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A mixing budget for the Strait of Georgia, British Columbia Samuels, Geoffrey 1979

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A MIXING BUDGET FOR THE STRAIT OF GEORGIA, BRITISH COLUMBIA by GEOFFREY SAMUELS B . S c , Humboldt State University, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE. OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Physics and Institute of Oceanography) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1979 Geoffrey Samuels 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Geof f rey Samuels Department nf Phy s i c s  The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date ^ y . 1979 i i ABSTRACT A mix ing budget f o r the S t x a i t of Georg ia was prepared summari-z i n g mix ing processes and e f f e c t s upon the p h y s i c a l oceanography of the s t r a i t . A m ix ing budget was d e f i n e d as an i t em i zed es t imate of mix ing mechanisms and the t o t a l s t a t e of mix ing i n the s t r a i t . M i x ing e f f e c t s i n the S t r a i t of Georg ia were es t imated from hy -drograph ic data and from monthly summaries of me teo r o l o g i c a l data f o r f o u r months: February , May, August and November of 1968. M i x i ng was e s -t imated q u a l i t a t i v e l y by depth-averag ing temperature, s a l i n i t y , d e n s i t y and oxygen concen t r a t i on s f o r f o u r r e p r e s e n t a t i v e l a y e r s , each 25 metres t h i c k and by producing contour p l o t s f o r each v a r i a b l e f o r the l a y e r s (two upper l a y e r s , an i n te rmed ia te l a y e r and a deep l a y e r ) . Q u a n t i t a t i v e e s t imates of mix ing were made by computing the p o t e n t i a l energy d e n s i t y and the energy d e n s i t y needed f o r t o t a l m ix ing f o r the r e p r e s e n t a t i v e l a y e r s p lu s the p o t e n t i a l energy d e n s i t y of t o t a l s t r a t i f i c a t i o n (a f r e s h water l a y e r over a l a y e r w i t h oceanic s a l i n i t y ) . Changes i n po -t e n t i a l energy were due t o mix ing p l u s a d v e c t i o n . Es t imates of the energy a v a i l a b l e f o r m ix ing were made f o r the d i f f e r e n t m ix ing mechanisms a c t i n g upon the s t r a i t : wind m i x i n g , buoyan-cy f l u x ( convect ion ) m ix i ng , t i d a l m i x i ng , mix ing by i n t e r n a l waves and entrainment m ix i ng . The S t r a i t of Georg ia has th ree d i f f e r e n t domains which a re i n -f l uenced by d i f f e r e n t mix ing mechanisms: the southern passages, the u p -per l a y e r s of the no r the rn s t r a i t and the deep water s . The southern pa s -sages ( i n c l u d i n g the San Juan A r ch i pe l a go and Haro and Rosa r i o S t r a i t s ) a re the s i t e of i n t e n s i v e t i d a l m ix ing which keeps the e n t i r e water c o l -umn w e l l mixed} convec t i on and wind mix ing a re a l s o important du r i n g the w i n t e r . The upper l a y e r s of the no r the rn s t r a i t ( no r th of Boundary P a s -i i i sage) a r e w e l l mixed by the wind i n the w i n t e r and by the wind and c o n -v e c t i o n i n the autumn. The uppermost b r a c k i s h l a y e r i s h i g h l y s t r a t i f i e d i n the s p r i n g and summer from the e f f e c t s of su r face h e a t i n g and f r e s h water r u n o f f ; i n te rmed ia te l a y e r s a re mixed by entra inment u p w e l l i n g . The deep waters of the s t r a i t a re i n f l u e n c e d c h i e f l y by a d v e c t i o n p r o -ce s se s : e s t ua r i ne f l o w and seasona l i n t r u s i o n s of new water masses. I n the w i n t e r , c o l d l o w - s a l i n i t y water i n t r u d e s and d i s p l a c e s the warm wa-t e r l e f t from the prev ious summer wh i l e i n the summer, warm s a l i n e water r ep l a ce s the c o l d w i n t e r water . i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGEMENTS x i i S e c t i o n 1. INTRODUCTION 1 2. REVIEW OF THE OCEANOGRAPHY OF THE STRAIT OF GEORGIA 2.1 E s t u a r i n e C o n d i t i o n s and R i v e r In f luence . . . . . . . . . . . . . . 4 2.2 T i d e s and T i d a l M i x i n g o 6 2.3 Deep Water o f the S t r a i t o f Georg ia 7 3. PHYSICAL PROCESSES 3.1 M i x i n g Mechanisms 0 . . . . . . . . . . . . . . 9 3.2 A d v e c t i o n and F l u s h i n g Mechanisms . . . . . .o... . . . . . . . . . . 12 3.3 Measurements o f M i x i n g . . . . . . . . .o.... 14 4. DATA DESCRIPTION 4.1 Oceanographic Data • • • • • • D . . . . . . . . . . . . . 20 4.2 M e t e o r o l o g i c a l Data . . . 2 1 4.3 T i d a l Data 23 4.4 Hydrometr ic Data 23 4.5 Ba thymet r ic Data « . . .••23 5. DATA ANALYSIS AND PRESENTATION 5.1 Observed P h y s i c a l P r o p e r t i e s . . . . . . . . . . .o. . . . . . . . . . . . . 26 5.2 Der ived P h y s i c a l P r o p e r t i e s 43 6. MIXING PROCESSES V 6.1 Wind M i x i n g 75 6.2 Buoyancy F l u x and G r a v i t a t i o n a l I n s t a b i l i t y 78 6.3 T i d a l M i x i n g 82 6.4 I n t e r n a l Waves 83 6.5 Entra inment M i x i n g . . . . . . . . . . . o .« • 88 7. INTERPRETATION AND DISCUSSION 7.1 D i s c u s s i o n of the P h y s i c a l Oceanography of the S t r a i t o f Georgia 91 7.2 Exchange Processes 100 7.3 M i x i n g Energ ies 104 7.4 E r r o r s • 115 8. CONCLUSION ° . . . . 120 REFERENCES o 259 v i LIST OF TABLES I M e t e o r o l o g i c a l da ta f o r s t a t i o n s around the S t r a i t of Georg ia 22 I I Average heat content s (and per cent v a r i a t i o n s ) i n Jou le s over a r e f e rence temperature o f O C 69 I I I Average s a l t content s (and seasona l v a r i a t i o n s i n per cen t ) pe r g r i d compartment ••••••••••••• 72 IV Average t i d a l energy a v a i l a b l e f o r m ix ing per month per g r i d compartment . . . 0 . . . . . . . . . . . . 8k V F r a s e r R i v e r r u n o f f and average s a l i n i t i e s f o r the upper 50 m (Layers 1 and 2) of the N o r t h -e r n and C e n t r a l r eg i on s p lu s f r e s h water c o n -t e n t s (F.W.) and f l u s h i n g t imes . . 