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Deep water renewal in the Strait of Georgia Doherty, Louis Ford 1987

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DEEP WATER RENEWAL IN THE STRAIT OF GEORGIA by LOUIS FORD DOHERTY B . S c , Dalhousie U n i v e r s i t y , 1982 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF OCEANOGRAPHY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA February 1, 1987 © L o u i s Ford Doherty, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) 1 1 ABSTRACT The seasonal and i n t e r a n n u a l v a r i a t i o n of the water p r o p e r t i e s and deep water renewal i n the S t r a i t of Georgia are examined. Temperature, s a l i n i t y and d i s s o l v e d oxygen data a c q u i r e d over an i n t e n s i v e l y sampled one year p e r i o d are presented to show the timing of renewal p e r i o d s and the v a r i a t i o n i n p r o p e r t i e s across the S t r a i t and with depth. The northward propagation of the renewal s i g n a l and of i t s v a r i a t i o n a c r o s s the S t r a i t of Georgia are d i s c u s s e d . A v o l u m e t r i c a n a l y s i s p r o v i d e s temperature and s a l i n i t y averages of the S t r a i t of Georgia waters and of renewal water dur i n g s e v e r a l stages of each renewal p e r i o d . Estimates of the renewal volume are c a l c u l a t e d using a heat and s a l t budget method. Data c o l l e c t e d i n the c e n t r a l p a r t of the S t r a i t over s e v e r a l decades are presented to show the i n t e r a n n u a l v a r i a t i o n i n water p r o p e r t i e s . C o r r e l a t i o n c o e f f i c i e n t s r e l a t i n g the wintertime a i r temperatures to the deep water p r o p e r t i e s some time l a t e r i n the S t r a i t are g i v e n . i i i TABLE OF CONTENTS Ab s t r a c t i i L i s t of t a b l e s v L i s t of f i g u r e s v i Acknowledgements x 1 . I n t r o d u c t i o n 1 1.1 General d e s c r i p t i o n of the study 1 1.2 P h y s i c a l d e s c r i p t i o n of the study area 2 1.3 H i s t o r i c a l review - general 5 1.4 Deep water renewal 5 2. Data d e s c r i p t i o n and r e d u c t i o n 10 2.1 Hydrographic data 10 2.1.1 Seasonal c y c l e 10 2 .1 .2 Interannual v a r i a t i o n 13 2.2 Bathymetry 14 3. Deep water renewal - seasonal v a r i a t i o n 15 3.1 A q u a l i t a t i v e p i c t u r e 15 3 . 2 T-S a n a l y s i s 19 3.3 Deep water p e n e t r a t i o n 27 3.3.1 Temperature 28 3.3.2 S a l i n i t y 35 3.3.3 D i s s o l v e d oxygen 39 3.4 The d e n s i t y s t r u c t u r e 44 3.5 V a r i a t i o n of the renewal with depth 47 3.6 L a t e r a l v a r i a b i l i t y 51 iv 4. V o l u m e t r i c , heat and s a l t a n a l y s e s 56 4.1 V o l u m e t r i c a n a l y s i s 56 4.1.1 S u r f a c e t o bottom 58 4.1.2 The s u r f a c e l a y e r (0 - 80 m) 60 4.1.3 The i n t e r m e d i a t e l a y e r (80 - 200 m) 61 4.1.4 The deep l a y e r - 200 m t o the bottom 66 4.2 Heat and s a l t budget 75 5. I n t e r a n n u a l v a r i a t i o n 85 5.1 P h y s i c a l p r o p e r t i e s 86 5.2 A i r - s e a e f f e c t s 93 6. Summary and c o n c l u s i o n 101 R e f e r e n c e s 190 V LIST OF TABLES 1.1 P h y s i c a l parameters of the S t r a i t of Georgia 4 2.1 C r u i s e dates - December 1 967 to December 1968 11 3.1 Time of occurrence of the minimum and maximum temperatures at l o c a t i o n s i n the S t r a i t of Georgia 22 3.2 C e n t r a l s e c t i o n v e l o c i t i e s from the temperature s i g n a l 35 3.3 C e n t r a l s e c t i o n v e l o c i t i e s from the s a l i n i t y s i g n a l 39 3.4 C e n t r a l s e c t i o n v e l o c i t i e s from the d i s s o l v e d oxygen s i g n a l 43 3.5 V e l o c i t i e s from the temperature and s a l i n i t y s i g n a l s d u r i n g the winter renewal at the 100 m l e v e l 54 4.1.1 S t r a i t of Georgia 61 4.1.2 Intermediate l a y e r , S t r a i t of Georgia 64 4.1.3 Deep l a y e r , c e n t r a l and southern S t r a i t of Georgia 68 4.1.4 Deep l a y e r , northern S t r a i t of Georgia 70 4.2.1 Renewal volume - intermediate l a y e r 80 4.2.2 Renewal volume - c e n t r a l b a s i n deep l a y e r 82 4.2.3 Renewal volume - northern b a s i n deep l a y e r 84 5.1 I n t e r a n n u a l data 87 5.1.1 Y e a r l y temperature and s a l i n i t y minima 89 5.1.2 Temperature and s a l i n i t y maxima 90 5.1.3 Deep water p e n e t r a t i o n 92 vi LIST OF FIGURES 1.1 Southern c o a s t of B r i t i s h Columbia 105 1.2 The S t r a i t of G e o r g i a , a d j a c e n t waters and l o c a l p l a c e names 106 1.3 Weekly r u n o f f i n t o the S t r a i t of G e o r g i a d r a i n a g e a r e a 107 1.4 C r o s s - s e c t i o n s of c h a n n e l s of the n o r t h e r n and s o u t h e r n approaches t o the S t r a i t of G e o r g i a 108 1.5 Temperature, s a l i n i t y and d i s s o l v e d oxygen c o n c e n t r a t i o n i n the c e n t r a l S t r a i t of G e o r g i a ... 109 2.1 S t r a i t of G e o r g i a and Juan de Fuca S t r a i t w i t h h y d r o g r a p h i c s t a t i o n s o c c u p i e d from December* 1967 to December 1968 110 2.2 S t r a i t of G e o r g i a showing the r e g i o n i n which the l o n g range d a t a i s l o c a t e d 111 2.3 P a r t of the c e n t r a l S t r a i t of G e o r g i a showing the l o c a t i o n s of s t a t i o n s sampled t o p r o v i d e the l o n g range d a t a • 112 2.4 The average depth f o r each 4X4 km square f o r the g r i d used i n the v o l u m e t r i c a n a l y s i s 113 3.1 Temperature d i s t r i b u t i o n i n the S t r a i t of G e o r g i a and Juan de Fuca S t r a i t , December 1967 t o December 1 968 114 3.2 S a l i n i t y d i s t r i b u t i o n i n the S t r a i t of G e o r g i a and Juan de Fuca S t r a i t , December 1967 t o December 1968 120 3.3 D e n s i t y d i s t r i b u t i o n i n the S t r a i t of G e o r g i a and Juan de Fuca S t r a i t , December 1967 t o December 1968 123 3.4 D i s s o l v e d oxygen d i s t r i b u t i o n i n the S t r a i t of G e o r g i a and Juan de Fuca S t r a i t , December 1967 t o December 1968 127 3.5 T-S diagrams a t a depth of 50 m i n the S t r a i t of G e o r g i a from December 1967 t o January 1969 133 3.6 T-S diagrams a t a depth of 100 m i n the S t r a i t of G e o r g i a from December 1967 t o January 1969 134 v i i 3.7 T-S diagrams a t a depth of 150 m i n the S t r a i t of G e o r g i a from December 1967 t o January 1969 135 3.8 T-S diagrams a t a depth of 200 m i n the S t r a i t of G e o r g i a from December 1967 t o January 1969 136 3.9 T-S diagrams a t a depth of 250 m i n the S t r a i t of G e o r g i a from December 1967 t o January 1969 137 3.10 T-S diagrams a t a depth of 300 and 350 m i n the S t r a i t of G e o r g i a from December 1967 t o J a n u a r y 1969 138 3.11 Temperature d i s t r i b u t i o n a t s e v e r a l l e v e l s from the s u r f a c e t o 300 m 139 3.12 S a l i n i t y d i s t r i b u t i o n a t s e v e r a l l e v e l s from the s u r f a c e t o 300 m 143 3.13 D i s s o l v e d oxygen d i s t r i b u t i o n a t s e v e r a l l e v e l s from the s u r f a c e t o 300 m 147 3.14 D e n s i t y d i s t r i b u t i o n a t s e v e r a l l e v e l s from the s u r f a c e t o 300 m 151 3.15 ^ V e r t i c a l d i s t r i b u t i o n of the temperature and the ^ s a l i n i t y a t s t a t i o n 42 155 3.16 V e r t i c a l d i s t r i b u t i o n of the temperature and the s a l i n i t y a t s t a t i o n 27 156 3.17 H o r i z o n t a l d i s t r i b u t i o n of t h e temperature and s a l i n i t y i n January 1968 157 3.18 H o r i z o n t a l d i s t r i b u t i o n of the temperature and s a l i n i t y i n A p r i l 1968 159 3 . 1 9 H o r i z o n t a l d i s t r i b u t i o n of t h e temperature and s a l i n i t y i n l a t e J u l y 1968 161 3.20 H o r i z o n t a l d i s t r i b u t i o n of the temperature and s a l i n i t y i n December 1968 163 3.21 Temperature d i s t r i b u t i o n a t a depth of 100 m a l o n g the e a s t e r n and western s i d e s of the S t r a i t of G e o r g i a 165 3.22 S a l i n i t y d i s t r i b u t i o n a t a depth of 100 m a l o n g the e a s t e r n and western s i d e s of the S t r a i t of G e o r g i a 166 vi i i 3.23 Temperature d i s t r i b u t i o n at a depth of 200 m along the e a s t e r n and western s i d e s of the S t r a i t of Georgia 167 3.24 S a l i n i t y d i s t r i b u t i o n at a depth of 200 m along the e a s t e r n and western s i d e s of the S t r a i t of Georgia 168 4.1 Volumetric t a b l e s f o r the S t r a i t of Georgia 169 4.2 Volumetric t a b l e s f o r the s u r f a c e l a y e r of the S t r a i t of Georgia 172 4.3 Volumetric t a b l e s f o r the int e r m e d i a t e l a y e r of the S t r a i t of Georgia 173 4.4 Volumetric t a b l e s f o r the deep l a y e r i n the c e n t r a l b a s i n of the S t r a i t of Georgia 176 4.5 Volumetric t a b l e s f o r the deep l a y e r i n the northern basin of the S t r a i t of Georgia 178 4.6 Box model of the S t r a i t of Georgia 180 4.7 V e r t i c a l d i s t r i b u t i o n of the s a l i n i t y at s t a t i o n 48 181 5.1 Interannual v a r i a t i o n of the temperature i n the c e n t r a l S t r a i t of Georgia 182 5.2 Interannual v a r i a t i o n of the s a l i n i t y i n the c e n t r a l S t r a i t of Georgia 183 5.3 Monthly averaged temperature i n the c e n t r a l S t r a i t of Georgia 184 5.4 Monthly averaged s a l i n i t y i n the c e n t r a l S t r a i t of Georgia 185 5.5 C o r r e l a t i o n c o e f f i c i e n t s f o r the mean monthly wintertime a i r temperatures and the temperature 0 to 10 months l a t e r i n the S t r a i t of Georgia 186 5.6 C o r r e l a t i o n c o e f f i c i e n t s f o r the mean monthly wintertime a i r temperatures and the s a l i n i t y 0 to 10 months l a t e r i n the S t r a i t of Georgia 187 5.7 C o r r e l a t i o n c o e f f i c i e n t s f o r the mean monthly wintertime a i r temperatures and the change i n temperature 0 to 10 months l a t e r i n the S t r a i t of Georgia 188 ix 5 . 8 C o r r e l a t i o n c o e f f i c i e n t s f o r t h e mean m o n t h l y w i n t e r t i m e a i r t e m p e r a t u r e s a n d t h e c h a n g e i n s a l i n i t y 0 t o 10 m o n t h s l a t e r i n t h e S t r a i t o f G e o r g i a 189 X ACKNOWLEDGEMENTS I would e s p e c i a l l y l i k e to thank my s u p e r v i s o r , Dr. Paul LeBlond, f o r h i s advice and endless p a t i e n c e d u r i n g the course of my t h e s i s work. He a l s o p r o v i d e d much needed f i n a n c i a l support. I am a l s o g r a t e f u l to Dr. S. Pond, Dr. A. Lewis and Dr. E. Carmack fo r reading the manuscript. I would a l s o l i k e to acknowledge f i n a n c i a l support from the U n i v e r s i t y of B r i t i s h Columbia, the Department of P h y s i c s and the Department of E l e c t r i c a l E n g i n e e r i n g at U.B.C. and S h e l l Canada Resources L i m i t e d . F i n a l l y , I would l i k e to thank my wife P a t r i c i a , f o r her un f l a g g i n g support and pa t i e n c e over the l a s t three y e a r s . 1. INTRODUCTION 1.1 GENERAL DESCRIPTION OF THE STUDY The S t r a i t of Georgia, l y i n g between the B r i t i s h Columbia mainland and Vancouver I s l a n d , has been the s u b j e c t of many s t u d i e s and r e p o r t s by b i o l o g i c a l , chemical and p h y s i c a l oceanographers over the past s e v e r a l decades. Perhaps because of the very a c t i v e s u r f a c e waters and sometimes dramatic s u r f a c e f e a t u r e s , p h y s i c a l oceanographers at l e a s t , have conc e n t r a t e d t h e i r a t t e n t i o n on the upper l a y e r . A few s t u d i e s have i n c l u d e d the e n t i r e water column ( T u l l y and Dodimead, 1951; Waldichuk, 1957; Samuels, 1979). T h i s study i s motivated by the lack of work done on the deep water of the S t r a i t of Georgia and by the e x i s t e n c e of an e x t e n s i v e data set (Crean and Ages, 1971) c o l l e c t e d s i n c e the previous s t u d i e s done in the 1950's. The primary aim i s to provide a thorough s y n o p t i c d e s c r i p t i o n of the water temperature, s a l i n i t y and d i s s o l v e d oxygen content at depth over the whole S t r a i t and over a twelve month p e r i o d . T h i s d e s c r i p t i o n i s s u f f i c i e n t l y d e t a i l e d i n time and space to provide i n f o r m a t i o n about deep water replacement in the S t r a i t . A secondary goal i s to d e s c r i b e the i n t e r a n n u a l c h a r a c t e r i s t i c s of the water in the deepest p a r t of the S t r a i t . Data spanning a 37 year p e r i o d and c o l l e c t e d i n an area over 400 m deep north of Nanaimo were used. Aside from d e s c r i b i n g the i n t e r a n n u a l v a r i a t i o n these data are u s e f u l 1 2 when extending the p i c t u r e obtained from the more i n t e n s i v e l y s t u d i e d one year p e r i o d mentioned above to other y e a r s . The f o l l o w i n g pages d e s c r i b e the study area and p r e v i o u s work done on the S t r a i t of Georgia by p h y s i c a l oceanographers and o t h e r s . 1.2 PHYSICAL DESCRIPTION OF THE STUDY AREA The S t r a i t of Georgia i s bounded to the north-east and south-west by the North American mainland and Vancouver I s l a n d ( F i g . 1.1). To the north Johnstone S t r a i t and Cardero Channel connect the S t r a i t of Georgia to the P a c i f i c Ocean through a maze of i s l a n d s extending over 200 km. These passages are t y p i c a l l y a few k i l o m e t r e s wide or l e s s and 200 to 300 meters deep, although some narrows r e s t r i c t the flow of water even f u r t h e r . Haro and Rosario S t r a i t s to the south are the main connecting channels to the open ocean v i a Juan de Fuca S t r a i t . A map of the S t r a i t of Georgia and Juan de Fuca S t r a i t i s given i n F i g . 1.2 and i n c l u d e s the bathymetry and l o c a l p l a c e names. The p h y s i c a l oceanography of the S t r a i t of Georgia i s dominated by the f r e s h water input of the F r a s e r R i v e r . F i g . 1.3 shows weekly val u e s of the F r a s e r River f l o w r a t e averaged over a 28 year p e r i o d along with the a s s o c i a t e d standard d e v i a t i o n s . The d i s c h a r g e peaks i n June at roughly 10,000 to 16,000 m3/s with l a r g e outflows (over 8,000 m 3/s) c o n t i n u i n g from mid-May to mid-August. T o t a l y e a r l y outflow 3 i s about 120 km3, four times the combined run o f f from a l l other r i v e r s and streams e n t e r i n g the S t r a i t (Waldichuk, 1957). T o t a l d i r e c t p r e c i p i t a t i o n i s about 10 km 3/year about twice the t o t a l e v a p o r a t i o n . Other u s e f u l s t a t i s t i c s which d e s c r i b e the S t r a i t , t i d e s and f r e s h water input are given below i n Table 1.1. The i n f l u e n c e of the many i n l e t s b o r d e r i n g the S t r a i t of Georgia have been ignored i n t h i s study. T h e i r combined s u r f a c e area and volume are much smaller than the area and volume of the S t r a i t . T h e i r presence does not s e r i o u s l y a f f e c t the water c h a r a c t e r i s t i c s i n the S t r a i t (Waldichuk (1957)). T h e i r main c o n t r i b u t i o n i s to the s u r f a c e outflow of b r a c k i s h water i n t o the S t r a i t of Georgia but the net f r e s h water input from the i n l e t s i s s t i l l much l e s s than the F r a s e r River d i s c h a r g e . The predominant wind p a t t e r n s o f f the B r i t i s h Columbia coast are the r e s u l t of the semi-permanent high and low pressure c e l l s i n the e a s t e r n P a c i f i c Ocean and south of the A l e u t i a n I s l a n d s r e s p e c t i v e l y . The high pressure c e l l i n t e n s i f i e s i n the summer cau s i n g northwest winds along the North American coast and u p w e l l i n g along the B r i t i s h Columbia c o a s t . In winter the h i g h pressure c e l l i s pushed southward and the A l e u t i a n low dominates the area causing southeast winds along the c o a s t . The winds i n the S t r a i t of Georgia f o l l o w t h i s g eneral p a t t e r n but are a l s o i n f l u e n c e d by the l o c a l topography (Thomson, 1981). As w e l l , small s c a l e e f f e c t s such as the sea breeze i n the summertime and 4 Table 1.1 P h y s i c a l Parameters of the S t r a i t of Georgia Length 220 km Average width 33 km Surface area 6900 km2 I s l a n d area 480 km2 Mean depth 156 m Mean volume 1025 km3 Mean t i d a l range 3.6 m Mean t i d a l prism 23.1 km3 T o t a l r u n o f f per year 180 km3 t T o t a l d i r e c t p r e c i p i t a t i o n per year 9.6 km3 T o t a l e v a p o r a t i o n per year 4.2 km3 S t a t i s t i c s from Waldichuk, 1957 t from LeBlond et a l . (1983) c o l d a i r outflow from the B r i t i s h Columbia i n t e r i o r along c o a s t a l i n l e t s i n the wintertime (Squamish type winds) may dominate i n some areas f o r a p e r i o d of time. Along with the f r e s h water input, the t i d e s i n the S t r a i t of Georgia/Juan de Fuca S t r a i t system p l a y a c r u c i a l r o l e i n the oceanography of the deep water of the S t r a i t of Geo r g i a . T i d a l c u r r e n t s i n Juan de Fuca S t r a i t and p a r t i c u l a r l y i n the channels through the Gulf and San Juan i s l a n d s mix the f r e s h s u r f a c e waters with the s a l t i e r deep water. Water v e l o c i t i e s over most of the S t r a i t are r e l a t i v e l y small at 20 cm/s or l e s s (Samuels, 1979). In the c o n s t r i c t e d passages between the S t r a i t s of Georgia and Juan de Fuca, v e l o c i t i e s can reach 200 cm/s, high enough to mix the e n t i r e water column to homogeneity (Crean, 1976). 5 1.3 HISTORICAL REVIEW - GENERAL The f i r s t comprehensive work p u b l i s h e d on the S t r a i t of Georgia was that of Hutchinson and Lucas (1931). They reviewed the e f f e c t of the F r a s e r River r u n o f f , the d i s t r i b u t i o n of water p r o p e r t i e s and t h e i r r e l a t i o n to plankton p r o d u c t i o n and salmon m i g r a t i o n . A l a t e r r e p o r t by T u l l y and Dodimead (1957) r e l a t e s b i o l o g i c a l a c t i v i t y and n u t r i e n t l e v e l s to p h y s i c a l processes i n the S t r a i t . Waldichuk (1957) c o n c e n t r a t e d on the p h y s i c a l oceanography of the S t r a i t with a review of the g e o g r a p h i c a l i n f l u e n c e s , water mass c h a r a c t e r i s t i c s , c i r c u l a t i o n , wind e f f e c t s , mixing, f r e s h water input and the heat budget. The mechanisms f o r deep water renewal which he suggested, remain u s e f u l conceptual models to t h i s day. More r e c e n t l y , a book by Thomson (1981) g i v e s a general d e s c r i p t i o n of the p h y s i c a l oceanography of the B r i t i s h Columbia coast i n c l u d i n g the S t r a i t of Georgia. F i n a l l y a paper by LeBlond (1983) o u l i n e s the dynamically i n t e r e s t i n g f e a t u r e s which occur i n the S t r a i t such as the F r a s e r River plume, deep water renewal and t i d e s ; i t a l s o i n c l u d e s an ex t e n s i v e b i b l i o g r a p h y of work p u b l i s h e d s i n c e 1970. 1.4 DEEP WATER RENEWAL Waldichuk (1957) proposed a mechanism f o r deep water renewal d r i v e n by the F r a s e r R i v e r d i s c h a r g e , m e t e o r o l o g i c a l f a c t o r s and mixing i n the southern S t r a i t of Georgia. In e a r l y winter, the reduced f r e s h water input, c o l d s u r f a c e 6 waters and mixing of the S t r a i t of Georgia waters with Juan de Fuca S t r a i t waters i n the c o n s t r i c t e d passages among the San Juan and Gulf i s l a n d s , allow the formation of water s u f f i c i e n t l y dense (cold) to s i n k along or near the bottom as i t t r a v e l s northward up the S t r a i t . I t was a l s o suggested that s u r f a c e c o o l i n g i n the northern S t r a i t i n winter may cause mixing of the water column to i n t e r m e d i a t e depths, at l e a s t d u r i n g p a r t i c u l a r l y c o l d w i n t e r s . During l a t e summer and autumn, enhanced e s t u a r i n e c i r c u l a t i o n f o l l o w i n g the p e r i o d s of peak F r a s e r R i v e r d i s c h a r g e i n May and June, and the appearance of above-average s a l i n i t y water i n Juan de Fuca S t r a i t cause an i n t r u s i o n i n t o intermediate depths of dense, s a l t y water. D i r e c t evidence of an e s t u a r i n e type c i r c u l a t i o n was obtained by Gross, Morse and Barnes (1969) using bottom d r i f t e r s r e l e a s e d o f f the mouth of the Columbia R i v e r and northward on the c o n t i n e n t a l s h e l f to Vancouver I s l a n d . D r i f t e r s were recovered along the shores of Juan de Fuca S t r a i t and the S t r a i t of Georgia i n d i c a t i n g the presence of a deep r e t u r n flow. A shallow outflow and deep r e t u r n flow were seen by Schumacher et a l . (1978) i n c u r r e n t meter data on a l i n e from Point Roberts to Mayne I s l a n d . Currents of 10 to 20 cm/s were seen i n the upper l a y e r above 30 meters and i n the lower l a y e r at 100 to 150 meters. T h e i r r e s u l t s , i n c l u d i n g c u r r e n t meter and STD data, showed two-layered flow through Haro S t r a i t and a n e a r l y uniform v e l o c i t y p r o f i l e i n Rosario 7 S t r a i t d u r i n g the o b s e r v a t i o n p e r i o d . T h i s suggests that R o s a r i o S t r a i t i s too shallow to allow s i g n i f i c a n t entry of dense, s a l t y Juan de Fuca water (see F i g . 1.4). Although the e s t u a r i n e c i r c u l a t i o n may be r e l a t i v e l y s t r o n g between the F r a s e r R i v er mouth and the southern passages, the s i t u a t i o n i s somewhat d i f f e r e n t to the north-west i n the S t r a i t of Georgia. Chang, Pond and Tabata (1976) found no s i g n i f i c a n t coherence, except at t i d a l f r e q u e n c i e s , among c u r r e n t meter records from depths of 3, 50, 140 and 200 meters along a l i n e running southwestward from Vancouver. S i m i l a r measurements over a three month p e r i o d made by Yao et a l . (1982) using a more c l o s e l y spaced a r r a y of three cyclesondes showed s i g n i f i c a n t coherence between the north-south c u r r e n t components at l o c a t i o n s 4.1 km a p a r t . However, the mean flow was a c r o s s the S t r a i t . The mechanisms a f f e c t i n g the t r a n s p o r t of water up the S t r a i t are c l e a r l y more complicated than a simple model of e s t u a r i n e c i r c u l a t i o n would i n d i c a t e . F u r t h e r s t u d i e s of flow dynamics i n the c e n t r a l S t r a i t by Stacey et a l (1986, 1987 a) have shown the importance of v e r t i c a l d i f f u s i o n and v o r t i c i t y a d v e c t i o n , with p o s s i b l e h i n t s of dynamic i n s t a b i l i t y . In a review of the annual and longer term v a r i a t i o n of deep water p r o p e r t i e s i n southern B r i t i s h Columbia i n l e t s and e s t u a r i e s , P i c k a r d (1975) presented an e i g h t year time s e r i e s of temperature, s a l i n i t y and d i s s o l v e d oxygen from a l o c a t i o n i n the deepest p a r t of the S t r a i t ( F i g . 1.5). The 8 data show a c l e a r seasonal s i g n a l with temperature and s a l i n i t y reaching a maximum i n the l a s t three months of each year. The same p r o p e r t i e s reach a minimum in the s p r i n g at the 100 m l e v e l and somewhat l a t e r (0 to 4 months) at the 300 m l e v e l . The data set used e x t e n s i v e l y i n t h i s study to observe the seasonal v a r i a t i o n of the p r o p e r t i e s of the deep water was used by Samuels (1979) to develop a mixing budget f o r the S t r a i t . The data, c o l l e c t e d over the p e r i o d December 1967 to December 1968, showed two major i n t r u s i o n s i n t o the deep water o c c u r i n g from February to May and from May to November. Both i n t r u s i o n s reached the bottom and no i n t e r m e d i a t e water was formed i n the summertime, c o n t r a r y to the p i c t u r e d e s c r i b e d by Waldichuk (1957) and o u t l i n e d at the beginning of t h i s s e c t i o n . T h i s study f o l l o w s the method used by Waldichuk and Samuels of i n f e r r i n g water movement from hydrographic data r a t h e r than from d i r e c t measurements of c u r r e n t s . I t examines both the seasonal v a r i a t i o n i n p r o p e r t i e s and renewal, and the i n t e r a n n u a l v a r i a t i o n . A q u a l i t a t i v e d e s c r i p t i o n of the renewal i s given f i r s t and i s followed by a d i s c u s s i o n of the seasonal v a r i a t i o n , i n terms of the temperature and s a l i n i t y at s e v e r a l l o c a t i o n s and depths w i t h i n the S t r a i t . The renewal i s c h a r a c t e r i s e d i n more p r e c i s e terms by the time of occurrence and speed of propagation up the S t r a i t of the new water. The v a r i a t i o n a c r o s s the S t r a i t and with depth, of the p r o p e r t i e s and of 9 the renewal, i s d i s c u s s e d . A v o l u m e t r i c a n a l y s i s i s used to f u r t h e r q u a n t i f y the p r o p e r t i e s of the water and to show the extent and time of renewal p e r i o d s . The volumes of water i n v o l v e d i n the renewal are estimated using a heat and s a l t balance method a p p l i e d to a three l a y e r box model of the S t r a i t . The second part of the study r e l a t e s the r e s u l t s obtained i n the f i r s t p a r t f o r a one year p e r i o d , to the "average" s i t u a t i o n d e s c r i b e d by data c o l l e c t e d over the past 38 y e a r s . I t a l s o e x p l o r e s the r e l a t i o n between the winter a i r temperature over the mixing zone i n the southern passages t o the deep water p r o p e r t i e s some time l a t e r i n the S t r a i t . 2. DATA DESCRIPTION AND REDUCTION 2.1 HYDROGRAPHIC DATA The data used i n t h i s study can be s p l i t i n t o two d i s t i n c t groups. R e s o l u t i o n of the seasonal c y c l e was obt a i n e d from a data set spanning a one year i n t e r v a l with r e l a t i v e l y dense spacing i n time and space and c o v e r i n g the e n t i r e S t r a i t of Georgia. The i n t e r a n n u a l v a r i a t i o n was analysed using a data set which covers s e v e r a l decades and co n c e n t r a t e s on the deepest p a r t of the S t r a i t o n l y . Each data set and i t s source i s d i s c u s s e d below. 2.1.1 SEASONAL CYCLE A t o t a l of up to 79 s t a t i o n s were occupied during each of 12 c r u i s e s from December 1967 to December 1968 (Crean and Ages, 1971). The c r u i s e s were spaced at approximately one month i n t e r v a l s and each r e q u i r e d a p e r i o d of 3 days to occupy a l l the s t a t i o n s . The exact dates f o r each c r u i s e ( i n c l u d i n g t r a v e l time) are given below i n Table 2.1. In the d i s c u s s i o n s which f o l l o w , i t w i l l g e n e r a l l y be more convenient to r e f e r to each c r u i s e by month r a t h e r than by number. U n f o r t u n a t e l y , there were three c r u i s e s i n the two months of J u l y and August. T h e r e f o r e , c r u i s e 7 w i l l be r e f e r r e d to as the " e a r l y J u l y " c r u i s e , 8 as the " l a t e # J u l y " c r u i s e and 9 as the "August" c r u i s e . The 80 s t a t i o n s cover the e n t i r e S t r a i t of Georgia/Juan de Fuca S t r a i t system from Cape F l a t t e r y at the mouth of 10 11 Table 2.1 C r u i s e Dates - December 1967 to December 1968 C r u i s e Dates 1 4 - 8 December 1967 2 8 - 1 2 January 1968 3 1 2 - 1 6 February 1968 4 1 8 - 2 2 March 1968 5 2 2 - 2 6 A p r i l 1968 6 2 6 - 3 1 May 1968 7 1 - 6 J u l y 1968 ( e a r l y J u l y ) 8 28 J u l y - 2 August 1968 ( l a t e J u l y ) 9 2 5 - 2 9 August 1968 10 30 September - 4 October 1968 11 4 - 8 November 1968 12 " 9 - 1 3 December 1968 Juan de Fuca S t r a i t to Cape Mudge at the extreme northern end of the S t r a i t of Georgia (see F i g . 