feet.  -54-  more saline i n the second year (August 1951 to May 1952), while the water between the depths of 450 feet and 900 feet stayed almost the same. Runoff from Rivers and Precipitation The volume of fresh water which i s transported into the i n l e t by the two r i v e r s at the head, has been estimated to be as large as 14,000 3  f t . / s e c , during the late spring. Nov/ the drainage area of Bute Inlet i s about 240 nautical square miles, not including that portion which i s covered by the drainage area of the Homathko and Southgate Rivers.  I f a l l the water from precipitation  within t h i s area drains into the i n l e t the volume of fresh water entering the i n l e t w i l l be appreciably large (8,400 ft.^/sec., for precipitation of one inch per day). However, as there are factors such as conditions of land, vegetation, etc,~ i t i s d i f f i c u l t to estimate the percentage of precipitation that w i l l actually drain into the i n l e t . For the purpose of the present discussion, however, i t i s assumed that about 50$ of the precipitation drains into the i n l e t .  Then the run-  off due to precipitation may be expressed by D » 4,200 r ( f t . ^ / s e c ) , where D i s the runoff from precipitation, and r the r a i n f a l l i n inches per day. The direct precipitation f a l l i n g into the i n l e t (about 80 square nautical miles) can be expressed by D « 2,800 r (ft.^/sec.) where the symbols have the same meanings as before. The t o t a l amount of fresh water  -55-  from precipitation w i l l then be D = 7,000 r ( f t . / s e c ) . Now the average r a i n f a l l i n inches per day at Thurlow during the summer (1950),autumn (1950), winter (1951) and spring (1951) was 0.05, 0.35, 0.29 and 0.14 respectively, which i s equivalent to a discharge of 350, 2,350, 2,030 and 980 ft.3/ ec. S  I t i s readily seen by comparing the precipitation during the spring (1951) and the r i v e r runoff that the l a t t e r i s the predominant factor i n the d i l u t i o n of i n l e t water. Hence during spring and summer and perhaps early autumn, precipitation may be neglected. However, when r i v e r runoff i s low, as i t i s during the winter, then precipitation should be considered.  When extremes are considered, such as the maximum  precipitation of 2.72 inches per day which was recorded at Thurlow . during the late autumn (1951), then precipitation w i l l be the predominant factor i n the d i l u t i o n of the inlet's water. Variation, o£ Xemperature The temporal variations of the temperature at the surface and at depths of 15 and 30 feet for the three regions are shown i n Figure 44a, and those at 60, 150 , 300 , 450, 600, 900, 1,200,:. 1,500:.and 1,800 feet are shown i n Figure 44b. I t i s seen that there are marked seasonal variations which are i n phase with those of the a i r temperature at the surface and to a depth of 150 feet and possibly to 300 feet, but below t h i s the data are inadequate to determine i f fluctuations are periodic or random. On comparing the monthly mean a i r temperatures (Figure 19)  -56-  MONTHS  '«(—i—i—i—i—i—I—i—i—i—i—i—r~i—r—i—i—i—i  1—1—1—1—1—1  1 1 1 1  1  1  I '  1  1  1  I  r—i  i  i  1  1  1  1  r  1  X ^ W / ^ , -  Figure 44a  0  7.70-2.02co»t - 0 SaeaaZI-O.TTiint 30 FEET  -i. \ .  Seasonal variation of temperature at the surface and depths of 15 and 30 feet.  -57-  Figure 44b.  Seasonal Variation of temperature at depths of 60 to 1,800 feet.  -58-  with the means of sea surface temperatures of t h i s i n l e t , a good phase agreement can be seen which indicates that the sea surface temperature i n Bute Inlet follows the climatological trend of t h i s region, as has been shown to be the case for the waters of Georgia S t r a i t (Pickard and McLeod, 1952). These periodic variations are, therefore, attributed mainly to the variations i n the strength and the extent of insolation during the seasons. The water at and near the surface i s generally colder at the head and progressively gets warmer toward the mouth, and i s warmed by insolation and also by mixing with the warmer water of the i n l e t . As seen from Figure 44a the rates of warming and cooling of the surface and the subsurface waters (15 feet) at the head, mid-inlet and the mouth are complimentary during the spring and autumn respectively, the value being about 2 Centigrade degrees per month. The monthly mean surface water temperatures at Yuculta Landing (September-1950 - September 1951) are also plotted against time and are shown i n Figure 44a.  The water at Yuculta Landing i s 2°C to 3°C warmer  than the surface water of Bute Inlet during the winter and i s 3°C to 4°C colder during the summer. This i s no doubt evidence of pronounced vert i c a l mixing at the rapids. I t i s apparent from these results that i n Bute Inlet the determining factors causing the fluctuations i n the temperature of the surface and subsurface waters are insolation and the cold inflowing fresh water.  -59-  Analysis of the Long Term Variation Using the temperature data from mid-inlet, an equation of the Fourier type may be f i t t e d to the observed values and to express the long term variations of the surface temperatures of t h i s i n l e t . A Fourier Equation of type, T^rb)  = 0 a  +  a  +  where T  l  c o s  *  +  a  bj s i n t  2  c o s  2t t ...  