103 VI Average changes of the mean d e n s i t y and p o t e n t -i a l energy f o r g r i d compartments i n the N o r t h -e rn and C e n t r a l r eg i on s 103 VI I E s t imates of mix ing energ ie s per g r i d compart-ment f o r Laye r 1 (0 m - 25 m) 108 V I I I E s t imates of m ix ing ene rg ie s pe r g r i d compart-ment f o r Laye r 2 (25 m - 50 m) 110 IX Es t imates of mix ing ene rg ie s f o r Laye r 7 (150 m - 175 m) 112 X Es t imates of m ix ing energ ie s f o r l a y e r 9 (200 m - 225 m) Ilk LIST OF FIGURES 1 The S t r a i t of Georg ia showing the main geographic f e a t u r e s . . . . 122 2 The f o u r r eg i on s of the S t r a i t of Georg ia • • 123 3 Schematic i l l u s t r a t i o n of the S t r a i t of G e o r g i a - S t r a i t o f Juan de Fuea system showing the d i f f e r e n t water masses (from Waldichuk, 1957) • • * • • *24 4 D ischarge of the Fxaser R i v e r f o r f o u r months of 1968 125 5 a Schematic i l l u s t r a t i o n of the w i n t e r f o rmat i on of deep wa-t e r masses i n w i n t e r (from Waldichuk, 1957) 126 b Schematic of the summer f o rmat i on of deep water masses (from Waldichuk, 1957) • * l 2 7 6 I n t e r n a l wave groups i n the southern S t r a i t of Geo r g i a . The l i n e s drawn d e l i n e a t e the a rea s of the wave groups photographed d u r i n g a f l i g h t i n May of 1968. The f l i g h t l i n e between P o i n t Roberts and East P o i n t i s a l s o shown (from Samuels and LeB lond, 1977) 128 7 a Schematic i l l u s t r a t i o n of a s t r a t i f i e d water column 129 b Schematic i l l u s t r a t i o n of a homogeneous water c o l u m n . . . . . . . . . . 129 8 L oca t i on s of the hydrographie da ta s t a t i o n s i n the S t r a i t of Georg ia f o r the f o u r r e p r e s e n t a t i v e months.• • • • • • 130 9 Loca t i on s of the m e t e o r o l o g i c a l da ta s t a t i o n s around the S t r a i t of Georg ia 131 10 I l l u s t r a t i o n of the g r i d system used t o approximate the o u t l i n e of the S t r a i t of Georg ia 132 11 a Layer 1 average temperatures f o r February 133 b Layer 1 average temperatures f o r May... • 134 c Layer 1 average temperatures f o r A u g u s t . . . . . . . . . . . . . . . . . . . . . . . 135 d Laye r 1 average temperatures f o r November. . . . . . • 136 12 a Layer 2 temperatures f o r February. .c . • 137 b Layer 2 temperatures f o r May 138 c Laye r 2 temperatures f o r A u g u s t . . . . . . . . . . . . . . . . . . . . . . . . 139 d Layer 2 temperatures f o r November 140 13 a Layer 7 temperatures f o r February • • 141 >b Layer 7 temperatures f o r May • 14*2 c Layer 7 temperatures f o r A u g u s t . . . . . . . . 143 d Layer 7 temperatures f o r November • 144 14 a Layer 9 temperatures f o r February 145 b Layer 9 temperatures f o r May... 146 c Layer 9 temperatures f o r August 147 d Layer 9 temperatures f o r November... . .• ••••••••••••• 148 v i i i 15 Reg iona l temperature averages f o r l a y e r 1 . . . . . . • • • • • • • 149 16 Reg iona l temperature averages f o r l a y e r 2 . . . . . . . . . . . . . . . . . . . . . 15° 17 Reg iona l temperature averages f o r l a y e r 7 . . . . . . . « • • • • • • • • • • • • • 151 18 Reg iona l temperature averages f o r l a y e r 9 • • 152 19 a Layer 1 average s a l i n i t i e s f o r F e b r u a r y . . . . . . . . . . . . . . . 153 b Layer 1 average s a l i n i t i e s f o r M a y . . . . . . . . . . 154 c Layer 1 average s a l i n i t i e s f o r August 155 d Layer 1 average s a l i n i t i e s f o r November.... I56 20 a l a y e r 2 s a l i n i t i e s f o r February . • 157 b Layer 2 s a l i n i t i e s f o r May . . . . . 158 c Layer 2 s a l i n i t i e s f o r August 159 d Layer 2 s a l i n i t i e s f o r November. 160 21 a Layer 7 s a l i n i t i e s f o r February 161 b Layer 7 s a l i n i t i e s f o r May 162 c Layer 7 s a l i n i t i e s f o r August 163 d Layer 7 s a l i n i t i e s f o r November •••• 164 22 a Layer 9 s a l i n i t i e s f o r F e b r u a r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I65 b Layer 9 s a l i n i t i e s f o r May.. . . . . . . . . . . . . o . . . . . . . . . . . . 166 c Layer 9 s a l i n i t i e s f o r August . I67 d Layer 9 s a l i n i t i e s f o r N o v e m b e r . . . . . . . . . . . •• 168 23 Reg iona l s a l i n i t y averages f o r l a y e r 1. I69 24 Reg iona l s a l i n i t y averages f o r l a y e r 2 . . . . . . . . . . . . . . . . . . . . . . . . 170 25 Reg iona l s a l i n i t y averages f o r l a y e r 7* • 171 26 Reg iona l s a l i n i t y averages f o r l a y e r 9 . . . . . 172 27 Contours of average s igma-t f o r l a y e r 1 i n February 173 28 Reg iona l d e n s i t y averages f o r l a y e r 1 • 174 29 Reg iona l d e n s i t y averages f o r l a y e r 2 . . . . • • • • • 175 30 Reg iona l d e n s i t y averages f o r l a y e r 7 . . . . . . . 176 31 Reg iona l d e n s i t y averages f o r l a y e r 9 • • • • 177 32 a Layer 1 oxygen concen t r a t i on s f o r February 178 b Layer 1 oxygen concen t r a t i on s f o r M a y . . . . . . . . . . 179 c Laye r 1 oxygen concen t r a t i on s f o r A u g u s t . . . . . . . . ••••••••• 180 d Layer 1 oxygen concen t r a t i on s f o r November •• 181 33 a Layer 2 oxygen concen t r a t i on s f o r February 182 b Laye r 2 oxygen concen t r a t i on s f o r May . . . . . . 183 c Layer 2 oxygen concen t r a t i on s f o r A u g u s t . . . . . . . . . . . . . . . . . . . . . . 184 d Layer 2 oxygen concen t r a t i on s f o r November. •• •• 135 i x 34 a Layer 7 oxygen concen t r a t i on s f o r Februa ry . • • • • • • • • • • • • • 186 b Layer 7 oxygen concen t r a t i on s f o r May 187 c Layer 7 oxygen concen t r a t i on s f o r August.•• • • • • 188 d Layer 7 oxygen concen t r a t i on s f o r November.. . . . 189 35 a Layer 9 oxygen concen t r a t i on s f o r February 190 b Laye r 9 oxygen concen t r a t i on s f o r May. • • • • • • • • • 191 c Layer 9 oxygen concen t r a t i on s f o r August. • • 192 d l a y e r 9 oxygen concen t r a t i on s f o r November 193 36 Reg iona l oxygen averages f o r l a y e r 1.. 