2.1). P. Crean has used the data set i n h i s numerical models of the S t r a i t of Georgia and Juan de Fuca S t r a i t (Crean, 1976). The data were a l s o used by Samuels (1979) i n a study of the mixing budget in the S t r a i t of Georgia. Samples fo r c o n d u c t i v i t y and d i s s o l v e d oxygen measurements were obtained from hydrographic c a s t s with Nansen b o t t l e s . Temperatures were measured with r e v e r s i n g thermometers. Nominal sampling depths were 0, 5, 10, 20, 30, 50, 75, 100, 150, 200, 250, 300, 350, 400 m and near the 12 bottom. A c t u a l sampling depths o f t e n v a r i e d somewhat from these values but the vast m a j o r i t y were w i t h i n one or two metres of the nominal depths. T y p i c a l r e a l i s t i c a c c u r a c i e s f o r temperature values are l i k e l y to be about ±0.02°C ( P i c k a r d and Emery, 1982). Nansen b o t t l e s c o l l e c t e d samples f o r the s a l i n i t y and oxygen a n a l y s e s . S a l i n i t i e s were determined on board using an Autolab I n d u c t i v e Salinometer (Model 601-2) with a p r e c i s i o n of 0.003°/oo- D i s s o l v e d oxygen val u e s were found using a m o d i f i e d Winkler method ( S t r i c k l a n d and Parsons 1960) with a p r e c i s i o n of 0.03 ml/1. The data were pr o v i d e d to the author on magnetic tape i n Oceans IV format with some p r e l i m i n a r y p r o c e s s i n g a l r e a d y done. The Oceans IV format i s d e s c r i b e d i n a r e p o r t by Sweers (1970). I n t e r p o l a t e d values were given at 5 m i n t e r v a l s above 150 m depth and i n 25 m i n t e r v a l s below 150 m. Of the v a r i o u s p l o t s r e f e r r e d to i n Chap. 3, a l l use data at or w i t h i n .10 m of the sampling depths. No f u r t h e r p r o c e s s i n g was done to the temperature, s a l i n i t y and oxygen v a l u e s . a f c v a l u e s were s u p p l i e d with the data but were not used. Instead, a f c values were c a l c u l a t e d using temperature and s a l i n i t y and a more recent formula given, f o r example, i n G i l l (1982) and based on The P r a c t i c a l S a l i n i t y S c a l e (Lewis, 1980). Exceptions to t h i s are the v e r t i c a l s e c t i o n s showing a f c contours reproduced d i r e c t l y from the data r e p o r t by Crean and Ages (1971). 13 Of the 79 s t a t i o n s occupied i n the December 1967 to December 1968 program, 31 were not used i n t h i s study. These i n c l u d e d s t a t i o n s i n Howe Sound, Juan de Fuca S t r a i t , Haro S t r a i t , Boundary Pass, Rosario S t r a i t , and one i n the S t r a i t of G eorgia. A l l but a few of the remaining 48 s t a t i o n s were used in the v o l u m e t r i c and heat and s a l t budget a n a l y s e s . The set was broken down f o r other analyses i n t o 3 l i n e s running p a r a l l e l to the major a x i s of the S t r a i t of Georgia (northwest/southeast), using a t o t a l of 34 s t a t i o n s ( F i g . 2.1). 9 s t a t i o n s along each of the three l i n e s were a l i g n e d to g i v e a r e c t a n g u l a r g r i d of 9 X 3 s t a t i o n s (with a s t a t i o n m i s s i n g at one g r i d p o i n t ) a l s o shown i n F i g . 2.1. A small amount of data c o l l e c t e d p r i o r to and f o l l o w i n g the c r u i s e program were a l s o a v a i l a b l e on the Oceans IV format magnetic tape. Of these, only the January 1969 data were used. 2.1.2 INTERANNUAL VARIATION The data used to examine the i n t e r a n n u a l v a r i a t i o n i n water p r o p e r t i e s (Chap. 5) were obtained from two sources. 1. on magnetic tape from the Marine Environmental Data S e r v i c e of the Department of F i s h e r i e s and Oceans i n Ottawa 2. from data r e p o r t s of the Department (or I n s t i t u t e ) of Oceanography at the U n i v e r s i t y of B r i t i s h Columbia 14 These data are r e s t r i c t e d to the c e n t r a l r e gion of the S t r a i t of Georgia south of Texada I s l a n d and west or northwest of Vancouver, i n the deepest part of the S t r a i t ( F i g . 2.2). The area with the bathymetry and s t a t i o n s occupied i s shown in F i g . 2.3. Temperature and s a l i n i t y v a l u e s were determined by a v a r i e t y of methods from r e v e r s i n g thermometers and t i t r a t i o n of b o t t l e samples, to CTD measurements. 2.2 BATHYMETRY The v o l u m e t r i c and heat and s a l t budget a n a l y s e s r e q u i r e that the bathymetry of the S t r a i t of Georgia be a v a i l a b l e i n a form s u i t a b l e to be read by a computer program. Average depths were c a l c u l a t e d f o r 4 km squares over the S t r a i t using a 2 km g r i d s u p p l i e d by P. Crean ( p e r s o n a l communication). The r e s u l t i n g 4 km g r i d c o v e r i n g the e n t i r e S t r a i t of Georgia i s shown i n F i g . 2.4. 3. DEEP WATER RENEWAL - SEASONAL VARIATION 3.1 A QUALITATIVE PICTURE A q u a l i t a t i v e understanding of the renewal process can be had by examining the v e r t i c a l s e c t i o n s with temperature contours i n F i g . 3.1 a-1 (from Crean and Ages, 1971). The s e c t i o n runs from the mouth of Juan de Fuca S t r a i t through the t i d a l passages to the S t r a i t of Georgia and up to i t s northern end along roughly c e n t r a l ^ a x e s to the two s t r a i t s . F i g . 3.1 a shows warm water (9.0 to 9.5°C) i n the S t r a i t of Georgia i n l a t e summer and f a l l . The beginnings of wintertime s u r f a c e c o o l i n g to about 50 m depth are evident i n the S t r a i t and to the bottom i n the t i d a l passages. A renewal episode has begun by mid-January ( F i g . 3.1 b) and by mid-February ( F i g . 3.1 c) has r e p l a c e d much of the warm summer water above the 200 m l e v e l by 8.0 to 9.0°C water. The winter renewal i s e s s e n t i a l l y complete by March i n the c e n t r a l S t r a i t (between s t a t i o n s 46 and 6) above 200 m with temperatures reaching a minimum of about 8.0°C in March and A p r i l and r i s i n g again i n May ( F i g . 3.1 d - f ) . The s i t u a t i o n i s somewhat d i f f e r e n t below 200 m with no a p p r e c i a b l e change o c c u r r i n g u n t i l February. A slow decrease i n temperature then takes p l a c e from February to May, r e s u l t i n g in minimum temperatures i n May of about 8.5°C. The summer renewal p e r i o d begins i n May, b r i n g i n g i n s l i g h t l y warmer water above 200 m. The water at a l l depths 15 16 g r a d u a l l y warms u n t i l November ( F i g . 3.1 f-k) peaking at 9.0 to 9.5°C. T h i s warming occurs d e s p i t e the presence of c o l d water (7.0°C at 100 m) i n Juan de Fuca S t r a i t from A p r i l to October. T h i s upwelling of c o l d water i s caused e i t h e r by processes o f f the west coast of B r i t i s h Columbia or by the i n c r e a s e d e s t u a r i n e c i r c u l a t i o n i n the summertime. The r o l e of mixing i n the southern S t r a i t must s t i l l be important d e s p i t e the r e l a t i v e l y high s t r a t i f i c a t i o n of the water column i n summer. By December, winter c o o l i n g i s evident near the s u r f a c e and in the southern passages but has not yet a f f e c t e d the deep water i n the S t r a i t . The renewal i s shown i n a l e s s dramatic f a s h i o n by the contour p l o t s of s a l i n i t y i n F i g . 3.2 a - f . A quick look through these p l o t s shows that the s a l i n i t y i s almost always i n c r e a s i n g m o n o t o n i c a l l y from the s u r f a c e to the bottom. Renewal i s marked by a r i s e or f a l l of the i s o h a l i n e s or by the appearance of s a l t i e r water near the bottom. The s i t u a t i o n f o l l o w i n g the summer renewal i s shown i n the f i r s t p l o t (December 1967). Subsequent p l o t s f o r February and May 1968 show the s a l i n i t y d e c r e a s i n g at a l l depths and the disappearance of 31.0°/ Oo water. By August, the summer renewal i n j e c t s water with s a l i n i t y g r e a t e r than 31.0°/ Oo i n t o the deepest water ( F i g . 3.2 d) and r a i s e s the 30.5°/ Oo i s o h a l i n e i n d i c a t i n g an i n c r e a s e i n s a l i n i t y at intermediate depths as w e l l . The renewal continues through November ( F i g . 3.2 e) and i n c r e a s e s the s a l i n i t y at a l l depths below 50 m. In 17 December, downwelling i n Juan de Fuca S t r a i t withdraws the high s a l i n i t y source water and causes a decrease i n s a l i n i t y , again below 50 m ( F i g . 3.2 f ) . The v a r i a t i o n i n the d e n s i t y of the deep water i s s i m i l a r to that of the s a l i n i t y . There i s a gradual r e d u c t i o n i n from December to A p r i l ( F i g . 3.3 a-b) p a r t i c u l a r l y below the 200 m l e v e l where the 24.0 i s o p y c n a l disappears a l t o g e t h e r . I t reappears b r i e f l y i n May but no s i g n i f i c a n t change i s evident u n t i l l a t e August ( F i g . 3.3 d-e) when the 24.0 i s o p y c n a l reappears. The i n c r e a s e i n the deep water c o n t i n u e s through November and has r e v e r s e d somewhat by December ( F i g . 3.3 f - g ) . Another u s e f u l t r a c e r f o r o b s e r v i n g deep water renewal in the S t r a i t of Georgia i s the c o n c e n t r a t i o n of d i s s o l v e d oxygen. In the absence of any water movement the oxygen content of water away from the s u r f a c e w i l l decrease with time as the d i s s o l v e d oxygen i s consumed by chemical combination with organic d e t r i t u s or organism r e s p i r a t i o n . The c o n c e n t r a t i o n at the s u r f a c e w i l l be near s a t u r a t i o n . P e r i o d s of renewal normally (but not always, depending on source water p r o p e r t i e s ) i n c r e a s e the oxygen content of the deep water. Contour p l o t s of d i s s o l v e d oxygen f o r a l l 12 c r u i s e s are shown in F i g . 3.4 a-1. The s i t u a t i o n f o l l o w i n g the summer renewal i s shown i n F i g . 3.4 a f o r December 1967. The oxygen content i n the mixing zone i n the southern passages i s n e a r l y homogeneous and has a r e l a t i v e l y high 18 value of about 5.0 ml/1. The winter renewal has begun by January, d e p r e s s i n g the i s o p l e t h s i n the intermediate water above 200 m but not having much e f f e c t on the deeper water. T h i s process continues through February ( F i g . 3.4 c) and a l s o p e n e t r a t e s i n t o the deep water. There i s l i t t l e change from February to A p r i l but i n May the onset of the summer renewal p e r i o d i s seen by the disappearance of 3.0 ml/1 and i t s replacement by 3.5 to 4.0 ml/1 water below 200 m i n the c e n t r a l part of the S t r a i t ( F i g . 3.4 c - f ) . In J u l y , the high s t r a t i f i c a t i o n of the water column i n the southern passages and the u p w e l l i n g i n Juan de Fuca S t r a i t are e v i d e n t . I t i s more d i f f i c u l t to i n t e r p r e t renewal i n the summertime from these p l o t s because of the very low oxygen c o n c e n t r a t i o n s present i n Juan de Fuca S t r a i t coupled with the h i g h l y s t r a t i f i e d water column which reduces mixing i n the southern passages and prevents a l a r g e i n c r e a s e i n oxygen content t h e r e . A gradual r e d u c t i o n of the oxygen c o n c e n t r a t i o n takes p l a c e from J u l y to October ( F i g . 3.4 g - j ) . T h i s c o u l d be due to low oxygen water e n t e r i n g from Juan de Fuca S t r a i t or to oxygen consumption by chemical or b i o l o g i c a l processes w i t h i n the S t r a i t of Georgia (Parsons, et a l . 1970). In December ( F i g . 3.4 1), mixing to the s u r f a c e i n the southern passages and the onset of the winter renewal i n c r e a s e l e v e l s i n the southern S t r a i t of Georgia above 200 m depth. 19 3.2 T-S ANALYSIS T h i s s e c t i o n p r e s e n t s a q u a n t i t a t i v e d e s c r i p t i o n of the temperature and s a l i n i t y in the S t r a i t of Georgia at v a r i o u s s t a t i o n s , depths and times. In order to do t h i s , four s t a t i o n s r e p r e s e n t a t i v e of the southern, c e n t r a l and northern S t r a i t are chosen. T-S diagrams with time as the t h i r d v a r i a b l e ( i n s t e a d of the usual depth) are presented for s e v e r a l depths. T-S diagrams f o r four s t a t i o n s and s e v e r a l depths are given i n F i g . 3.5 to 3.10. The four s t a t i o n s 46, 39, 2 and 14 (see F i g . 2.1 f o r l o c a t i o n s ) are spread at roughly equal i n t e r v a l s from a p o i n t j u s t i n s i d e the S t r a i t near the southern passages, to the northern end near Johnstone S t r a i t . Temperatures f o r t h i s year at 50 metres depth ( F i g . 3.5) are from 7.5 to 8.0°C i n the l a t e winter and s p r i n g (February through A p r i l ) and from 9.0 to 10.0°C in the summer and f a l l . T r a n s i t i o n s between these modes occur from November to January and from May to J u l y . The v a r i a t i o n i n s a l i n i t y i s l e s s c l e a r but g e n e r a l l y f o l l o w s that of the temperature: s a l t i e r water i s present i n the summer and f a l l a long with warmer water, and f r e s h e r water i s present i n the winter and s p r i n g . However, the change i n s a l i n i t y between these two modes i s q u i t e s m a l l , only a few tenths of a part per thousand, s i g n i f i c a n t l y l e s s than the month to month v a r i a t i o n s . 20 The l a r g e s c a t t e r i n month to month values of the temperature and s a l i n i t y at 50 m depth i s l i k e l y due to two f a c t o r s : the p r o x i m i t y of s t a t i o n s 14 and 46 to the northern and southern passages to the P a c i f i c and mixing of s u r f a c e waters down to the 50 m l e v e l which would a f f e c t a l l s t a t i o n s . Although these diagrams may be u s e f u l i n c h a r a c t e r i z i n g the source water of i n t r u s i o n s moving i n t o the S t r a i t ( s t n . 46 i n p a r t i c u l a r ) , no c o n c l u s i o n s can be drawn from them about movement of water w i t h i n the S t r a i t . F i g u r e 3.6 shows the T-S diagrams f o r the same s t a t i o n s but at 100 m depth. The smaller range of v a l u e s i s immediately apparent f o r a l l the the s t a t i o n s except 46 which shows the i n f l u e n c e of the southern t i d a l channels. T-S p r o p e r t i e s i n the main body of the S t r a i t are shown i n F i g . 3.6 b-d. The p r o p e r t i e s are s i m i l a r i n the three diagrams with a low temperature group or mode between 7.6 and 8.5°C and a high temperature mode between 8.5 and 9.5°C. The s a l i n i t y f o r the low temperature mode at s t n s . 39 and 2 v a r i e s from 29.7 to 3 0 . 2 ° / o o with an upward s h i f t of 0.2 to 0 . 3 ° / o o to the high temperature mode. The s i t u a t i o n at s t n . 14 i s more complicated with a marked i n c r e a s e i n s a l i n i t y from December 1967 to February 1968 and from A p r i l to J u l y 1968. The general shape of t h i s curve p e r s i s t s to the 150 m l e v e l as shown in F i g . 3.7 d. The most s i g n i f i c a n t f e a t u r e of F i g . 3.6 b-d i s the change in phase of the v a r i a t i o n i n temperature and s a l i n i t y as one progresses from the southern to the northern ends of 2 1 the S t r a i t of Georgia. At s t n s . 3 9 and 2 i n the southern and c e n t r a l S t r a i t the t r a n s i t i o n from the low to high mode occurs from January to February while i n the north at s t n . 1 4 i t occurs from February to March. The reverse t r a n s i t i o n occurs from May to J u l y i n the south, from J u l y or August to October at s t n . 2 and from August to November in the n o r t h . The change in phase i s a l s o apparent i n the time of occurrence of the minimum and maximum temperature reached at a p a r t i c u l a r depth over the course of the year. Table 3 . 1 l i s t s these times f o r s e v e r a l depths. There i s a c l e a r p r o g r e s s i o n of the time of the minimum temperature at 1 0 0 and 1 5 0 m depth, from February i n the southern S t r a i t to A p r i l at the northern end. The maximum temperatures at 1 0 0 to 1 5 0 m depth, occur i n August to October i n the south and in December i n the northern S t r a i t . A l l t h i s suggests the a r r i v a l of water i n the southern end of the S t r a i t and subsequent movement northward up the S t r a i t with a propagation time of about 2 months. T e m p e r a t u r e / s a l i n i t y diagrams at 1 5 0 m depth are shown in F i g . 3 . 7 . The range of temperature and s a l i n i t y values i s again reduced f o r a l l s t a t i o n s except 4 6 . Low springtime temperatures are i n the 8 . 1 to 8 . 4 ° C range while h i g h f a l l temperatures are between 8 . 9 and 9 . 3 ° C . Springtime s a l i n i t i e s vary from 3 0 . 2 to 3 0 . 5 ° / O o - S a l i n i t i e s then r i s e to year end by about 0 . 1 ° / o o at s t n . 1 4 , and by 0 . 3 to 0 . 4 ° / o o i n the c e n t r a l S t r a i t at s t n . 3 9 . The p r o p e r t i e s of 22 Table 3.1 Time of occurrence of the minimum and maximum temperatures at l o c a t i o n s i n the S t r a i t of Georgia Depth S t a t i o n Minimum Maximum (m) 100 46 Feb. Oct. 39 Mar. Oct. and Nov. 2 Mar. Oct. or Nov. (a) 1 4 Apr. Dec. 1 50 46 Jan. or Feb. (a) Aug. 39 Mar. Nov. 2 Apr. Oct. or Nov. (a) 1 4 Apr. Dec. 200 46 - (b) - (b) 39 May Dec (c) 2 Apr. Dec (c) 14 Apr. Jan (c) 250 46 - (b) - (b) 39 May Dec (c) 2 J u l y Jan (c) 14 J u l y Jan (c) (a) Data from one or other of the two months are m i s s i n g , making the r e s o l u t i o n of the p r e c i s e month i m p o s s i b l e . (b) The bottom i s l e s s than 200 m deep at s t n . 46 (c) Using data at the end of the previous year's summer renewal p e r i o d ( i . e . December 1967 or January 1968) . the water flowing through the southern passages can be roughly approximated by l o o k i n g at s t n . 46 at 150 m depth. Here the spread i n low to high s a l i n i t y i s c l o s e to 0 . 8 ° / o o C l e a r l y , water e n t e r i n g the S t r a i t i s s u b j e c t to a l a r g e amount of mixing with the water a l r e a d y i n the S t r a i t . Mixing continues as the i n f l o w moves up the S t r a i t but the 23 e f f e c t on water p r o p e r t i e s decreases q u i c k l y away from the t i d a l passages. Nevertheless s i g n i f i c a n t mixing seems to take pla c e along the e n t i r e S t r a i t of Georgia as i n d i c a t e d by the gradual r e d u c t i o n i n the seasonal v a r i a b i l i t y of the T-S p r o p e r t i e s . The bi-modal nature of the seasonal temperature v a r i a t i o n i s brought out most s t r i k i n g l y at the 200 m l e v e l i n F i g . 3.8 (note the change in s c a l e from F i g . 3.7). S t a t i o n 46 i s not shown because i t l i e s i n water shallower than 200 m. S p r i n g and summer temperatures are i n the 8.4 to 8.6°C range. These temperatures develop i n January and February at s t n s . 39 and 2 and i n February to A p r i l at s t n . 14. A summer or f a l l t r a n s i t i o n to the warmer water at 9.0 to 9.2°C occurs i n August and September at s t n . 39, i n September and October at s t n . 2 and i n October and November at s t n . 14. T h i s i n d i c a t e s a time l a g of roughly two months fo r the appearance of warm, s a l t y water from the c e n t r a l s e c t i o n to the northern end of the S t r a i t of Georgia. Springtime s a l i n i t i e s are from 30.5 to 3 0 . 7 ° / o o f o r s t n s . 39 and 2 and from 30.3 to 30.6 f o r s t n . 14. Late f a l l and e a r l y winter s a l i n i t i e s are about 0 . 2 ° / o o higher at 30.6 to 30.9 f o r s t n s . 39 and 2 and 30.6 to 30.7 f o r s t n . 14. The t r a n s i t i o n from one mode to the other i s not w e l l marked in the s a l i n i t y v alues as the v a r i a b i l i t y w i t h i n each mode i s as great or g r e a t e r than the d i f f e r e n c e i n average s a l i n i t y between the modes. 24 T e m p e r a t u r e - s a l i n i t y p r o p e r t i e s f o r the three s t a t i o n s are p l o t t e d i n F i g . 3.9 f o r the 250 m l e v e l . Temperature values are s i m i l a r to those at 200 m but with a somewhat reduced range. A t h i r d grouping of monthly v a l u e s appears at a temperature of 8.8°C i n l a t e winter and e a r l y s p r i n g i n d i c a t i n g that the move from wintertime to summer/fall temperature values may occur i n two or more d i s c r e t e s t e p s . The f i r s t step in January and February lowers the temperature by 0.2°C from 9.0 to 8.8°C. T h i s i s evident i n the southern and c e n t r a l S t r a i t at s t n s . 39 and 2 at 250 m depth and at s t n . 39 at 300 m depth. The second step or s e r i e s of steps occur at d i f f e r e n t times from March to the end of June and lower the temperature another 0.2°C from 8.8 to 8.5 or 8.6°C. C l e a r l y deep water renewal in the S t r a i t of Georgia does not always proceed i n a smooth continuous f a s h i o n but may i n v o l v e two or more episodes which may or may not ( i . e . formation of an intermediate l a y e r ) i n v o l v e new water p e n e t r a t i n g to the bottom. One s t r i k i n g f e a t u r e apparent at the 250 m l e v e l ( F i g . 3.9) i s that the c o l d e s t temperatures occur i n the summertime and the warmest temperatures occur i n the wintertime. The time f o r a water mass to move from the southern S t r a i t i n t o the c e n t r a l S t r a i t can account f o r up to 2 months of what appears to be c l o s e to a 6 month l a g . The remaining 4 month l a g suggests the i n f l u e n c e of other i n t e r n a l processes o c c u r r i n g i n the S t r a i t . 25 There are s e v e r a l s i g n i f i c a n t d i f f e r e n c e s i n the T-S p r o p e r t i e s from one l e v e l to the next, the major ones being a c o n s i s t e n t r i s e i n s a l i n i t y w ith i n c r e a s i n g depth and a r e d u c t i o n of the v a r i a b i l i t y i n p r o p e r t i e s with depth. The shape of the T-S curves can a l s o change with depth. S t a t i o n 2 at 200 m ( F i g . 3.8 b) shows a marked r i s e i n temperature and s a l i n i t y i n May f o l l o w e d immediately by a s i m i l a r drop i n both p r o p e r t i e s . T h i s behaviour does not appear e i t h e r above or below the 200 m l e v e l (see F i g . 3.7 c and 3.9 b ) . Assuming that the data i s reasonably a c c u r a t e , some t r a n s i e n t e f f e c t such as an i n t e r n a l wave or other d i s t u r b a n c e may have r a i s e d the i s o p l e t h s to produce t h i s measurement (a r i s e of roughly 20 to 30 m would be n e c e s s a r y ) . The minimum and maximum temperatures given i n Table 3.1 above i n d i c a t e a l a g i n the time of renewal from the i n t e r m e d i a t e l e v e l s (100 to 150 m) to the deeper water (below 200 m). The minimum temperature occurs i n March at 100 and 150 m depth at s t n . 39 and i n May at 200 and 250 m. The l a g i s more dramatic f u r t h e r n o r t h i n the S t r a i t , f o r example at s t n . 2 where the minimum occurs i n March at 100 m and i n J u l y at 250 m. Another obvious depth-dependent f e a t u r e i s the t r a n s i t i o n from warm to c o l d c o n d i t i o n s at s t n . 39 below 200 m. In mid-January to mid-February an i n f l u x of c o l d water lowers the temperature from 9.1 to 8.8°C at 250 m depth, with a small e f f e c t at 300 m and no e f f e c t at 350 m 26 (see F i g . 3.9 a and F i g . 3.10 a , c ) . A second pulse of c o l d water lowers the temperature at 300 m to 8.8°C i n February to March while l e a v i n g the 250 and 300 m l e v e l s unchanged. A subsequent event i n March to A p r i l lowers the temperature at the 250 m l e v e l to 8.5°C with no e f f e c t being f e l t f u r t h e r down. F i n a l l y i n A p r i l to May c o l d water moves to the 350 m l e v e l b r i n g i n g temperatures everywhere down to 8.4°C. C l e a r l y the c h a r a c t e r of renewal episodes can be h i g h l y depth dependent. Before c o n t i n u i n g , i t may be h e l p f u l to summarize the main f e a t u r e s shown by the T-S diagrams. The higher v a r i a b i l i t y of the temperature and s a l i n i t y at the higher l e v e l s and near the southern passages i n d i c a t e s the more d i r e c t i n f l u e n c e of s u r f a c e f l u x e s of heat and f r e s h water and of the mixing i n the southern S t r a i t . There i s a p o s i t i v e c o r r e l a t i o n between temperature and s a l i n i t y with f r e s h , c o l d water o c c u r r i n g i n the winter and s p r i n g and s a l t y , warm water f i l l i n g the S t r a i t i n summer and f a l l . A bi-modal s t r u c t u r e i s o f t e n apparent where there i s a r e l a t i v e l y quick t r a n s i t i o n from winter to summer c o n d i t i o n s (and v i c e v e r s a ) , preceded and f o l l o w e d by p e r i o d s of low v a r i a b i l i t y . The a r r i v a l of new water at depth ( g r e a t e r than 200 m) i s s i g n i f i c a n t l y l a t e r than at higher l e v e l s and leads to the unusual circumstance of having the warmest water occur i n the wintertime and the c o l d e s t water occur i n the summertime. F i n a l l y , there i s a c l e a r l a g of about 2 months from the time of a r r i v a l of new water from the 27 southern to the northern ends of the S t r a i t . 3.3 DEEP WATER PENETRATION The T-S a n a l y s i s used i n the pre v i o u s s e c t i o n i s u s e f u l i n t a b u l a t i n g the valu e s of the two p r o p e r t i e s at v a r i o u s p o i n t s i n the S t r a i t and g i v e s an i n d i c a t i o n of the many f e a t u r e s of the deep water renewal. However, other r e p r e s e n t a t i o n s of the data are needed to examine more c l o s e l y such t h i n g s as the l a t e r a l v a r i a t i o n and the movement of a water mass as i t enter s the S t r a i t and proceeds northward. In t h i s s e c t i o n contour p l o t s of s a l i n i t y , temperature and oxygen with axes of time and d i s t a n c e (along the center of the S t r a i t ) are used to t r a c e the new water as i t enters and t r a v e l s northward up the S t r a i t . An estimate of the v e l o c i t y of the i n f l o w i n g water i s made. The depth to which seasonal h e a t i n g , c o o l i n g and f r e s h water input at the su r f a c e a f f e c t water p r o p e r t i e s i s estimated. The v a r i a t i o n of the renewal process a c r o s s the S t r a i t i s a l s o shown. The p l o t s ( F i g . 3.11 to 3.13) cover the e n t i r e c r u i s e program from December 1967 to December 1968 on the v e r t i c a l a x i s and the l e n g t h of the S t r a i t of Georgia (along i t s major a x i s ) from Haro S t . to near Cape Mudge on the h o r i z o n t a l a x i s . The f o l l o w i n g d i s c u s s i o n based on these p l o t s has been d i v i d e d up i n t o 3 s e c t i o n s , one f o r each p r o p e r t y . 