t b2 s i n 2t *  i s the temperature i n °G,  t  i s the phase angle, taking January 10th as 0° and increasing by 30° monthly, and 0> l > 2 > a  a  a  etc.,  are constants to be determined, i s used here. The higher terms,  cos 3t + ...and  s i n 3t + . . .  are small and have been neglected. The following equations are the results of t h i s analysis f o r the changes occurring at mid-inlet at depths (feet): Depth (feet) I'd\= 9.19 T 4-. 54-' cos t - 0.06; cos' 2't: -. 0.04.:. s i n " ,t:/+ 01131 s i n 2't'.  0 15  \^  30  .T  °0  3 0 =  9.00  - 3.04,  cos t + 0.4.0 cos 2 f - 0.65 s i n t + 0.05 s i n  2t,  7..-70 - 2.02 cos t - 0.38 c o s i 2 t - 0.77 s i n t ,  60= 7.59 - i>Q7 cos t + 0.15 cos 2t ~ 0.69 s i n t - 0.06 s i n 2 t ,  T  and  150« 7.14- - 0.56 s i n t + 0.10 s i n 2t - 0.05 cos t + 0.15 cos 2t.  T  -60  These curves are drawn i n Figure 44. I t i s seen that the f i r s t two terms are sufficient to i l l u s t r a t e the variations to a depth of 60 feet. I t i s evident that" similar equations and therefore curves could be drawn to f i t the observational values.  VII.  ,  EDDY DIFFUSIVITY  B r i e f remarks have been made previously under various topics on the minimum temperature layer, a s t r a t i f i e d layer of cold water characterized by a well-defined minimum i n the temperature-depth curves and occurring at depths which vary from 125 feet to about 4Q0 feet. This cold layer whose minimum temperature i s about 6°C and which appears as a tongue of cold water extends from the head to almost the mouth of the i n l e t , gradually increasing i n temperature seaward u n t i l i t becomes i n distinguishable near the mouth. The temperature of t h i s layer generally increases with time from i t s inception i n the Spring Transitional period (March) u n t i l i t becomes indistinguishable i n Winter (January, February). The pattern of t h i s layer can be seen from any of the longitudinal vert i c a l sections of temperature and temperature profiles during i t s existence (see, for example, Figure 10). The minimum temperature layer i s subjected to heat i n f l u x from both the overlying and the underlying water. From the distribution of  -61-  temperature adjacent to t h i s layer an eddy coefficient of heat transfer has been calculated. Consider a left-hand coordinate system with the positive xaxis directed seaward from the head, the y-axis to the right-hand shore, and the z-axis v e r t i c a l l y downward. The distribution of conservative concentrations (concentrations that are altered l o c a l l y , except at the boundaries,by processes of diffusion and advection only) i n the sea can be written  _  where  -+  ( Us")  S  dCsv->  -t  9CS^A)^  i s any conservative concentration, such as s a l i n i t y or heat content,  j3 - density, A*,Ay,An = eddy coefficients i n the x, y and z directions respectively, and <A,V,* *' «= components of velocity i n x, y, and z directions t  respectively. Since sea water i s considered to be incompressible, the equation  -620  may be written  2* -  2L  /AX  d$\  - f u3s  ^ J W A M 2s \  -t  -+•  ^  /A?  3s\  S }  Since the temperature -is proportional to the heat content, 1  CyoT  of a unit volume, where C , jo , and X  are the specific heat,  density, and temperature respectively of the sea water, the above equation for heat transfer may be written  At the depth near the minimum temperature layer, the transverse temperature distribution i s generally uniform i n the y-direction and since the v e r t i c a l temperature gradients are much larger than the horizontal temperature gradients as evident from the d i s t r i b u t i o n of temperature at t h i s depth, the heat transfer i n the horizontal direction may be neglected.  I t i s assumed that at the depth considered the  horizontal advection terms may be neglected also;  -63-  v e r t i c a l velocity to be negligible compared to the eddy transfer, the above equation reduces t o  at  32-  f  '  a similar equation to that for heat conduction i n a s o l i d . For numerical computation t h i s i s approximated by the difference equation  where  =  and T7  change of temperature i n Centigrade degrees/month, and  are temperatures at equi-distant depths, A 2  ,  - (meters) above and below z£o respectively. 1°  i s the temperature at depth ^© at which the second  derivative i s required, and The temperature, U  i s obtained from temperature-depth curve  at the depth where the  -^-T* i s largest.  The values calculated for C.G.S. u n i t s ) .  i s taken as 1 g./cm.^.  are given i n Table I I (reduced to  TABLE I I . Coefficients of v e r t i c a l eddy d i f f u s i v i t y (A ) above and below the minimum temperature layer. z  Date  AT Above Minimum Temp. Layer Below Minimum Temp. Layer At " Depth S t a b i l i t y Coeff. (A ) Depth S t a b i l i t y Coeff. ( A ) (C°/month) (g./cm./sec.) (m.) 105 (g./cm./sec. (».) 