194 37 Reg iona l oxygen averages f o r l a y e r 2 195 38 Reg iona l oxygen averages f o r l a y e r 7 . . . 196 39 Reg iona l oxygen averages f o r l a y e r 9*.........*..<> • • 197 40 a Layer 1 p o t e n t i a l energy d e n s i t i e s (X 10^ ) f o r F e b r u a r y . . . . . . . 198 b Layer 1 p o t e n t i a l energy d e n s i t i e s (X i O j j f o r May 199 c Layer 1 p o t e n t i a l energy d e n s i t i e s (X lO^J f o r A u g u s t . . . . 200 d Layer 1 p o t e n t i a l energy d e n s i t i e s (X 10 ) f o r November . . . . . . . 201 / 4\ 41 a Layer 2 p o t e n t i a l energy d e n s i t i e s (X 10^ ) f o r February • 202 b Layer 2 p o t e n t i a l energy d e n s i t i e s (X I0jj f o r M a y . . . . . . . . . . . . 203 c Layer 2 p o t e n t i a l energy d e n s i t i e s (X 10 )^ f o r A u g u s t . . . . 204 d Layer 2 p o t e n t i a l energy d e n s i t i e s (X 10 ) f o r November • 205 4\ 42 a Layer 7 p o t e n t i a l energy d e n s i t i e s (X 10K ) f o r February 206 b Layer 7 p o t e n t i a l energy d e n s i t i e s (X 10^ ) f o r May . . . . . 207 c Layer 7 p o t e n t i a l energy d e n s i t i e s (X 10 )^ f o r A u g u s t . . . . . . . . . 208 d Layer 7 p o t e n t i a l energy d e n s i t i e s (X 10 ) f o r November . . . . . . . 209 4\ 43 a Layer 9 p o t e n t i a l energy d e n s i t i e s (X 10 )^ f o r F e b r u a r y . . . . . . . 210 b Layer 9 p o t e n t i a l energy d e n s i t i e s (X 10^ ^ f o r May. . . . 211 c VLayer 9 p o t e n t i a l energy d e n s i t i e s (X l O j J f o r A u g u s t . . . . . . . . . 212 d Layer 9 p o t e n t i a l energy d e n s i t i e s (X 10 } f o r November.. 213 44 Reg iona l p o t e n t i a l energy averages f o r l a y e r 1.. • • • • 214 45 Reg iona l p o t e n t i a l energy averages f o r l a y e r 2 • 215 46 Reg iona l p o t e n t i a l energy averages f o r l a y e r 7 « . . » . 216 47 Reg iona l p o t e n t i a l energy averages f o r l a y e r 9 . . . . . . . . . . . . . . . . 217 48 a Layer 1 m ix ing energy d e n s i t i e s f o r F e b r u a r y . . . . . . . . . . . . . . . . . . 218 b Layer 1 m ix ing energy d e n s i t i e s f o r May 219 c Layer 1 m ix ing energy d e n s i t i e s f o r A u g u s t . • • • • • • • • . . . . . . . . . . . 220 d Layer 1 m ix ing energy d e n s i t i e s f o r N o v e m b e r . . . . . . . . . . . . . . . . . . 221 49 a Layer 2 m ix i ng energy d e n s i t i e s f o r F e b r u a r y . . . . . . . . . . . . . . . . . . 222 b Layer 2 m ix ing energy d e n s i t i e s f o r May. 223 c Layer 2 m ix i ng energy d e n s i t i e s f o r A u g u s t . . . . . . . . . . . . . . . . . . . . 224 d Layer 2 m ix ing energy d e n s i t i e s f o r N o v e m b e r . . . . . . 225 X 50 a Layer 7 m ix ing energy d e n s i t i e s f o r February* • •••••a* •« 226 b Layer 7 m ix ing energy d e n s i t i e s f o r May . . . . . . • 227 c Laye r 7 m ix ing energy d e n s i t i e s f o r August • . • 228 d Layer 7 m ix i ng energy d e n s i t i e s f o r November 229 51 a Layer 9 m ix ing energy d e n s i t i e s f o r February . . . . .••••••••••••• 230 b Layer 9 m ix ing energy d e n s i t i e s f o r May 231 c Layer 9 m ix ing energy d e n s i t i e s f o r August. 232 d Layer 9 m ix ing energy d e n s i t i e s f o r November . . . . . . . . . . . » 233 52 Reg iona l m ix ing energy averages f o r l a y e r 1 . . . . . . . . . . . . . . . . . . . 234 53 ; Reg iona l m ix i ng energy averages f o r l a y e r 2 . . . . . . . . . . . . . . . . . . . 235 54 Reg iona l m ix ing energy averages f o r l a y e r 7 » » • • • • • • • 236 55 Reg iona l m ix i ng energy averages f o r l a y e r 9 237 56 Reg iona l averages of two-Layer p o t e n t i a l energy f o r l a y e r 1 „ 238 57 Reg iona l averages of t w o - l a y e r p o t e n t i a l energy f o r l a y e r 2 239 58 Reg iona l averages of t w o - l a y e r p o t e n t i a l energy f o r l a y e r 7 o 240 59 Reg iona l averages of two-Layer p o t e n t i a l energy f o r l a y e r 9. . . o 241 60 Reg iona l averages of wind mix ing e n e r g y . . . . . . . . . . . . •••••• 242 61 Reg iona l averages of buoyancy f l u x m ix ing energy. <• 243 62 Reg iona l averages of the Monin-Obukhov l e n g t h . . . . . 244 63 Reg iona l averages of a i r t e m p e r a t u r e s . . . . . . . . . . . . . . . . . . . . . . . . . 245 64 a Temperature d i s t r i b u t i o n f o r February (from Crean and Ages. 1971) 246 b Temperature d i s t r i b u t i o n f o r May (from Crean and Ages, 1971) 247 c Temperature d i s t r i b u t i o n f o r August (from Crean and Ages, 1971) 248 d Temperature d i s t r i b u t i o n f o r November (from Crean and Ages, 1971) • 249 65 a S a l i n i t y d i s t r i b u t i o n f o r February (from Crean and Ages, 1971) 250 b S a l i n i t y d i s t r i b u t i o n f o r May (from Crean and Ages, 197l) .«»«« 251 c S a l i n i t y d i s t r i b u t i o n f o r August (from Crean and Ages, 1971) 252 d S a l i n i t y d i s t r i b u t i o n f o r November (from Crean and Ages, 1971) 253 x i 66 a Oxygen d i s t r i b u t i o n f o r February (from Crean and Ages, 1971) 254 b Oxygen d i s t r i b u t i o n f o r May (from Crean and Ages, 1971)••••••• 255 c Oxygen d i s t r i b u t i o n f o r August (from Crean and Ages, I9?i)f» 256 d Oxygen d i s t r i b u t i o n f o r November (from Crean and Ages, 1971) . 257 67 Dens i ty ( s i gma- t ) d i s t r i b u t i o n f o r February (from Crean and Ages, 1971).. • 258 x i i ACKNOWLEDGMENTS I would l i k e t o g r a t e f u l l y thank my s u p e r v i s o r , Dr . LeBlond f o r the guidance and h e l p he gave d u r i n g the e n t i r e t h e s i s study and f o r h i s end les s pat ience and humor. Dr . Fond has a l s o g i ven many h e l p f u l sugges-t i o n s and c r i t i c i s m s wh i l e Dr . Crean and James H e l b i g c o n t r i b u t e d many h e l p f u l d a t a f o r the models of t i d e and wind m i x i n g . The f i n a n c i a l s up -po r t and v a l u ab l e guidance prov ided by Dr . Farmer of I.O.S. i s g r a t e -f u l l y acknowledged. I would a l s o l i k e t o thank the s t a f f o f the U.B.C. Computing Cen -r e , e s p e c i a l l y John Cou l tha rd f o r t h e i r h e l p and suggest ions f o r the computer programs t h a t ana l yzed and p l o t t e d the t h e s i s d a t a . L a s t (and i n t h i s case l e a s t ) I would l i k e t o thank Roar f o r spending two ted i ou s days con tou r i n g hydrographic c h a r t s . 