28 3.3.1 TEMPERATURE Water temperatures at s t a t i o n s along the c e n t r a l a x i s of the S t r a i t are p l o t t e d i n F i g . 3.11 f o r s e v e r a l depths from the s u r f a c e to 300 m. At the surface ( F i g . 3.11 a) contour l i n e s are roughly h o r i z o n t a l over most of the year and over most of the S t r a i t . The s u r f a c e temperatures are dominated by seasonal h e a t i n g and c o o l i n g which a f f e c t the e n t i r e S t r a i t i n a uniform and simultaneous manner. Maximum temperatures occur in J u l y d u r i n g the h o t t e s t p a r t of the year, both i n terms of a i r temperature and i n s o l a t i o n . Minimum temperatures occur i n January and February s h o r t l y a f t e r the p e r i o d of minimum a i r temperatures and i n s o l a t i o n . T h i s delay i s r e l a t e d to the high thermal i n e r t i a of the s u r f a c e waters and an i n c r e a s e i n the s u r f a c e mixed l a y e r depth brought on by a decrease in f r e s h water input and c o o l i n g at the s u r f a c e i n winter. There i s one p a r t i c u l a r l y h i g h measurement (over 21°C) at s t n . 27 i n J u l y which i s perhaps i n d i c a t i v e of the p a t c h i n e s s that occurs i n the s u r f a c e water p r o p e r t i e s i n the c e n t r a l and southern S t r a i t due to the combined e f f e c t of the F r a s e r R i v e r , t i d e s and winds. A more important f e a t u r e i s the c o l d s u r f a c e water i n the southern passages ( s t n . 59, 56) i n the summer months. T i d a l mixing b r i n g s c o l d e r subsurface water upward m a i n t a i n i n g the s u r f a c e waters at 5°C l e s s than i n the c e n t r a l S t r a i t . The e f f e c t s of mixing are a l s o f e l t at s t n . 46 p a r t i c u l a r l y i n May, 29 June and September. The high temperatures i n J u l y are the r e s u l t of the decreased mixing i n the very s t a b l e water column caused by the l a r g e amount of f r e s h water present at that time and perhaps a l s o by upwelling i n Juan de Fuca S t r a i t , which p r o v i d e s high d e n s i t y water at depth. In the winter months (January and Fe b r u a r y ) , t i d a l mixing produces a small warming of the s u r f a c e waters which r e s u l t s i n an inc r e a s e of about 1°C at s t n . 56 and 59. The temperatures at 50 m and 75 m depth along the c e n t r a l a x i s of the S t r a i t ( F i g . 3.11 b & c) show evidence of processes other than s u r f a c e h e a t i n g and c o o l i n g . However the contours do not i n d i c a t e any process which covers the e n t i r e S t r a i t i n a c o n s i s t e n t and uniform manner. Temperatures at v a r i o u s s t a t i o n s and times are being i n f l u e n c e d by l o c a l events ( f o r example the anomalously high temperature i n J u l y at s t n . 3, 50 m) and water i n f l o w through the northern passages may a l s o be s i g n i f i c a n t . Water temperatures at 100 m depth at s t a t i o n s on the c e n t r a l a x i s of the S t r a i t are contoured in F i g . 3.11 d. The s e r i e s of c l o s e l y spaced l i n e s from the 8.0 to the 9.0°C contour from December 1967 to March 1968 i n d i c a t e a renewal episode beginning i n November or December 1967 i n the southern end of the S t r a i t and c o n t i n u i n g u n t i l January 1968. T h i s c o l d water then moves up the S t r a i t as shown by the sloped contour l i n e s . The e f f e c t of the i n f u s i o n of new c o l d water i s f i n i s h e d by February 1968 i n the south but only s t a r t s i n January i n the northern end and continues 30 u n t i l A p r i l . An estimate of the v e l o c i t y at which t h i s replacement progresses can be c a l c u l a t e d and i s d i s c u s s e d l a t e r i n t h i s s e c t i o n . T h i s f i r s t renewal episode i s c l o s e l y f o l l o w e d by a second, i n which warm water moves i n t o the S t r a i t and d i s p l a c e s the c o l d "winter" water. Water temperatures i n the southern end reach a low of about 7.3°C i n February and immediately begin to r i s e , e v e n t u a l l y peaking at 9.6°C i n September. The warm water again takes about two months to reach the northern end. Strong mixing i n the southern S t r a i t causes the c o l d water (below 7.6°C) at s t n . 46, 56 and 59 i n February to warm to 7.8°C by March i n the c e n t r a l S t r a i t n o r t h of s t n . 42. I t i s i n t e r e s t i n g to note that the h o r i z o n t a l temperature s t r u c t u r e i s f a i r l y uniform through the region of most vigorous ( v e r t i c a l ) mixing and that i t i s only when the incoming water meets the water i n the S t r a i t of Georgia b a s i n t h a t i t s temperature changes in a short d i s t a n c e . T h i s i s p a r t l y a r e s u l t of the f a c t that temperatures i n the S t r a i t of Georgia are not too d i f f e r e n t from those at an a p p r o p r i a t e l e v e l (50 - 100 m) i n Juan de Fuca S t r a i t (see F i g . 3.1 a-1). Temperatures t h e r e f o r e tend to be f a i r l y uniform i n the mixing zone even though they may be d i f f e r e n t because of s u r f a c e h e a t i n g or c o o l i n g from those f u r t h e r north i n the S t r a i t of Georgia. As w i l l be apparent l a t e r , t h i s i s i n sharp c o n t r a s t to the s i t u a t i o n f o r the s a l i n i t y which i s always higher i n Juan de Fuca S t r a i t than the 31 highest value found i n the S t r a i t of Georgia ( F i g . 3.2 a - f ) . The same p l o t at the 150 m l e v e l i s q u a l i t a t i v e l y very s i m i l a r to the p l o t at 100 m ( F i g . 3.11 e ) . The isotherms again show the temperature s i g n a l moving northward f o r both the winter and summer renewals. The minimum temperature reached a f t e r the winter renewal i n the c e n t r a l S t r a i t i s , at 8.0°C, 0.2°C higher than at 100 m and the maximum reached f o l l o w i n g the summer renewal i s 0.2°C lower at 9.2°C. One f e a t u r e that i s a l s o apparent at the 100 m l e v e l but i s s u r p r i s i n g l y stronger at 150 m, i s the temperature maximum (over 9.4°C) at s t n . 46 i n August to October. There does not seem to be a source f o r such high temperature water at the 150 m l e v e l . Presumably, e i t h e r mixing or some other process has brought warmer water downward. Why t h i s should happen at s t n . 46 and not i n the southern passages at s t n s . 56 and 59 where there i s a l s o warm water above (over 9.4°C at 100 m depth), i s an i n t e r e s t i n g q u e s t i o n , p a r t i c u l a r l y s i n c e the phenomenon i s s u s t a i n e d f o r 2 or 3 months. Perhaps the higher p r o p o r t i o n of c o l d e r Juan de Fuca water i n the southern passages obscures the e f f e c t s of v e r t i c a l mixing. The next p l o t at 200 m depth, again shows a decrease with i n c r e a s i n g depth of the seasonal v a r i a b i l i t y of the temperature i n the c e n t r a l S t r a i t of G e o r g i a . The minimum springtime temperature f o l l o w i n g the winter renewal i s 8.4 to 8.6°C compared to 8.0 to 8.4°C at 150 m depth. Maximum 32' temperatures appear to stay below 9.2°C, except i n the southern t h i r d of the S t r a i t (south of s t n . 27) where they are somewhat h i g h e r . The two renewal episodes are s t i l l w e l l d e f i n e d and each seems to occur i n a r e l a t i v e l y short time. The bi-modal c h a r a c t e r of the temperature v a r i a t i o n at t h i s depth has a l r e a d y been documented i n the T-S a n a l y s i s . The T-S curves f o r s t n s . 39 and 2 at 200 m depth ( F i g . 3.8 a,b) show a very s t r o n g bi-modal s t r u c t u r e . T h i s suggests that renewal below the 200 m l e v e l , takes p l a c e d u r i n g two w e l l d e f i n e d ( i . e . w e l l separated) p e r i o d s . At 250 and 300 m ( F i g . 3.11 g,h) much of the S t r a i t i s shallower than the sample depth, hence the gaps i n the south ( s t n s . 59-42) and near Hornby I s l a n d ( s t n s . 6-9). The S t r a i t i s e f f e c t i v e l y separated i n t o a northern and c e n t r a l b a s i n with a s i l l between Hornby and the southern end of Texada I s l a n d of 200 m. The minimum depth between the northern t i p of Texada I s l a n d and the B r i t i s h Columbia mainland i s s i g n i f i c a n t l y higher at c l o s e to 100 m depth. The bi-modal temperature s t r u c t u r e i s no longer evident at 250 and 300 m, except perhaps i n the northern b a s i n . However, the seasonal v a r i a t i o n of the temperature i s c l e a r , w ith a minimum i n June of 8.4 to 8.6°C i n the c e n t r a l S t r a i t and maximum i n December of 8.8 to 9.2°C. The northward moving temperature s i g n a l i s s t i l l c l e a r at both depths although the isotherms are not as n e a t l y a l i g n e d as at the higher l e v e l s . 33 As mentioned e a r l i e r , a d v e c t i o n of a water mass northward up the S t r a i t of Georgia i s i n d i c a t e d by the sloped contour l i n e s of temperature, s a l i n i t y and d i s s o l v e d oxygen i n F i g . 3.11 to 3.14. An estimate of the v e l o c i t y of adv e c t i o n of the water can be made by e v a l u a t i n g the r e c i p r o c a l of the slope of a given contour l i n e . T h i s has been done f o r the temperature p l o t s at 100, 150 and 200 m depth ( F i g . 3.11 d - f ) . The v e l o c i t i e s and a s s o c i a t e d e r r o r s given i n Table 3.2 were c a l c u l a t e d using the data f o r the S t r a i t of Georgia e x c l u d i n g the southern passages and extreme southern and northern S t r a i t . As a r e s u l t , s t a t i o n s 59, 56 and 16 were not used. A contour l i n e ( i . e . a value of temperature) w e l l w i t h i n the renewal phase was chosen f o r each p r o p e r t y and depth. A f o u r t h - or lower - order polynomial was f i t t e d to a maximum of f i v e data p o i n t s spanning the contour l i n e . An estimate of the time of occurrence of the temperature was then found using the i n t e r p o l a t i n g p o l y n o m i a l . T h i s process was repeated f o r each s t a t i o n r e s u l t i n g i n a set of p o i n t s (t,x) where t i s the estimated time of occurrence of the pr o p e r t y value at a s t a t i o n and x i s the p o s i t i o n of that s t a t i o n along the s e c t i o n . A s t r a i g h t l i n e was then f i t t e d to the set of (t,x) p o i n t s using a l e a s t squares a n a l y s i s . The v e l o c i t y i s then found by c a l c u l a t i n g the r e c i p r o c a l of the slope of the l i n e . The e r r o r s given i n Table 3.2 ( g i v i n g the 95% con f i d e n c e i n t e r v a l ) r e f l e c t the extent to which the set of 34 p o i n t s (t,x) l i e o f f the f i t t e d l i n e . Both the method of a n a l y s i s and p h y s i c a l f a c t o r s may c o n t r i b u t e to t h i s . The e r r o r r e f l e c t s the small number of data p o i n t s used (about 10) and the i n a c c u r a c i e s i n v o l v e d i n i n t e r p o l a t i n g between data p o i n t s . The a c t u a l v e l o c i t y of water p a r t i c l e s no doubt v a r i e s along the S t r a i t because of the uneven bathymetry and l a t e r a l c o n s t r i c t i o n s . The a s s o c i a t e d v e l o c i t i e s with e r r o r s are given i n Table 3.2. The e r r o r s r e f l e c t the s p a r s i t y of data and the waviness of the contour l i n e - not the l i k e l i h o o d of the a c t u a l v e l o c i t y of the water mass being w i t h i n the given range. The a c t u a l v e l o c i t y of water p a r t i c l e s would l i k e l y be somewhat higher than these v a l u e s because mixing with water p r e v i o u s l y i n p l a c e reduces the magnitude of the change in the p r o p e r t y and hence slows down the apparent movement of the water. T h i s f a c t o r however i s probably not very l a r g e s i n c e most of the mixing takes place i n the southern passages and extreme southern S t r a i t of Georgia (Samuels 1979). The r e s u l t s show that the v e l o c i t y of water p a r t i c l e s at the 100 and 150 m l e v e l s i n the S t r a i t d u r i n g the winter renewal are roughly from 0.020 to 0.030 m/s corresponding to a t r a v e l time from one end of the S t r a i t to the other of 2.5 to 3.5 months (a d i s t a n c e of about 200 km). The v e l o c i t i e s at 200 m are s u b s t a n t i a l l y l a r g e r at about 0.032 m/s but u n f o r t u n a t e l y there i s not enough data at t h i s l e v e l t o be a b l e to deduce that there i s a s i g n i f i c a n t d i f f e r e n c e from 35 Table 3.2 C e n t r a l S e c t i o n V e l o c i t i e s from the Temperature S i g n a l Renewal Depth Contour V e l o c i t y E r r o r Per iod (m.) (°C) (m/s) (m/s) winter 100 8.6 0.023 0.006 winter 1 50 8.6 0.023 0.010 winter 200 8.8 0.032 0.013 winter 250 8.9 0.13 0.20 winter 300 8.9 0.014 0.013 summer 100 8.6 0.017 0.005 summer 1 50 8.6 0.026 0.006 summer 200 8.8 0.033 0.010 summer 250 8.7 0.018 0.013 summer 300 8.8 0.022 0.052 t 95% conf idence i n t e r v a l the upper l a y e r . 3.3.2 SALINITY The s u r f a c e water s a l i n i t y d i s t r i b u t i o n i s dominated by the f r e s h water input of the F r a s e r R i v e r ( F i g . 3.12 a ) . S t a t i o n 42, d i r e c t l y o p p o s i t e the mouth of the F r a s e r , shows s a l i n i t y values as low as 10 ° / o c w only 1/3 that of the average f o r the S t r a i t . T h i s f r e s h water spreads northward and s i g n i f i c a n t l y reduces s u r f a c e s a l i n i t i e s over most of the S t r a i t of Georgia i n the summertime. To the south the f r e s h water i s mixed i n t o the water column i n the t i d a l passages r e s u l t i n g i n a sharp i n c r e a s e i n s a l i n i t y between s t n s . 56 and 42. The d i r e c t e f f e c t of the F r a s e r R i v e r i s minimal i n December to A p r i l , p r i m a r i l y due to the s h a r p l y 36 decreased r u n o f f and a i d e d by higher winds and s u r f a c e c o o l i n g which i n c r e a s e the s u r f a c e mixed l a y e r depth. F i g u r e s 3.12 b,c show s a l i n i t y values at 50 and 75 m again along the c e n t r a l a x i s of the S t r a i t . As i n the corresponding p l o t s of water temperature the contours are not s u f f i c i e n t l y coherent to show c l e a r evidence of any renewal p r o c e s s . The i n f l u e n c e of high s a l i n i t y Juan de Fuca water i s seen at both l e v e l s as the sharp s a l i n i t y g r a d i e n t between s t n s . 46 and 59. T h i s g r a d i e n t i s i n sharp c o n t r a s t to the temperature d i s t r i b u t i o n which i s r e l a t i v e l y uniform through the southern passages ( F i g . 3.11 b - f ) . Two renewal episodes ( c o i n c i d e n t with those d e s c r i b e d above using the temperature p l o t s ) can be seen i n F i g . 3.12 d where s a l i n i t y contours at 100 m depth are p l o t t e d . The f i r s t episode begins i n December or January at s t n . 46 with 30.0 to 3 0 . 2 ° / o o water moving to the northern end of the S t r a i t by March. The s i g n a l cannot be seen south of s t n . 46 where the h o r i z o n t a l s a l i n i t y g r a d i e n t through the t i d a l passages (or a s s o c i a t e d mixing) dominates. The second renewal episode occurs i n May to J u l y with only a small delay i n d i c a t e d f o r propagation to the northern end of the S t r a i t from s t n . 42. The s a l i n i t y contours do not show the p r o g r e s s i o n of the renewal events as c l e a r l y as do the temperature contours ( e s p e c i a l l y the winter renewal), however the general slope of the contour l i n e s f o r the r e g i o n w i t h i n the S t r a i t and the maxima and minima i n s a l i n i t y with time are f a i r l y e v i d e n t . Although changes i n 37 s a l i n i t y are too small to use t h i s property very e f f e c t i v e l y as a t r a c e r , the s a l i n i t y n e v e r t h e l e s s dominates the d e n s i t y s t r u c t u r e which i n tu r n governs the dynamics of the system. The renewal s i g n a l at 150 m ( F i g . 3.12 e) i s seen i n the 30.4 and 30.6°/ Oo contour l i n e s . The seasonal v a r i a b i l i t y of the s a l i n i t y i n the c e n t r a l and northern S t r a i t i s somewhat l e s s than at the 100 m l e v e l ( F i g . 3.12 d), making the i d e n t i f i c a t i o n of the beginning and end of the renewal p e r i o d more d i f f i c u l t . The s a l i n i t y g r a d i e n t through the southern mixing zone ( s t n s . 59-46) i s somewhat l a r g e r at t h i s l e v e l i n d i c a t i n g that high s a l i n i t y Juan de Fuca water i s more s u c c e s s f u l at p e n e t r a t i n g i n t o the mixing zone at g r e a t e r depth. Although the seasonal v a r i a t i o n ^ o f the s a l i n i t y i s s t i l l c l e a r below 150 m at 200 to 300 m ( F i g . 3.12 f - h ) , the movement of the renewal s i g n a l northward, up the S t r a i t i s no longer e v i d e n t . In f a c t , the slopes of the 30.8 and 3 0 . 6 ° / o o contour l i n e s at the 200 m l e v e l i n F i g . 3.12 f in December to March are nega t i v e , a c t u a l l y i n d i c a t i n g a southward propagating s i g n a l . At 250 m depth the contour l i n e s a r e , on average, n e a r l y h o r i z o n t a l i n the c e n t r a l S t r a i t . The 30.9 and 3 1 . 0 ° / o o contour l i n e s at 300 m ( F i g . 3.12 h) do show evidence of the northward moving s i g n a l i n the c e n t r a l S t r a i t but i t i s d i f f i c u l t to say whether i t i s s i g n i f i c a n t due to the lack of data and to the disappearance of the s i g n a l at 200 and 250 m depth. 38 The e f f e c t s of the s i l l at 200 m depth, s e p a r a t i n g the northern and c e n t r a l s e c t i o n s of the S t r a i t are apparent i n the s a l i n i t y at the 250 and 300 m l e v e l s ( F i g . 3.12 g,h). S a l i n i t y v a l u e s are about 0 . 2 ° / o o lower i n the northern S t r a i t , c orresponding, not too s u r p r i s i n g l y , to s a l i n i t i e s at the 200 m l e v e l i n the c e n t r a l and northern S t r a i t . The v a r i a t i o n ( i . e . the i n c r e a s e or decrease) of the s a l i n i t y at depth i n the northern s e c t i o n c l o s e l y f o l l o w s the v a r i a t i o n everywhere in the S t r a i t at and above the 200 m l e v e l . I t i s l i k e l y t h a t water that appears at the northern s i l l at 200 m depth d u r i n g a renewal p e r i o d , s i n k s to the deeper l e v e l s i n the northern S t r a i t . The time of occurrence of p a r t i c u l a r values of the s a l i n i t i e s f o r each s t a t i o n and renewal p e r i o d have been -c a l c u l a t e d and a s t r a i g h t l i n e f i t t e d to them, as done e a r l i e r f o r the temperature. V e l o c i t i e s o b tained from the slope of these l i n e s are given i n Table 3.3 f o r s e v e r a l depths and both renewal p e r i o d s . The r e s u l t s agree (to w i t h i n the s t a t e d e r r o r s ) with the v e l o c i t i e s obtained using temperature. E r r o r s again d e f i n e the 95% c o n f i d e n c e i n t e r v a l . The very l a r g e e r r o r at 100 m depth d u r i n g the summer renewal (3 ±200 m/s) r e f l e c t s the f a c t that the f i t t e d l i n e i s n e a r l y h o r i z o n t a l with a slope c l o s e to zero and that the r e c i p r o c a l of the slope i s used to c a l c u l a t e the v e l o c i t y . 39 Table 3.3 C e n t r a l S e c t i o n V e l o c i t i e s from the S a l i n i t y S i g n a l Renewal Depth Contour Veloc i t y E r r o r f P e r i o d (m.) (Voo) (m/s) (m/s) winter 100 30. 1 0.028 0.008 winter 1 50 30.4 0.028 0.014 winter 200 - - -winter 250 30.9 0.07 0.55 winter 300 31.0 0.036 0.033 summer 100 30.3 3 200 summer 1 50 30.6 0.037 0.027 summer 200 30.8 0.035 0.067 summer 250 30.9 0.014 0.015 summer 300 31 .0 0.011 0.015 t 95% conf idence i n t e r v a l 3.3.3 DISSOLVED OXYGEN A t h i r d p r o p e r t y which shows the renewal process and i t s p r o g r e s s i o n i s the c o n c e n t r a t i o n of d i s s o l v e d oxygen. A u s e f u l amount of data i s a v a i l a b l e only f o r the l i n e of s t a t i o n s along the c e n t r a l a x i s of the S t r a i t . These data are p l o t t e d i n F i g . 3.13 from the su r f a c e to 300 m depth. The d i s s o l v e d oxygen c o n c e n t r a t i o n at the s u r f a c e ( F i g . 3.13 a) r e f l e c t s the mixing of the water column i n the southern passages with low v a l u e s at s t n s . 59 and 56 throughout the c r u i s e program. The high value at s t n . 39 i n March i s perhaps due to a phytoplankton bloom. The o v e r a l l p a t c h i n e s s of the oxygen c o n c e n t r a t i o n , p a r t i c u l a r l y i n s p r i n g and summer, a l s o i n d i c a t e s that b i o l o g i c a l processes are important at t h i s time of the year. 40 At 50 m depth ( F i g . 3.13 b) the i n f l u e n c e of mixing i n the southern passages has been r e p l a c e d by a c l e a r seasonal s i g n a l with high oxygen c o n c e n t r a t i o n i n February and low i n J u l y and August. Northward propagation of t h i s s i g n a l i s not p a r t i c u l a r l y c l e a r . Indeed i f there i s outflow i n the s u r f a c e l a y e r then one might expect that the d i s t r i b u t i o n of p r o p e r t i e s i n the l a y e r would produce contour l i n e s of opp o s i t e s i g n to those seen at lower depths i n the temperature and s a l i n i t y p l o t s . However mixing with the deeper water and the p o s i t i o n of f r e s h water inflow near the area of exchange through the southern passages would reduce or e l i m i n a t e t h i s e f f e c t i n the S t r a i t of Georgia. In F i g . 3.13 b the i s o p l e t h s are e s s e n t i a l l y h o r i z o n t a l i n d i c a t i n g a seasonal s i g n a l but not i t s propagation n o r t h or south. The s i t u a t i o n at 75 m depth ( F i g . 3.13 c) i s s i m i l a r . F i g . 3.13 d shows the d i s s o l v e d oxygen c o n c e n t r a t i o n at 100 m depth. T h i s p l o t i s remarkably s i m i l a r to the corresp o n d i n g temperature p l o t ( F i g . 3.11 d) and c l e a r l y shows the northward propagation of the hi g h oxygen winter water from the southern passages i n December and January -and e a r l i e r - reaching the northern end of the S t r a i t by March. The d i s s o l v e d oxygen c o n c e n t r a t i o n then decreases from March to June i n the southern passages as warm summer water e n t e r s the S t r a i t and moves northward a r r i v i n g at the northern end by May to September. High oxygen water appears i n winter f o r two reasons. The i n c r e a s e d mixing i n the t i d a l 41 passages b r i n g s h i g h l y oxygenated s u r f a c e water downward and in c r e a s e s the t o t a l oxygen content of the water column by mixing low oxygen deep water upward and exposing i t to the atmosphere (the higher s a t u r a t i o n c o n c e n t r a t i o n of d i s s o l v e d oxygen in c o l d water enhances t h i s e f f e c t ) . As w e l l , the wintertime c e s s a t i o n of upwelling i n Juan de Fuca S t r a i t (see F i g . 3.4 a,e) s u p p l i e s higher oxygen source water. Conversely, decreased mixing i n the t i d a l passages and upwe l l i n g in Juan de Fuca S t r a i t lower the oxygen c o n c e n t r a t i o n d u r i n g the s p r i n g and summer warm water renewal. T h i s r e s u l t s i n a minimum oxygen c o n c e n t r a t i o n i n the c e n t r a l S t r a i t of Georgia i n October ( F i g . 3.13 d ) . At 150 m depth, the c o n c e n t r a t i o n of d i s s o l v e d oxygen shows the winter renewal, with h i g h l y oxygenated water i n the southern passages from December to February moving northward to end the renewal p e r i o d at s t n . 16 i n A p r i l . The summer renewal, i n d i c a t e d by d e c r e a s i n g oxygen c o n c e n t r a t i o n , proceeds from March to August i n the south and from May to November in the no r t h . The small s c a l e s p a t i a l and temporal v a r i a b i l i t y at the 150 m l e v e l a l l o w s the seasonal v a r i a t i o n of the d i s s o l v e d oxygen c o n c e n t r a t i o n to be seen but co n c e a l s to some extent the propagation of any northward moving s i g n a l , p a r t i c u l a r l y d u r i n g the summer renewal. Movement through the southern passages and i n t o the S t r a i t of Georgia i s i n d i c a t e d i n March t o J u l y at s t n s . 59 to 42 by the p o s i t i v e slope of the contour l i n e s . The s i g n a l i s much l e s s apparent no r t h of 42 s t n . 42 and i s r e p l a c e d by almost h o r i z o n t a l or convoluted contour l i n e s . The p a t c h i n e s s e v i d e n t at 150 m again appears at the 200 m l e v e l ( F i g . 3.13 f ) . However, the region of high v a r i a b i l i t y i s r e s t r i c t e d to the time between the winter and summer renewal so each renewal s i g n a l i s s t i l l f a i r l y obvious. Again, the s i m i l a r i t y between the c h a r a c t e r i s t i c s of the renewal p e r i o d s (as r e f l e c t e d i n the oxygen and temperature d i s t r i b u t i o n s ) i s s t r i k i n g , p a r t i c u l a r l y i f one ignores the small s c a l e v a r i a b i l i t y ( F i g . 3.13 f and 3.11 f ) . The two renewal p e r i o d s are r e l a t i v e l y b r i e f and are separated by many months (March to J u l y ) of weak v a r i a b i l i t y (again e x c l u d i n g the smaller s c a l e s ) . P l o t s at the 250 and 300 m l e v e l s ( F i g . 3.13 g,h) are f a i r l y s i m i l a r and again show a high degree of p a t c h i n e s s . The winter renewal occurs somewhat l a t e r , with an abrupt i n c r e a s e i n the oxygen c o n c e n t r a t i o n from 3.2 ml/1 to a maximum of 3.8 to 4.0 ml/1 at s t n . 