105 s ^ i d *. /  z  z  Aug. 1950  0.42  30  4,400  0.74  110  500  0.58  Sept. 19501  0.42  30  4,000  1.47  110  300  1.25  May 1951  0.21  20  3,400  0.74  90  700  0.23  Aug. 1951  0.26  40  1,700  0.20  90  1,000  0,63  Oct. 1951  0.26  80  1,000  0.56  130  500  0.55  Aug. 1952  0.21  50  2,200  0.17  110  400  0.21  Means  0.30  42  2,800  0.65  107  600  0.58  -65-  In the layer of wat.er above the minimum temperature layer where the s t a b i l i t y (E» = 10^ 3 ^  ) i s 2,800, the average value of the  coefficients i s 0.65 g./cm./sec, while i n the layer of water below the minimum temperature layer and of s t a b i l i t y 600, i t s value i s 0.58 g./cm./sec. As shown i n Table I I , there are appreciable variations, although the order of magnitude i s the same. The numerical values of eddy d i f f u s i v i t y for the Danish water ("Schultz's Grund" Lightship) are shown i n Table I I I . I t may be seen by comparing Tables I I and I I I that the coeff i c i e n t s of eddy d i f f u s i v i t y for the water of" Bute Inlet have values which are or the same order of magnitude as those for the Danish water for which the v e r t i c a l s t a b i l i t i e s are also of the same order.  VIII.  SUMMARY AND CONCLUSIONS  The shallow s a l i n i t y structures of the water during the various seasons can be classified under two main groups; those occurring at periods of small runoff (winter) and. those occurring at periods of large r i v e r runoff (summer). As i n other estuaries of t h i s character the surface s a l i n i t y generally increases with distance from the head to the mouth. During heavy runoff periods t h i s increase i n s a l i n i t y i s from 1 %o at the head to 15 %> at the mouth while during reduced runoff i t i s from 20 %o  TABLE I I I Numerical values of eddy d i f f u s i v i t y as derived from observed time and space variations of s a l i n i t y at Schultz's Grund (Jacobsen, 1913).  Depth Horizontal S t a b i l i t y (1C-5 )? s t a b i l i t y (1C-5 ^ § • " Coefficient As (m.) Currents at station Da-21. • at "Schultz's Grund" l i g h t (g./cm./sec.) (m./sec.) (56°07.9« N., 11°11.1« E.) ship. (56°08v? N., .11°11.2« E.) :  1  0  7.8  2.5  6.4  12,000  8,000  7.5  1.7  12,000  20,000  0.18  12.5  7.6  110,000  100,000  0 04  17.5  13.3  72,000  50,000  0.74  20  17.4 8,000  23 25  0,3  o  2.1  8,000  Computed from Jacobsen, J.P. (1913), assuming temperature of water to be 5°C  -67to 29 %> » The surface s a l i n i t y reaches a maximum during the winter, corresponding to the lowest r i v e r runoff and attains a minimum during the summer when the runoff i s largest.' The surface water along the right-hand shore (looking seaward) i s almost always observed to be less saline than that along the other shore.  ^  This i s due to the  C o r i o l i s force which appears to be p a r t i a l l y balanced by the transverse pressure gradients. The progressive seaward increase i n s a l i n i t y i n the upper layer i s attributed to the gradual mixing of salt water with the surface waters of the i n l e t .  During a l l seasons the s a l i n i t y  almost invariably increases with depth. The most marked feature i n the seasonal s a l i n i t y variation i s that while i t s fluctuations are well-marked at the surface, no regular cycle below 60 feet i s evident. During both periods of small r i v e r runoff and large river runoff the s a l i n i t y of the deep water i s 30.6 %o . The temperature distributions for the different seasons may be grouped generally under the headings of the Winter and the Summer. The horizontal and v e r t i c a l temperature distributions are less simple than those of s a l i n i t y .  In the shallower depths the temperature generally  increases to seaward from the head to the mouth during a l l seasons. During the winter the temperature increases with depth from the sea surface to a maximum at mid-depths, then slowly decreases toward the bottom. However, during the summer i t decreases rather rapidly at depths corresponding to the halocline, and then decreases more slowly to a well-defined minimum at intermediate depths. From t h i s depth i t  -68-  increases to a maximum which i s , similar to that found during the winter, and then decreases slowly toward the bottom.  This minimum temperature  pattern i s less evident near the mouth. The seasonal temperature variation of the surface and subsurface waters i s i n phase with the seasonal a i r temperature cycle and follows the climatological trend of the l o c a l i t y .  This variation i s  well-marked i n the surface layer to a depth of 150 feet and possibly to a depth of 300 feet, but below this depth the water changes very l i t t l e i n temperature during the year. Insolation and the cold runoff water from the rivers are the predominant factors i n determining the fluctuations i n the temperature. The concentration of dissolved oxygen i s usually very high i n the surface layer with maxima:, of 90$ to 130$ occurring near the mixing depth butrhot necessarily coinciding with i t .  The high oxygen  values above 100$ i n the surface layer are associated with phytoplankton blooms.  