1 1. INTRODUCTION M ix ing processes a re some of the more important p h y s i c a l p r o ce s s -es i n c o a s t a l waters and e s t u a r i e s ( O f f i c e r , 1976) and i n the open ocean ( P h i l l i p s , 1966} Denman and Miyake, 1973). Th i s t h e s i s i s an at tempt t o prov ide an e s t imate of the mix ing processes and e f f e c t s t h a t take p lace i n the S t r a i t of Georg ia , the c o a s t a l e s tua ry t h a t l i e s between Vancou-v e r I s l and and the mainland of North America (F igure l ) . S p e c i f i c a l l y , t h i s t h e s i s summarizes a study of a m ix ing budget f o r the S t r a i t of Geo rg i a . A mix ing budget i s here d e f i n e d as an i t e m -i z e d es t imate of m ix ing mechanisms and t h e i r e f f e c t s , g i v i n g an a p p r a i -s a l of the t o t a l m ix ing of the water column p lu s the r e l a t i v e c o n t r i b u -t i o n s of the v a r i ou s mix ing processes . These mix ing mechanisms may vary con s i de rab l y both s p a t i a l l y , w i t h a geographic o r depth dependence, o r s ea sona l l y w i t h v a r i a t i o n s i n t ime . An example would be wind mix ing of the upper l a y e r of the s t r a i t which depends upon the s ea sona l l y v a r i a b l e wind and which u s u a l l y a f f e c t s on ly the uppermost l a y e r of the water column depending upon the s t r a t i f i c a t i o n . M i x i ng was de f i ned i n t h i s study t o be a v e r t i c a l p roces s , c o n -s i s t i n g of t r a n s f e r s of heat and s a l t between s t r a t i f i e d l a y e r s t h a t were assumed t o be l a t e r a l l y homogeneous over s c a l e s the same order of magnitude as the v e r t i c a l s c a l e s . While the S t r a i t of Georg ia e x h i b i t s con s i de rab l e l a t e r a l v a r i a t i o n and ' p a t c h i n e s s 1 , over s ho r t d i s t a n c e s p h y s i c a l p r o p e r t i e s show f a r l e s s v a r i a t i o n i n the h o r i z o n t a l d imens ion than i n the v e r t i c a l (except near f r o n t s ) . In t h i s t h e s i s any r e fe rence s t o mix ing w i l l s t r i c t l y mean v e r t i c a l m i x i n g . Fo r want of a b e t t e r term a l l l a t e r a l t r a n s f e r s of heat and s a l t l n the S t r a i t o f Georg ia a re lumped toge the r under the term a d v e c t i o n . Th i s term i n c l ude s a l l l a t e r a l m ix ing and d i f f u s i o n e f f e c t s , movement of 2 water masses due t o t i d a l e x cu r s i on s , a d v ec t i o n by c u r r e n t s and seasona l i n t r u s i o n of d i f f e r e n t water masses i n t o the S t r a i t of Georg i a . Advec -t i o n a l s o i n c l ude s f l u s h i n g , d e f i n e d as the cont inuous removal of f r e s h water from the s t r a i t . A thorough study of f l u s h i n g and ad v ec t i o n i s b e -yond the scope of t h i s t h e s i s a l though some es t imates w i l l be made. Wa l -d ichuk (1957) d i s c u s s e s f l u s h i n g of the S t r a i t of Georg ia In d e t a i l , r e -l a t i n g i t t o the f r e s h water r u n o f f of the F r a s e r R i v e r and t o the base s a l i n i t y of the water i n the S t r a i t of Juan de Fuca . Th i s study w i l l main ly concern i t s e l f w i t h the v e r t i c a l m ix i ng o f the water column a s i t occurs i n the S t r a i t of Geo rg i a . Such a study i s i n t e r e s t i n g f o r a number of reasons . The mix ing of f r e s h water from r i -ve r r u n o f f and p r e c i p i t a t i o n w i t h sea water i s recogn i zed a s a major f a c t o r i n the gene ra l e s t ua r i ne c i r c u l a t i o n (Waldichuk, 1957} T u l l y and Dodimead, 1957$ O f f i c e r , 1976). Sea water i s mixed i n t o a l a y e r of f r e s h water a s i t f l ows seaward, i nduc i n g a f l o w of sea water back i n t o the s t r a i t . Th i s e s t ua r i n e c i r c u l a t i o n i s a f f e c t e d by the r a t e of m ix ing b e -tween the f r e s h water from r u n o f f and the unde r l y i n g sea water . I n o rder t o prov ide e s t imates of m i x i n g , v a r i ou s p h y s i c a l p r o p e r t i e s w i l l be s t ud i ed i n depth and t h i s study can shed l i g h t upon the gene ra l water s t r u c t u r e and f o rmat i on bes ides p r o v i d i n g another d e s c r i p t i o n of the p h y s i c a l oceanography of the S t r a i t of Geo rg i a . Another i n t e r e s t i n g f e a -t u r e , the f o rmat i on and renewal of the deep water i n the s t r a i t and the i n t r u s i o n of d i f f e r e n t water masses can be i l l u s t r a t e d by a mix ing s t u d -y . A p r a c t i c a l reason f o r a m ix ing budget i n the env i r onmenta l l y c o n -s c i ou s age i s t h a t e s t imate s of m ix ing can be an a i d i n p r e d i c t i o n s of p o l l u t a n t d i s p e r s a l . Th i s study has the advantage of a n a l y z i n g oceanographic data (Crean and Ages, 1971) which have not been i n v e s t i g a t e d I n d e t a i l b e -3 f o r e . A more d e t a i l e d d e s c r i p t i o n of these da ta i s g i ven i n s e c t i o n s 4 and 5« These da ta can be used t o prov ide a d e t a i l e d d e s c r i p t i o n of the p h y s i c a l p r o p e r t i e s of the S t r a i t of Georg ia and by examining changes i n these p r o p e r t i e s e s t imates can be made of the t o t a l amount of m ix i ng i n the water column and of the r e l a t i v e c o n t r i b u t i o n s by v a r i ou s p h y s i c a l mechanismss a m ix ing budget. Due t o l i m i t a t i o n s i n some of the da ta used i n the study on l y o r -de r of magnitude e s t imates of mix ing can be made. Nonethe less , even o r -de r of magnitude e s t imates can i l l u s t r a t e the r e l a t i v e importance of the v a r i ou s processes t h a t mix the S t r a i t of Geo rg i a . 