27 i n A p r i l and May at both l e v e l s i n the c e n t r a l S t r a i t . A slower decrease marks the summer renewal i n J u l y to September. The northern b a s i n behaves somewhat d i f f e r e n t l y by d i s p l a y i n g a gradual i n c r e a s e from December 1967 to May 1968. Not s u r p r i s i n g l y , t h i s resembles the v a r i a t i o n at the 200 m l e v e l . There i s no c l e a r s i g n a l , at e i t h e r l e v e l , showing the northward propagation of water d u r i n g a renewal p e r i o d . V e l o c i t i e s c a l c u l a t e d from the d i s s o l v e d oxygen data are given below in Table 3.4. There i s a f a i r amount of 43 Table 3.4 C e n t r a l S e c t i o n V e l o c i t i e s from the D i s s o l v e d Oxygen S i g n a l Renewal Depth Contour V e l o c i t y E r r o r f P e r i o d (m.) ( ml/1) (m/s) (m/s) winter 100 4.2 0.015 0.007 winter 150 3.8 0.025 0.020 winter 200 3.4 0.037 0.024 summer 100 4.2 0.068 0.043 summer 150 3.8 1 22 summer 200 3.4 0.036 0.037 t 95% conf i d e n c e i n t e r v a l « s c a t t e r among these values and those c a l c u l a t e d u s i n g temperature and s a l i n i t y data but the s c a t t e r i s c o n s i s t e n t with the given e r r o r s . The r e s u l t s obtained i n the l a s t three s e c t i o n s w i l l now be summarised. The s u r f a c e f e a t u r e s of the three p r o p e r t i e s (temperature, s a l i n i t y and d i s s o l v e d oxygen) are dominated by the e f f e c t s of seasonal h e a t i n g or c o o l i n g at the s u r f a c e , f r e s h water i n f l o w from r i v e r s and i n p a r t i c u l a r the F r a s e r R i v e r and from b i o l o g i c a l a c t i v i t y r e s p e c t i v e l y . These e f f e c t s are moderated i n the southern passages where mixing of the water column b r i n g s deeper water up to the s u r f a c e . T h i s deeper water lowers the summertime temperature, r a i s e s s l i g h t l y the wintertime temperature, 44 r a i s e s the summertime s a l i n i t y and lowers the d i s s o l v e d oxygen c o n c e n t r a t i o n . At the near s u r f a c e depths of 50 and 75 m the seasonal i n f l u e n c e of su r f a c e h e a t i n g and c o o l i n g and f r e s h water input are f e l t where there i s s u f f i c i e n t mixing of the su r f a c e waters down to these depths. The e f f e c t of smal l s c a l e events (both i n time and space) i s e v i d e n t . At 100 m depth and below, the e f f e c t of two renewal episodes are seen i n the v a r i a t i o n of a l l three p r o p e r t i e s . The f i r s t event began p r i o r to December 1967 i n the southern end of the S t r a i t and continued through January 1968. The e f f e c t s of t h i s r e l a t i v e l y c o l d , f r e s h and high oxygen water inflow were f e l t about two months l a t e r at the northern end of the S t r a i t where the winter renewal continued u n t i l A p r i l . The second renewal p e r i o d began i n March i n the southern passages b r i n g i n g warm, high s a l i n i t y and low oxygen water i n t o the S t r a i t u n t i l J u l y or August 1968. Again approximately two months l a g oc c u r r e d between the appearance of the water i n the southern passages and i t s a r r i v a l at the northern end of the S t r a i t of Georgia. 3.4 THE DENSITY STRUCTURE The d e n s i t y v a r i a t i o n w i t h i n the S t r a i t of Georgia and p a r t i c u l a r l y d u r i n g p e r i o d s of renewal i s important because i t governs the i n t e r n a l dynamics of the system, through the thermal wind equations (Stacey et a l . , 1987b). In t h i s s e c t i o n , p l o t s s i m i l a r to those used i n the preceding 45 s e c t i o n s to d e s c r i b e the temperature, s a l i n i t y and d i s s o l v e d oxygen d i s t r i b u t i o n are presented f o r 0fc ( F i g . 3.14 a-h). Before s t a r t i n g , i t should be po i n t e d out that a comparison of these p l o t s with the corresponding s a l i n i t y p l o t s at each depth ( F i g . 3.12 a-h) shows that the d e n s i t y and s a l i n i t y s t r u c t u r e s are very c l o s e l y l i n k e d . Indeed, i t i s p o i n t l e s s to d e s c r i b e the temporal v a r i a b i l i t y of the renewal p e r i o d s i n terms of d e n s i t y , because there i s , i n p r a c t i c e , l i t t l e d i f f e r e n c e from the r e s u l t s a l r e a d y o btained from the s a l i n i t y data. Since the d e n s i t y at depth i n the S t r a i t of Georgia would presumably i n c r e a s e d u r i n g a renewal episode there must a l s o be a p e r i o d when the d e n s i t y decreases due to upward t u r b u l e n t d i f f u s i o n of s a l t . F i g . 3.14 d-h shows a decrease i n a f c of about 0.1 from January to A p r i l 1968 at the 100 to 300 m l e v e l s . T h i s p e r i o d corresponds to the f i n a l month of the winter renewal through to the onset of the summer renewal. During t h i s time s u r f a c e c o o l i n g , wind s t i r r i n g and the low f r e s h water input from the F r a s e r reduce the s t r a t i f i c a t i o n of the water column and f a c i l i t a t e mixing. The i n c r e a s e d s t r a t i f i c a t i o n d u r i n g the summer exchange i n h i b i t s the upward d i f f u s i o n of s a l t and, along with high s a l i n i t y water e n t e r i n g at depth from Juan de Fuca S t r a i t , r e s u l t i n a gradual i n c r e a s e in a f c w i t h i n the S t r a i t from A p r i l to October. That mixing i n the deep water in the S t r a i t of Georgia can allow f o r s u f f i c i e n t upward d i f f u s i o n of s a l t to d r i v e a 46 twice y e a r l y renewal i s understandable given the very a c t i v e c u r r e n t f i e l d w i t h i n the S t r a i t . A n a l y s i s of c u r r e n t meter records by Chang(l976) and Chang et a l (1976), at three moorings' running a c r o s s the S t r a i t near Vancouver showed that the energy a s s o c i a t e d with the low frequency v a r i a b i l i t y (centered on a 30 day pe r i o d ) was equal to t i d a l e n e r g i e s at 50 m depth and dropped to 30% of the t o t a l energy at 200 m depth. Coherence between s t a t i o n s (spaced 10 km apa r t ) was e s s e n t i a l l y zero i n d i c a t i n g that these motions have a r e l a t i v e l y small s p a t i a l s c a l e and, together with the r e l a t i v e l y l a r g e e n e r g i e s , may c o n t r i b u t e and i.ndeed dominate mixing processes i n the deep water. More r e c e n t l y , Stacey et a l . (1987 a) found that wind s t r e s s at the s u r f a c e and the n o n l i n e a r i n t e r a c t i o n of the t i d e s with the bottom topography f o r c e d much of the low-frequency motion measured by a c u r r e n t meter and cyclesonde a r r a y i n the same area o f f Vancouver. The near bottom response to t i d a l f o r c i n g r e s u l t e d i n c u r r e n t s of up to 30 cm/s w i t h i n 50 m of the bottom at one s t a t i o n . S i g n i f i c a n t e n e r g i e s were observed at a l l depths. The measured flow was a l s o found to be p o s s i b l y u n s t a b l e , i n d i c a t i n g that b a r o c l i n i c i n s t a b i l i t y or some other mechanism might allow the energy i n the l a r g e s c a l e motion to be made a v a i l a b l e f o r mixing. 47 3.5 VARIATION OF THE RENEWAL WITH DEPTH It has a l r e a d y been shown i n the T-S a n a l y s i s that s i g n i f i c a n t d i f f e r e n c e s occur with depth i n water p r o p e r t i e s and i n renewal processes. For example renewal was shown to occur i n s e v e r a l stages i n the main body of the S t r a i t (at l e a s t at one s t a t i o n , see F i g . 3.9 b) with s u c c e s s i v e events p e n e t r a t i n g to deeper l a y e r s and e v e n t u a l l y reaching the bottom. One depth-dependent f e a t u r e which stands out c l e a r l y i n the temperature, s a l i n i t y and d i s s o l v e d oxygen contour p l o t s i s the change i n ti m i n g of the renewal above and below the 200 m l e v e l . F i g . 3.11 d and e, 3.12 d and e and 3.13 d and e a l l show the wintertime renewal ( c o l d , f r e s h , high oxygen water) ending i n February to March i n the southern end of the S t r a i t at s t n . 46 and 42 at 100 and 150 m depth. The corresponding p l o t s at the 250 and 300 m l e v e l ( F i g . 3.11 g and h, 3.12 g and h, 3.13 g and h) show the same extreme c o n d i t i o n s somewhat l a t e r (minimum temperature and s a l i n i t y , maximum d i s s o l v e d oxygen), i n May and June. The s i t u a t i o n at the 200 m l e v e l i s somewhat ambiguous because the temperature minimum and oxygen maximum occur i n May and June while the s a l i n i t y minimum occurs s l i g h t l y e a r l i e r i n A p r i l . In order to d i s p l a y these f e a t u r e s more c l e a r l y , contour p l o t s of temperature and s a l i n i t y with axes of depth and time are given i n F i g . 3.15 and 3.16. S t a t i o n 42 ( F i g . 3.15) l i e s o f f the mouth of the F r a s e r River and s t n . 27 ( F i g . 3.16) i s northeast of Namaimo (see 48 F i g . 2.1). The temperature at s t n . 42 ( F i g . 3.15 a) reaches a minimum f o r the year in mid to l a t e February at and above the 180 m l e v e l . The minimum f o r the year below t h i s l e v e l occurs i n e a r l y June, about 3 i months l a t e r . In c o n t r a s t , the timing of the t r a n s i t i o n from summer to winter renewal i s l e s s s e n s i t i v e to depth. The maximum temperature occurs i n October at the 100 m l e v e l and probably one or two months l a t e r at the 250 m l e v e l . T h e ^ s a l i n i t y at s t n . 42 ( F i g . 3.15 b) reaches a minimum i n February or March above the 200 m l e v e l . The minimum then s h i f t s to A p r i l at 200 m and J u l y at 300 m. Again the maximum f o l l o w i n g the summer renewal shows r e l a t i v e l y l i t t l e v a r i a t i o n with depth and occurs i n October or November at a l l l e v e l s below 50 m. F i g . 3.16 shows the temperature and s a l i n i t y v a r i a t i o n at s t n . 27, near Nanaimo. The minimum temperature and s a l i n i t y i n the 75 to 175 m l a y e r occur i n March or A p r i l , somewhat l a t e r than at s t n . 42. The minima at 300 m occur i n June. The evidence t h e r e f o r e suggest that the winter renewal p e r i o d below the 200 m l e v e l continues f o r roughly 3 months past the end of the renewal p e r i o d above the 200 m l e v e l . That the depth of 200 m i s important i n the renewal process - f o r t h i s year at l e a s t - i s not s u r p r i s i n g s i n c e i t corresponds to the depth of the s i l l s e p a r a t i n g the S t r a i t of Georgia from Juan de Fuca S t r a i t and the P a c i f i c Ocean. Exchange above t h i s l e v e l o ccurs i n a continuous and 49 vig o r o u s way with the wide range in p r o p e r t i e s from winter to summer water (+1.6°C, +0.6°/oof -1.5 ml/1) i n d i c a t i n g t h a t a l a r g e volume of water i s i n v o l v e d . The range i n the p r o p e r t i e s of the source water from Juan de Fuca S t r a i t i s roughly twice as l a r g e . The bathymetry of the S t r a i t of Georgia i n c l u d e s r i s e s to about 180 m between Hornby and La s q u e t i i s l a n d s , to 200 m i n the very narrow c o n s t r i c t i o n between L a s q u e t i and Texada i s l a n d s and to 100 m from the northern t i p of Texada to Harwood I s l a n d and the B.C. mainland ( F i g . 1.2). T h i s e f f e c t i v e l y separates the northern basin of the S t r a i t of Georgia (west and northwest of Texada I s l a n d , s t n s . 12,14) below the 200 m l e v e l , from the r e s t of the S t r a i t ( s t n s . 2,3,27,39,42). T h i s i s r e f l e c t e d i n the temperature, s a l i n i t y and d i s s o l v e d oxygen d i s t r i b u t i o n s at the 250 m and 300 m l e v e l s ( F i g . 3.11 g and h, 3.12 g and h, 3.13 g and h ) . In p a r t i c u l a r the s a l i n i t y p l o t s at the two l e v e l s show no l i n k between s a l i n i t y v a l u e s at s t a t i o n s 3 and 12. S t a t i o n s 6 and 9 s t r a d d l e the shallow area between Hornby and L a s q u e t i i s l a n d s . Deep water (below 200 m) i n the northern b a s i n i s formed from water that comes over the 200 m s i l l from the southern b a s i n . T h i s i s borne out by the low s a l i n i t y at s t a t i o n s 12 and 14 north of Hornby I s l a n d at 300 m depth compared to the s a l i n i t y at the same l e v e l at s t n . 2: 30.5 - 30.8°/ Oo in the no r t h over the 12 month p e r i o d compared to 30.8 - 31.1°/ 0O i n the south. The 30.5 - 3 0 . 8 ° / o o range matches s a l i n i t y v a l u e s found at the 50 200 m l e v e l i n the c e n t r a l part of the S t r a i t . An estimate can be made of the depth of "zero motion" w i t h i n the S t r a i t of Georgia and i t s connection to Juan de Fuca S t r a i t through the southern passages. T h i s depth, at which the outgoing upper l a y e r meets the incoming lower l a y e r i n the standard e s t u a r i n e c i r c u l a t i o n , i s governed by the p h y s i c a l dimensions of the s i l l and the s t r a t i f i c a t i o n of the water column and perhaps by the C o r i o l i s f o r c e . F i g . 3.11 a-c show the v a r i a t i o n of the temperature with time along the major a x i s of the S t r a i t f o r depths of 0,50 and 75 m. At the s u r f a c e ( F i g . 3.11 a) the seasonal p a t t e r n of a i r - s e a h e a t i n g and c o o l i n g dominates the water temperature and has a uniform e f f e c t over the e n t i r e S t r a i t , except i n the mixing zone i n the south ( s t n s . 59, 56 and 46). At the 50 m l e v e l , there i s some evidence of northward moving water i n the southern and c e n t r a l S t r a i t (south of s t n . 27) from December 1967 to June 1968. The s i g n a l d i s a p p e a r s north of s t n . 27. T h i s may be a r e f l e c t i o n of the f a c t that the near s u r f a c e d e n s i t y s t r a t i f i c a t i o n i s u s u a l l y higher i n the c e n t r a l S t r a i t of Georgia than i t i s f u r t h e r north ( F i g . 3.3 a-b). T h i s c o u l d r e s u l t i n the depth of flow r e v e r s a l being somewhat higher than 50 m i n the c e n t r a l S t r a i t and somewhat lower than 50 m i n the northern S t r a i t . A northward moving s i g n a l i s present everywhere i n the S t r a i t at the 75 m l e v e l , thereby l i m i t i n g the estimate to l e s s than 75 m. 51 3.6 LATERAL VARIABILITY The preceding s e c t i o n s have provided d e s c r i p t i o n s of the temporal v a r i a b i l i t y and the d i s t r i b u t i o n with depth and along the major a x i s of the S t r a i t of Georgia, of the temperature, s a l i n i t y and d i s s o l v e d oxygen c o n c e n t r a t i o n . No account has yet been made of the v a r i a b i l i t y a cross the S t r a i t and of what t h i s may say about the renewal pr o c e s s . S i m p l i f i e d maps of water p r o p e r t i e s i n the S t r a i t of Georgia northeast of the F r a s e r R i v e r mouth are shown i n F i g . 3.17 to 3.20 f o r four c r u i s e s (January, A p r i l , J u l y and December 1968) and three depths (100, 150 and 200 m). These p l o t s are based on data from the three l i n e s of s t a t i o n s running p a r a l l e l to the northwest/southeast a x i s of the S t r a i t ( F i g . 2.1). The d i s t a n c e between the l i n e s i s assumed constant and no account i s taken of the c o a s t l i n e . T h i s i d e a l i z a t i o n i s s u f f i c i e n t f o r the q u a l i t a t i v e a n a l y s i s which f o l l o w s . The s t a t i o n s marked along the h o r i z o n t a l a x i s r e f e r to the c e n t r a l l i n e of s t a t i o n s o n l y . The January and J u l y c r u i s e s c o i n c i d e with the winter and summer renewal p e r i o d s . In January ( F i g . 3.17 a ) , c o l d water i s seen along the eastern s i d e of the S t r a i t ( o p p o s i t e s t n s . 27, 39 and 42) at 150 m depth and to some extent at 100 m depth. T h i s s i g n a l i s not apparent i n the deeper water at 200 m. A s i m i l a r p a t t e r n of northward flow p e n e t r a t i o n along the eas t e r n boundary i s found i n the corresp o n d i n g s a l i n i t y p l o t s ( F i g . 3.17 b ) . 52 The summer renewal produces a somewhat stronger l a t e r a l v a r i a t i o n with c l e a r s i g n a l s at the 150 and 200 m l e v e l s i n the temperature f i e l d ( F i g . 3.19 a ) , and i n the s a l i n i t y at 150 m depth ( F i g . 3.19 b ) . Warm, s a l t y water appears along the e a s t e r n l i n e of s t a t i o n s i n the c e n t r a l p a r t of the S t r a i t . A weaker s i g n a l i s a l s o apparent i n the temperature at 100 m and the s a l i n i t y at 100 and 200 m. Very f r e s h water - f o r the depth - i s seen at the 100 m l e v e l i n December 1968 at s t n . 43 along the eastern l i n e o p posite s t n . 42. Whether t h i s i s due to the onset of winter renewal or j u s t l o c a l mixing i s d i f f i c u l t t o say. The lowest s a l i n i t y measured anywhere i n the S t r a i t d u r i n g the p r e v i o u s winter (December 1967 to March 1968) was only 29.8°/oo/ w e l l above the 2 9 . 2 ° / 0 0 water found at s t n . 43 i n December 1968. The l a t e r a l v a r i a t i o n of the renewal s i g n a l i s perhaps b e t t e r d e s c r i b e d by the use of contour p l o t s showing the temporal v a r i a t i o n of the p r o p e r t i e s along the e a s t e r n , c e n t r a l and western l i n e s . These p l o t s f o r the c e n t r a l l i n e ( F i g . 3.11-3.14) have a l r e a d y been used to show the v a r i a b i l i t y of p r o p e r t i e s along the major a x i s of the S t r a i t and to d e s c r i b e the renewal s i g n a l . The e a s t e r n and western s e c t i o n s are presented i n F i g . 3.21 and 3.22. Comparison of the temperature contour p l o t s at the 100 m l e v e l f o r the e a s t e r n and western s e c t i o n s ( F i g . 3.21 a and b) and f o r the c e n t r a l s e c t i o n ( F i g . 3.11 d) shows evidence of a f l a t t e n i n g of the contour l i n e s (corresponding to an i n c r e a s e i n v e l o c i t y ) from west to e a s t . A s l i g h t 53 i n t e n s i f i c a t i o n of the s i g n a l a l s o occurs along the e a s t e r n s e c t i o n i n the winter, lowering temperatures to l e s s than 7.8°C nor t h of s t n . 37 i n March as opposed to a minimum of gre a t e r than 7.8°C i n the c e n t r a l and western s e c t i o n s . The v a r i a t i o n i n c h a r a c t e r i s t i c s of the summer renewal i s more dramatic, with a very f a s t i n c r e a s e of 1.0°C from 8.4°C o c c u r r i n g at s t n s . 37 to 20 i n the east from J u l y to September. The corresponding t r a n s i t i o n i s much slower i n the c e n t r a l and western s e c t i o n s and indeed, probably does not reach 9.4°C before the onset of winter renewal d u r i n g or f o l l o w i n g December 1968. The corresponding s a l i n i t y p l o t s ( F i g . 3.22 a,b and 3.12 d) show s i m i l a r f e a t u r e s with the i n c r e a s e d s i g n a l v e l o c i t y i n the east being somewhat more pronounced. Temperature p l o t s at the 200 m l e v e l do not show any s i g n i f i c a n t a c r o s s - S t r a i t v a r i a b i l i t y . The s a l i n i t y p l o t s at 200 m are d i f f e r e n t from west to east with water of s a l i n i t y l e s s than 30.6°/ Oo w e l l e s t a b l i s h e d i n March along the e a s t e r n and c e n t r a l s e c t i o n . However i t i s d i f f i c u l t to say whether t h i s i s s i g n i f i c a n t or not because of the lack of data at s e v e r a l of the s t a t i o n s ( f o r example s t n . 40 has a nominal depth of 150 m). The v e l o c i t i e s of the renewal s i g n a l a s s o c i a t e d with the northward movement of water with a given temperature or s a l i n i t y have been estimated from the data at 100 m depth f o r the e a s t e r n and western s e c t i o n s and are given below i n Table 3.5. 54 Table 3.5 V e l o c i t i e s from the Temperature and S a l i n i t y S i g n a l s During the Winter Renewal at the 100 m l e v e l P r o p e rty S e c t i o n Contour V e l o c i t y (m/s) E r r o r t (m/s) Temperature East C e n t r a l West 8.6°C 8.6°C 8.6°C 0.031 0.023 0.022 0.008 0.006 0.005 S a l i n i t y East C e n t r a l West 30.1°/oo 30.1°/oo 30.0°/oo 0.041 0.028 0.030 0.017 0.008 0.021 t 95% con f i d e n c e i n t e r v a l There i s an i n d i c a t i o n of a change i n v e l o c i t i e s a c r o s s the S t r a i t , with the high v a l u e s of 0.031 ±.008 m/s and 0.041 ±.017 m/s i n the eas t e r n s e c t i o n , and v e l o c i t i e s at the c e n t r a l and western s e c t i o n s c o n s i s t e n t l y 0.008 to 0.011 m/s lower. An a p p r o p r i a t e s c a l e f o r motion i n a s t r a t i f i e d r o t a t i n g f l u i d i s the i n t e r n a l Rossby r a d i u s (LeBlond and Mysak, 1978). A simple estimate based on a 2 l a y e r model can be made. An e a r l i e r d i s c u s s i o n of the depth of flow r e v e r s a l or "zero motion" showed that the upper o u t f l o w i n g l a y e r would l i k e l y be about 50 m t h i c k . Reasonable parameters might t h e r e f o r e be a 50 m upper l a y e r , a 250 m lower l a y e r and d e n s i t y v a l u e s taken at 25 m and 200 m (a f c = 22.0 and 23.7, see F i g . 3.7 i i ) . The r e s u l t i s an i n t e r n a l Rossby r a d i u s of about 10 km. T h i s corresponds to the e x p o n e n t i a l s c a l e of t r a p p i n g of a flow by the C o r i o l i s f o r c e on the 55 r i g h t hand w a l l of the S t r a i t . I t i s perhaps then, not s u r p r i s i n g to f i n d a somewhat gr e a t e r speed of s i g n a l propagation on the eas t e r n s i d e , s i n c e a t h i c k e r l a y e r of replacement f l u i d i s found t h e r e . If mixing i s important i n a t t e n u a t i n g the property c o n t r a s t of renewal waters, i t would then be expected that i t would be most important when the advected l a y e r i s t h i n n e s t ; waters on the western s i d e would l o s e t h e i r c o n t r a s t more q u i c k l y and appear to t r a v e l north more slowly than on the other s i d e of the S t r a i t , where a t h i c k e r l a y e r i s found. Dynamical e f f e c t s may a l s o r e i n f o r c e t h i s e f f e c t . 4. VOLUMETRIC, HEAT AND SALT ANALYSES 4.1 VOLUMETRIC ANALYSIS In order to determine the r e l a t i v e importance of d i f f e r e n t c l a s s e s of water p r o p e r t i e s i n the S t r a i t of Georgia with a given temperature and s a l i n i t y range, and to observe t h e i r v a r i a t i o n with the seasons, a v o l u m e t r i c a n a l yses of the S t r a i t was done. The a n a l y s i s was f i r s t a p p l i e d to the whole S t r a i t from the s u r f a c e to the bottom. The water column was then d i v i d e d i n t o three l a y e r s (0 - 80 m, 80 - 200 m, 200 m - bottom) and the a n a l y s i s c a r r i e d out on each l a y e r s e p a r a t e l y . The l a y e r s were chosen on the b a s i s of e a r l i e r r e s u l t s from t h i s study which i n d i c a t e that the water p r o p e r t i e s w i t h i n each l a y e r have c h a r a c t e r i s t i c s d i s t i n c t from the other l a y e r s (at l e a s t f o r some p e r i o d s of time) and that t h i s i n d i c a t e s something about the renewal p r o c e s s . I t might seem n a t u r a l to choose a l a y e r boundary of 50 m i n s t e a d of 80 m given the p r e v i o u s d i s c u s s i o n on the depth of flow r e v e r s a l i n the e s t u a r y . However, i t was a l s o shown th a t , even at 50 m depth, there are s t i l l s i g n i f i c a n t s u r f a c e and small s c a l e e f f e c t s . A l a y e r boundary of 80 m has been chosen i n order to exclude d i r e c t s u r f a c e e f f e c t s p a r t i c u l a r l y away from the mixing zone i n the southern S t r a i t and passages. The data p r o c e s s i n g part of the v o l u m e t r i c a n a l y s i s c o n s i s t s of counting the volume of water i n a l l or a p a r t of the S t r a i t which has p r o p e r t i e s w i t h i n s p e c i f i c temperature 56 57 and s a l i n i t y i n t e r v a l s . Summing the volume over a l l the i n t e r v a l s g i v e s the t o t a l volume in the region and l a y e r being c o n s i d e r e d . A d e s c r i p t i o n of the a l g o r i t h m f o l l o w s . The S t r a i t of Georgia i s d i v i d e d i n t o 4 km X 4 km squares using the g r i d d e s c r i b e d i n Chapter 2 under bathymetry (see F i g . 2.4). Each g r i d square i s a s s i g n e d a p a r t i c u l a r nearby s t a t i o n . The data from that s t a t i o n ( i f a v a i l a b l e ) i s used to set the temperature and s a l i n i t y v a l u e s f o r the volume of water i n the g r i d square. Property val u e s f o r each s t a t i o n are determined, i n the v e r t i c a l d i r e c t i o n , at 20 m i n t e r v a l s over the whole water column. The 4 km g r i d i s then scanned and a running t o t a l i s made of the number of boxes (4 km X 4 km X 20 m) belonging to each T-S range. If there are no data at the s t a t i o n a s s o c i a t e d with a p a r t i c u l a r g r i d square ( u s u a l l y because the s t a t i o n i s i n water shallower than the g r i d square depth) then the next nearest s t a t i o n i s t r i e d . T h i s process continues u n t i l data at the d e s i r e d depth are found. Once the e n t i r e r e g i o n i s covered, the heat and s a l t content are c a l c u l a t e d by simply m u l t i p l y i n g the volume a s s o c i a t e d with each T-S range by the temperature and s a l i n i t y and by a p p l y i n g an a p p r o p r i a t e s c a l i n g f a c t o r . Volume t o t a l s f o r each T-S range (or box) are rounded to the nearest i n t e g e r and p r i n t e d . In some cases ( i n p a r t i c u l a r the upper l a y e r i n summer) there are l i k e l y to be many volume t o t a l s below 0.5 km3 which do not show at a l l . T h i s however does not s i g n i f i c a n t l y a f f e c t the o v e r a l l 58 volume t o t a l which agrees with more accurate c a l c u l a t i o n s t o w i t h i n 0.5%. One c a u t i o n a r y note should be made before proceeding f u r t h e r . Although i t i s tempting to c a l l water i n one T-S box ( i . e . the water having temperature and s a l i n i t y i n the range T 0 to T 0+AT and S 0 to S 0+AS) " d i f f e r e n t " and separate from water i n some other T-S box at a d i f f e r e n t time, i t should not be done because of the e x t e n s i v e mixing that occurs. For example a l l of the e a r l y summer deep water (below 200 m) i n the S t r a i t of Georgia i s c o l d e r than 8.8°C and 99% of the water i n the same region 6 months l a t e r i s warmer than 8.8°C. One may however not conclude that 99% of the deep water was r e p l a c e d d u r i n g the summer/fall renewal. 4.1.1 SURFACE TO BOTTOM Re s u l t s of the v o l u m e t r i c a n a l y s i s a p p l i e d to the whole water column i n the S t r a i t of Georgia f o r a l l 12 c r u i s e s are presented i n F i g . 4.1. The t o t a l volume of the S t r a i t i s 1167 km3. The numbers are i n km3 and r e f e r to the volume of water found to have i t s temperature and s a l i n i t y w i t h i n the range T 0 to T 0+AT and S 0 to S 0+AS. T 0 and S 0 are the values along the axes opposite the number and AT and AS are the increments to the next t i c k mark from T 0 and S 0 ( i . e . 0.5°C and 0.5°/oo)« F o r example i n F i g . 4.1 a the volume of water with temperature and s a l i n i t y i n the range 8.0 to 8.5°C and 27.5 to 2 8 . 0 ° / o o i s 19 km3. 59 A quick scan of the t a b l e s i n F i g . 4.1 show that the high s a l i n i t y water v a r i e s l i t t l e from month to month i n both s a l i n i t y and temperature, whereas the low s a l i n i t y water (say <29.0°/ Oo) c o v e r s , at one time or another, the complete range of temperatures (5 to 19.5°C) and reaches a low s a l i n i t y of l 9 ° / 0 0 . T h i s i s c l e a r l y the r e s u l t of the su r f a c e water being s u b j e c t e d to the d i r e c t f r e s h water input of the Fra s e r r i v e r and to summer h e a t i n g and winter c o o l i n g . In summer, i n p a r t i c u l a r ( F i g . 4.1 g - i ) , the h i g h l y s t r a t i f i e d s u r f a c e l a y e r , high i n s o l a t i o n and high f r e s h water input f u r t h e r encourages l a r g e g r a d i e n t s i n temperature and s a l i n i t y . A c h a r a c t e r i s t i c of the s a l i n i t y s t r u c t u r e i n the S t r a i t i s that i t always i n c r e a s e s with depth at any given l o c a t i o n and that the deepest p a r t of the S t r a i t almost always has the highest s a l i n i t y . S a l t y Juan de Fuca water does o c c a s i o n a l l y appear at depth over the s i l l i n the southern passages. T h i s water i s r a p i d l y mixed with the surrounding water as i t enter s the S t r a i t , d e c r e a s i n g the s a l i n i t y below the l e v e l i n the deepest region f o r a l l but a few s t a t i o n s next to or i n the southern passages. For a l l p r a c t i c a l purposes then, the s a l i n i t y i s a good i n d i c a t i o n of depth. The temperature i n v e r s i o n which appears i n winter (warm, summer water at depth and c o l d , a i r - c o o l e d water at the s u r f a c e ) i s i n d i c a t e d by the p o s i t i v e c o r r e l a t i o n between temperature and s a l i n i t y which i s c l e a r i n F i g . 