The waters at the greater depths are not stagnant  as evidenced by the degree of oxygen saturation (40$)« There are four characteristic water types i n t h i s i n l e t as follows: (a) The Runoff Water which i s the fresh water from river d i s charges, (b) the Intermediate Water which l i e s between the mixed Runo f f Water and the Deep Water,  -69-  (c) the Surface Winter Water which i s formed during the Winter, and, the Deep Water, which has a s a l i n i t y over 30 %o and a  (d)  temperature of about S°C and which changes l i t t l e i n s a l i n i t y and temperature during the year. Three d i s t i n c t layers i n the oceanographic  structures i n the  water masses are evident. The surface brackish layer i s formed by the mixing of saline water of the i n l e t with the fresh r i v e r water. Below t h i s layer l i e s the mixed layer which i s essentially the Runoff Water which has undergone more intensive mixing with the Intermediate Water. The layer below this i s broadly classed a lower layer, a body of water which does not change much i n i t s structures compared to those of other layers. The shallow well-defined upper layer which i s present during the runoff periods i s absent i n the winter owing to the reduction i n runoff. However, i n i t s place a well-mixed homogeneous layer of water i s formed during the winter. During the year only one main circulation pattern i s apparent. This i s the general estuarine circulation i n which there i s a net downi n l e t flow i n the upper layer accompanied by a net up-inlet flow below t h i s layer.  This flow occurs throughout the seasons though less pro-  nounced during the winter. Eddy coefficients of d i f f u s i v i t y have been computed using a  -70-  simplified conduction formula. The values determined are 0.65 and 0.58 g./cm./sec, for the water above and below the layer of minimum temperature respectively.  The magnitudes of these coefficients are  of the same order as those determined i n Danish waters for which the v e r t i c a l s t a b i l i t i e s are also of the same order.  -71-  REFERENCES  Bancroft, J.A.  Geology of the coast and islands between the Strait  of Georgia and Queen Charlotte Sound, B.C. 1913.  Dept. of Mines, Ottawa. Cameron, W.M.  Mem. 23, Canada,  On the dynamics of i n l e t circulations. Unpublished  Doctoral dissertation, Scripps Inst, of Oceanogr., Univ, of Cal., Los Angeles, 1951a* Carter, N.M.  The physiography and oceanography of some B r i t i s h Columbia  fjords,  Proc, F i f t h Pac. S c i . Congr., 4 (3)  Gran, H.H., and T.G. Thompson,  : 721«733.  The diatoms and the physical and chemical  conditions of the sea water of the San Juan Archipelago. Puget Sound B i o l . Station U. of Wash., 7. Hachey, H.B.  Pub.  1931*  Surface water temperatures of the Canadian Atlantic coast.  J . Fish. Res. Bd. Can., 4. Hachey, H.G., and H.J. McLennan.  1939. Trends and cycles i n surface temper-  atures of the Canadian A t l a n t i c ,  1948.  1933,  J . Fish. Res. Bd, Can., 7  (6).  -72-  Hutchinson, A.H., C.C. Lucas, and M, McPhail.  Seasonal variations i n  chemical and physical properties of the water, of the S t r a i t of Georgia i n r e l a t i o n to phytoplankton. Trans. Roy. Soc. Can.,  13 ( 5 ) .  1929.  Hutchinson, A.H., and C.C. Lucas.  The epithalassa of the Strait of  Georgia. Can. J . Res., 5 : 231-284. 1931. Jacobsen, J.P.  Beitrag zur Hydrographic der Danischen gewasser, Koram.  f. Havunders. Medd., Ser. Hydr., 2 (2), Lauzier, L.  1913.  Variation of temperature and s a l i n i t y i n shallow waters  of the Southwestern Gulf of St. Lawrence.  M.S., Atlantic  Oceanogr. Group, Joint Comm. on Oceanogr., St. Andrews, N.B. October 1952. Pickard, G.L.  Oceanography of B r i t i s h Columbia Mainland Inlets. I I I .  Internal Waves. Fish. Res. Bd. Can., Progress Reports of P a c i f i c Coast Stations.  (In Press).  Pickard, G.L., and D.C. McLeod.  1954.  The seasonal variation of the temper-  ature and s a l i n i t y of the surface waters of the B r i t i s h Columbia coast. J . Fish. Res. Bd. Can., 10 (3) 125-145. 1953. Pritchard, D.W.  The physical structure, circulation, and mixing i n  a coastal plain estuary. Tech. Rept. 3, Refi 52-2, Ches. Bay Inst., Johns Hopkins Univ., Baltimore, Md. May 1952.  •73-  Pritchard, D.W.  A review of our present knowledge of the dynamics Tech. Rept. 4., Ref. 52-7, Ches.  and flushing of estuaries.  Bay Inst., Johns Hopkins Univ., Baltimore, Md. March 1952. -Saur, J.T.F.  Oceanographic features of Nodales Channel with application  to underwater sound. Rept. 188, U.S. Navy Electronics Lab., San Diego, Cal. June 1950  o  Spilhaus, A.F,  A bathythermograph. J . Mar. Res. 1 (2) : 95-100,  A p r i l 1938. Stommel, H,  ;  Recent developments i n the study of t i d a l estuaries.  Tech, Rept., Ref. 51-33, Woods Hole Oceanogr. Inst., Cambridge, Mass.  1951.  Sverdrup, H.U., W.M. Johnson, and R.H. Fleming.  The oceans.  Prentice-  H a l l , Inc., New York. 1942. Tully, J.P. (1). Tully, J.P.  Oceanography of Nootka Sound.  J . B i o l . Bd. of Can., 3  1937a. Oceanography and prediction of pulp m i l l pollution i n  Alberni Inlet.  Fish. Res. Bd. Can. B u l l . 88. 1949.  Proceedings of the colloquium on the flushing of estuaries. Oceanogr. Inst., Cambridge, Mass.  September 1950.  Woods Hole  -74-  The surface water supply of Canada, Pacific Drainage,  No, 80, Dom.  Water Power and Hydrom, Bur., Canada, Dept. of Mines and Res,, King's Printer, Ottawa.  1941.  Tide Tables f o r the Pacific Coast of Canada.  Can. Hydrographic Serv,,  Canada. Dept. of Mines and Tech. Serv,, King's Printer, Ottawa. 1949, 1950,  1951*  Monthly records of Meteorological observations. A i r . Serv., Met. Div., Dept. of Transport, Canada. Manual of Oceanographic Methods, A p r i l 1950,  Canadian Joint Comm.  on Oceanogr., Pacific Oceanogr., Group, Nanaimo, B.C.  -75-  APPENDIX  DISTRIBUTION OF SALINITY, TEMPERATURE, AND OXYGEN  The oceanographic conditions that occurred i n Bute Inlet from August 1950 to August 1952 are i l l u s t r a t e d i n the following series of sets of v e r t i c a l sections. Longitudinal and transverse v e r t i c a l sections of s a l i n i t y , temperature, and oxygen, a l l of which are prepared from the data of Cruise I to V (P.O.G.) and Cruise 51-2 to 52-3 (I.O.U.B.C.) are shown. Oxygen w i l l be dealt with separately. Internal waves are known to be present i n Bute Inlet (Pickard, 1954, In Press), However, at present, a method f o r correcting the observed values of s a l i n i t y and temperature have not been devised.  There-  fore, i n the description to follow no attempt has been made to take internal waves into account. Distribution of S a l i n i t y and Temperature Crui.se I - August 2, 1950 As only two hydrographic stations, namely, Stations 5B and 6B, were occupied during t h i s cruise, the v e r t i c a l sections w i l l be indicated by dotted lines and are drawn together with those of Cruise I I (September 10, 1950) i n Figure 45.  -76-  Figure 45. Character of water i n Bute Inlet (Cruise II-September 10, 1950) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 750 feet, •(c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 750 feet. Note. Bathythermograph casts (750 feet) made at each station.  -77The s a l i n i t y increased very l i t t l e with depth during the f i r s t 12 feet interval (from 4.2 $o to 4.7 %o ) but from t h i s depth i t increased rapidly (halocline) to 25.3 f*> at a depth of 28 feet from where i t gradu a l l y increased t o 30.2 %o at a depth of 450 feet. The mixing depth which may be defined by the i n f l e c t i o n point on the s a l i n i t y gradient was at about 20 feet. The water was isothermal (about 12°C) for the f i r s t 15 feet interval but decreased to 9.2°C at a -depth of 36 feet and thence more slowly t o a well-defined minimum of 5.2°C at a depth of 250 feet and then increased t o 7.0°C at a depth of 450 feet. CruJ.se J J - September Ip., 1950 In Figure 45 are presented the longitudinal v e r t i c a l sections of s a l i n i t y and temperature which describe the conditions that existed during t h i s cruise. The surface s a l i n i t y increased horizontally from 0.9 %o at the head t o 16.0 %o at the mouth of the i n l e t and a l l along the length the s a l i n i t y increased v e r t i c a l l y to about 18.0 %o at the mixing depth which occurred at about 10 feet. The s a l i n i t y at a depth of 750 feet was 30.5 i<*> • The mixing depth varied only by 1 l foot along the entire length of the i n l e t except at the mouth where i t was shallower. In Figure 45a the progressive increase of s a l i n i t y seaward i s clearly shown. Vertical s a l i n i t y gradients were generally similar i n shape to those found during Cruise I and are typical of those during runoff periods.  -78-  The surface temperature also increased progressively from 6.7°C at the head to 12.0°C at the lower reaches of the i n l e t (Figure 45c) and, i n general, the temperature decreased with depth to a well-defined minimum (5.4°C and 7.0°C i n the upper and lower reaches of the i n l e t respectively) at a depth of about 250 feet. This mLnimum temperature layer revealed i t s e l f as an axis of a tongue of cold water which extends from the head seaward (Figure 45d), Cruise H I - November 2g, 22., 20., 19TO Typical conditions that existed during this cruise are represented by longitudinal and transverse v e r t i c a l sections of s a l i n i t y and temperature i n Figures 46 and 47• During this cruise the surface s a l i n i t i e s were higher than those on previous occasions.  Along the greater part of the i n l e t the s a l i n i t y  range was within 7,4 %o (20.2 %o and 27,6 %o at the head and mouth respectively) but at Station 6B, f i v e nautical miles from the head the s a l i n i t y was as low as 11,9 $° . As i l l u s t r a t e d i n Figure 47a, c, the s a l i n i t y of the upper layer along the right-hand shore was generally less than that along the other side. In the lower reaches of the i n l e t i t was less by 5.3 -%o during "Low Water" and 0.2 % during the ebb, while i n the upper reaches i t was less by 4.6 %> during the ebb. However, during the flood i t was 2.4 %o more than on the other side. The s a l i n i t y structure below the depth'of 20 feet was similar to that encountered i n the previous cruises.  -79'  SALINITY (%.) •  •  •  NAUTICAL MILES DEPTH  TEMPERATURE CO  Figure 46. Character of water i n Bute Inlet (Cruise Ill-November 28, 2 9 ,  30, 1950) (a) (b) (c) (d)  longitudinal longitudinal longitudinal longitudinal  Note.  section section section section  of s a l i n i t y i n the upper 150 feet, of s a l i n i t y to a depth of 900 feet, of temperature i n the upper 150 feet, of temperature to a depth of 900 feet,  Bathythermograph casts (840 feet) made at each station.  -80-  STATIONS Wist  Figure 47.  W  3  E  Eoit  West  W  3  E  East  Character of water i n Bute Inlet (Cruise Ill-November 28, 29, 30,  1950)  (a) transverse Station 3, (b) transverse Station 3, (c) transverse Station 5, (d) transverse Station 5.  