4 2. REVIEW OP THE OCEANOGRAPHY OF THE STRAIT OF GEORGIA Th i s s e c t i o n w i l l p resent a b r i e f rev iew of the oceanographic f e a t u r e s of the S t r a i t of Georg ia t h a t a re important t o m i x i n g . A t h o r -ough d e s c r i p t i o n of the p h y s i c a l oceanography and of the p h y s i c a l water p r o p e r t i e s has been g i ven by Waldichuk (1957) and by T u l l y and Dodimead (1957). Fo r convenience i n d e s c r i b i n g the p h y s i c a l oceanographic f e a -t u r e s , the S t r a i t of Georg ia has been d i v i d e d i n t o f o u r r eg i on s ( F i gu re 2). Three of them, the Southern, C e n t r a l and Northern reg i on s a re the same as de s c r i bed by Waldichuk (1957)» w i t h the Southern r e g i o n the s i t e of i n t e n s i v e t i d a l m i x i n g , the C e n t r a l r e g i o n the a rea of major F r a s e r R i v e r i n f l u e n c e and the Northern r e g i o n i n f l u e n c e d by both the F r a s e r R i v e r r u n o f f and by the nor thern t i d a l channels which form the no r the rn boundary of the S t r a i t of Geo rg i a . In a d d i t i o n t o Wald ichuk*s scheme, a r e g i on compr i s i ng Haro S t r a i t , the San Juan A r ch i pe l a go and Rosa r io S t r a i t has been added and f o r convenience has been a r b i t r a r i l y l a b e l l e d the San Juan r e g i o n . Th i s r e g i on i s a s i t e ©f i n t e n s i v e t i d a l m ix ing (as i s the Southern reg i on ) and i s i n f l u e n c e d by the waters o f the S t r a i t o f Juan de Fuca w i t h which i t has f r e e communication. 2.1 E s tua r i ne Cond i t i on s and R i v e r I n f l uence The S t r a i t of Georg ia meets the d e f i n i t i o n of an e s tua r y as g i ven by Cameron and P r i t c h a r d (1965)« " a semi-enc losed body of water hav ing a f r e e connect ion w i t h the open sea and w i t h i n which sea water i s measur-a b l y d i l u t e d w i t h f r e s h .wa te r d e r i v e d from l and d r a i n a g e " . I t i s an e s -t ua r y i n t o which the F r a s e r R i v e r empt ies , fo rming a b r a c k i s h upper zone. Th i s b r a c k i s h water e v e n t u a l l y i s removed from the s t r a i t , p a r t l y by evapora t i on but most ly by f l o w i n g t o the sea through the channels a t the no r the rn and southern ends of the s t r a i t . As t h i s b r a c k i s h l a y e r 5 f l ows t o the sea i t e n t r a i n s sea water from the u n d e r l y i n g l a y e r . To compensate f o r the l o s s o f sea water en t r a i ned i n t o the upper zone the re i s a f l o w of sea water i n t o the s t r a i t a t deeper l e v e l s . Most of the wa-t e r exchange takes p lace a t the southern end of the s t r a i t s i n ce the no r the rn channels a r e r e l a t i v e l y s ha l l ow and a re not a s e f f i c i e n t i n f l u s h i n g the s t r a i t (Waldichuk, 1957). Because of i n t e n s i v e t i d a l m ix ing i n the southern passages the compensating deep e s t ua r i n e f l o w i n t o the s t r a i t i s not pure sea water but a mixture of the b r a c k i s h su r f ace water and the s a l i n e deep water from the S t r a i t of Juan de Puca ( F i gu re 3). The f r e s h water i npu t from the F r a s e r R i v e r i s the s i n g l e most important f a c t o r i n the oceanography of the upper l a y e r i n the s t r a i t , p a r t i c u l a r l y i n the Northern and C e n t r a l r e g i o n s . The F r a s e r R i v e r p r o -v i de s rough ly 80% of the t o t a l f r e s h water i npu t t o the S t r a i t of Geor -g i a and i s the dominant i n f l u e n c e on s a l i n i t y i n the upper zone of the C e n t r a l r e g i on of the s t r a i t (Waldichuk, 1957). In the C e n t r a l and Northern reg i on s the water mass i s c h a r a c t e r i z e d by an upper zone of b r a c k i s h water w i t h a s t r ong h a l o c l i n e s epa ra t i n g the upper zone from the more s a l i n e lower l a y e r , fo rming a d i s t i n c t two- l aye red system ( F i g -u re 65). The r i v e r r u n o f f has a s t r ong seasona l c y c l e (F i gu re 4) w i t h a minimum d i scharge i n February o r March and a peak r u n o f f i n l a t e J ;une. Dur ing the low-d i scharge pe r i od of the w i n t e r ( l a t e November t o F e b r u -a r y ) when su r face hea t i n g of the upper l a y e r i s a t a minimum, s t r ong winds can break down the s t r a t i f i c a t i o n caused by f r e s h water r u n o f f and mix ing can occur t o l a r g e depths . Dur ing the h i gh -d i s cha rge pe r i od of the r i v e r from May t o October the b r a c k i s h upper l a y e r i s a ga i n present and w i t h the su r f ace hea t i n g of the upper l a y e r due t o i n c rea sed i n s o l a -t i o n a d i s t i n c t t w o - l a y e r system i s formed a g a i n . To summarize, the upper l a y e r of the Northern and C e n t r a l reg ions 6 of the strait has a low salinity due to the fresh water runoff of the Fraser River for most of the year with surface heating important in maintaining the stratification. As the low salinity water is removed through the southern channels a combination of the low salinity surface water and the deep sea water is formed by tidal mixing and flows back into the strait completing the estuarine circulation. 