4.1 b-d (January to March 1968). 60 It i s i n t e r e s t i n g to compare the v o l u m e t r i c t a b l e s f o r the p e r i o d s between summer and winter renewal. F i g . 4.1 a, e and 1 (December 1967, A p r i l and December 1968), are based on data gathered d u r i n g these p e r i o d s . Three boxes i n each t a b l e d e f i n e the c o n t r i b u t i o n s made by each of the three l a y e r s . The o v e r l a p between l a y e r s i s p a r t l y due to sloped i s o p l e t h s ( i . e . not h o r i z o n t a l ) , p a r t l y to a temperature i n v e r s i o n (temperature maximum at 80 m i n December 1967) and near i s o t h e r m a l c o n d i t i o n s and a l s o to the l a r g e T-S square s i z e (0.5°C X 0.5°/oo)« F o r example, the o v e r l a p between the intermediate and deep l a y e r s i n December 1967 i s 262 km3 ( F i g . 1.4 a) whereas the same s t a t i s t i c f o r a square s i z e reduced to 0.2°C X 0 . 2 ° / o o i s 178 km3. The intermediate and deep water i n December 1967 should be c l o s e to t h e i r y e a r l y maxima i n temperature and s a l i n i t y . In order to q u a n t i f y t h i s and s i m i l a r f e a t u r e s , the ranges i n temperature and s a l i n i t y r e q u i r e d to i n c l u d e 50% and 90% of the t o t a l volume of water were c a l c u l a t e d and are shown below i n Table 4.1.1. For example, 90% of the water in the S t r a i t undergoes a change of about -1.0°C and between 0 and -0.5°/oo over the course of the winter renewal p e r i o d . I t then r e t u r n s i n December 1968 to roughly the same s t a t e as i t was i n December 1967. 4.1.2 THE SURFACE LAYER (0 - 80 m) Volumetric a n a l y s i s t a b l e s f o r the s u r f a c e l a y e r (0 -80 m depth) are given i n F i g . 4.2 using the same box s i z e 61 Table 4.1.1 S t r a i t of Georgia Month Mode (%) Range T (°C) Range S ( % o ) Dec 67 50 9.0 - 9.5 29.5 -- 31 .0 90 8.5 - 10.0 28.0 -- 31 .5 Apr 68 50 7.5 - 9.0 29.5 -- 31 .0 90 7.5 - 9.0 28.0 • - 31 .0 Dec 68 50 9.0 - 9.5 29.5 • - 31 .0 90 7.5 - 9.5 27.0 • - 31 .5 as f o r F i g . 4.1. These t a b l e s are not of much importance to the deep water renewal but have been i n c l u d e d i n order to show how the extreme v a l u e s i n temperature and s a l i n i t y noted i n the previous s e c t i o n and seen i n F i g . 4.1 are e n t i r e l y due to the upper l a y e r v a r i a b i l i t y . Examples from the January, A p r i l , l a t e J u l y and November 1968 c r u i s e s have been chosen i n order to cover a wide range of p r e v a i l i n g c o n d i t i o n s . Two i n t e r e s t i n g f e a t u r e s that are evident i n these t a b l e s are the q u i t e dramatic negative c o r r e l a t i o n between s a l i n i t y and temperature d u r i n g summer c o n d i t i o n s ( F i g . 4.2 c ) , and the almost i s o t h e r m a l c o n d i t i o n s i n November ( F i g . 4.2 d) as the s u r f a c e water c o o l s . 4.1.3 THE INTERMEDIATE LAYER (80 - 200 m) I t i s i n t h i s l a y e r that the strongest renewal s i g n a l should occur i n the v o l u m e t r i c a n a l y s e s . V o l u m e t r i c t a b l e s f o r the water in the S t r a i t of Georgia between 80 and 200 m depth are given i n F i g . 4.3 with a l l 12 c r u i s e s i n c l u d e d . 6 2 The t o t a l volume i n t h i s l a y e r i s 4 6 7 km3. These t a b l e s provide a dramatic p i c t u r e of the e f f e c t of renewal on the water p r o p e r t i e s i n t h i s l e v e l . F i g . 4 . 3 a (December 1 9 6 7 ) shows the s i t u a t i o n f o l l o w i n g the summer renewal and p r i o r to the onset of the winter renewal. The water i s found w i t h i n a f a i r l y narrow range i n temperature and s a l i n i t y with no d i s t i n c t d i v i s i o n s i d e n t i f y i n g one water mass from another. F i g . 4 . 3 b (January 1 9 6 8 ) on the other hand shows the December 1 9 6 7 water centered at about 9 . 0 ° C and 3 0 . 4 ° / o o r but an o b v i o u s l y separate water mass has a l s o appeared, centered around 7 . 8 ° C and 3 0 . 1 ° / o o and c o n s t i t u t i n g 1 0 % of the t o t a l water volume. One month l a t e r ( F i g . 4 . 3 c) the 7 . 8 ° C water seen i n January has disappeared presumably mixing with the warm water, b r i n g i n g i t s temperature down by about 0 . 4 ° C to an average of about 8 . 6 ° C . However a l a r g e volume of mostly 7 . 2 to 7 . 4 ° C water has appeared making up 1 5 % of the t o t a l . The f a c t that there i s an a c t u a l gap at 7 . 8 to 8 . 0 ° C s e p a r a t i n g the two water masses i n d i c a t e s t h at the new water seen i n January has had time to be mixed in with the o l d summer water before a f r e s h i n t r u s i o n of c o l d water took p l a c e . T h i s shows that the renewal process may e x h i b i t b u r s t s of new water at times, r a t h e r than being a uniform and continuous i n f l o w . In the t a b l e f o r March ( F i g . 4 . 3 d) the two separate water masses seen i n February have p a r t l y mixed, reducing the t o t a l range i n p r o p e r t i e s . The remnants of separate water masses are s t i l l d i s c e r n i b l e and are 63 brought out by the boxes e n c l o s i n g 50% of the t o t a l volume. A month l a t e r , the process i s complete, r e s u l t i n g i n a s i n g l e water mass with a r e l a t i v e l y narrow range of temperature and s a l i n i t y . T r a c i n g the behaviour of water masses as they appear or are transformed d u r i n g renewal can be done i n a more q u a n t i t a t i v e f a s h i o n by c a l c u l a t i n g the range of p r o p e r t i e s which encloses 50% or 90% of the t o t a l volume of water i n the S t r a i t w i t h i n the l a y e r . In p r a c t i c e , t h i s means that the minimum number of T-S boxes whose t o t a l volume make up 50% and 90% of the t o t a l volume, are i s o l a t e d from the r e s t ( i . e . box volumes are summed s t a r t i n g with the h i g h e s t value and c o n t i n u i n g i n descending order u n t i l 50% and then 90% of the t o t a l volume i s i n c l u d e d ) . The mininum spread i n temperature and s a l i n i t y needed to i n c l u d e a l l the box i s then found. Table 4.1.2 below, l i s t s these ranges f o r each of the c r u i s e s . The 50% mode i s most u s e f u l i n determining the l o c a t i o n on the T-S graph of the l a r g e s t c o n c e n t r a t i o n or block of water i n the S t r a i t . T h e r e f o r e , i f the water i n the S t r a i t as a whole i s behaving i n a c e r t a i n way then the 50% s t a t i s t i c s should show i t . The 90% mode r e a c t s to the o v e r a l l behaviour of the water as w e l l , but i s a l s o s e n s i t i v e to small but s i g n i f i c a n t departures from the dominant s t a t e . The drop i n December to January of the 50% temperature range from 9.2 - 9.6 to 8.8 - 9.2°C i n d i c a t e s t h a t , a l r e a d y , 64 Table 4.1.2 Intermediate Layer, S t r a i t of Georgia Month Mode (%) Range T (°C) Range S (°/o Dec 67 50 9.2 - 9.6 30.2 - 30.8 90 8.6 - 9.6 30.0 - 31.0 Jan 68 50 8.8 - 9.2 30.2 - 30.8 90 7.4 - 8.2 30.0 -31.0 8.4 - 9.4 Feb 50 8.0 - 8.8 29.6 - 39.8 30.0 - 30.6 90 7.2 - 7.6 29.6 - 30.8 8.0 - 9.2 Mar 50 7.6 - 8.2 29.8 - 30.6 8.4 - 8.6 90 7.6 - 8.8 29.6 - 30.6 Apr 50 7.8 - 8.4 29.8 - 30.4 90 7.8 - 8.6 29.6 - 30.6 May 50 8.0 - 8.6 30.0 - 30.6 90 7.8 - 8.8 29.8 - 30.8 J u l e a r l y 50 8.2 - 8.6 30.0 - 30.6 90 8.0 - 8.8 29.8' - 30.8 J u l l a t e 50 8.2 - 8.8 30.0 - 30.6 90 8.2 - 9.2 29.8 - 30.8 Aug 50 8.4 - 8.8 30.2 - 30.8 90 8.4 - 9.0 29.8 - 30.8 9.4 - 9.8 Oct 50 8.6 - 9.4 30.4 - 30.8 90 8.6 - 10.0 30.0 - 31.0 Nov 50 9.2 - 9.4 30.2 - 30.8 90 8.8 - 9.4 30.0 -31.0 Dec 50 9.0 - 9.4 30.2 - 30.8 90 8.6 - 8.8 29.8 - 30.8 9.0 - 9.4 a s i g n i f i c a n t amount of new winter water has appeared and mixed through a l a r g e p a r t or a l l of the S t r a i t . The s p l i t 65 i n the 90% mode temperatures (7.4 - 8.2°C and 8.4 - 9.4°C) shows a separate water mass e n t e r i n g the l a y e r with temperature c e n t e r e d at 7.8°C. The s a l i n i t y does not change much i n d i c a t i n g that the s a l i n i t y of the renewal water i s not s u b s t a n t i a l l y d i f f e r e n t from the s a l i n i t y of the water a l r e a d y i n the l a y e r . The new water seen i n January (90% mode) h e l p s to drop the February 50% mode temperatures by about 0.6°C. Other c o l d and f r e s h water has a l s o entered the l a y e r with p r o p e r t i e s c e ntered at 7.4°C and 2 9 . 7 ° / 0 0 . S l i g h t l y warmer, new water seen i n March (50% mode) continues the winter renewal. The intermediate l a y e r temperature and s a l i n i t y reach t h e i r lowest values f o r the year i n A p r i l at 7.8 -8.4°C and 29.8 - 3 0 . 4 ° / o o (50% mode). The net decrease d u r i n g the winter renewal p e r i o d from December 1967 to A p r i l 1968 i s 1.3°C and 0 . 4 ° / o o . The s i t u a t i o n f o l l o w i n g A p r i l v a r i e s much more g r a d u a l l y , at l e a s t u n t i l August. No separate water mass i s seen u n t i l the l a t e August c r u i s e . Measurements from each c r u i s e from A p r i l to August show a c o n s i s t e n t r i s e of 0.1 -0.2°C from month to month. The t o t a l r i s e i n temperature f o r 50% of the water i s only about 0.5°C over the 3 i month p e r i o d (7.8 - 8.4°C to 8.4 - 8.8°C). The s a l i n i t y , however, r i s e s a p p r e c i a b l y from i t s low of 29.8 - 30.4°/ Oo i n A p r i l to resume i t s December 1967 value of 30.2 - 30.8, a net gain of 0.4°/oo« T h i s happens in two steps of 0 . 2 ° / o o each i n A p r i l to May and l a t e J u l y to l a t e August. No subsequent 66 i n c r e a s e i n s a l i n i t y occurs f o r the remainder of the year. Instead, the temperature begins a p e r i o d of r a p i d change when a new water mass appears at 9.4 to 9.8°C (90% mode i n August). The new water reaches 10.0°C in October before mixing reduces the range to 8.8 - 9.4°C i n November. The temperature t h e r e f o r e undergoes a net i n c r e a s e of 0.6°C f o r 50% of the water i n the S t r a i t i n t h i s l a y e r , with no change in s a l i n i t y . 4.1.4 THE DEEP LAYER - 200 M TO THE BOTTOM The S t r a i t of Georgia c o n s i s t s of two basins connected over two s i l l s l o c a t e d between L a s q u e t i I s l a n d and the southern t i p of Texada I s l a n d ( s i l l depth i s 180 m), and between L a s q u e t i and Hornby I s l a n d s (200 m). Although the s i l l does not appear to a f f e c t the p r o p e r t i e s of the water from the s u r f a c e to 200 m depth anywhere i n the S t r a i t , i t s e f f e c t i s n o t i c e a b l e i n the northern basin below the 200 m l e v e l . The s a l i n i t y i n p a r t i c u l a r , i s sometimes s i g n i f i c a n t l y lower north of the s i l l at the 250 and 300 m l e v e l s than i t i s south of the s i l l at the same depths (see F i g . 3.7 k and 3.10 g-h" f o r example). As a r e s u l t , the deep l a y e r below 200 metres i s t r e a t e d as two separate b a s i n s i n the v o l u m e t r i c a n a l y s i s which f o l l o w s . For convenience, the area of the S t r a i t which l i e s southeast of the s i l l near L a s q u e t i I s l a n d w i l l be r e f e r r e d to as the c e n t r a l b a s i n , and the area north of the s i l l as the northern b a s i n . 67 Volumetric t a b l e s f o r the twelve c r u i s e s are shown i n F i g . 4.4 f o r the c e n t r a l b a s i n below 200 m depth. The t o t a l volume i s 177.8 km3. The corresponding t a b l e s f o r the northern b a s i n are given i n F i g . 4.5. The northern basin volume i s 27.2 km3. The box s i z e i s 0.1°C X 0.1°/oo» a re d u c t i o n of 75% from that used i n the intermediate l a y e r . The v o l u m e t r i c t a b l e f o r the c e n t r a l b a s i n i n December 1967 ( F i g . 4.4 a) shows a f a i r l y l a r g e range i n temperature and s a l i n i t y i n d i c a t i n g that perhaps new water has r e c e n t l y entered the l a y e r . In c o n t r a s t , the t a b l e one month l a t e r ( F i g . 4.4 b) shows a very homogeneous water mass with the major p a r t of the v a r i a n c e due to the v e r t i c a l s a l i n i t y g r a d i e n t . The 50% mode changes very l i t t l e from December to January (Table 4.1.3 below), whereas the range f o r the 90% mode (temperature) decreases by 50%. Th i s i n d i c a t e s that inhomogeneities i n the water p r o p e r t i e s i n the l a y e r have been reduced - by mixing - and that l i t t l e new water, with p r o p e r t i e s d i f f e r e n t from the average i n the l a y e r , has entered. The northern b a s i n r e s u l t s f o r December 1967 ( F i g . 4.5 a) show a s i m i l a r d i s t r i b u t i o n in temperature (9.0 - 9.2°C f o r the 50% mode, see Table 4.1.4). However, a s i g n i f i c a n t d i f f e r e n c e from the c e n t r a l basin shows up i n the s a l i n i t y , which i s l e s s by about 0.2°/ Oo (50% mode: 30.7 - 30.8°/oo compared to 30.9 - 31.1°/ 0o)« One month l a t e r , i n January, the average temperature and the 50% mode have i n c r e a s e d by about 0.1°C, i n d i c a t i n g that the t a i l end of 68 Table 4.1.3 Deep Layer, C e n t r a l and Southern S t r a i t of Georgia Month Mode (%) Range T (°C) Range S (Voo) Dec 67 50 9. 0 - 9. 3 30 .9 - 31 . , 1 90 8. 9 - 9. 4 30 .8 - 31 . ,2 Jan 68 50 9. 0 - 9. ,2 30 .9 - 31 . , 1 90 9. 0 - 9. .2 30 .7 - 31 . ,2 Feb 50 8. 8 - 9. , 1 30 .8 - 31 . , 1 90 8. 5 - 9. , 1 30 .6 - 31 . . 1 Mar 50 8. 7 - 9. ,0 30 .7 - 31 , .0 90 8. 5 - 9. , 1 30 .6 - 31 . 0 Apr 50 8. 6 - 9. ,0 30 .6 - 30, .9 90 8. 4 " 9. ,0 30 .5 - 30, .9 May 50 8. 3 - 8. ,5 30 .7 - 30, .9 8. 7 - 8. ,9 90 8. 1 - 8. .9 30 .6 - 30, .9 J u l y e a r l y 50 8. 4 - 8. ,6 30 .7 - 30, .9 90 8. 4 - 8. .8 30 .6 - 30, .9 J u l y l a t e 50 8. 5 - 8. .6 30 .7 - 30, .9 90 8. 5 - 8. .7 30 .6 - 30, .9 Aug 50 8. 5 - 8. .8 30 .8 - 30, .9 8. 9 - 9. .0 31 .0 - 31 , . 1 90 8. 5 - 9, .0 30 .8 - 31 , .2 Oct 50 8. 7 - 9, .0 30 .8 - 31 .2 90 8. 6 - 9. , 1 30 .7 - 3 1 , .2 Nov 50 8. 9 - 9. . 1 30 .9 - 31 . 1 90 8. 7 - 9, .2 30 .7 - 31 .2 Dec 50 8. 9 - 9, .0 30 .9 - 31 . 1 90 8. 9 - 9, . 1 30 .8 - 31 , . 1 the summer renewal p e r i o d , marked by i n c r e a s i n g temperature, i s s t i l l having an e f f e c t . The p r o p e r t i e s have a very l i m i t e d range, as i n the c e n t r a l b a s i n at t h i s time. 6 9 The r e l a t i v e l y narrow property ranges i n both basins i n January are d i s r u p t e d i n February by a l a r g e inflow of c o l d , f r e s h water h e r a l d i n g the onset of the winter renewal p e r i o d . Whereas only 5% of the water i n January has a temperature below 9.0°C, 78% of the water i n February i s below 9.0°C. The 50% mode drops from 9.0 - 9.2°C to 8.8 -9.1°C. The s a l i n i t y a l s o shows a small drop from 30.9 -31.1 ° / o o to 30.8 - 31.1 ° / o o f o r the 50% mode. The northern basin temperatures behave i n a s i m i l a r manner and show a 0.1°C drop i n the 50% mode. The presence of new, low temperature water i s seen i n the lower l i m i t of the 90% mode temperature ranges: 8.8°C i n the north and 8.5°C in the c e n t r a l b a s i n . No great change occurs from February to March ( F i g . 4.4 c, d) i n the c e n t r a l b a s i n . A sm a l l s h i f t of the 50% volumes has o c c u r r e d r e s u l t i n g i n ranges of 8.7 - 9.0°C and 30.7 - 31.0 o / o o » T n e northern b a s i n , however, shows marked drops i n both temperature and s a l i n i t y of 0.3 - 0.4°C and 0.1 - 0.2 ° / oo r e s p e c t i v e l y (see Table 4.1.4 and F i g . 4.5 c - d ) . These low s a l i n i t i e s correspond more c l o s e l y to the i n termediate l a y e r range f o r March of 29.8 to 3 0 . 6 ° / o o (Table 4.1.2). T h i s i s not s u r p r i s i n g because the northern b a s i n deep water must have come over the 200 m s i l l which separates the two b a s i n s , i n other words from the intermediate l a y e r i n the c e n t r a l b a s i n . The reason t h i s water s i n k s to the deep l a y e r i n the northern basin and not in the c e n t r a l basin i s , of course, that the d e n s i t y i n the 70 Table 4.1.4 Deep Layer, Northern S t r a i t of Georgia Month Mode (%) Range T (°C) Range S (Voo) Dec 67 50 9.0 - 9.2 30.7 - 30.9 90 9.0 - 9.3 30.7 - 30.9 Jan 68 50 9.1 - 9.3 30.7 — 30.8 90 9.1 - 9.3 30.7 — 30.9 Feb 50 9.0 - 9.2 30.7 — 30.8 90 8.8 - 9.2 30.6 — 30.8 Mar 50 8.6 - 8.9 30.5 — 30.7 90 8.6 - 9.0 30.5 - 30.7 Apr 50 8.4 - 8.7 30.4 — 30.6 90 8.4 - 8.8 30.3 — 30.6 May 50 8.4 - 8.5 30.4 — 30.6 90 8.3 - 8.6 30.4 — 30.6 J u l e a r l y 50 8.4 - 8.5 30.5 — 30.6 90 8.3 - 8.5 30.5 — 30.6 J u l l a t e 50 8.4 - 8.5 30.5 _ 30.6 90 8.4 - 8.5 30.5 - 30.6 Aug 50 8.5 - 8.6 30.6 — 30.7 90 8.5 - 8.6 30.5 — 30.7 Oct 50 8.6 - 8.7 30.7 — 30.8 90 8.6 - 8.8 30.6 — 30.8 Nov 50 8.8 - 8.9 30.7 _ 30.8 90 8.8 - 9.1 30.7 — 30.8 Dec 50 9.0 - 9.1 30.7 — 30.8 90 9.0 - 9.2 30.6 - 30.8 deep l a y e r i s l e s s i n the north to begin with. The gradual lowering of the temperature and s a l i n i t y throughout the S t r a i t i n the deep l a y e r c o n t i n u e s through A p r i l with a small drop i n the 50% ranges to 8.6 - 9.0°C and 30.6 - 30.9°/oo ( F i g . 4.4 e) i n the c e n t r a l b a s i n . Again 71 the northern basin has the lowest s a l i n i t i e s at 30.4 to 30.6°/oo. In May ( F i g . 4.4 f) c o l d and somewhat s a l t y water appears i n the l a y e r i n the c e n t r a l basin only, s p l i t t i n g the 50% mode i n t o two p a r t s with the new water at 8.3 to 8.5°C. The appearance of t h i s new water does not f i t e i t h e r s c e n a r i o of c o l d , f r e s h winter water or warm, s a l t y summer water. In f a c t i t seems to be a mixture of the warm, s a l t y water j u s t e n t e r i n g the S t r a i t i n the intermediate l a y e r (compare F i g . 4.3 e, f or Table 4.1.2 A p r i l , May) and the c o l d winter water s t i l l dominating that l a y e r . Table 4.1.2 shows that the onset of the summer water i n f l o w i n t o the inte r m e d i a t e l a y e r has r a i s e d the 50% mode by 0 . 2 ° / o o (roughly 50% of the range f o r the year) from A p r i l to May, while the temperature has only i n c r e a s e d by 0.2°C ( l e s s than 20% of the range f o r the y e a r ) . The summer inf l o w has t h e r e f o r e s u p p l i e d s a l t y water to the intermediate l a y e r without s u b s t a n t i a l l y r a i s i n g the temperature of that l a y e r , e s p e c i a l l y when compared to the higher temperature (by 0.6 to 0.8°C) i n the deep l a y e r . The s a l i n i t y of the new water i s comparable to and perhaps s l i g h t l y g r e a t e r than the s a l i n i t y i n the lower l a y e r ( F i g . 4.3 f shows 3 km3 of 30.8 to 30.9°/oo water) and, s i n c e i t i s c o l d e r , has no t r o u b l e s i n k i n g below 200 m. The next c r u i s e at the beginning of J u l y ( F i g . 4.4 g) shows that water p r o p e r t i e s are somewhat more homogeneous. Water with temperature above 8.7°C has mostly disappeared, 72 with the 50% mode now r e s t r i c t e d to the range 8.4 to 8.6°C in the c e n t r a l b a s i n . The s a l i n i t y has not changed a p p r e c i a b l y . Although water as warm as 9.0°C has appeared i n the intermediate l a y e r at t h i s time ( F i g . 4.3 g) the bulk of the water remains at a much lower temperature, between 8.2 and 8.6°C. There i s a l s o q u i t e h i g h s a l i n i t y water present i n the intermediate l a y e r (7 km3 above 3 0 . 8 ° / o o ) so the same process of new summer water mixing with c o o l i n t e r mediate water can account f o r the drop i n temperatures in the deep l a y e r . The e f f e c t of the summer renewal extends to the northern basin ( F i g . 4.5 g ) , r a i s i n g the s a l i n i t y there by about 0.1°/oo f o r most of the water to 30.5 -3 0 . 6 ° / o o (50% mode, Table 4.1.4). The temperature i s i n i t i a l l y lower i n the northern basin so i t does not drop but remains the same. The s i t u a t i o n a few weeks l a t e r i n l a t e J u l y i s unchanged i n terms of average p r o p e r t i e s but the water has had a chance to mix r e s u l t i n g i n a very narrow range of p r o p e r t i e s i n both basins ( F i g . 4.4 h, 4.5 h ) . The p r o p e r t i e s are a l s o very c l e a r l y d i f f e r e n t between b a s i n s . There i s no o v e r l a p of the 90% modes between ba s i n s f o r the temperature or s a l i n i t y . In l a t e August ( F i g . 4.4 i , 4.5 i ) , summer renewal (as d e f i n e d by an i n c r e a s e i n temperature and s a l i n i t y ) has begun in earnest i n the deep l a y e r , 3 months l a t e r than i n the intermediate l a y e r . The i n f l u x of warm, s a l t y water (about 8.9°C and 31.1°/ 0o) has a f f e c t e d most or a l l of the 73 water i n the deep l a y e r i n c l u d i n g the northern basin which experiences a r i s e of about 0.1°C and 0.1°/oo (50% mode, Table 4.1.4). The c e n t r a l b a s i n 50% mode i s s p l i t i n t o two p a r t s along the s a l i n i t y a x i s : the o l d deep water at 30.8 -3 0 . 9 ° / o o and the new water at 31.0 - 31.1°/ 0o• By t h i s time the i n t e r m e d i a t e l a y e r temperatures w i t h i n the 50% mode have r i s e n to the 8.4 - 8.8°C range and the 90% mode shows water at 9.4 - 9.8°C so the new water has no t r o u b l e r a i s i n g temperatures i n the deep l a y e r from the l a t e J u l y low of 8.5 - 8.6°C. The summer renewal continues over the next three months ( F i g . 4.4 j-k, 4.5 j - k ) , g r a d u a l l y r a i s i n g both temperature and s a l i n i t y . The 50% mode in the c e n t r a l b a s i n in October i s 8.5 - 9.0°C, 30.8 - 3 1 . 2 ° / 0 0 , r i s i n g to a December h i g h of 8.9 - 9.0°C, 30.9 - 3 1 . 1 ° / 0 0 (Table 4.1.3). The northern b a s i n water reaches a somewhat higher temperature of 9.0 - 9.1°C and lower s a l i n i t y of 30.7 - 3 0 . 8 ° / o o (50% mode, Table 4.1.4) i n December, again r e f l e c t i n g i t s intermediate l a y e r o r i g i n . The s e r i e s of events c o n s t i t u t i n g the summer renewal presented above e x p l a i n s why the c o l d e s t temperatures near the bottom of the S t r a i t of Georgia occur i n mid-summer ( J u l y i n 1968), d u r i n g the warmest part of the year. During winter and s p r i n g , temperatures drop i n the intermediate and deep l a y e r s . The i ntermediate l a y e r i s l e f t c o l d e r than the deep l a y e r . The summer renewal i n i t i a l l y s u p p l i e s new water to the intermediate l a y e r . T h i s new water i s warmer than 74 intermediate l a y e r temperatures at the time but c o l d e r than the deep l a y e r . The new water then moves to the warmer deep l a y e r (perhaps e n t r a i n i n g c o l d i n t e r mediate l a y e r water on the way) and c o n t i n u e s to lower temperatures there u n t i l J u l y . A somewhat d i f f e r e n t p i c t u r e precedes the peak temperatures i n December, which f o l l o w and are a r e s u l t of the summer renewal. Temperatures i n c r e a s e i n both intermediate and deep layers^ to November. The temperature d i f f e r e n c e between the two l a y e r s i s r e l a t i v e l y small (about 0.3°C compared to 0.7°C in A p r i l ) . When winter renewal water does appear i n the intermediate l a y e r (December) i t i s c o l d e r than e i t h e r l a y e r and soon produces a drop i n the lower l a y e r temperature (February). It i s u s e f u l to summarize the v o l u m e t r i c a n a l y s i s r e s u l t s before proceeding to the next s e c t i o n . The s u r f a c e l a y e r c o n t r i b u t e s most of the v a r i a n c e i n temperature and s a l i n i t y due to the d i r e c t e f f e c t s of f r e s h water in p u t , summer h e a t i n g and winter c o o l i n g . In the i n termediate l a y e r (80 - 200 m), the winter renewal reduces the temperature and s a l i n i t y from December 1967 to A p r i l 1968. The 50% mode temperature drops from 9.2 -9.6°C to 7.8 - 8.4°C and the s a l i n i t y from 30.2 - 3 0 . 8 ° / o o to 29.8 - 30.4 0/oo» Renewal water i s o f t e n seen i n the v o l u m e t r i c t a b l e s as a separate water mass with p r o p e r t i e s d i s t i n c t from those of the o l d water i n the l a y e r . 75 The intermediate l a y e r summer renewal p e r i o d s t a r t s i n May and continues u n t i l November. The water p r o p e r t i e s r e t u r n to t h e i r December 1967 v a l u e s , but i n a much more gradual manner than d u r i n g the winter renewal p e r i o d . P a r t i c u l a r l y vigorous renewal does take p l a c e i n August when a high temperature and s a l i n i t y water mass appears, separate from the o l d water i n the l a y e r . 4.2 HEAT AND SALT BUDGET The p r e v i o u s s e c t i o n d e s c r i b e s the v a r i a n c e of the major c l a s s e s of water p r o p e r t i e s i n the S t r a i t of Georgia. At v a r i o u s times over the course of the c r u i s e program, renewal water i s shown by the v o l u m e t r i c t a b l e s to be d i s t i n c t i n temperature and/or s a l i n i t y from the bulk of the water ( o l d water) i n the S t r a i t . However, t h i s new water f a i l s to e x p l a i n a l l of the v a r i a n c e of water p r o p e r t i e s d u r i n g p e r i o d s of renewal. For example, measurements from the December 1967 c r u i s e i n the intermediate l a y e r (80 -200 m, F i g . 4.3 a ) , show two p o s s i b l e sources of renewal water. One i s the low s a l i n i t y " t a i l " of 20 - 30 km3 extending to 2 9 . 2 ° / 0 0 and the other i s the 26 km3 volume with p r o p e r t i e s i n the range 8.6 - 8.8°C and 30.4 -30.6°/oo- N e i t h e r accounts f o r the s h i f t i n temperature of the bulk of the water from 9.2 - 9.6°C to 8.8 - 9.2°C (50% mode) from December 1967 to January 1968. Presumably, a s u b s t a n t i a l volume of new water, perhaps resembling that seen i n January 1968 (7.4 - 8.2°C), has a l r e a d y had time (by 76 the January c r u i s e ) to be mixed i n with a l a r g e volume of the o l d water, thereby producing the 0.4°C s h i f t i n the 50% mode. The volume of the renewal in an e s t u a r y i s c l e a r l y an important parameter d e s c r i b i n g the renewal p r o c e s s . T h i s s e c t i o n i s , t h e r e f o r e , devoted to e s t i m a t i n g the volume of new water e n t e r i n g the S t r a i t over the c r u i s e program, using a simple method based on c o n s e r v a t i o n of water p r o p e r t i e s . A d e s c r i p t i o n of the method f o l l o w s . If T^n^t) a n (3 T o u t ( t ) a r e t n e time v a r y i n g temperatures of the water flowing i n and out of a given box, and and Tbox a r e fc^e a v e r a 9 e temperatures of the water i n the box at the beginning and-end of the p e r i o d t ^ to t ^ , then c o n s e r v a t i o n of heat and volume r e q u i r e that ( T b o x " T b o x * V = ^ { T i n ( t ) - T o u t ( t ) } v ( t ) d t ' ( 4 - 1 ) i V i s the volume of the box and v ( t ) i s the flow r a t e i n t o or out of the box. S i m i l a r l y , c o n s e r v a t i o n of s a l t and volume l e a d to ( S b o x " Sbox> V • ^ { S i n ( t ) " S o u t ( t ) } v ( t ) d t « ( 4 ' 2 ) These r e l a t i o n s w i l l be a p p l i e d to the "boxes" used in the p r e v i o u s s e c t i o n which d i v i d e the S t r a i t v e r t i c a l l y i n t o 3 l a y e r s and h o r i z o n t a l l y i n t o a c e n t r a l and northern b a s i n f o r the deep l a y e r . Time averaged v e r s i o n s of these 77 equations w i l l be used to c a l c u l a t e the t o t a l volume of water which has entered each box d u r i n g each one month i n t e r v a l between s u c c e s s i v e c r u i s e s . Estimates of the average temperature and s a l i n i t y i n each l a y e r and du r i n g each c r u i s e ( i . e . T ^ o x f Tbox' Sbox a n c ^ s£ Q X ) are c a l c u l a t e d using v o l u m e t r i c t a b l e s s i m i l a r to those given i n F i g . 