section of s a l i n i t y i n the upper 150 feet at section of temperature i n the upper 150 feet at section of s a l i n i t y i n the upper 150 feet at section of temperature i n the upper 150 feet at  Note. Bathythermograph casts (840 feet) made at each station.  -81-  By this time a reversal i n the temperature gradients i n the upper 100 feet has taken place and a l l along the inlet.the positive gradients of previous cruises were now being replaced by the negative gradients which are characteristic of winter conditions, (See Figure 13 for t y p i c a l v e r t i c a l temperature profiles of winter.)  The minimum temper-  ature layer which has increased i n temperature since the preceding cruise now occurred at a depth of about 320 feet, which i s 70 feet deeper than i t was during the l a s t cruise.  Eetween t h i s layer and the surface  existed a body of warm water i n which two c e l l s with maximum temperatures of 7.8°C and 8 0°C occurred at a depth of 200 feet. o  A tongue-  l i k e body of warm water characterized by the 8 0°C isotherm also occurred 0  at a depth of about 600 feet at the mouth and penetrated several miles up the i n l e t and f i n a l l y terminated i t s e l f at a depth of about 800 feet at Station 3B (Figure 46d). Cruise IV - January JJ,, 1251 As shown i n Figures 48a and 48b the general s a l i n i t y pattern of both the surface and subsurface waters was similar to that found i n November. At the sea surface the s a l i n i t i e s were 18.4 %° and 27 7 %o e  at the head and mouth respectively, values which were almost the same as those of the preceding cruise. Again, the surface temperature increased progressively downi n l e t (3.3°C at the head to 6.5°C at the mouth).  In the intermediate  depth the minimum temperature layer, which was clearly recognizable  -82-  STATIONS 1  2  3  4  SALINITY  3  (%.)  6  7  8  „  „  STATIONS u  NAUTICAL  1  MILES  2  3  4  5  6  7  8  TEMPERATURE CO  DEPTH  Figure 48.  Character of water i n Bute Inlet (Cruise IV-January 11, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 450 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 450 feet. Note. Bathythermograph casts (450 feet) made at each station.  -83-  during the previous cruises, was less evident at t h i s time.  In Figure  48d i s shown a body o f warm water with a temperature of 8.G°C occurring at a depth of 450 feet. Cruise, £ - February 20, 2 1 , 22, 1251 The surface s a l i n i t y was almost uniform along the length of the i n l e t (26.6 fdo and 27.7 %o at the head and mouth respectively). But, as noted during Cruise I I I , water of r e l a t i v e l y low s a l i n i t y (21.3 °U ) existed at Station 6B. Comparison with conditions encountered during Cruise IV indicates s i m i l a r i t y i n the s a l i n i t y distribution (compare Figures 48a and 48b with Figures 49a and 49b).  Typical transverse ver-  t i c a l sections of s a l i n i t y (shallow) are shown i n Figures 50a and 50c. Note that the surface water along the right-hand shore was less saline than that along the other shore, both during the flood and ebb. In general, the temperature above the depth of 100 feet was about 1C° colder than that occurring at corresponding depths i n January (Figures 49c and 49d).  A patch of cold water (4.3°C) occurred at Station  6B where the water was less saline also. As i l l u s t r a t e d i n Figure 49d, the body of warm water with a maximum temperature of 8.3°C i n the lower reaches of the i n l e t was s t i l l evident i n the intermediate depths.  Cruise 51-2-1 - May  1251  Conditions occurring during t h i s period are shown by typical longitudinal and transverse v e r t i c a l sections of s a l i n i t y and temperature  ••84"  Figure 49. Character of water i n Bute Inlet (Cruise V-February 20, 21, 22, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,650 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature t o a depth of 1,650 feet. Note. Bathythermograph casts (450 feet) made at each station.  -85-  STATION 5  Figure 50. Character of water i n Bute Inlet (Cruise V-February 20, 21, 22,  1951)  (a) transverse Station 3, (b) transverse Station 3, (c) transverse Station 5, (d) transverse Station 5.  section of s a l i n i t y i n the upper 150 feet at section of temperature i n the upper 150 feet at section of s a l i n i t y i n the upper 150 feet at section of temperature i n the upper 150 feet at  Mote. Bathythermograph casts (450 feet) made at each station.  -Sp-  i n Figure 51. As i l l u s t r a t e d i n the t y p i c a l s a l i n i t y section (Figure 51a), surface d i l u t i o n was evident throughout the i n l e t .  The surface  s a l i n i t y increased progressively from 0.4 i*> at the head to 2 0 l %o o  at the mouth. The salinity-depth p r o f i l e s were similar to those found i n August and September 1950, and the upper and lower l i m i t s of the mixing layer occurred on the average at about 10 feet and 24 feet respectively.  