2.2 Tides and Tidal Mixing Tides in the Strait of Georgia are primarily of the mixed semi-diurnal variety (Crean, 1976) and are strongly decllnational. Over most of the Northern region and throughout the Central region tidal veloci-ties are small, less than 20 cm s * (0.4 knots). However, in the rela-tively narrow channels at the southern boundary of the strait tidal ve-locities rise to 200 cm s * (4 knots) or more, making the tides the most dominant oceanographic feature of the Southern and San Juan regions. The tide propagates up the Strait of Juan de Fuca as a progressive wave but as i t enters the southern tidal passages i t becomes strongly affected by friction, recovering its free wave characteristics as it enters the Strait of Georgia. The lateral constrictions and shallow sills (150 me-tres or less) of the tidal passages between the Gulf Islands and the San Juan Archipelago (Figure l) effectively isolate the deep waters of the Strait of Georgia from the direct influence of the Strait of Juan de Fuca or the Pacific Ocean. In these southern channels the tidal flow is turbulent with Rey-Q nolds numbers of the order of 6 X 10 (Tully and Dodimead, 1957) and the water column is mixed to homogeneity or near homogeneity. Waldichuk (1957) has termed the flow through southern tidal passages bulk ex-change, with little variation of tidal currents or salinity with depth 7 as opposed t o the t w o - l a y e r f l o w i n the Northern and C e n t r a l r e g i o n s . The water mass t h a t i s formed through mix ing i s a mixture o f b r a c k i s h F r a s e r R i v e r water and the more s a l i n e deep water from the S t r a i t o f Juan de Fuca and becomes the source water f o r the deep and i n te rmed ia te waters i n the S t r a i t of Geo rg i a . The same s i t u a t i o n of t i d a l m ix ing e x i s t s f o r the passages t h a t form the nor thern boundary of the s t r a i t bu t w i t h s ha l l ower s i l l s and s m a l l e r c r o s s - s e c t i o n a l a rea they have l e s s i n f l u e n c e upon the s t r a i t . Waldichuk (1957) i n d i c a t e s t h a t the no r the rn channels may sometimes be the source f o r an i n te rmed ia te water mass t h a t i s formed d u r i n g the w i n -t e r i n the Northern r e g i o n but have no major i n f l u e n c e upon the deep wa-t e r s of the s t r a i t , u n l i k e the southern channe l s . 2 . 3 Deep Water of the S t r a i t o f Georg ia In c o n t r a s t t o the upper b r a c k i s h l a y e r t h a t e x i s t s i n the N o r t h -e m and C e n t r a l r e g i o n s , the deeper water ( a t depths g r e a t e r than 100 metres) i n the S t r a i t of Georg ia i s r e l a t i v e l y homogeneous, w i t h l i t t l e change from summer t o w i n t e r . T i d a l v e l o c i t i e s i n the C e n t r a l and N o r t h -e rn reg i on s a r e l e s s than one knot and t i d a l m ix ing i s s m a l l . Advec t i on i s the most important p h y s i c a l process a f f e c t i n g the deep water of the s t r a i t . There i s a s teady northward f l o w of deep water i n t o the S t r a i t of Georg ia due t o the e s t ua r i ne c i r c u l a t i o n t h a t has been i n f e r r e d by 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 s t r a i t and by bottom d r i f t e r ob -s e r va t i on s (Gross, Morse and Barnes, 1969). Schumacher e t a l . (1978) measured the f l o w of oceanic water i n t o the S t r a i t of Geo r g i a , f i n d i n g the f l o w entered through Haro S t r a i t w i t h Rosa r i o S t r a i t be i ng too s h a l -low t o a l l o w e n t r y of the deep wate r . I n the c e n t r a l s t r a i t c u r r e n t mea-surements show a more complex s i t u a t i o n (Chang e t a l . , 1976) but the re i s 8 s t i l l a s i g n i f i c a n t northward f l o w a t s u b t i d a l f r e q u e n c i e s . In a d d i t i o n t o the steady e s t ua r i n e c i r c u l a t i o n the re a r e season-a l i n t r u s i o n s of d i f f e r e n t water masses i n t o the deep waters of the s t r a i t ( F i gu re 5)» I n the w i n t e r a Deep Water i s formed i n the southern s t r a i t and i n t r ude s i n t o the C e n t r a l r e g i o n d i s p l a c i n g the warmer water l e f t from the summer. O c c a s i o n a l l y a c o l d Intermediate Water i n t r u d e s i n t o the Northern r e g i o n but t h i s water mass i s l e s s s a l i n e and hence l e s s dense than the c o l d deep water formed i n the southern passages. In a d d i t i o n , t h i s no r the rn Intermediate Water i s not formed every w i n t e r , only d u r i n g ve ry c o l d w in te r s when there may be convec t i ve c o o l i n g i n the no r the rn s t r a i t . I n the l a t e summer h i gh s a l i n i t y water from the S t r a i t of Juan de Fuca i n t r u d e s i n t o the Southern and San Juan reg ions and i s mixed w i t h warm su r face water t o form a summer Intermediate Water which i n t r u d e s i n t o the C e n t r a l r e g i o n . Th i s water mass e v e n t u a l l y d i f f u s e s o r i s a d -vected throughout the s t r a i t f o rming the deep water mass u n t i l the nes t w i n t e r i n t r u s i o n of o o l d deep water . 9 3. PHYSICAL PROCESSES There a re s e v e r a l p h y s i c a l processes ope ra t i ng t o mix and move the waters of the S t r a i t of Geo rg i a . I n o rder t o produce a m ix ing budget the importance of each mechanism must be e s t ima ted , t a k i n g i n t o account the f a c t t h a t the d i f f e r e n t processes may vary w i t h t i m e , geog raph i ca l l o c a t i o n o r d e p t h . Th i s s e c t i o n con ta i n s a l i s t of the p h y s i c a l mechan-isms t h a t a re f e l t t o be important i n mix ing and renewing the waters i n the S t r a i t of Geo rg i a . 