4.1 to 4.5. A maximum box s i z e of 0.05°C x 0.1°/oo i s used. The volume c o n t r i b u t i o n of each box i s assigned a temperature and s a l i n i t y c o r r e s p o n d i n g to the ce n t e r of the box. An average temperature and s a l i n i t y i s then c a l c u l a t e d f o r the l a y e r and c r u i s e . Since there are no data a v a i l a b l e between c r u i s e s , the infl o w and outflow temperatures and s a l i n i t i e s are assumed to vary l i n e a r l y with time. Time averaged values f o r the p e r i o d are then equal to the mean of the value s at the beginning and end of the p e r i o d . Inflow and outflow r a t e s are taken to be constant over the p e r i o d . As w i l l be seen below, these approximations u s u a l l y lead to reasonable values of the net flow r a t e except d u r i n g the i n t e r v a l s between the summer and winter renewal p e r i o d s i n A p r i l and November or December. The p r o p e r t i e s of the i n f l o w i n g (or renewal) water f o r the intermediate l a y e r f o r the whole S t r a i t and the deep l a y e r i n the c e n t r a l basin are estimated using data from a l i n e of s t a t i o n s running a c r o s s the S t r a i t near the southern passages ( s t n s . 47, 48, 49 and 50). Measurements from the four s t a t i o n s are averaged together at each of many c l o s e l y 78 spaced v e r t i c a l l e v e l s (5 to 25 m i n t e r v a l s ) and then averaged over the l a y e r (80 - 200 m) to o b t a i n one value f o r each p r o p e r t y . Data from two of the c r u i s e s do not extend below the 150 m l e v e l so a s t r a i g h t l i n e f i t to the data between 80 and 150 m i s used to estimate p r o p e r t i e s below 150 m. T h i s i s a reasonable procedure to f o l l o w , f o r our purposes, below the t h e r m o / h a l o c l i n e . The renewal water e n t e r i n g the deep l a y e r i n the northern b a s i n i s assumed to o r i g i n a t e from w i t h i n the intermediate l a y e r . T h e r e f o r e , the average i n f l o w temperature and s a l i n i t y f o r each p e r i o d ( i . e . from one c r u i s e to the next) are set to the average temperature and s a l i n i t y i n the intermediate l a y e r f o r the p e r i o d . The outflow from the S t r a i t i s presumably c o n f i n e d to a s u r f a c e l a y e r moving southward and having average p r o p e r t i e s which are d i f f i c u l t to estimate because of the l a r g e g r a d i e n t s near the s u r f a c e . However, the outflows from the in t e r m e d i a t e (80 - 200 m) and deep (below 200 m) l a y e r s are moving v e r t i c a l l y i n t o the s u r f a c e and intermediate l a y e r s r e s p e c t i v e l y , and have p r o p e r t i e s which are r e l a t i v e l y easy to estimate. For t h i s a n a l y s i s , the water fl o w i n g out of a l a y e r i s assumed to have the p r o p e r t i e s of that l a y e r . The water f l o w i n g from the deep l a y e r s to the i n t e r m e d i a t e l a y e r i s ignored when c a l c u l a t i n g the in t e r m e d i a t e l a y e r renewal volumes. T h i s g e n e r a l l y leads to an e r r o r of about 10% except i n March to A p r i l 1968 and i n October to November 1968 when the e r r o r s are somewhat 79 h i g h e r . F i g . 4.6 shows the box model of the S t r a i t along with the o r i g i n and p r o p e r t i e s of water f l o w i n g i n t o and out of each box. Given a l l the assumptions o u t l i n e d above equations 4.1 and 4.2 reduce to T f - T 1 = _J>OX b O X _ v ( 4 t 3 ) i n m _ m i n box S f - S 1 V. = — ^ 2 2 ^ox_ V. (4.4) i n S. - S u i n box V^ n i s the net inflow during the p e r i o d and T^ n the mean of the i n i t i a l and f i n a l i n flow temperatures d u r i n g the p e r i o d . Tbox a n < ^ Tbox a r e t h e a v e r a 9 e temperatures i n the box at the beginning and end of the p e r i o d and T ^ ^ i s t h e i r mean. The temperature and s a l i n i t y inputs and the r e s u l t i n g i n f l o w volume f o r each c r u i s e are l i s t e d i n Table 4.2.1. Since the c a l c u l a t i o n of V. i n v o l v e s the r a t i o of i n d i f f e r e n c e s of f a i r l y c l o s e numbers, the e r r o r s are q u i t e l a r g e . In one case in p a r t i c u l a r (March to A p r i l 1968), there i s a drop i n the average s a l i n i t y i n the l a y e r over the p e r i o d , whereas the renewal water i n d i c a t e s that an i n c r e a s e should occur ( i . e . S. -S, >0). There i s a l s o no in box s i g n i f i c a n t c o r r e l a t i o n between the two s e t s of i n f l o w volumes c a l c u l a t e d u s i n g temperature and s a l i n i t y (the c o r r e l a t i o n c o e f f i c i e n t i s -0.11 with the 95% c o n f i d e n c e l e v e l at 0.63). However, t h i s may be l a r g e l y the f a u l t of 8 0 Table 4 . 2 . 1 Renewal Volume - Intermediate Layer ( 8 0 - 2 0 0 m, t o t a l volume = 4 6 7 km3) Month T. T, in box ( ° C ) ( ° C ) Dec 6 7 8 . 6 7 3 8 9 . 2 6 2 6 Jan 6 8 7 . 7 3 6 8 8 . 8 5 1 7 Feb 7 . 2 4 9 0 8 . 3 4 4 2 Mar 7 . 7 2 7 6 8 . 1 4 1 4 Apr 8 . 0 6 3 0 8 . 0 9 5 0 May 8 . 4 7 1 1 8 . 2 7 1 2 J u l e a r l y 8 . 8 2 6 7 8 . 4 5 8 2 J u l l a t e 9 . 2 1 2 4 8 . 6 1 9 4 Aug 9 . 4 9 3 3 8 . 7 6 4 6 Oct 9 . 5 7 7 1 9 . 0 9 5 1 Nov 9 . 2 2 3 6 9 . 1 6 8 4 Dec 8 . 8 0 3 3 9 . 1 3 3 7 box box in box i n ( ° c ) ( ° C ) (km 3) - 0 . 4 1 0 9 - 0 . 8 5 1 9 2 2 5 - 0 . 5 0 7 5 - 1 . 1 0 5 1 2 1 4 - 0 . 2 0 2 8 - 0 . 7 5 4 5 1 2 6 - 0 . 0 4 6 4 - 0 . 2 2 2 9 9 7 0 . 1 7 6 2 0 . 0 8 4 0 9 8 0 0 . 1 8 7 0 0 . 2 8 4 2 3 0 7 0 . 1 6 1 2 0 . 4 8 0 8 1 5 7 0 . 1 4 5 2 0 . 6 6 0 9 1 0 3 0 . 3 3 0 5 0 . 6 0 5 4 2 5 5 0 . 0 7 3 3 0 . 2 6 8 6 1 2 7 - 0 . 0 3 4 7 - 0 . 1 3 7 6 1 1 8 Month s . S, in box (° /oo) ( ° / o o ) Dec 6 7 3 0 . 4 9 2 0 3 0 . 3 9 9 3 Jan 6 8 3 0 . 3 9 0 4 3 0 . 4 1 8 4 Feb 3 0 . 7 6 6 0 3 0 . 2 4 1 6 Mar 3 0 . 8 5 5 1 3 0 . 1 2 0 5 Apr 3 0 . 5 3 7 0 3 0 . 0 9 4 3 May 3 0 . 5 4 2 6 3 0 . 2 7 0 3 J u l e a r l y 3 0 . 9 0 3 0 3 0 . 3 3 5 8 J u l l a t e 3 0 . 7 3 2 4 3 0 . 3 5 7 9 Aug 3 0 . 6 7 7 8 3 0 . 4 5 2 7 Oct 3 0 . 7 4 3 6 3 0 . 5 3 1 2 Nov 3 0 . 5 0 5 6 3 0 . 5 6 6 0 Dec 3 0 . 2 7 4 5 3 0 . 3 9 5 1 s - s 1 s - s box box i n box (Voo) (Voo) (km 3) 0 . 0 1 9 1 0 . 0 3 2 4 2 7 5 - 0 . 1 7 6 8 - 0 . 2 5 1 8 3 2 8 - 0 . 1 2 1 1 - 0 . 3 7 0 5 1 5 3 - 0 . 0 2 6 2 0 . 0 8 8 7 -0 . 1 7 6 0 0 . 3 5 7 5 2 3 0 0 . 0 6 5 5 0 . 4 1 9 8 7 3 0 . 0 2 2 1 0 . 4 7 0 9 2 2 0 . 0 9 4 8 0 . 2 9 9 8 1 4 8 0 . 0 7 8 5 0 . 2 1 8 8 1 6 8 0 . 0 3 4 8 0 . 0 7 6 0 2 1 4 - 0 . 1 7 0 9 - 0 . 0 9 0 5 8 8 2 the estimates of the in f l o w s a l i n i t y which are d i f f i c u l t to make because they depend s t r o n g l y on the p r e c i s e c h a r a c t e r of the i n f l o w . In p a r t i c u l a r , the l a r g e v e r t i c a l s a l i n i t y g r a d i e n t which i s present f o r most of the year ( F i g . 4 . 7 ) i n the southern S t r a i t makes the i n f l o w s a l i n i t y h i g h l y dependent on the chosen i n f l o w l a y e r depth. Indeed, dur i n g 81 the winter months (December 1967 to March 1968) when the s a l i n i t y g r a d i e n t i s r e l a t i v e l y s m a l l , the in f l o w volumes based on the two p r o p e r t i e s match q u i t e w e l l , although one set i s c o n s i s t e n t l y higher than the other ( i . e . T: 225, 214, 126 km3 ; S: 275, 328, 153 km3, see Table 4.2.1). The month to month v a r i a t i o n d u r i n g the winter renewal p e r i o d i s reasonable, with high flow r a t e s d u r i n g the c o l d e s t p a r t of the year i n December to February (225 and 214 km 3/month), t a p e r i n g to 126 km3/month in February to March and again to 97 km3/month i n March to A p r i l at the end of the renewal p e r i o d . The t r a n s i t i o n to the summer renewal p e r i o d , when the two p r o p e r t i e s are i n c r e a s i n g , i s marked by a much too l a r g e volume of 980 km3 from A p r i l to May using the temperature data (the t o t a l volume of the l a y e r i s only 467 km 3), and a meaningless negative value using the s a l i n i t y i n March to A p r i l . Another high value in May to e a r l y J u l y (307 km3) i s fo l l o w e d by moderate val u e s of mostly 100 - 160 km3 with one hi g h volume of 255 km3 corresponding to a l a r g e i n c r e a s e i n the average temperature of the l a y e r . In ge n e r a l , the r e s u l t s are i n the 100 - 250 km3 range and represent a replacement of from 20% to 50% of the water i n the l a y e r each month. The inflow volumes f o r the deep l a y e r below 200 m i n the c e n t r a l b a s i n are given i n Table 4.2.2 using temperature data o n l y . The t o t a l volume of the l a y e r i s 177 km3. Large v a l u e s occur between the renewal p e r i o d s Table 4.2.2 Renewal Volume - C e n t r a l Basin Deep Layer (below 200 m, t o t a l volume = 177 km3) Month T. i n °C) T. -T, in box (°C) (km 3) V. i n Dec 67 Jan 68 8.6738 7.7368 7.2490 7.7276 8.0630 8.4711 8.8267 9.2124 9.4933 9.5771 9.2236 8.8033 9.1141 9.0789 8.8691 8.8025 8.7226 8.5277 8.5409 8.5754 8.7652 8.8648 8.9478 8.9806 -0.0352 -0.2098 -0.0666 -0.0799 -0.1949 -0.0132 0.0345 0.1898 0.0996 0.0830 0.0328 -0.8912 -1.4811 -1.3475 -0.8673 -0.3581 0.1146 0.4614 0.6826 0.7202 0.4941 0.0493 7 25 9 16 96 20 13 49 24 30 1 18 Feb Mar Apr May J u l e a r l y J u l l a t e Aug Oct Nov Dec (96 km3 i n A p r i l to May and 118 km3 i n November to December) and are l a r g e l y a r e s u l t of the small d i f f e r e n c e at those times between the temperature of the renewal water and the average i n the l a y e r . A l a r g e renewal volume a l s o occurs i n l a t e J u l y to August and produces a l a r g e change i n the average temperature i n the l a y e r . T y p i c a l volumes range from 10 to 30 km3 f o r each monthly p e r i o d and are equal to 5% to 20% of the t o t a l volume i n the l a y e r . These f i g u r e s i n d i c a t e that the deep l a y e r i s probably l e s s a c t i v e i n terms of renewal than the intermediate l a y e r . However, the a c t u a l volume e n t e r i n g the l a y e r has l i k e l y been underestimated because i t would c o n s i s t of a mixture of new water and of o l d intermediate l a y e r water. The intermediate l a y e r water would tend to reduce the c o n t r a s t i n p r o p e r t i e s between the water e n t e r i n g the deep l a y e r and the o l d water 83 a l r e a d y i n the l a y e r . T h e r e f o r e , the c o n t r a s t i n p r o p e r t i e s ( i . e . T i n - T b Q x and § i n - S f a o x) has probably been overestimated and the volumes underestimated. R e s u l t s f o r the deep l a y e r i n the northern basin are given i n Table 4.2.3. The t o t a l volume i s 27 km3. There i s a f a i r l y narrow range i n the c a l c u l a t e d volumes with most va l u e s from 9 to-12 km3 or 30% to 45% of the l a y e r volume. Higher values again occur at the renewal p e r i o d t r a n s i t i o n s (15 km3 i n May to e a r l y J u l y and 24 km3 i n November to December) but there i s a l s o a high value of 19 km3 i n October to November caused by a l a r g e change in the average temperature of the S t r a i t . As p o i n t e d out e a r l i e r , the i n f l o w water i s assumed to come from the i n t e r m e d i a t e l a y e r because of the 200 m ^ s i l l s e p a r a t i n g the deep water of the northern b a s i n from the r e s t of the S t r a i t . T h e r e f o r e , the c o n t r a s t between the temperature of the new and o l d water i s g e n e r a l l y l e s s than f o r the c e n t r a l b a s i n . T h i s accounts f o r the higher replacement r a t e s i n the north. To sum up t h i s s e c t i o n , reasonable volume r a t e s of exchange were obtained using the heat and s a l t budget methods, f o r the times of the year during which e i t h e r the winter or summer renewal are i n p r o g r e s s . Data gathered f o l l o w i n g the winter ( A p r i l 1968) and summer (December 1968) renewal p e r i o d s g e n e r a l l y gave poor r e s u l t s due to the small c o n t r a s t i n the p r o p e r t i e s of the o l d water a l r e a d y i n the S t r a i t and the new water e n t e r i n g the S t r a i t measured at s t a t i o n s 47,48,49 and 50 The temporary c e s s a t i o n of water 84 Table 4.2.3 Renewal Volume - Northern Basin Deep Layer (below 200 m, t o t a l volume = 27 km3) Month Dec 67 Jan 68 Feb Mar Apr May J u l e a r l y J u l l a t e Aug Oct Nov Dec T. i n (°C) 9.2626 8.8517 8.3442 8.1414 8.0950 8.2712 8.4582 8.6194 8.7646 9.0951 9.1684 9.1337 box (°C) 9.0921 9.1923 9.0294 8.7810 8.5769 8.4431 8.4089 8.4464 8.5383 8.6803 8.9143 9.0598 •pf _ipi box box (°C) 0.1002 -0.1629 -0.2484 -0.2041 -0.1338 -0.0342 0.0375 0919 1 420 0.2340 0.1455 0 0 T. -T, in box (°C) -0.0851 -0.5129 -0.6624 -0.5608 -0.3269 -0.0613 0.1112 1997 3206 3345 1640 0, 0, 0, 0, V. i n (km 3) 9 10 10 1 1 1 5 9 12 12 19 24 flow i n t o the S t r a i t at depth through the southern passages, would allow o l d water to move southward to the l i n e of s t a t i o n s , thereby reducing the c o n t r a s t . Inflow volumes du r i n g renewal p e r i o d s were 100 to 250 km3/month i n t o the inte r m e d i a t e l a y e r (20% to 50% of the l a y e r volume/month), 10 to 30 km 3/month i n t o the c e n t r a l basin deep l a y e r (5% to 20% of the l a y e r volume/month) and 9 to 12 km3/month i n t o the northern basin deep l a y e r (30% to 45% of the l a y e r volume). The r e s u l t s show that the renewal i s c o n s i s t e n t l y s t r o nger i n the intermediate l a y e r than i n the c e n t r a l basin deep l a y e r . 5. INTERANNUAL VARIATION In order to complete the d e s c r i p t i o n of the water p r o p e r t i e s and renewal w i t h i n the S t r a i t of Georgia, the year to year v a r i a t i o n w i l l now be examined. P i c k a r d (1975) presents a 7 year temperature and s a l i n i t y time s e r i e s c o l l e c t e d at a s t a t i o n northeast of Nanaimo in the deepest p a r t of the S t r a i t ( F i g . 1.5). The data show that the main f e a t u r e s of the seasonal s i g n a l , documented in the preceding chapters of t h i s study, are present d u r i n g other y e a r s . In p a r t i c u l a r , y e a r l y temperature and s a l i n i t y maxima at the 100 m l e v e l occur i n the f i r s t few months of the year. The minima at the 300 m l e v e l occur 2 to 4 months l a t e r . These times correspond w e l l to the seasonal v a r i a b i l i t y of the p r o p e r t i e s d e s c r i b e d i n e a r l i e r c hapters f o r the December 1967 to December 1968 p e r i o d . Although the c h a r a c t e r of the seasonal temperature and s a l i n i t y s i g n a l s are q u a l i t a t i v e l y s i m i l a r from year to year, there n e v e r t h e l e s s e x i s t s a s u b s t a n t i a l v a r i a n c e i n s e v e r a l key q u a n t i t i e s . For example, the magnitude of the y e a r l y minimum temperature at the 100 m l e v e l v a r i e s from a low of l e s s than 7.0°C in 1969 and 1972 to a high of over 8.0°C in 1970 ( F i g . 1.5). S i g n i f i c a n t i n t e r a n n u a l v a r i a b i l i t y a l s o e x i s t s f o r the temperature at 300 m and the s a l i n i t y at both l e v e l s . The i n t e r a n n u a l data used below spans a p e r i o d of 37 years from 1949 to 1985 and c o n s i s t s of temperature and 85 86 s a l i n i t y measurements taken i n an area northeast of Nanaimo, in the deepest part of the S t r a i t ( F i g . 2.2). The p e r i o d from November 1967 to J u l y 1974 i s by f a r the most densely sampled with a t o t a l of only 5 months without data. Table 5.1 l i s t s the lowest standard depth reached (one of 100, 150, 200, 250 or 300 m) i n each month f o r which there i s some data. The next s e c t i o n d e s c r i b e s the i n t e r a n n u a l v a r i a b i l i t y of the temperature and s a l i n i t y at the standard depths. The l a s t s e c t i o n uses the i n t e r a n n u a l data to i d e n t i f y a l i n k between the wintertime weather i n the southern S t r a i t and the p r o p e r t i e s of the winter renewal water. 5.1 PHYSICAL PROPERTIES Data from the r e l a t i v e l y densely sampled p e r i o d from 1967 to 1978 i s presented as temperature and s a l i n i t y time s e r i e s i n F i g . 5.1 and 5.2. The annual c y c l e of winter and summer renewal i s c l e a r in both p r o p e r t i e s and at a l l depths. Many of the c h a r a c t e r i s t i c s of the annual c y c l e i d e n t i f i e d i n the p r e v i o u s c h a p t e r s using the one year d a t a s e t , are evident here. One such c h a r a c t e r i s t i c i s the decrease i n the range i n p r o p e r t i e s with i n c r e a s i n g depth. The t y p i c a l temperature range at the 100 m l e v e l i s 7.5 - 9.4°C, a d i f f e r e n c e of almost 2.0°C. At 200 m, the range i s 8.0 - 9.0°C a d i f f e r e n c e of 1.0°C, and at 300 m, 8.3 - 9.0°C, f o r a d i f f e r e n c e of 0.7°C. S i m i l a r l y , the s a l i n i t y range drops 87 Table 5.1 Interannual Data Year Jan Feb Mar Apr May Jun J u l Aug Sep Oct Nov Dec 49 250 50 100 250 52 100 250 53 100 58 300 59 300 61 300 T 64 300 E 65 300 300 M 67 100 1 00 100 1 00 250 300 P 68 300 300 300 300 300 300 300 300 300 300 300 E 69 300 300 300 300 300 300 300 300 300 300 300 300 R 70 300 300 300 300 300 300 300 300 300 300 300 A 71 300 300 300 300 300 300 300 300 300 300 300 T 72 300 300 300 300 300 300 300 300 300 300 300 U 73 300 300 300 300 300 300 300 300 300 300 300 R 74 300 300 300 300 300 300 300 300 E 75 300 300 300 300 300 76 300 300 300 300 300 300 300 300 77 300 300 300 300 300 300 300 300 300 300 78 300 300 300 79 300 300 300 80 300 300 81 300 300 84 300 300 85 300 300 300 300 49 250 50 200 250 52 100 250 53 100 58 300 61 250 S 65 300 A 67 250 300 L 68 300 300 300 300 300 300 300 300 300 300 300 I 69 300 300 300 300 300 300 300 300 300 300 300 300 N 70 300 300 300 300 300 300 300 300 300 300 300 I 71 300 300 300 300 300 300 300 300 300 300 300 T 72 300 300 300 300 300 300 300 300 300 300 300 y 73 300 300 300 300 300 300 300 300 300 300 300 74 300 300 300 300 300 300 300 300 75 300 300 300 300 300 76 300 300 300 300 300 300 300 300 77 300 300 300 300 300 300 300 300 300 300 78 300 300 300 79 300 300 300 80 300 300 81 300 300 88 from 0 . 6 ° / o o (30.0 - 3 0 . 6 ° / O 0 ) at the 100 m l e v e l , to 0 . 4 ° / o o (30.6 - 3 1 . 0 ° / o o ) at 200 m and f i n a l l y to 0 . 3 ° / o o (30.8 - 3 1 . 1 ° / 0 0 ) at the 300 m l e v e l . The i n t e r a n n u a l v a r i a t i o n i n the temperature or s a l i n i t y ranges f o r any given year i s s u b s t a n t i a l , though somewhat l e s s than the annual c y c l e . For example, p a r t i c u l a r l y low minimum temperatures occur i n 1969 and 1972 (7.0°C at 100 m) and a high minimum temperature i n 1970 (8.1°C at 100 m). The timing of the minimum and maximum temperature and s a l i n i t y f o r each year v a r i e s somewhat from year to year and with depth. F i g u r e s f o r the y e a r l y extrema and the months i n which they occur are l i s t e d i n Table 5.1.1 and 5.1.2. Only those years that have s u f f i c i e n t data to p i n p o i n t one month as the one during which the extremum occu r s , are g i v e n . The minimum temperature f o l l o w i n g each year's winter renewal p e r i o d occurs i n March or A p r i l at the 100 and 150 m l e v e l s (Table 5.2.1). There i s a gr e a t e r s c a t t e r at the 200 and 250 m l e v e l s , with minima o c c u r i n g from February to June and from March to June r e s p e c t i v e l y . At 300 m, temperature minima occur from A p r i l to J u l y . The average values of the minima r i s e c o n s i s t e n t l y with depth from a low of 7.4°C at 100 m to a high of 8.3°C at 300 m. The s a l i n i t y minima a l s o show a l a g with depth, and occur i n A p r i l at 100 m and May or June at 300 m. The maximum temperatures and s a l i n i t i e s f o l l o w i n g the summer renewal p e r i o d are given i n Table 5.1.2. 89 Table 5.1.1 Y e a r l y temperature and s a l i n i t y minima 100 m 150 m 200 m 250 m 300 m Year Mo Temp Mo Temp Mo Temp Mo Temp Mo Temp 68 3 7.80 3 7.96 5 8.18 - - - -69 3 6.99 4 7.09 2 7.57 5 8.22 6 8.32 71 5 7.39 3 7.55 4 7.72 3 8.00 - -72 4 7.01 4 7.20 3 7.46 6 8.02 7 8.09 73 3 7.29 3 7.53 2 8.02 7 8.28 6 8.28 74 4 7.57 4 7.91 6 8.34 6 8.40 6 8.52 77 4 7.95 5 8.04 5 8.07 6 8.19 5 8.10 Av. 4 7.43 4 7.61 4 7.91 6 8.19 6 8.26 Year Mo Sa l Mo Sal Mo Sal Mo Sa l Mo Sal 68 4 29.88 3 30.23 4 30.59 - - — -69 4 29.78 4 30.02 2 30.40 5 30.59 6 30.66 71 5 30. 19 5 30.42 4 30.63 3 30.74 5 30.89 72 5 29.91 5 30.28 5 30.50 6 30.65 7 30.71 73 3 30. 16 3 30.34 2 30.63 5 30.79 5 30.84 74 4 29.80 4 30.21 . 5 30.59 6 30.80 6 30.84 77 4 30. 18 4 30.39 4 30.65 6 30.80 5 30.85 Av. 4 29.99 4 30.27 4 30.57 5 30.73 5 30.79 The u n i t s are °C and p a r t s per thousand f o r the temperature and s a l i n i t y v a l u e s . U n f o r t u n a t e l y , there are only f i v e years f o r which there are complete time s e r i e s i n the months of i n t e r e s t ( g e n e r a l l y from October to Janua r y ) . The amount of s c a t t e r i n the tim i n g of the maxima of e i t h e r the temperature or s a l i n i t y does not show an obvious trend with depth. The data does suggest that the maximum temperature occurs s l i g h t l y l a t e r at 300 m than at 100 m. There i s no i n d i c a t i o n of any such l a g i n the s a l i n i t y d a t a. T h i s suggests that the summer renewal d i s p l a c e s water at a l l l e v e l s s i m u l taneously (or ne a r l y so) whereas the winter renewal takes some time to 90 Table 5.1.2 Temperature and s a l i n i t y maxima 100 m 150 m 200 m 250 m 300 m Year Mo Temp Mo Temp Mo Temp Mo Temp Mo Temp 68 1 1 9.33 12 9.20 12 9.10 1* 9.03 2* 9.06 69 9 9.25 1 1 9.21 1 1 9.10 1 1 9. 15 1 1 9.14 70 10 9.66 9 9.53 9 9.40 9 9.36 10 9.42 71 1 1 9.32 1 1 9.15 1 1 9.10 1 1 9.07 12 8.85 76 12 9.10 10 9.04 12 8.84 1 2 8.74 1* 8.73 Av. 1 1 9.33 1 1 9.23 1 1 9.1 1 1 1 9.07 1 2 9.05 Year Mo Sal Mo Sal Mo Sal Mo S a l Mo Sal 68 10 30.47 9 30.75 10 30.88 10 30.96 1 1 31 .05 69 12 30.42 10 30.75 1 1 30.91 1 1 30.99 1 1 31 .03 70 1 1 30.78 1 1 31 .05 1 1 31.16 1 1 31 .21 1 1 31 .25 71 1 1 30.64 1 1 30.89 1 1 30.96 1 1 31 .03 10 31 .08 76 - - 1 1 30.78 1 1 30.90 1 1 30.99 1 1 31 .06 Av. 1 1 30.58 10 30.84 1 1 30.96 1 1 31 .04 1 1 31 .09 * January and February of the f o l l o w i n g year The u n i t s are °C and p a r t s per thousand f o r the temperature and s a l i n i t y v a l u e s . p e n e t r a t e to the deeper water, as i s the case i n 1968 (see F i g . 3.16). The average maximum temperatures show a decrease with i n c r e a s i n g depth from 9.33°C at 100 m to 9.05°C at 300 m. The average maximum s a l i n i t y i n c r e a s e s with depth from 3 0 . 5 8 ° / o o at 100 m to 3 1 . 0 ° / o o at 300 m In order to examine the p e n e t r a t i o n of new water to v a r i o u s depths, c o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d f o r the minimum and maximum temperatures and s a l i n i t i e s at depths below 100 m with those at 100 m. The c o e f f i c i e n t s are presented below i n Table 5.1.3. Minimum temperatures f o l l o w i n g the winter renewal are f a i r l y w e l l c o r r e l a t e d down 91 to the 200 m l e v e l . Temperatures at the 250 and 300 m l e v e l s show no s i g n i f i c a n t c o r r e l a t i o n with the 100 m temperatures. C o r r e l a t i o n c o e f f i c i e n t s based on the s a l i n i t y data are below the 95% c o n f i d e n c e l e v e l f o r depths below 150 m. T h i s suggests that the process by which renewal water p e n e t r a t e s i n t o the S t r a i t may be d i f f e r e n t f o r the two l a y e r s ( i . e . above and below 200 m). The c o r r e l a t i o n c o e f f i c i e n t s f o r the summer renewal show a q u i t e d i f f e r e n t behaviour. Maximum temperatures are w e l l c o r r e l a t e d at a l l l e v e l s down to 300 m. The s a l i n i t i e s at a l l l e v e l s a l s o show a s t r o n g c o r r e l a t i o n although the c o e f f i c i e n t s are below the 95% c o n f i d e n c e l e v e l because of the small sample s i z e (5 p o i n t s ) . As a r e s u l t , the summer renewal appears to penetrate r e a d i l y to at l e a s t the 300 m l e v e l . The mean temperature and s a l i n i t y f o r each month of the year and at each standard depth are p l o t t e d i n F i g . 5.3 and 5.4 along with the standard d e v i a t i o n about the mean. A l l of the a v a i l a b l e data from 1949 to 1985 i s i n c l u d e d . I t i s again apparent that the magnitude of the year to year v a r i a b i l i t y (as shown by the standard d e v i a t i o n ) i s a s i g n i f i c a n t f r a c t i o n of the average seasonal v a r i a t i o n . The mean temperature at the 100 m l e v e l i n d i c a t e s a minimum i n May which c o n t r a d i c t s the r e s u l t s found e a r l i e r which showed t y p i c a l minima o c c u r i n g i n March or A p r i l . The reason f o r the discrepancy i s that s e v e r a l high values i n March and A p r i l (averaging about 8.2°C in March) were l e f t 92 Table 5.1.3 Deep water p e n e t r a t i o n C o r r e l a t i o n c o e f f i c i e n t s f o r the temperature and s a l i n i t y f o l l o w i n g the winter renewal p e r i o d . Depth (m) Temperature S a l i n i ty C o r r . 95% C o r r . 95% 100 1 .00 1 .00 1 50 0.97 0.75 0.89 0.75 200 0.79 0.75 0.73 0.75 250 0.29 0.81 0.55 0.81 300 -0.014 0.88 0.71 0.81 C o r r e l a t i o n c o e f f i c i e n t s f o r the temperature and s a l i n i t y f o l l o w i n g the summer renewal p e r i o d . Depth (m) Temperature S a l i n i ty C o r r . 95% C o r r . 95% 100 1 .00 1 .00 1 50 0.97 0.88 0.99 0.95 200 0.98 0.88 0.92 0.95 250 0.90 0.88 0.91 0.95 300 0.87 0.88 0.92 0.95 out of the pr e v i o u s a n a l y s i s because of the lack of data i n nearby months. The minimum i n the mean i s q u i t e broad, with l i t t l e v a r i a t i o n from March to May (<0.1°C), so that i t i s d i f f i c u l t to s p e c i f y e x a c t l y the month i n which the minimum o c c u r s . The d i f f e r e n c e i n the c h a r a c t e r i s t i c s of the summer and winter renewal i s again brought out i n these p l o t s . There i s a r a p i d decrease i n temperature at the 100 m and 150 m l e v e l s f o r two months d u r i n g the winter renewal p e r i o d from December to February. A corresponding i n c r e a s e d u r i n g the summer takes p l a c e more sl o w l y , over a p e r i o d of about 4 93 months. At 250 and 300 m the winter renewal a l s o takes p l a c e r e l a t i v e l y slowly r e s u l t i n g i n a minimum temperature i n June. The steep d e c l i n e at the upper l e v e l s r e f l e c t s the sharp drop seen every year i n December to February ( F i g . 