During t h i s cruise, the mixing depth varied by about  t 3 feet, but during a short time i n t e r v a l ; f o r example, from May 17 to May 19, i t was almost constant along the length of the i n l e t except at the mouth where i t was shallower and at Station 6 where i t was deeper. As shown i n Figure 52a, water of lower s a l i n i t y was present along the right-hand shore. The d i s t r i b u t i o n of s a l i n i t y was comparable to that of September 1950. The surface temperature over the entire i n l e t had increased considerably (by about 6C°) since February, but t h i s effect became less evident with depth and at a depth of 120 feet the water was colder by 0.5°C than i t was i n February. A minimum temperature layer again appeared as a tongue of cold water which can be followed to Station 2B where i t became less evident (see Figure 51d).  Another tongue of warm water  which protruded w e l l into mid-inlet also occurred i n the deeper depths. Cruise i l - 2 - U - August 4., 125J. Here again, as i n Cruise 51-2-1, the surface water was almost  -87-  Figure 51,  Character of water i n Bute Inlet (Cruise 51-2-I-May 17-26, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,800 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,800 feet. Note. Bathythermograph casts (840 feet) made at each station.  —88'"  STATIONS  STATION 4  ^Figure 5 2 ,  Character of water i n Bute Inlet (Cruise 51-2-I-May 17-26, 1951) (a) transverse section of salinity i n the upper 150 feet at Station 4, (b) transverse section of temperature i n the upper 150 feet at Station 4. Note:  Bathythermograph casts (450 feet) made at each station.  -89-  fresh (2.2%,  at Station 6) and as shown i n Figure 53a, the salinity  structure was quite similar to that encountered during the preceding cruise. The surface temperature had increased since May (Compare Figure 51c with Figure 52c), and at this time a surface temperature as high as 16.0°C was recorded.  The minimum temperature layer which had increased  in temperature by 0„5°C since May was at a depth of 200 feet and was 70 feet lower than i t was i n May. Cruise i l - i - October 23., 2L, 1251 In Figures 54 and 55 are presented the longitudinal and transverse vertical sections of salinity and temperature which typify the conditions that existed during this cruise. As illustrated i n Figure 54a, the surface water showed l i t t l e fresh water to be present.  The distribution of salinity i n the inter-  mediate and greater depths was the same as that of Cruise 51-2.  Again,  as was the case i n the previous transverse sections, the water on the right-hand shore was less saline as shown i n Figure 55a. A drop of about 6C° i n the surface temperature had occurred since August 1951, and consequently a layer of warm water characterized by a tongue-like distribution and having a maximum of 8.8°C at the mouth and 8.5°C at the head occurred at intermediate depth (Figure 54c). Below this, a tongue of cold water (minimum temperature layer) was evident, below which another large tongue of warm water (8.0°C) occurred (Figure 54d).  -90-  STATIONS  STATIONS  0  SALINITY (%.)'  8  10  N'AU'TIOAL M'ILES  TEMPERATURE CO  Figure 53. Character of water i n Bute Inlet (Cruise 51-2-II-August 4, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,250 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,250 feet. Note. Bathythermograph casts (840 feet) made at each station.  -91-  Figure 54.  Character of water i n Bute Inlet (Cruise 51-3-October 25, 26, 1951) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,650 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,650 feet. Note. Bathythermograph casts (840 feet) made at each station.  -92-  Eaal  SALINITY ( • * , . )  NAUTICAL MILES  DEPTH 0 -T-i FEET  Wctl  W ^  •(b)  TEMPERATURE CO  NAUTICAL MILES  STATION 3 Figure 55.  Character of water i n Bute Inlet (Cruise 51-3-October 25, 26, 1951) (a) transverse section of s a l i n i t y i n the upper 150 feet at Station 3, (b) transverse section of temperature i n the upper 150 feet at Station 3. Note. Bathythermograph casts (840 feet) made at each station  -93-  PrhAse 52-1 - March 20, 1252 Conditions that existed during t h i s cruise are described by the longitudinal v e r t i c a l sections of s a l i n i t y and temperature i n Figure 56. There was, at t h i s time, a marked change i n the s a l i n i t y distribution above the depth of 120 feet from that of the previous cruises, as seen by comparing Figure 56a with Figure 54a for example. The surface s a l i n i t y at the head was 13.0 %o , at Station 6B i t was 27.3 %» , and at Station 6 i t was 28.6 %o indicating a r e l a t i v e l y large horizontal s a l i n i t y gradient. In Figure 23 are drawn the t y p i c a l salinity-depth curves of t h i s period. Note that at Station 3 and Station 5, less saline water than the surface i s present at depths of 12 feet and 24 feet respectively.  The s a l i n i t y  structure below the depth of 150 feet was, however, similar to that of the preceding cruise (51-2). Figure 56c shows the shallow longitudinal v e r t i c a l section of temperature.  I t i s evident from t h i s that the temperature pattern was  quite dissimilar and more complicated than that observed during a l l previous cruises. A tongue of cold water with minimum ranging from 5.0°C at the head to 6.5°C in-the lower reaches again reappeared i n the intermediate depths, below which a body of warm water (maximum 8.3°C) was present. Cruise 5Z-Z - May 22, 20, 2L>  1, 8.'1952  The distribution of s a l i n i t y and temperature was similar to that of the corresponding period of the preceding year (compare Figure 51  -94-  .  