3.1 M i x ing Mechanisms M i x i ng mechanisms t o be cons idered a r e those important f o r v e r t i -c a l m ix ing of the water column. They a re p r i n c i p a l l y boundary phenomena, a c t i n g e i t h e r upon the su r face l a y e r o r a l ong a bottom f r i c t i o n l a y e r . The p o s s i b i l i t y of i n t e r n a l m i x i n g , by p e n e t r a t i n g j e t s f o r example, i s not r e j e c t e d but the e f f e c t w i l l s t i l l be v e r t i c a l m ix ing of s t r a t i f i e d l a y e r s . (a) Wind M i x i ng Wind mix ing i s the s i n g l e most important m ix i ng process f o r the upper l a y e r , t end ing t o mix the su r f ace b r a c k i s h l a y e r w i t h the u n d e r l y -i n g sea water l n the Northern and C e n t r a l reg ions of the s t r a i t bes ides d r i v i n g su r f ace c u r r e n t s i n a gene ra l c oun te r - c l o ckw i s e c i r c u l a t i o n ( a t l e a s t a c c o r d i n g t o Wa ld l chuk ' s (1957) i n t e r p r e t a t i o n ) . The winds i n the S t r a i t of Georg ia blow p r i m a r i l y from the southeast and northwest quad-r a n t s w i t h an annua l c y c l e of wind speeds from a maximum i n m id -w in te r t o a minimum i n summer ( T u l l y and Dodimead, 1957). The s t rong s o u t h -southeast component i n s p r i n g i s a lmost a s g rea t a s the w i n t e r maximum. As the wind b lows, a mixed l a y e r forms a t the s u r f a c e , w i t h u n i -form temperatures i n the upper l a y e r (Denman and Miyake, 1973) and w i t h 10 the depth of the mixed l a y e r dependent upon the s t r a t i f i c a t i o n of the water column and the mean wind s t r e s s ( P o l l a r d . Bhines and Thompson, 1973). S t ab l e s t r a t i f i c a t i o n tends t o i n h i b i t deepening of the mixed l a y e r and f o r the Northern and C e n t r a l r eg i on s the mixed l a y e r depth i s q u i t e sha l l ow d u r i n g the summer and f a l l . With decreased r u n o f f i n the w i n t e r and h i ghe r mean wind speeds wind mix ing can occur t o l a r g e depths . In the Southern and San Juan r e g i o n s , w i t h t h e i r homogeneous water mass-e s , wind mix ing can occur t o g r e a t e r depths than i n the r e s t of the s t r a i t but wind m ix i ng i s probably overshadowed by the t i d a l mix ing i n these r e g i on s . (b) I n t e r n a l Waves I n t e r n a l waves a re generated by the f l o o d t i d e f l o w i n g over the sha l l ow s i l l s i n the southern end of the s t r a i t and propagate northwards (F i gu re 6), e v e n t u a l l y b reak ing and d i s s i p a t i n g t h e i r energy and mix ing the water column. These i n t e r n a l waves t r a v e l a l o n g the sha l l ow pycno-c l i n e due t o the s t r a t i f i c a t i o n caused by the r u n o f f of the F r a s e r R i -ver} t h e r e f o r e any m ix ing caused by b reak ing i n t e r n a l waves should be concent rated i n the upper l a y e r of the S t r a i t of Geo rg i a . I n t e r n a l wave groups generated l n the southern passes have on ly been observed i n the C e n t r a l reg ion} a l though i t i s not unreasonable t o suppose t h a t i n t e r n a l waves a re generated i n the no r the rn t i d a l passages and propagate i n t o the Northern r e g i o n , such waves have not been measured, u n l i k e the i n - , t e r n a l waves i n the C e n t r a l r e g i o n (Hughes, 1969} Shand, 1953). The waves a r e dependent upon the s t r a t i f i c a t i o n which i s i t s e l f s ea sona l l y v a r i a b l e . The gene ra t i on mechanism, the f l o o d t i d e , has a two-week v a r -i a t i o n of sp r i ng s and neaps but averaged over a month i t does not va ry g r e a t l y over the yea r and may be cons idered con s t an t . Garget t (19?6) 11 prov ides a d e s c r i p t i o n of the gene ra t i on and propagat ion of i n t e r n a l waves i n the S t r a i t o f Georg i a . (c ) G r a v i t a t i o n a l I n s t a b i l i t y A s ea sona l l y important m ix i ng mechanism i s g r a v i t a t i o n a l i n s t a -b i l i t y caused by evapo ra t i on and su r face c o o l i n g l e a d i n g t o p e n e t r a t i v e c o n v e c t i o n . As the su r f ace l a y e r becomes g r a v i t a t i o n a l l y u n s t a b l e , c o n -v e c t i o n occurs and f l u i d from the u n d e r l y i n g l a y e r i s e n t r a i n e d i n t o the t u r b u l e n t su r face l a y e r . Convect ion mixes the su r face l a y e r and i t s c e n -t e r of mass i s l i f t e d , i n c r e a s i n g the p o t e n t i a l energy of the l a y e r . G r a v i t a t i o n a l i n s t a b i l i t y can be important i n the l a t e autumn and w i n t e r when f o rmat i on of a s t a b l y s t r a t i f i e d upper l a y e r from f r e s h water r u n -o f f and su r face hea t i n g i s a t a minimum. Waldichuk (195?) p resents e v i -dence t h a t convec t i ve mix ing can be important i n the Northern r e g i o n of the s t r a i t . (d) T i d a l M i x i n g As the t i d e en te r s the narrow t i d a l passages a t the nor thern and southern boundar ies of the s t r a i t , t i d a l v e l o c i t i e s r i s e t o 4 knots o r g r e a t e r and the f l o w becomes t u r b u l e n t enough t o overcome the s t r a t i f i -c a t i o n , v e r t i c a l l y mix ing the water column t o homogeneity. Most of the t i d a l exchange of waters takes p l ace i n the Southern and San Juan r e -g ions of the s t r a i t and t i d a l m ix ing i s the most important p h y s i c a l p r o -cess i n these r e g i o n s ; i t may a l s o c o n t r i b u t e somewhat t o the t o t a l m i x -i n g i n the no r the rn s t r a i t . I n a d d i t i o n the re may be a bottom f r i c t i o n l a y e r i n the C e n t r a l and Northern reg ions where t i d a l m ix i ng can h e l p t o mix and d i f f u s e the deep water of the s t r a i t . 12 (c ) Entrainment As the "brackish upper l a y e r l eave s the S t r a i t of Georg ia through the southern t i d a l passages i t e n t r a i n s s a l i n e water from the u n d e r l y i n g l a y e r * Some s t u d i e s have been made of entra inment i n the s t r a i t . W a l d i -chuk (1957) d i s cu s se s ou t f l ow of en t r a i ned water from the s t r a i t as p a r t of a f r e s h water budget and entra inment of water i n t o the F r a s e r R i v e r plume. Fu r t he r s t u d i e s of entra inment I n t o the F r a s e r R i v e r plume have been made by Cordes (1977) and de Lange Boom (1976). 