5.1) and the f a c t that t h i s d e c l i n e occurs at very n e a r l y the same time each year. 5.2 AIR-SEA EFFECTS Much has been s a i d i n the e a r l i e r p a r t s of t h i s study on the e f f e c t of t i d a l mixing i n and near the southern passages of the S t r a i t . The winter renewal, i n p a r t i c u l a r , i s thought to be s t r o n g l y i n f l u e n c e d by the mixing that occurs when s t r a t i f i c a t i o n i s weak and s u r f a c e c o o l i n g i s t a k i n g p l a c e . I f , i n f a c t , the winter renewal source water i s formed i n the mixing zone, then i t s p r o p e r t i e s should r e f l e c t the c o n d i t i o n s present i n that zone at the time of water formation. T h i s s e c t i o n examines the l i n k between the wintertime weather and the temperature of the winter renewal water. I d e a l l y , the net heat f l u x out of the water d u r i n g the renewal p e r i o d would be c a l c u l a t e d ( t a k i n g i n t o account the many environmental f a c t o r s i n f l u e n c i n g the f l u x ) and then compared to the temperature of the water some time l a t e r i n the S t r a i t . However, a complete heat f l u x c a l c u l a t i o n i n v o l v e s a s u b s t a n t i a l amount of work so a s i m p l i f i e d procedure w i l l be used i n s t e a d . The procedure and a r a t i o n a l e f o r i t s use are given i n the next few paragraphs. 94 The heat f l u x through the a i r - s e a i n t e r f a c e c o n s i s t s of a sum of the f l u x e s due to i n s o l a t i o n (short wave r a d i a t i o n ) , upward long wave r a d i a t i o n from the water, s e n s i b l e heat f l u x , and l a t e n t heat f l u x from evaporation or condensation ( P i c k a r d and Emery, 1982). The environmental c o n d i t i o n s which a f f e c t these f l u x e s i n c l u d e the a i r and sea s u r f a c e temperatures, winds, c l o u d cover, a i r humidity and the sea s t a t e (see f o r example Large and Pond, 1982). Each of the f l u x terms w i l l now be examined in turn to determine whether i t r e p r e s e n t s a net gain or l o s s of heat to the water and under what c o n d i t i o n s the f l u x i s enhanced. Wintertime c o n d i t i o n s w i l l be assumed. T y p i c a l sea s u r f a c e temperatures i n December to February are 7 to 8°C (see F i g . 3.8 a ) . Mean monthly temperatures at V i c t o r i a and Vancouver a i r p o r t s f o r January are 0 to 5°C, and 1 and 2°C higher i n December and February r e s p e c t i v e l y . T h e r e f o r e , the a i r temperature w i l l g e n e r a l l y be lower than the sea s u r f a c e temperature and w i l l e x h i b i t stronger i n t e r a n n u a l v a r i a b i l i t y . The s e n s i b l e heat f l u x i s p r o p o r t i o n a l to the a i r - s e a temperature d i f f e r e n c e and the s t r e n g t h of the winds. With T . <T , heat i s l o s t to the a i r . Using T - T . =5°C a i r sea' ^ sea a i r and winds of 10 m/s the s e n s i b l e heat f l u x i s about 60 W/m2 (Smith, 1980). The l a t e n t heat f l u x i s p r o p o r t i o n a l to the v e r t i c a l g r a d i e n t of the vapour pressure and to the wind. The vapour pressure g r a d i e n t i s normally estimated by assuming that the 95 a i r j u s t above the sea s u r f a c e i s s a t u r a t e d and at the same temperature as the sea s u r f a c e . The vapour pressure at a height of 10 m i s c a l c u l a t e d u s i n g a i r temperature and r e l a t i v e humidity. For T . < T , the l a t e n t heat f l u x cl 1 IT S 6 3 i n c r e a s e s as the a i r temperature and humidity decrease. Using T o < = 7 0 C , T . =2°C, winds of 10 m/s and t y p i c a l 5 6 a a l l r e l a t i v e h u m i d i t i e s of 98% and 75% at the sea s u r f a c e and at 10 m, the l a t e n t heat f l u x i s 50-60 W/m2 ( F r i e h e and Schmitt, 1976). The back r a d i a t i o n depends s t r o n g l y on the c l o u d cover and to a l e s s e r extent on the water temperature and vapour p r e s s u r e . The range corresponding to c o l d and dry to warm and moist winter weather i s 110 to 95 W/m2 on a c l e a r day ( P i c k a r d and Emery, 1982). Overcast c o n d i t i o n s can reduce the f l u x by 80%. The s o l a r r a d i a t i o n term i s the only one which adds heat to the water. The average wintertime f l u x i s 30 to 50 W/m2 on a c l e a r day at a l a t i t u d e of 49° ( P i c k a r d and Emery, 1982). Again, c l o u d cover w i l l reduce the f l u x by up to 70% on an overcast day. Since the c l o u d cover a f f e c t s the s o l a r and back r a d i a t i o n i n very s i m i l a r ways and because there are no other f a c t o r s which s t r o n g l y i n f l u e n c e e i t h e r term, i t i s c l e a r t h a t the net f l u x from the two terms w i l l r e s u l t i n a l o s s from the water to the a i r . The r a t e of l o s s i s high on c l e a r days (50-70 W/m2) and much l e s s on cloudy days (about 10 W/m2). 96 Wintertime atmospheric c o n d i t i o n s on the southern west coast of B r i t i s h Columbia are l a r g e l y governed by two p r i n c i p a l weather p a t t e r n s . Low pressure systems moving onto the coast from the P a c i f i c b r i n g warm, moist a i r and overcast or cloudy c o n d i t i o n s to the area. These low pressure systems compete with h i g h pressure systems which move i n t o the area from the c o n t i n e n t and b r i n g c l e a r , c o l d and dry a i r . T h e r e f o r e , the c o n d i t i o n s which tend to enhance the upward heat f l u x components (low humidity, c l o u d and temperature) tend to occur t o g e t h e r . C o r r e l a t i o n c o e f f i c i e n t s r e l a t i n g the temperature, winds, humidity and c l o u d cover t o each other, were c a l c u l a t e d u s ing mean d a i l y v a l u e s f o r the p e r i o d of December 1, 1967 to February 2"9, 1968. The c o e f f i c i e n t f o r temperature and winds i s 0.37 (95% confidence l e v e l i s 0.21). T h i s leads to an ambiguous r e s u l t : t h a t higher winds in c r e a s e the s e n s i b l e heat f l u x while at the same time higher a i r temperatures tend to decrease i t . However, the upper range of l i k e l y a i r temperatures (the mean and standard d e v i a t i o n are 4.3 ±3.7°C) i s equal t o or grea t e r than the sea s u r f a c e temperature (7 - 8°C), while the low range i n winds i s s t i l l above zero (11.9 ±8.5 m/s), so the net e f f e c t i s l i k e l y to be a g r e a t e r f l u x at lower temperatures. Although the r e l a t i v e humidity and the winds are not c o r r e l a t e d (-0.11, 95%:0.21) the range i n r e l a t i v e humidity i s small (84 ±11%) so the vapour pressure would be mainly a 97 f u n c t i o n of the a i r temperature. T h e r e f o r e , the same argument used above f o r the s e n s i b l e heat f l u x term holds f o r the l a t e n t heat f l u x . The v a r i a t i o n s that do occur i n the r e l a t i v e humidity are l i n k e d to the temperature v a r i a t i o n ( c o r r e l a t i o n c o e f f i c i e n t i s 0.51, 95%:0.21), and t h i s would tend to favor a higher heat f l u x at low temperatures. The c l o u d cover i s a l s o c o r r e l a t e d with the temperature (0.38, 95%:0.21) so that low temperatures tend to i n d i c a t e a high net r a d i a t i v e f l u x , which, as i n d i c a t e d e a r l i e r i n t h i s s e c t i o n , i s upward out of the water. The net r e s u l t i s t h a t , to a rough approximation, the a i r temperature alone can be used as a measure of the net s u r f a c e heat f l u x . In p a r t i c u l a r , more heat would be l o s t to the a i r d u r i n g winters with r e l a t i v e l y low mean temperatures. Assuming that the source water temperature i s f a i r l y uniform from year to year, r e l a t i v e to the drop produced by the net heat l o s s , . t h e n the temperature of the winter renewal water e n t e r i n g the S t r a i t of Georgia w i l l show the e f f e c t s of the year to year v a r i a t i o n in mean a i r temperature. C o r r e l a t i o n c o e f f i c i e n t s r e l a t i n g the mean temperature f o r each winter month (December to February) to water temperatures i n the S t r a i t d u r i n g each of the next 8 months, were c a l c u l a t e d and are presented i n F i g . 5.5. The number of years f o r which there are data at the 100 m l e v e l ranges from 10 to 15 (see Table 5.1), which r e s u l t s i n confidence 98 l e v e l s f o r each c o e f f i c i e n t ranging from 0.63 to 0.71. The December and January c o e f f i c i e n t s at 100 m ( F i g . 5.5 a) r i s e s h a r p l y from a l a g of 0 to a peak in March (a l a g of 2 months f o r January and 3 months f o r December) and are s i g n i f i c a n t at the 95% c o n f i d e n c e l e v e l . The c o e f f i c i e n t s then drop but remain c o n s i s t e n t l y above zero up to a l a g of 8 months. The same p l o t at 150 m depth ( F i g . 5.5 b) shows a somewhat stronger s i g n a l , again peaking at 2 to 3 months. At 200 m ( F i g . 5.5 c ) , the r i s e from 0 l a g i s s t i l l c l e a r but the peak i s spread from a l a g of 1 to 4 months ( d i s r e g a r d i n g the high value at lag=7 months) and the. subsequent drop i s more gradual than at 150 m. There i s a s u b s t a n t i a l drop i n the magnitude of the c o e f f i c i e n t s at 250 m ( F i g . 5.5 d) but the shape of the curves remain s i m i l a r to those at the 200 m l e v e l . These p l o t s can be i n t e r p r e t e d i n l i g h t of the r e s u l t s o btained e a r l i e r i n t h i s study which estimated the speed of the renewal s i g n a l , i t s v a r i a t i o n with depth and the timing of the summer renewal. The peak a t 2 to 3 months corresponds roughly to the t r a v e l time of the s i g n a l from the southern passages to the sampling r e g i o n , although i t overestimates i t somewhat, based on the t i m e - d i s t a n c e p l o t s of F i g . 3.8. The f a s t drop i n the c o e f f i c i e n t s f o l l o w i n g the peak, at the 100, 150 and 200 m l e v e l s shows the e f f e c t of the summer renewal water which, presumably, i s not connected with wintertime a i r temperatures. F i n a l l y , the o v e r a l l drop of 99 the c o e f f i c i e n t s at the 250 and 300 m l e v e l s i s perhaps an i n d i c a t i o n of the d i f f i c u l t y with which the winter renewal water penetrates to these depths and the m o d i f i c a t i o n which i t s u f f e r s i n the process. The same procedure used above to produce the a i r / s e a temperature c o r r e l a t i o n c o e f f i c i e n t s was a p p l i e d to the a i r temperature and the s a l i n i t y i n the c e n t r a l S t r a i t . At the 100 and 150 m l e v e l s , the c o e f f i c i e n t s g r a d u a l l y r i s e to a maximum at a l a g of 8 months, and then drop. T h i s t r e n d continues down to 300 m f o r the December a i r temperature. Based on these data, i t i s d i f f i c u l t to determine whether or not t h i s behaviour i s s i g n i f i c a n t and, i f so, what process may account f o r i t . The wintertime s u r f a c e heat f l u x produces a net change in water temperatures over the course of the winter p e r i o d . T h e r e f o r e , i t i s perhaps more reasonable, i n theory, to c o r r e l a t e the change (as opposed to the value at any one time) i n water temperature (and s a l i n i t y ) i n the S t r a i t with the wintertime a i r temperatures. These c o e f f i c i e n t s are presented i n F i g . 5.7 and 5.8. The i n i t i a l water temperatures and s a l i n i t i e s were set to the values i n the S t r a i t at each l e v e l (100, 150, 200, 250 and 300 m) d u r i n g the p r e v i o u s November. The f i n a l values are the same as the values used i n F i g . 5.5 and 5.6. The l a c k of November data in some years r e s u l t s i n fewer p o i n t s being used i n the c o r r e l a t i o n s , and higher 95% c o n f i d e n c e l e v e l s . In g e n e r a l , the r e s u l t s ( F i g . 5.7 and 5.8) show some of the same 100 behaviour as those a l r e a d y presented i n F i g . 5.5 and 5.6. However, the 2 to 3 month peak i n the temperature c o r r e l a t i o n s i s l e s s c l e a r , there i s c o n s i d e r a b l y more s c a t t e r and the c o e f f i c i e n t s are, i n g e n e r a l , somewhat lower. The poorer r e s u l t s are l i k e l y due to an i n a p p r o p r i a t e c h o i c e of the i n i t i a l temperature and s a l i n i t y . T h i s c h o i c e f a i l s to take i n t o account the presence of Juan de Fuca S t r a i t water i n the winter renewal water and assumes that the renewal water comes from a p a r t i c u l a r l e v e l i n the S t r a i t of Georgia ( i . e . the same as that used f o r the f i n a l temperature). In c o n c l u s i o n , the winter a i r temperatures over the southern S t r a i t of Georgia are s i g n i f i c a n t l y c o r r e l a t e d with the water temperatures w i t h i n the c e n t r a l S t r a i t 2 to 3 months l a t e r . T h i s corresponds roughly to the t r a v e l time of the renewal water from the southern S t r a i t , determined e a r l i e r i n t h i s study. Using the change i n water temperature from the pr e v i o u s November leads to somewhat lower c o e f f i c i e n t s and higher degree of s c a t t e r among the p o i n t s . There are other f a c t o r s which i n f l u e n c e the temperature i n the S t r a i t of Georgia apart from the wintertime a i r temperatures. In order to a c c u r a t e l y p r e d i c t these temperatures (and s a l i n i t i e s or other p r o p e r t i e s ) one might have to i n v e s t i g a t e the i n f l u e n c e of the F r a s e r River r u n o f f , the winds w i t h i n the S t r a i t of Georgia, the e f f e c t s of s e a s o n a l l y v a r y i n g t i d a l h e i g h t s and i n f l o w from the northern passages. 6. SUMMARY AND CONCLUSION Hydrographic data from a December 1967 to December 1968 c r u i s e program have been used to d e s c r i b e the p r o p e r t i e s of the deep water i n the S t r a i t of Georgia and t h e i r v a r i a t i o n in time and space. Two d i s t i n c t renewal episodes occur over the one year p e r i o d . A wintertime i n t r u s i o n of f r e s h , c o l d and h i g h l y oxygenated water begins i n December 1967 to January 1968 and q u i c k l y lowers the temperature and s a l i n i t y i n the S t r a i t . These p r o p e r t i e s continue to decrease through A p r i l at i n t e r m e d i a t e depths of 100 to 200 m, and i n t o J u l y at lower depths below 200 m. In May, an i n f l o w of warm, s a l t y and p o o r l y oxygenated water i n c r e a s e s the temperature and s a l i n i t y of the very c o l d i n t e r mediate water but not of the deep water (below 200 m). The summer renewal begins to a f f e c t the deep water p r o p e r t i e s i n J u l y . The temperature and s a l i n i t y r i s e through November 1968 i n the intermediate l a y e r , and to the end of the c r u i s e program i n December 1968 in the deep l a y e r . From a q u a l i t a t i v e s t a n d p o i n t , there i s l i t t l e d i f f e r e n c e between the c h a r a c t e r i s t i c s of the renewal i n the c e n t r a l and northern b a s i n s . However, there are s i g n i f i c a n t d i f f e r e n c e s to be found i n the p r o p e r t y v a l u e s . Average minimum and maximum temperatures and s a l i n i t i e s reached between renewal p e r i o d s i n the northern b a s i n deep water are between those reached i n the i n t e r m e d i a t e l a y e r and the c e n t r a l b a s i n deep l a y e r , and i n d i c a t e the i n t e r m e d i a t e 101 1 02 l a y e r o r i g i n of the northern b a s i n deep water. The two renewal episodes behave q u i t e d i f f e r e n t l y not only in t h e i r e f f e c t on the water p r o p e r t i e s ( i . e . one i n c r e a s e s , the other decreases the temperature and s a l i n i t y ) but a l s o i n t h e i r s p a t i a l and temporal v a r i a t i o n . The winter renewal i n the intermediate l a y e r produces an abrupt change i n p r o p e r t i e s in a short time (December to February) while the summer renewal i s more g r a d u a l . There i s a 2 to 3 month l a g from the end of the winter renewal p e r i o d i n the intermediate to the deep l a y e r . The corresponding l a g f o r the end of the summer renewal p e r i o d i s l e s s than 2 months and i n d i c a t e s that the winter renewal water has more d i f f i c u l t y p e n e t r a t i n g to lower depths than the more dense summer water. The v a r i a t i o n a c r o s s the S t r a i t of Georgia i s q u a l i t a t i v e l y c o n s i s t e n t with the i n f l u e n c e of r o t a t i o n . Water f l o w i n g i n t o the S t r a i t from the south at depth tends to p r e f e r the eastern s i d e of the S t r a i t . A v o l u m e t r i c a n a l y s i s of the water i n the S t r a i t shows new water, with temperature and s a l i n i t y d i s t i n c t from the bulk of the water i n the b a s i n , e n t e r i n g and a l t e r i n g the average v a l u e s of the p r o p e r t i e s . The p r o g r e s s i o n of the renewal i s seen as being q u i t e v a r i a b l e i n i t s e f f e c t s on the p r o p e r t i e s i n the S t r a i t from month to month. Est i m a t e s of renewal water volume in f l o w based on a heat and s a l t budget a n a l y s i s show r a t e s of from 100 to 250 km3/mo i n t o the i n t e r m e d i a t e l a y e r d u r i n g a renewal 103 p e r i o d . Flow r a t e s f o r renewal water e n t e r i n g the deep l a y e r i n the c e n t r a l b a s i n range from 10 to 30 km3/mo and i n t o the northern basin deep l a y e r , from 9 to 12 km3/mo. Re s u l t s at the times between renewal p e r i o d s are l e s s meaningful and r e f l e c t the very s i m i l a r p r o p e r t i e s of the source and S t r a i t of Georgia waters, and the one month sampling i n t e r v a l . Data c o l l e c t e d over many years i n the deepest area of the S t r a i t i n the c e n t r a l basin are used to examine the in t e r a n n u a l v a r i a t i o n of the renewal. S e v e r a l of the main f e a t u r e s as i d e n t i f i e d i n the one year dataset are a l s o apparent i n the l e s s dense m u l t i - y e a r data. The timing of both renewal p e r i o d s i n c l u d i n g i t s v a r i a t i o n with depth are apparent. The s t r e n g t h and b r e v i t y of the winter renewal r e l a t i v e to the summer renewal are a l s o seen. Temperature and s a l i n i t y at the 100 m l e v e l are p o o r l y c o r r e l a t e d with those below the 200 m l e v e l d u r i n g the winter renewal p e r i o d but w e l l c o r r e l a t e d d u r i n g the summer renewal p e r i o d , i n d i c a t i n g that the summer renewal takes p l a c e with equal s t r e n g t h at a l l l e v e l s . F i n a l l y , a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n was found between the wintertime a i r temperatures and the sea temperatures some time l a t e r i n the S t r a i t . The c o r r e l a t i o n peaks at 2 to 3 months l a g . Features i d e n t i f i e d i n t h i s study and not i n pr e v i o u s s t u d i e s i n c l u d e the northward propagation of renewal water and estimates of i t s v e l o c i t y and volume flow r a t e . D i f f e r e n c e s of the renewal in the c e n t r a l and northern 1 04 b a s i n s and from the i n t e r m e d i a t e to the deep l a y e r s were noted. A v o l u m e t r i c a n a l y s i s of the S t r a i t water showed the p r o g r e s s i o n of the renewal and i t s v a r i a t i o n i n s t r e n g t h . A s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n was found between the wintertime a i r temperature and water temperatures. Although t h i s study has p r o v i d e d a d e t a i l e d d e s c r i p t i o n of the e f f e c t s of renewal on the water p r o p e r t i e s w i t h i n the S t r a i t , i t has not examined the dynamics of the renewal pro c e s s . F a c t o r s such as the t i d e s , winds, the e a r t h ' s r o t a t i o n and, of course, the presence of dense water i n Juan de Fuca S t r a i t a l l combine to c r e a t e a very complex dynamical system. The next step i s to develop a p h y s i c a l model by which some or a l l of the f e a t u r e s i d e n t i f i e d here may be- e x p l a i n e d . 105 Fig. 1.1 Southern coast of British Columbia 106 l ~ r ^— Fig. 1.2 The Strait of Georgia, adjacent waters and local place names Waldichuk, 1957) rn o r - _ , CD , ca cc CNJ cn. 0 ~ m o p ; . . a CO CE O m _ U_ m en t + + + + t + + t + t «• T * + 0.0 7.D 14.D 2J.Q 2B.Q WEEK tt 35.0 42.0 49.0 56 Fig. 1.3 Weekly runoff (means and standard deviations) into the Strait of Georgia drainage area (from LeBlond et al., 1983) 108 Fig. 1.4 Cross-sections of channels of the northern (top) and southern (bottom) approaches to the Strait of Georgia (from Waldichuk, 1957) 109 Fig. 1.5 Temperature, salinity and dissolved oxygen concentration in the central Strait of Georgia from 1967 to 1974 (from Pickard, 1975). 110 Fig. 2.1 Strait of Georgia and Juan de Fuca Strait with hydrographic stations occupied from December 1967 to December 1968 (Crean and Ages, 1971). Three sections parallel to the major axis of the Strait of Georgia and nine sections running across the Strait are marked. I l l Fig. 2.2 Strait of Georgia showing the region in which the l o n g range data is located. Fig. 2.3 Part of the central Strait of Georgia showing the locations of stations sampled to provide the long range data. The number of samples taken at each location is marked unless it is fewer than three. 113 62 108 239 163 63 64 98 215 125 59 34 139 253 218 7 1 74 190 254 128 89 76 158 122 243 106 162 195 212 150 24 1 146 185 31 232 144 52 164 262 160 169 28 131 45 143 298 229 69 28 7 1 6 1 185 305 166 39 71 84 84 208 282 193 132 131 32 30 18 27 134 292 2 79 194 86 72 27 23 61 83 179 305 240 147 1 13 185 30 59 125 179 284 188 226 34 81 132 144 24 1 330 224 178 27 25 28 1 12 123 136 163 86 132 287 308 18 1 251 237 255 29 73 14 14 1 167 181 287 7 1 204 49 135 100 131 16 1 189 282 280 70 70 193 242 180 161 157 225 325 196 170 274 87 197 337 179 132 125 207 320 207 50 234 189 342 334 288 302 78 75 242 180 2 10 337 296 210 71 265 310 40 1 13 207 224 132 139 173 43 278 31 1 141 133 326 257 96 54 254 318 166 91 175 313 278 1 18 197 288 268 162 362 253 79 93 138 199 278 354 382 223 23 39 115 338 291 322 382 240 74 10 33 338 372 287 351 222 143 62 304 391 379 341 197 176 27 81 290 400 400 365 182 144 144 20 310 399 326 347 198 141 106 77 187 349 366 347 1 18 155 87 57 102 334 371 279 132 146 142 69 1 18 319 377 254 191 1G7 153 1 13 294 379 316 250 195 168 83 133 30 59 30 283 375 359 313 187 168 102 189 217 54 55 55 220 373 362 334 2 10 175 143 33 52 51 163 254 357 340 322 222 189 173 28 155 226 365 338 3 17 288 236 244 182 104 154 54 212 267 337 299 254 262 235 198 92 105 100 259 309 291 239 196 198 142 58 4 32 33 102 253 281 243 182 130 92 1 1 3 19 127 248 231 198 79 12 3 3 134 215 206 158 30 3 3 96 184 17 1 135 20 3 3 99 160 149 123 27 3 109 142 127 1 1 1 43 6 124 126 1 18 1 14 3 137 130 123 124 34 3 3 3 128 169 150 147 51 14 1 1 5 3 93 195 195 170 88 4 1 23 6 1 1 1 185 210 153 87 48 14 13 9 102 137 197 1 10 53 28 3 75 61 150 49 52 13 4 62 59 84 1 16 81 47 48 42 3 29 74 15 6 Fig. 2.4 The average depth in metres for each 4X4 km square is shown for the grid used in the volumetric analysis of the Strait of Georgia waters. C. FLATTERY J U A N DE F U C A ST.-BOUNDARY - H A R O - -PASS. -ST. 114 C. MUDGE ST. OF GEORGIA 1 Fig. 3.1 b January 1968 Fig 3.1 a-l Temperature ( ° C ) distribution in the Strait of Georgia and Juan de Fuca Strait, December 1967 to December 1968 (from Crean and Ages, 1971). 115 C. FLATTERY JUAN DE FUCA ST-BCHJNDARY C. MUDGE S T A T I O N 75 72 69 6S 62 -HARO- -PASS.-ST. -ST OF GEORGIA-I F R A S E R R IVER 56 46 42 39 27 2 3 6 9 1 12 14 16 H 8:5 30 Cf Fig. 3.1 c February 1968 C. FLATTERY JUAN DE FUCA ST.-BOUNDARY C. MUDGE r-HARO-i -PASS-ST. -ST OF GEORGIA-46 42 39 / 27 2 3 6 9 12 14 16 Fig. 3.1 d March 1968 116 117 113 119 C. FLATTERY -JUAN DE FUCA ST.-BOUNDARY C. MUDGE f-HARO--PASS.-ST. -ST OF GEORGIA-CD 2 3 G 9 12 14 16 Fig. 3.1 k 3ocj- November 1968 120 C. FLATTERY JUAN DE FUCA ST.-BOUNDARY C. MUDGE STATION 75 72 69 f-HARO- -PASS.-ST 65 62 59 56 -ST. OF GEORGIA-I FRASER 1"-; RIVER JO 42 39/ 27 2 3 6 9 12 14 16 ' 29.0 T 20C*-, Fig. 3.2 a December 1967 400 C. FLATTERY JUAN DE FUCA ST.-BOUNDARY C. MUDGE STATION 75 72 69 [-HARO- -PASS.-ST. 65 62 59 56 -ST OF GEORGIA-FRASER O RIVER Fig. 3.2 a-f Salinity ( ° / 0 o)d is t r ibut ion in the Strait of Georgia and Juan de Fuca Strait, December 1967 to December 1968 (from Crean and Ages, 1971) 121 1 2 2 123 C. FLATTERY JUAN OE FUCA ST.-BOUN'DARY C. MUDGE STATION 75 72 6 9 65 62 l-HARO-i -PASS.-ST. 59 56 ST OF GEORGIA-N S 24.5, 25.0 Fig. 3.3 a Joof- December 1967 C. FLATTERY JUAN DE FUCA ST.-BOUNDARY C. MUDGE STATION 7 5 72 6 9 f-HARO-1 -PASS.-ST. 59 56 -ST OF GEORGIA-I FRASER RIVER 46 42 39 27 2 3 6 9 12 14 16 Fig. 3.3 a-g Density ( a f c ) distribution in the Strait of Georgia and Juan de Fuca Strait, December 1967 to December 1968 (from Crean and Ages, 1971) 4001 125 126 C. FLATTERY JUAN DE FUCA ST-BOUNDARY C. 127 M U C G E STATION 75 72 69 -HARO--PASSr ST. 59 56 -ST. O F GEORGIA-2 L J 20d-400 1 Fig. 3.4 a December 1967 C. FLATTERY JUAN DE FUCA ST-BOUNDARY -HARO--PASS.-ST. 59 S6 -ST OF GEORGIA-|FRASER I RIVER ' 46 42 39 27 2 3 6 9 12 14 16 Fig. 3.4 b January 1968 400 Fig. 3.4 a-l Dissolved Oxygen (ml / I) distribution in the Strait of Georgia and Juan de Fuca Strait, December 1967 to December 1968 (from Crean and Ages, 1971) 128 4001 129 130 131 C. FLATTERY JUAN OE FUCA ST-BOUNDARY C. MUDGE -HARO-ST. PASS: -ST OF GEORGIA-| FRASER RIVER 56 | 46 42 39 27 2 3 6 9 '2 14 10 132 133 Fig. 3.5 T - S diagrams at a depth of 50 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 46 (southern Strait); b) stn. 39 (off Vancouver); c) stn. 2 (Lasqueti Island); d) stn. 14 (northern Strait) 134 Fig. 3.6 T - S diagrams at a depth of 100 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 46 (southern Strait); b) stn. 39 (off Vancouver); c) stn. 2 (Lasqueti Island); d) stn. 14 (northern Strait) 135 32.0 Fig. 3.7 T - S diagrams at a depth of 150 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 46 (southern Strait); b) stn. 39 (off Vancouver); c) stn. 2 (Lasqueti island); d) stn. 14 (northern Strait) ' 136 j i STP.TION 3S <>CEC JOBS ' i ' i ! co i i i j : 3G. 5_ 3! .0 3! .5 30.0 30.5 ~'i 0 5 ; S (PPT . ! Fig. 3.8 T - S diagrams at a depth of 200 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 39 (off Vancouver); b) stn. 2 (Lasqueti Island); c) stn. 14 (northern Strait) STSTION 22 f COCO / / £>°C7 L J _ - <*.FEB t 7 / <f,JUL 30.0 30. 