STATIONS  Figure 56. Character of water i n Bute Inlet (Cruise 52-1-March 30, 1952) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,800 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,800 feet. Note. Bathythermograph casts (840 feet) made at each station  -95-  with Figure 57)• The essential facts can be extracted from the above figures. Cruise 32-1 - August 9.-12, 1252 Conditions typifying t h i s period are shown i n the longitudinal v e r t i c a l sections of s a l i n i t y and temperature (Figure 58). The d i s t r i b u t i o n of s a l i n i t y and temperature i s again similar to that of the same period of the previous years.  Distribution o£ Oxygen In Figure 59a the distribution of dissolved oxygen i n a longitudinal section along the i n l e t f o r Cruise I I (September 1950) i s shown. The surface water was supersaturated with dissolved oxygen and possessed a maximum of 110$.  The oxygen values dropped rather  rapidly t o about 70$ at a depth of 60 feet and the.n decreased to 60$ at depths of 130, 300, and 400 feet at the mouth, mid-inlet, and head respectively. A c e l l of r e l a t i v e l y high oxygen with maximum of 73$ occurred at a depth of about 250 feet near the minimum temperature layer i n the upper reaches of the i n l e t . During Cruise I (August 1950) supersaturation of surface water was also evident (125$).  The maximum of 73$ at intermediate depth  occurred at the same position as i n Cruise I I .  -96-  STATIONS T 2  3  4  5  6  7  8  DEPTH  STATIONS 1 2  3  4  5  6  7  8  FEET  SALINITY  (%•)  o 10 i i i i i I NAUTICAL MILES  TEMPERATURE C O  Figure 57. Character of water i n Bute Inlet (Cruise 52-2-May 29, 30, 31, ' June 7, 8, 1952) (a) longitudinal section of s a l i n i t y i n the upper 150 feet, (b) longitudinal section of s a l i n i t y to a depth of 1,500 feet, (c) longitudinal section of temperature i n the upper 150 feet, (d) longitudinal section of temperature to a depth of 1,500 feet. Note. Bathythermograph casts (840 feet) made at each station.  -97-  Figure 58,  Character of water i n Bute Inlet (Cruise 52-3-August 9-13,  1952) (a) (b) (c) (d)  longitudinal longitudinal longitudinal longitudinal  section section section section  of s a l i n i t y i n the upper 150 feet, of s a l i n i t y to a depth of 1,800 feet, of temperature i n the upper 150 feet, of temperature to a depth of 1,800 feet.  Note, Bathythermograph casts (840 feet) made at each station.  ,-98-  SATURATION OF OXYGEN STATIONS  (%)  STATIONS  *  »U0  Figure 59a. Distribution of oxygen i n a longitudinal section along the inlet (September 10, 1950). Values from August 2, 1950 are also entered.  2,  l»50  Figure" 59b. '  Distribution of oxygen i n a longitudinal seet i o n along the i n l e t (January 11, 1951).  During Cruise IV (January 1951) no evidence of supersaturation of shrface water was observed; however, the saturations reached 80$ and 95$ i n the lower and upper reaches of the i n l e t respectively. In the intermediate depths the general pattern of the distribution was s i m i l a r to that of Cruise I I (Figure 59b). In Cruise V (February 1951) oxygen values from the greater depths  •99.  were obtained. Near the mouth, the saturation was as high as 140$ but at the middle and upper reaches of the i n l e t saturations were about 95$. In the intermediate depth the distribution was. almost the same as that of Cruise I I (Figure 60a).  Even at a depth of 1,200 feet, no evidence  of water stagnation was seen.  figure 60a.  Distribution of oxygen i n a longitudinal section a l ong the i n l e t (February 1951).  Figure 60b. >  Distribution of oxygen i n a longitudinal section along the i n l e t (May 1951).  In Figure 60b i s i l l u s t r a t e d the d i s t r i b u t i o n of oxygen i n a longitudinal section along the i n l e t which t y p i f i e s the condition during  -100-  Cruise 51-2-1 (May 1951). The maximum value of saturation was about 130$ and supersaturation was evident along the entire length of the inlet.  As seen from Figures 61 and 62, there i s an indication of less  oxygen i n the deeper waters of the i n l e t from that of Cruise V. The d i s t r i b u t i o n of oxygen i n Cruise 51-2-II (August 1951) appeared to be similar to that of Cruise 51-2-1 (Figure 6la)» During Cruise 51-3 (October ,^19 51) oxygen values were available from only two stations, one at mid-inlet and the other at the head. At mid-inlet the surface value was 96$ but at the head i t was 6 l $ . This l a t t e r value was accompanied by values of 66$ at 18 and 30 feet and 58$ at 45 and 60 feet.  Below the depth of 60 feet, the general d i s t r i b u t i o n  was similar to that of Cruise 51-2-II.  SATURATION OF OXYGEN (%) STATIONS 1  2  3  4  5  6  7  NAUTICAL  "Figure 6 l a . Distribution of oxygen i n a longitudinal section along the i n l e t (August 4, 1951 and October 26, 1951)o  MILES  -Figure 6lb»  Distribution of oxygen i n a longitudinal sect i o n along the i n l e t (May 2 9 , 1952).  -101The general distribution during Cruise 52-2  (May, June  was generally similar to that of Cruise 51-2-1 (-^ay 1951)  1952)  but i n the  greater depths i n the upper reaches of the i n l e t the values were lower during this cruise (Figure  6lb).  

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