3; .0 0.; STfiTION 2 4>FEB J^ QO**J^M«rf OCT 3! .0 LOco 31 .5 30.0 I I A / .fdCT >.QDP ^ j p'dUG SiriTION ii ; T - S diagrams at a depth of 250 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 39 (off Vancouver); b) stn. 2 (Lasqueti Island); c) stn. 14 (northern Strait) 138 30.0 30.5 31.0 31.5 S (PPT .) Fig. 3.10 T - S diagrams at a depth of 300 and 350 m in the Strait of Georgia from December 1967 to January 1969. a) stn. 39 (off Vancouver) at 300 m; b) stn. 14 (northern Strait) at 300 m; c) stn. 39, at 350 m 139 DEC NOV OCT SEP AUG 1968 J U L_ JUN MAY APR MAR FEB JAN DEC 1967 NOV 1968 OEC NOV OCT SEP RUG JUL JUN MAY APR MAR FEB JAN 1967 D E C J NOV a) surface i i i i 1 1 r 59 56 46 42 39 27 2 STATION NUMBER 12 16 b) 50 m level 59 56 46 42 "i—r 39 27 STATION NUMBER Fig. 3.11 a-h Temperature distribution ( ° C ) at several levels from the to 300 m, with axes of time and the distance along th of the Strait of Georgia. surface e centre 140 1968 1967 1968 1967 NOV i i i i i i i i—i 1 1 1 r 59 56 46 42 39 27 2 3 6 9 12 14 16 STATION NUMBER Fig. 3.11 d) 100 m level with lines fitted to the 8.6°C contour 141 142 143 1968 J U^J DEC NOV OCT SEP AUG 1968 J U L J JUN MAY APR MAR FEB JAN 1967 D E C J NOV "i r 4 2 39 2 7 2 STATION NUMBER 296 294292290288- / / \<-294 292290288.. 50 m level Fig. 3.12 59 a-h ~T" 5 6 4 6 4 2 T T T 3 6 3 9 2 7 STATION NUMBER Salinity distribution (% 0) a t several levels from the surface to 300 m, with axes of time and the distance along the centre of the Strait of Georgia. 144 Fig. 3.12 d) 100 m level with lines fitted to the 30.1 and 30.3 contou r 145 146 147 1968 J U L J 1967 1968 1967 DEC NOV OCT SEP RUG JUL JUN MAY APR MAR FEB JAN DEC NOV T 59 T 56 1 46 i r 39 27 2 3 6 STATION NUMBER gf,S2 30 ,49 46 b) 50 m level 59 56 46 42 T 12 16 n i i i i 39 27 2 3 6 STATION NUMBER Fig. 3.13 a-h Dissolved oxygen distribution (mi/I) at several levels from the surface to 300 m, with axes of time and the distance along the centre of the Strait of Georgia. 148 149 150 151 1968 1967 1968 1967 OEC NOV OCT SEP AUG JUL JUN MAY APR MAR FEB JAN DEC NOV 59 I r 56 46 i i i i r 42 39 27 2 3 6 STATION NUMBER 12 i r 14 16 229 22B22?292324^ *?2>y' \V^ -22722622S24?23 -b) 50 m level —i i i 1 1 1 1 — i — r 1 1 1 r~ 59 56 46 42 39 27 2 3 6 9 12 14 16 STATION NUMBER Fig. 3.14 a-h Density distribution (a f c ) at several levels from the surface to 300 m, with axes of time and the distance along the centre of the Strait of Georgia. 152 153 154 1968 1967 NOV i i i i i i i— i— i 1 1 1 r 59 56 46 42 39 27 2 3 6 9 12 14 16 Fig. 3.14 g) 250 m level STATION NUMBER 1968 1967 59 56 46 42 39 27 2 3 6 0 \2 14 16 STATION NUMBER Fig. 3.14 h) 300 m level 155 Fig. 3.15 Vertical distribution of the temperature (a, top) and the salinity (b) from December 1967 to December 1968 at Stn. 42 in the Strait of Georgia (off the mouth of the Fraser River). 156 o -I i i i : i i i 1 1 1 1 1 r DEC67 JF1N68 FEB MAR APR MAY JUN JUL RUG SEP OCT NOV DEC Fig. 3.16 Vertical distribution of the temperature (a, top) and the salinity (b) from December 1967 to December 1968 at Stn. 27 in the Strait of Georgia (off Nanaimo). 157 100 m 14 12 9 6 3 2 27 39 42 150 m I 1 1 1 1 1 r 14 12 9 6 3 2 27 39 42 ERST 200 m 915 910 UEST 920 905 900 895 915-i 1 1 1 1 1 1 1 T 14 12 9 6 3 2 27 39 42 F i g . 3.17 Hor i zon ta l d i s t r i bu t i on of the tempera tu re (a, above ) and sa l i n i t y (b, next page ) at the 100 (top), 150 (centre) and 200 m l eve l s ( bo t t om) fo r the St ra i t o f G e o r g i a in January 1968. The s ta t i ons marked are those used a long the central s e c t i o n of the S t ra i t . 158 100 m b) salinity, January 1968 159 100 m ERST 79 / 79 78 I 80 79 80 \ UEST \ \ I 79 \ T 14 12 9 6 3 2 27 39 42 150 m 14 12 9 6 3 2 27 39 42 200 m i i i i i i r 14 12 9 6 3 2 27 39 42 F i g . 3.18 Hor i zon ta l d i s t r i bu t i on of the temperature (a, above ) and sa l i n i t y (b, next page) at the 100 (top), 150 (centre) and 200 m leve l s ( bo t t om) for the St ra i t of G e o r g i a in Ap r i l 1968. The s ta t i ons marked are those used a long the centra l s e c t i o n of the S t ra i t . 160 100 m b) s a l i n i t y , A p r i l 1968 161 100 m ERST UEST 150 m i r 12 9 6 3 2 27 39 42 Hor i zon ta l d i s t r i bu t i on of the tempera ture (a, above ) and sa l i n i t y (b, next page ) at the 100 (top), 150 (centre) and 200 m l eve l s ( bo t t om) for the St ra i t o f G e o r g i a in late Ju l y 1968. The s t a t i o n s marked are those used a long the cent ra l s e c t i o n of the S t ra i t . 162 b) salinity, late July 1968 163 100 m EAST UEST 150 m EAST UEST ERST 9! 9! 1 1 1 1 1 1 T 14 12 9 6 3 2 27 39 42 F i g . 3 .20 H o r i z o n t a l d i s t r i b u t i o n o f t h e t e m p e r a t u r e (a , a b o v e ) a n d s a l i n i t y (b , n e x t p a g e ) at t h e 100 ( t o p ) , 150 ( c e n t r e ) a n d 2 0 0 m l e v e l s ( b o t t o m ) f o r t h e S t r a i t o f G e o r g i a in D e c e m b e r 1 9 6 8 . T h e s t a t i o n s m a r k e d a r e t h o s e u s e d a l o n g the c e n t r a l s e c t i o n o f t he S t r a i t . 150 m 14 12 9 6 3 2 27 39 42 200 m UEST 1 l I I 1 1 1 1 T 14 12 9 6 3 2 27 39 42 b ) s a l i n i t y , D e c e m b e r 1 9 6 8 165 NOV i i i i i i i—i—i—i—i 1—r 51 49 44 43 37 28 24 23 22 21 20 13 18 STATION NUMBER NOV I I I I I I I I 1 1 1 59 56 46 41 40 26 1 4 5 II 15 STATION NUNBER Fig. 3.21 Temperature distribution ( ° C ) at a depth of 100 m, with axes of time and the distance along the eastern (a) and western (b) sides of the Strait of Georgia. Lines are fitted to the 8.6°C contour. 166 1968 1967 D E C J 1968 1967 D E C J NOV Fig. 3.22 51 49 44 T 43 37 28 STATION NUMBER i i r 24 23 22 21 20 i—r 13 18 40 26 1 4 STATION NUMBER Salinity distribution ( ° / 0 0 ) a t a depth of 100 m, with axes of time and the distance along the eastern (a) and western (b) sides of the Strait of Georgia. Lines are fitted to the 30.1 (a) and 30.0 (b) contours. 167 Fig. 3.23 Temperature distribution ( ° C ) at a depth of 200 m, with axes of time and the distance along the eastern (a) and western (b) sides of the Strait of Georgia. 168 Fig. 3.24 Salinity distribution ( ° / 0 0 ) at a depth of 200 m, with axes of time and the distance along the eastern (a) and western (b) sides of the Strait of Georgia. 169 I 0.00 I 9 . 50 I 9 .00 [ 8 . 50 I 8.00 I 7 . 50 I 7 .00 I S . 50 I 6.00 I 5 . 50 I 5.00 I I -10.00 9 . 50 9 .OO B . 50 8.00 7 . 50 a) December 1967 f25! 10 | 2.1 6o"|T.-p '99 TTfT]" LJ0_ _32 l'_93 _2 3J~ 20 2 I H 2 • I -19.00 20.00 21.00 22.00 23.00 SALINITY PPT. b) January 1968 3 102 240 10 75 120 G  9 5 1 36 29 2 2 6 1 30 39 3 1 4 21 .12 18 1-  30 19 .1 3 3 3 2 23.00 24.00 SALINITY PPT. 10.00 9 . 50 9 O  8 . 50 8.00 7.50 7 .00 6 . 50 6 .00 5 . 50 5.00 c) February 1968 10 5 2 34 8 6 6 1 19 4 105 202 1 2 1 89 t.10 24 34 65 9 14 45 98 42 5 1 3 3 1 4 SALINITY PPT. 10.00 I 9.50 I 9.00 I 8.50 I 8.00 I 50 I 00 I 50 1 00 I 50 I 00 I I -d) March 1968 10 9 3 6 2 45 220 14 1 2 2 7 30 63 150 19 12 18 20 54 72 96 225 50 21.00 22.00 23.00 24.00 25.00 26.00 27 00 28.00 SALINITY PPT . j ,o.oo . e) A P r i l 1968 E y.50 1 1 5 M 9.OO I 16 3 2 p 8.501 1 .1 1 15 13 17 E 8.00 I 13 *<ST_ 67 93 9I|229| 401 „ 7 SO I 4 '^3 76 |TB1 | 3 I | ~ 1 , 7 00 I 2 3 ~ ~^ * 6.50 I U G 0 0 ' " 5.00 I i — i — i — i — i — i — i — i — i — i — i — i — t — I — i — i — i — i — i — i — i — i — i — i — i — i — r 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00 3 1.00 SALINITY PPT. Fig 4.1 a-l Volumetric tables for the Strait of Georgia (all depths) for each of 12 cruises from December 1967 to December 1968. The units are km 3 and the total volume is 1167 km 3 . 170 16.00 I 15 .50 I 15 .00 I 14 .50 I 1 4 .00 1 13 .50 I I 3 .OO I 12 .50 I 12 00 I I 1 .50 1 1 t . 0 0 I 1 0 . 5 0 I 10 .00 I 9 . 5 0 I 9 . 0 0 I 8 . 5 0 I 8 . 00 1 7 . 5 0 I 7 . 0 0 I 6 . 50 I 6 . 0 0 I 5 . 5 0 I 5 . 0 0 I I f) May 1968 32 26 102 IG3 273 191 62 2 I I I 22 . OO 2 3 . 0 0 - _ [ . - -2G .00 t • I I 3 0 . 0 0 3 1.00 19 .00 20 OO 2 8 . 0 0 2 3 . 0 0 SALINITY P P T . 19 .50 I 19 .00 I 18 .50 I 18 .00 I 17 .50 I 17 .00 I 16 .50 I 1 6 . 0 0 I 1 5 . 5 0 I 1 5 . 0 0 I 14 50 I 1 4 . 0 0 I 13 .50 I 13 .00 I 12 .50 I 12 .00 I I I . 50 I 11 .00 I 1 0 . 5 0 I 10 .00 I 9 . 5 0 I 9 . 0 0 I 8 . 5 0 I 8 . 00 I 7 50 I 7 .OO I 6 . 5 0 I 6 . 0 0 I 5 . 50 I 5 . 0 0 I I-g) early July 1968 2 3 3 4 26 1 37 •10 3 4 14 12 32 96 16 57 105 223 173 150 i i I---I 1 I---1 i-.-i---19.00 20 00 2 1 . 0 0 2 2 . 0 0 2 3 . 0 0 2 4 . 0 0 2 6 . 0 0 27 00 2 8 . 0 0 2 9 . 0 0 3 0 . 0 0 3 1.00 SALINITY P P T . 19 .50 I 19 00 I 18 .50 I 18 .00 I 17 .50 I 17 .00 1 16 .50 I 16 .00 I 15 50 I 15 .00 I 14 .50 1 14.OO I 13 50 I I 3 00 I I 2 . 50 I I 2 . 0 0 I . 50 1 1 .00 10 .50 I 10 .00 I 3 . 50 1 9 . C O I 8 . 50 I 8 00 I 7 50 1 7 . 00 I 6 . 5 0 1 6 .00 I 5 50 I 5 . 0 0 I I I I h) late July 1968 2 3 1 2 2 2 2 4 7 1 5 1 7 10 2 2 3 2 1 3 2 14 1 1 4 4 3 25 23 29 2 3 3 10 37 6D 13 15 22 117 284 150 4 5 I . . . I I i 30 . 00 3 I . 00 SALINITY P P T . Fig. 4.1 171 '«•«> 1 i ) August 1968 1 3 . 0 0 I 2 3 M . 50 I I 4 3 2 ' l t . 00 I I 3 3 2 2 -\ y 13.50 I I 3 2 4 3 ' 13 .00 I 2 3 2 2 3 3 ' 1 2 . 5 0 I I 3 6 R 12 00 I 2 3 2 2 1 1 1 2 3 1 12 30 14 5 3 3 1 23 2G 99 157 3 15 4 G t 18 I 1 .50 I I 3 14 2 I I 00 I 1 1 13 3 7 10 10 .50 I 1 1 2 7 3 1 1 0 . 0 0 I 17 9 . 5 0 I 9 9 . 0 0 I 3 8 . 50 I 8 . 0 0 I 7 50 1 7 .00 I 6 . 50 I 6 . 0 0 I 5 . 50 [ 5 . 0 0 I I I » 1 I I I I I I I I I I I I I I I I I I I I I I I 19 .00 2 0 . 0 0 2 1 . 0 0 2 2 . 0 0 2 3 . 0 0 24 00 2 5 . 0 0 2 6 . 0 0 2 7 . 0 0 2 8 . 0 0 2 9 . 0 0 3 0 . 0 0 3 1.00 SALINITY P P T . 16 .00 I 15 .50 I 15 .00 I 14 .50 I 14 .00 I 13 50 I 13 .00 I 12 .50 I 12 .00 I 1 I . 50 I 8 . 0 0 I 7 . 50 I 7 . 00 I 6 . 50 I 6 . 0 0 I 5 . 50 I 5 . 0 0 I I -j) October 1968 r 11 .00 I 3 2 3 7 13 16 u 10 .50 I 1 4 7 26 13 R 10 .00 I 1 6 32 25 2 1 F. 9 50 I 13 62 12 58 1 1 9 . 00 I 18 92 1 12 140 2 1 "c 8 50 I 6 2 1 59 254 50 — I — I -24 .00 SALINITY P P T . 1 10 .00 1 E 9 .50 I M 9 .00 I P 8 .50 I E 8 .00 I ft 7 .50 I A . 7 .00 I r 6 . 50 I u 6 00 I R 5 50 I £ 5 00 I t k) November 1968 15 9 6 3 51 34 108 6 176 266 3 4 157 36 5 1 2 2 . 0 0 2 3 . 0 0 2 8 . 0 0 2 9 . 0 0 SALINITY P P T . ! 10 .00 I M 9 ^ 0 0 i I) December 1968 9rToT~24.i 2491 1 P 8 . 5 0 I _ |_ I0_^50 55 53 34 _76_ _56_] E 8 . 0 0 I 5 I0'_:17_ J l _ J _ IG_ I8_T R 7 50 I 5 1 12 Jj23J 10 3 A 7 . 0 0 I 3 2 3 1 5 1 3 1 6 2 T 6 . 5 0 [ 2 1 U 6 . 0 0 I R 5 . 5 0 I E 5 . 0 0 I i — * — i — i - - - i - - - i - - - i — i — • — i — i — f — i — i — r — i — i — i — i — i — i — r — i — i — i — r — i t 1 9 . 0 0 2 0 . 0 0 21 .OO 2 2 . 0 0 2 3 . 0 0 2 4 . 0 0 2 5 . 0 0 2 6 . 0 0 2 7 . 0 0 2 8 . 0 0 2 9 . 0 0 3 0 . 0 0 3 1 . 0 0 SALINITY P P T . Fig. 4.1 172 0 00 I 3 . 50 I 9 . OO I 8 00 I 8 . 00 I 7 . 50 I 7 .00 I 6 . 50 I 6 . 00 I 5 . 50 I 5 .00 I I -a) January 1968 3 7 lO 70 2 9 5 1 3 1 3 2 6 t 30 32 5 24 42 IB 14 30 19 4 3 3 3 2 2 8 . 0 0 2 9 . 0 0 SALINITY P I T . E ' 9 5 0 i b) April 1968 M 9.00 I 1 6 3 2 P 8 . 50 1 1 4 1 1 - 1 1 3 17 E 8 . 0 0 I 13 58 G7 93 50 R 7 . 5 0 I 5 23 7G 38 A 7 0 0 I 2 3 T G 50 I U 6 00 I R 5 . 5 0 I E 5 . 0 0 I ! [ , | l i I I I - — r - — I 1 I I I I I---I I---I I I I C 1 9 . 0 0 2 0 . 0 0 2 1 . 0 0 2 2 . 0 0 2 3 . 0 0 2 4 . 0 0 2 5 . 0 0 2 G . 0 0 2 7 . 0 0 2 8 . 0 0 2 9 . 0 0 3 0 . 0 0 SALINITY PPT 19 . 50 10 .00 18 . 50 18 00 17 .50 17 .00 I G . 50 1G.00 15. 50 15 .00 14 . 50 1 -I . 00 13 . 50 13 .00 12 . 50 12 .00 I I . 50 I 1 .00 10 . 50 10 .00 9 . 50 9 00 8 . 50 8 .00 7 . 50 c) late July 1968 3 23 3 29 9 2 37 1 1 69 20 13 90 18 SALINITY PPT . d) November 1968 9 . 50 I 5 9 . C O I I I 5 11 13 5 7 G 9 8 34 G 1 I 0 1 50 p 8 50 I •! 1 1 G .1 G 5 0 OO I 1 2 . 1 1 . 1 3 I 7 50 I * 6 . 5 0 I G O O I " 5.01J I I . . . ] _ - | ! -3 0 . 0 0 2 1.00 2 2 . 0 0 2 3 . 0 0 2 4 . 0 0 2 5 . 0 0 2 G . 0 0 2 7 . 0 0 2 8 . 0 0 2 9 . 0 0 3 0 . 0 0 SALINITY PPI . Fig 4.2 a-d Volumetric tables for the surface layer (down to 80 m) of the Strait of Georgia for January, April , late July and November 1968. The units are km 3 and the total volume is 495 km 3 . 173 9 . 40 I 9 . 20 I 9 .00 I 8.80 I 8 .60 I 8 . 40 I 8 . 20 I 8 .00 I 7 7 7 7 7 a) December 1967 80 I 60 I 40 I 20 I oo I i — i — i -28 . 40 .1 32 67 34 19 1 2 2 32 55 4 9 4 6 12 12 19 2 3 9 4 , 1 2 r L _ 2 G J 3 - - i — r — i — i-28.80 29.20 29.60 _ _ j i I I I I I I 30.00 30.40 30.80 3 1.20 31.60 SALINITY PPT. T 9 9 40 20 I I b) January 1968 2 24 19 ~ r E 9 00 I I 2 1 28 34 64 M 8 80 I 2 1 9 31 49 23 P 8 60 I 1 3 1 1 3 14 18 _ 7_ E 8 40 I ,_I4_ _ 6_T 4 1 R 8 20 I 4 4 2 A 8 00 I 2 1 T 7 80 I 5 l 5 l 2 U 7 60 I 15, 2 4 1 R E 7 7 7 40 20 00 I I I 1 !Ai 4 2 C I-- - i — i — i — i - - - i — i - - - i - - - I - - - i - - - I -- - I - - - I -28 . 40 28 .80 29 . 20 29.60 30.00 30.40 --I 1-30.80 --I I I I 31.20 31.60 T E M P E R A T U R E 9.40 I 9.20 I 9.00 I 8.80 I 8.60 I 8 .40 I 8 . 20 I 8 .00 I 7 .80 I 7 .60 I 7 . 40 I 7.20 I 7 .00 I I I I 28 . 40 SALINITY PPT. c) February 1968 2 :,v " 8 ^ 1 12 17 19 9 1 2 'JJ.I 27 16 13 • 7 2 2 1 1 13 1 13 1 T i l " 2 1 3i 26 27 3 1 I 5 1 2 I 22 f 14 j 1 . . - I i I - - - I I I I I---I I I I I I---I I 28.80 29.20 29.60 30.00. 30.40 30.80 31.20 31.60 9.40 I 9.20 I 9 .00 8 . 80 8.60 8 . 40 8 . 20 8 OO SALINITY PPT. 80 60 40 20 00 d) March 1968 — I — i — i — i — i — i — i — i — r — I — i — i — i — i — i — i — i — i 28.40 28.80 29.20 29.60 30.00 30.40 30.80 3 1.20 31.60 SALINITY PPT. Fig 4.3 a-l Volumetric tables for the intermediate layer (80 to 200 m) of the Strait of Georgia for each of 12 cruises from December 1967 to December 1968. The units are km ] and the total volume is 467 knv 174 9 40 I 9 9 20 00 I I e) April 1968 8 80 I 8 60 I 5 8 40 I 2 6 8 20 I 1 r*i2 2 615 8 00 I 30 65 46_, 7 80 I 2 [_46 | 83 28 , 4 7 60 I 1 1 7 40 I 7 20 I 7 00 I I- - - i - - - I — I — i - - -I 1 I- - - I - - - I -"18 1 •I-28 . 40 28 . 80 29 . 20 29 . 60 30.00 30. 40 30. 80 ---I - - - I • 31 .20 •I • 3 1 . 60 SALINITY PPT. T E M P E R A T U R E 9 40 I 9 9 20 00 I I May 1968 8 80 I 2 1 8 60 I 1 1 6 8 40 I 6 r 2 7 | 44 8 20 I 8 23 61 GO 8 00 I 10 r 3 8 6S 39j 4 7 7 80 60 I I 2 7 40 I 7 20 I 7 00 I I-- i — i - - -I I 1 I- - - I - --I 1-14 15 .1_2J •I • 28 .40 28 .80 29 . 20 29.60 30.00 30.40 30.80 31 . 20 ---I 31 .60 SALINITY PPT. 9 . 40 9 . 20 9 .00 8 .80 8.60 8 . 40 8 . 20 8 .00 80 60 40 20 00 g) early July 1968 9 J_ 10 1 2_ 16 T 13 | 46 78J*5Q~) f32 I 50 64 [~30~f" , 8 11 ! 4 •I- •I- I-28 . 40 28 . 80 29 . 20 29.60 - - - I - - -30.00 30.40 30.80 31 . 20 31 .60 SALINITY PPT 10. 40 10. 20 10.00 9 . 80 h) late July 1968 9 60 I 3 2 9 40 I 1 6 9 20 I 2 1 9 8 OO 80 I I 5 r~ 8-r~5~» 4 7 6 1 8 60 I J ^ 35 56 8 40 I f~20 17 46 59 8 8 20 OO I I L i 2 | 42 34 1 1 7 80 I 7 60 I 7 40 I 7 20 I 7 00 I 4 6 3 _ 3 U 28 . 40 28 . 80 29 . 20 29 . 60 30.00 30 . 40 ---I 30.80 - - - I - - -3 1 . 20 ---I 3 1 .60 SALINITY PPT. Fig. 4.3 175 80 I GO i j) August 1968 . 40 I . 20 I .00 I 8 . 80 I 8 .60 I 8 . 40 I 8.20 I 8.00 I 80 I 60 I 40 I 20 I 00 I I -r 9 -! 5 5 22 7 r 8- 1 7 L? 1 1 J 2 4 5 7 3 2 2 10 30 2 1 —\ 20 31 65 55 66 30 ! ! ! j j i i i i 1 I I I I I 28.40 28.80 29.20 29.60 30.00 30.40 30.80 31.20 31.60 10. 20 10.00 9 . 80 9.60 9.40 9.20 9.00 8 . 80 8.60 8.40 8 . 20 8 .OO 80 60 40 20 00 S A L I N I T Y P P T . j) October 1968 • i - • i - • i -28 . 40 28 . 80 29 . 20 29 . 60 30.00 30 . 40 30. 80 ---I I-3 1 . 20 3 1 . 60 S A L I N I T Y P P T . 9 . 60 9 . 40 9 . 20 9.00 8 . 80 8 . 60 8 . 40 8 . 20 8 .00 80 60 40 20 I 00 I I k) November 1968 5 f l 5 1 65 92 63 (^7 ~ 6-"1 6 40 5 4_ j 14 [_36_ 26_T 6 4 3 •I-28 . 40 - - - I - - -28 . 80 29 . 20 - - - I - - -29 .60 •I- •I-30.00 30 . 40 30. 80 3 1 . 20 3 1 . 60 I 7 0 67 13"« _ 3 J - SO 89 6 —I I S A L I N I T Y P P T . 9 -60 I 1 V ^ T 9.40 I ') December 1968 E 9 . 20 I _T"l9 M 9 .OO I 4_5 P 8.80 I 4 4 E 8.60 I 5 £j9 R 8.40 I 1 3 A 8.20 I T 8.00 I 2 U 7.80 I R 7.60 I E 7.40 I 7 . 20 I °C 7 .00 I I 1 1 1 I I I I - - - I I 28.40 28.80 29.20 29.60 30.00 30.40 1 1 •I • • I • •I-30. 80 31 . 20 31 .60 Fig. 4.3 S A L I N I T Y P P T 176 . 50 . 40 . 30 .20 10 .00 8 .90 8 .80 70 60 50 40 30 20 10 8.00 a) December 1967 16 3 ll 4 1 29 -6~j J L J • i -30.40 30. 60 30.80 31 .00 31 .20 9 20 I 9 10 I 9 OO I 8 90 I 8 80 I 8 70 I 8 60 I 8 50 I 8 40 I 8 30 I 8 20 I 8 10 I 8 00 I I-b) January 1968 3 L_ 1 5 £. H I <J 4_ 24 5~ 29 2 14 66 | 3 J I3 • i -30. 40 I I I I 30.60 30.80 31.00 31.20 SALINITY PPT. SALINITY PPT. 9 . 20 9 . 10 9 .00 8 .90 8 .80 8 . 70 8.60 8 . 50 8 . 40 8 . 30 8 . 20 8 . 10 8 .00 I I I I I I I I I I I I I I--30. 40 c) February 1968 4 2 r r 5 1 1 3 * 4' 15 - - - I - - -30.60 r 4" 16 19 I 1 1 3 30 f 27 j 1-- - I - -d) March 1968 30.80 31.00 3t.20 9 20 I 9 10 I 9 00 I 8 90 I 8 80 I 8 70 I 8 60 I 2 8 50 I 2 8 40 I 4 8 30 I 8 20 I 8 10 I 8 00 I 30 . 40 2 1 '~8 I 16 ! 15 11 r 4 3 17 23 30.60 30.80 31 .00 31 .20 SALINITY PPT. SALINITY PPT. 9 . 20 9 . 10 9 .00 8 .90 8 . 80 8 . 70 8.60 8 . 50 8 .40 8 . 30 8.20 I 8.101 8 .00 I I • e) April 1968 17 - L i 14 16 8 J '16' 33 27 22 30. 40 30 . 60 - - - I - - -30.80 3 1 .00 9 20 I 9 10 I 9 00 I 8 90 I 8 80 I 8 70 I 8 60 I 8 50 I 8 40 I 8 30 I 8 20 I 8 10 I 8 00 I f) May 1968 31 . 20 30. 40 2 2 1 r - 7 9 3 15 19 18 30 29 • i -30 . 60 30.80 31 .00 31 . 20 SALINITY PPT. SALINITY PPT. Fig 4.4 a-l Volumetric tables for the deep layer (200 to the bottom) in the central basin of the Strait of Georgia for each of 12 cruises from December 1967 to December 1968. The units are km 3 and the total volume is 178 km J . 177 9 . 20 T 9.10 £ 9 . 0 0 M 8 . 90 P 8.80 E 8.70 R 8.60 A 8 . 50 T 8.40 U 8.30 R 8.20 E 8. 10 8.00 g) early July 1968 2 _5_ 1 6 2 2 r i2 ' 36 48 44 30.40 ---I---30.60 30. 80 ---I---31 .00 ---I 31 . 20 9 . 20 9 . 10 9 .00 8.90 8 . 80 8 . 70 8.60 8.50 I 8 .40 I 8 . 30 8 . 20 8 . 10 8 .00 h) la te J u l y 1 9 6 8 i i i i I---30.40 17 15 61 63 30.60 30.80 31 .00 ---I - - -31 . 20 SALINITY PPT. SALINITY PPT. T E M P E R A T U 8 R 8 9.20 I 9. 10 I 9.00 I 8.90 I 8.80 I 8 . 70 8.60 8 . 50 8 .40 30 20 8 . 10 8 .00 i) August 1968 I i i i i i i i i — 30. 40 4 3 - J"B"fTri 3 7 1 4 1 3 J 7j 13 r 3 23 16 29 1-i 30.60 30. 80 31 .00 3 1 . 20 9.20 9 . 10 9 .00 8 . 90 8 . 80 8.70 8.60 8 . 50 8.40 8.30 I 8.20 I 8 . 10 I 8.00 I I--30.40 j) October 1968 j i _ 6 10 10 22 12 4 f r | 29 I 11 2 i 16 13 j - 2 '8--Lrr-! 30. 60 30.80 I I I 31.00 31.20 SALINITY PPT. SALINITY PPT. 20 I k) November 1968 I) December 1968 9 9 20 I T 9 10 I 9 10 I E 9 00 I 1 16 23 13 "1 9 00 I 3 [~2i" ~25 1 1 M 8 90 I 2 16 34 " 1 8 90 I L 7 |49 55 P 8 80 I L~5 16 15 3 8 80 I 4 5 E 8 70 I 3-[_5 . 3 8 70 I 2 R 8 60 I 1 1 8 60 I A 8 50 I 8 50 I T 8 40 I 8 40 I U 8 30 I 8 30 I R 8 20 I 8 20 I E 8 10 I 8 10 I a OO I 8 00 I °C 30.40 30. 60 30.80 3 1 .00 3 1 . 20 30.40 30.60 30.80 31 •I I I 00 3 1 .20 SALINITY PPT. SALINITY PPT. Fig. 4.4 178 9 30 I T 9 20 I E 9 10 I M 9 00 I P 8 90 I E 8 80 I R 8 70 I A 8 60 I T 8 50 I U 8 40 I R 8 30 I E 8 20 I 8 10 I c c 8 00 I a) December 1967 ---I---I 30. 2 0 30.40 30.60 30.80 9 . 30 I 9 . 20 I 9 . 10 9 .00 8 . 90 8 . 80 8 . 70 8 . 60 8 . 50 8 .40 8.30 I 8 . 20 I 8.101 8.00 I ; 10 i 12 b) January 1968 • i -30. 20 30.40 • i -30. 60 30.80 SALINITY PPT. SALINITY PPT. 9 . 30 9 . 20 9 . 10 9.00 8 .90 8.80 8 . 70 60 50 40 30 8 . 20 8 . 10 8 .00 I 2 c) February 1968 - - i — 30. 20 30. 40 30.60 30. 80 9 . 30 9.20 9. 10 9.00 8.90 8.80 8 . 70 8 . 60 50 40 30 20 10 00 d) March 1968 4 I 30. 20 30.40 30.60 30.80 SALINITY PPT. SALINITY PPT. 9 30 I 9 20 I T 9 10 I E 9 00 I M 8 90 I P 8 80 I E 8 70 I R 8 60 I A 8 50 I T 8 40 I U 8 30 I R 8 20 I E 8 10 I 8 00 I t I e) April 1968 ---I — I-30. 20 --I 1-30. 40 30 20 10 00 90 80 70 60 8.50 8 . 40 8 . 30 8 . 20 8 . 10 8 .00 f) May 1968 ! 1 1 •I- -I - •I-30.60 30.80 30. 20 30. 40 30.60 30.80 SALINITY PPT. SALINITY PPT, Fig 4.5 a-l Volumetric tables for the deep layer (200 to the bottom) in the northern basin of the Strait of Georgia for each of 12 cruises from December 1967 to December 1968. The units are km 1 and the total volume is 27 km 3 . 179 9.30 i g) e a r l y J u l y 1968 I h) late J u l y 1968 T 9.20 I ' E 9 . 1 01 9.10 I M g . o o j 9.00 I P 8.90 I 8.90 I E 8.80 I 8.80 I R 8.70 I 8.70 I A g . s o I 8.60 I T 8.50 I 8.50 I 8 . 10 I 8 . 10 I U 4  M a i 4 1 | 26 R 8.30 I 1 3 1 5 1 8.30 I E 8.20 I ' 8.20 I C s.OO I 8 - 0 0 1 ! ! T i i i 1 I 1- I I I I I I 1 I I-30.20 30.40 30.60 30.80 30.20 30.40 30.60 30.80 SALINITY PPT. SALINITY PPT. 9 . 30 9.20 9 . 10 9.00 8.90 8 .80 70 60 50 40 30 20 10 8 .00 i) August 1968 L.3.] 2 22 - - I - - -30. 20 30 20 10 00 8.90 8 .80 8.70 8 .60 8 . 50 40 30 20 10 00 j) October 1968 8 ! 12 30.40 30.60 30.80 30. 20 •I-30.40 30.60 30. 80 SALINITY PPT. SALINITY PPT. k) November 1968 I) December 1968 j 9.30 I 9.30 I E 9.20 I 9.20 I M 9 . 1 0 1 9. 10 I r 4 ~ l p 9 • OO I 6 i 9.00 I | 8 f l T E 8.90 I i 10 | 8.90 I ~ R A T U R E 8.80 I | 1 1 | 8.80 I 8.70 I 8.70 I 8.60 I 8.60 I 8.50 I 8.50 I 8.40 I 8.40 I 8.30 I 8.30 I 8.20 I 8.20 I 8 . 1 0 1 8.10 I 8.00 I 8.00 I I I I I 1 1 I I I- I I I 1 I I I 1 I-30.20 30.40 30.60 30.80 30.20 30.40 30.60 30.80 SALINITY PPT. SALINITY PPT. Fig. 4.5 130 0 m 80 m 200 m 495 km 3 T inter 467 km 3 Sinter "''deep n. T a e e p c 2 7 km 3 i 178 km 3 T source 'source Fig. 4.6 Box model of the Strait of Georgia showing the water properties used to calculate the volume inflow into each box (see text). The volume and depth of each layer are also given. 181 0 -250 -300 i i I l I I I I l I l I i i 0EC67 JAN68 FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Fig. 4.7 Vertical distribution of the salinity from December 1967 to December 1968 at Stn. 48 in the southern Strait of Georgia. 183 31 • D 1 i i i i i 1 1 1 1 1 1 1967 1969 1971 1979 1975 1977 Fig. 5.2 Interannual variation of the salinity ( ° / 0 0 ) in the central Strait of Georgia from 1967 to 1979 at the 100, 150, 200, 250 and 300 m levels. 100 M 150 M 134 ^ ^ ^ & & 0 o v ^ tfP ^ ^ ^ & j>- 0c-v 200 M 250 M ^ i& ^  >s* ^ j** j>' ^ ° <£? oo^  ^  & ^ 300 M Fig. 5.3 Monthly averaged temperature ( ° C ) and standard deviations in the central Strait of Georgia, a) 100 m b) 150 m c) 200 m d) 250 m e) 300 m 135 100 M 150 M 200 M 250 M 300 M Fig. 5.4 Monthly averaged salinity ( ° / 0 0 ) and standard deviations in the central Strait of Georgia, a) 100 m b) 150 m c) 200 m d) 250 m e) 300 m 136 e) 300 m Fig. 5.5 Correlation coefficients for the mean monthly wintertime air temperatures (December to February) and the temperature 0 to 10 months later (the lag) at 5 standard depths in the central § Strait of Georgia. The thick solid curve indicates the 95% confidence level. t o.o December January 4 6 8 L a g (months) February 100 m b) 150 m Lag (months) Lag (months) Lag (months) Lag (months) e) 300 m Fig. 5.6 Correlation coefficients for the mean monthly wintertime air temperatures (December to February) and the salinity 0 to 10 months later (the lag) at 5 standard depths in the central Strait of Georgia. The thick solid curve indicates the 95% confidence level. December Lag (months) January — February — 188 b) 150 m Lag (months) Lag (months) c) 200 m d) 250 m Lag (months) Lag (months) e) 300 m Lag (months) Fig. 5.7 Wintertime (December, January and February) air temperatures correlated with the change in temperature at several depths in the central Strait of Georgia over the course of the winter. The November water temperature is used as the initial temperature. The thick solid curve indicates the 95% confidence level. December January February — 189 a) 100 m b) 150 m Lag (months) Lag (months) c) 200 m d) 250 m Lag (months) Lag (months) e) 300 m Lag (months) Fig. 5.8 Wintertime (December, January and February) air temperatures correlated with the change in salinity at several depths in the central Strait of Georgia over the course of the winter. The November salinity is used as the initial salinity. The thick solid curve indicates the 95% confidence level. December January February 190 REFERENCES Chang P., S. Pond and S. Tabata (1976) Subsurface c u r r e n t s i n the S t r a i t of Georgia, West of Sturgeon Bank. J . F i s h . Res. Bd. Can. 33 pp. 2218-2241. Crean P.B. (1976) Numerical model s t u d i e s of the t i d e s between Vancouver I s l a n d and the mainland c o a s t . J . F i s h . Res. Bd. Can. 33 pp. 2340-2344. Crean P.B. (1978) A numerical model of b a r o t r o p i c mixed t i d e s between Vancouver I s l a n d and the mainland and i t s r e l a t i o n to s t u d i e s of the e s t u a r i e s c i r c u l a t i o n . Hydrodynamics of E s t u a r i e s and F j o r d s , J.C.J. Nihoul (ed.) E l s e v i e r , New York pp. 546. Crean P.B. and A.B. Ages (1971) Oceanographic records from twelve c r u i s e s i n the S t r a i t of Georgia and Juan de Fuca S t r a i t , 1968. Dept. of Energy, Mines and Resources, Marine Research Sciences Branch, Canada. 1-5 pp.389. F r i e h e C A . and K.F. Schmitt (1976) P a r a m e t e r i z a t i o n of a i r - s e a i n t e r f a c e f l u x e s of s e n s i b l e heat and moisture by bulk aerodynamic formulas. J . Phys. Oc. 6 pp. 801-809. G i l l E.G. (1982) Atmosphere-Ocean Dynamics. Academic Press Inc., New York pp. 662. Gross M.G., B.A. Morse and C A . Barnes (1969) Movement of near bottom waters on the c o n t i n e n t a l s h e l f o f f the northwestern United S t a t e s . J . Geophys. Res. 74 pp. 7044-7047. Hutchinson A.H. and C C Lucas (1931) E p i t h a l a s s a of the S t r a i t of G eorgia. Can. J . Res. 5 pp. 231-284. Large W.G. and S. Pond (1982) S e n s i b l e and l a t e n t heat f l u x measurements over the ocean. J . Phys. Oc. 12 pp. 464-482. LeBlond P.H. (1983) The S t r a i t of Georgia: f u n c t i o n a l anatomy of a c o a s t a l sea. Can. J . F i s h . Aq. S c i . 40 pp. 1033-1063. LeBlond P.H., K. Dyck, K. Perry and D. Cumming (1983) Runoff and p r e c i p i t a t i o n time s e r i e s f o r the c o a s t s of B r i t i s h Columbia and Washington S t a t e . Dept. Oc. U n i v e r s i t y of B r i t i s h Columbia, Man. Rep. No. 39. pp. 133. LeBlond P.H. and L.A. Mysak (1978) Waves i n the Ocean. E l s e v i e r , Amsterdam pp. 602. 191 Lewis E.L. 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L a i r d (1978) Regional response to f o r c i n g i n southern S t r a i t of Georgia. E s t . C o a s t a l Mar. S c i . 7 pp. 79-91. Stacey M.W., S. Pond and P.H. LeBlond (1986) A wind-forced Ekman s p i r a l as a good s t a t i s t i c a l f i t to low-frequency c u r r e n t s i n a c o a s t a l s t r a i t . Science 233 pp. 470-472. Stacey M.W., S. Pond, P.H. LeBlond, H.J. F r e e l a n d and D.M. Farmer (1987 a) An a n a l y s i s of the low-freqency c u r r e n t f l u c t u a t i o n s i n the S t r a i t of Georgia, from June 1984 u n t i l January 1985. J . Phys. Oc. i n p r e s s . Stacey M.W., S. Pond and P.H. LeBlond (1987 b) D e t e c t i o n of subsurface eddies i n the S t r a i t of Georgia and an a n a l y s i s of the dynamics of the low-frequency c u r r e n t s u sing the technique of o b j e c t i v e a n a l y s i s . Atm.-Oc. submitted. S t r i c k l a n d J.D.H. and T.R. Parsons (1960) A Manual of Sea Water A n a l y s i s . B u l l . F i s h . Res. Bd. Can. No. 125. pp. 311. Smith S.D. (1980) Wind s t r e s s and heat f l u x over the ocean i n gale f o r c e winds. J . Phys. Oc. K) pp. 709-726. Sweers H.E. (1970) Oceans IV: a p r o c e s s i n g , a r c h i v i n g and r e t r i e v a l system f o r oceanographic s t a t i o n d a ta. Dept. Energy, Mines and Resources, Mar. S c i . Branch, Manuscript r e p o r t s e r i e s no. 15, pp. 137. Thomson R.E. (1981) Oceanography of the B r i t i s h Columbia Coast. Can. Spec. Publ. F i s h . Aquat. S c i . 56 pp. 291. T u l l y J.P. and A.J. Dodimead (1957) P r o p e r t i e s of the water i n the S t r a i t of Georgia, B r i t i s h Columbia, and i n f l u e n c i n g f a c t o r s . J . F i s h . Res. Bd. Can. 14 pp. 241-319. 192 UNESCO (1981) Tenth r e p o r t of the j o i n t panel on oceanographic t a b l e s and standards. UNESCO T e c h n i c a l Papers i n Marine Science No. 36. UNESCO, P a r i s . Waldichuk M. (1957) P h y s i c a l oceanography of the S t r a i t of Georgia, B r i t i s h Columbia. J . F i s h . Res. Bd. Can. 14 pp. 321-486. Yao T., S. Pond and L.A. Mysak (1982) Low-frequency subsurface c u r r e n t and d e n s i t y f l u c t u a t i o n s i n the S t r a i t of Georgia. Atm.-Oc. 20 pp. 340-356. 

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