3.2 Advec t i on and F l u s h i n g Mechanisms Bes ides v e r t i c a l m i x i n g , l a t e r a l t r a n s f e r s of mass can be impor -t a n t i n a l t e r i n g the p h y s i c a l p r o p e r t i e s of the water column which cou l d be a f a c t o r i n deterraing the s t a t e of m i x i n g . (a) F l u s h i n g E v e n t u a l l y , a l l of the f r e s h water t h a t en te r s the S t r a i t of Georg ia i s removed, by evapora t i on o r a d v e c t i o n . Removal by evapo ra t i on i s s m a l l , about 3% of the t o t a l f r e s h water i n f l o w (Waldichuk, 1957) l e a v i n g most of the f r e s h water l n the s t r a i t t o be removed by out f low t o the P a c i f i c Ocean v i a the S t r a i t of Juan de Fuca (measurements by Thompson (1976) i n Johnstone S t r a i t i n d i c a t e t h a t about 3% of the t o t a l f r e s h water l eave s through the no r the rn end of the S t r a i t of Geo r g i a ) . Th i s out f low or f l u s h i n g causes a s teady renewal of the upper l a y e r of the s t r a i t . The f l u s h i n g r a t e depends p r i m a r i l y upon the out f l ow of the F r a s e r R i v e r and t h i s f l u s h i n g mechanism i s most important i n the upper l a y e r of the C e n t r a l and Southern r e g i on s where most of the f r e s h water l e a v e s the S t r a i t of Geo rg i a . 13 (b) E s tua r i ne Advec t i on To ab lance the l o s s of sea water t h a t i s en t r a i ned i n t o the upper l a y e r a s i t f l ows out of the s t r a i t the re i s a steady a d v e c t i o n of s a -l i n e water i n t o the s t r a i t a t deep o r i n te rmed ia te l e v e l s . Th i s water i s not pure sea water but a mixture of deep water from the S t r a i t of Juan de Fuca and the ou t f l ow i n g b r a c k i s h water . As noted i n s e c t i o n 2. t h i s f l o w can be i n f e r r e d by the d i s t r i b u t i o n of temperature and s a l i n i t y i n the s t r a i t , by the r e s u l t s of d r i f t e r f l o a t exper iments and by d i r e c t c u r r e n t measurements. Schumacher e t a l , , (1978) found the deep a d v e c t i o n i n t o the s t r a i t through Haro S t r a i t t o be r e l a t e d t o the amount of F r a -s e r R i v e r r u n o f f a t the s u r f a c e . (c) T i d a l F l u s h i n g Superimposed on any c i r c u l a t i o n p a t t e r n i n the S t r a i t of Georg ia a r e the motions caused by the t i d e s . The f l o o d t i d e tends t o advect more s a l i n e water i n t o the s t r a i t and the ebb t i d e advect s l e s s s a l i n e water out of the s t r a i t . F l u s h i n g t imes due t o the t i d e tend t o be s m a l l e r than the f l u s h i n g t imes f o r e s t ua r i n e f l u s h i n g by f r e s h water r u n o f f ( O f f i c e r , 1976). T i d a l f l u s h i n g w i l l be important i n the extreme n o r t h -e r n and southern ends of the s t r a i t where the t i d a l excu r s i on s of the f l o o d t i d e a re of the order of 17 km (11 m i l e s ) . I t i s not l i k e l y t h a t water i n the s t r a i t t h a t l i e s more t h a t 40 km (25 m i l e s ) from the t i d a l passages would be advected out of the s t r a i t by the ebb t i d e . (d) I n t r u s i o n The seasona l replacement of the deep water masses i n the S t r a i t of Georg ia can be an important process i n changing the p h y s i c a l c h a r a c -t e r s l t l c s of the water column. Waldichuk (1957) d i s cu s se s the f o rmat i on and i n t r u s i o n of d i f f e r e n t water masses i n t o the s t r a i t . 14 I n w i n t e r c o l d Deep Water f l ows i n t o the C e n t r a l and Northern r e -g ions of the s t r a i t from the Southern r e g i o n , d i s p l a c i n g the warm water mass l e f t from the summer ( F i gu re 5a). A c o l d In termediate Water may a l -so f l o w i n t o the Northern r e g i o n . I n l a t e summer a warm, s a l i n e I n t e r -mediate Water f l ows i n t o the C e n t r a l r e g i o n of the s t r a i t and e v e n t u a l l y d i s p e r s e s , fo rming the deep water mass ( F i gu re 5b), Seasonal i n t r u s i o n s of d i f f e r e n t water masses may be important t o the deep water masses i n the s t r a i t where o ther m ix ing processes may be m in ima l . The i n t r u s i o n s can be q u a l i t a t i v e l y t r a ced by n o t i n g the d i s -s o l v e d oxygen c o n c e n t r a t i o n of the deep water of the s t r a i t s i n ce an i n -t r u s i o n of a d i f f e r e n t water mass u s u a l l y r e p l e n i s h e s the d i s s o l v e d oxy -gen supp l y . 3.3 Measurements of M i x i ng U n f o r t u n a t e l y , no s i n g l e v a r i a b l e can d i r e c t l y i n d i c a t e how mixed the water column i s . Nonetheless v a r i ou s parameters can be c a l c u l a t e d which can g i ve e s t imate s of how much mix ing has occu r red . Th i s s e c t i o n w i l l d e f i n e these parameters and present an i n t e r p r e t a t i o n of t h e i r p h y s i c a l meaning. (a) P o t e n t i a l Energy Dens i t y As a s t a b l y s t r a t i f i e d water column i s mixed i t s c e n t e r of mass i s r a i s e d and the column ga in s g r a v i t a t i o n a l p o t e n t i a l energy. Assuming t h a t mix ing mechanisms a r e the on ly processes t h a t a r e changing the d e n -s i t y s t r u c t u r e , then changes i n the p o t e n t i a l energy w i l l measure the work done upon the water column by m i x i n g . To i l l u s t r a t e the use of the p o t e n t i a l energy d e n s i t y c o n s i d e r a water column of u n i t a rea and t h i c kne s s H t h a t i s s t r a t i f i e d w i t h an u p -per l a y e r w i t h d e n s i t y ^ ^ and t h i c kne s s h^ and a lower l a y e r w i t h d e n -15 s i t y and t h i c k n e s s h 2 ( F i gu re 7 a ) . The p o t e n t i a l energy per u n i t volume i s found by i n t e g r a t i n g from the bottom of the l a y e r ( z » -H) t o the t op ( z •» 0) w i t h the v e r t i c a l z - a x i s p o i n t i n g upwards and the s u r -f a c e taken as the ze ro p o t e n t i a l energy re fe rence l e v e l . The. p o t e n t i a l energy per u n i t volume (E^) i s g i ven by p • o 3.1 Changes i n E^ w i l l r e f l e c t changes due t o mix ing (and a d v e c t i o n ) . The ab so l u te va lue of E i s a measure of the work needed t o l i f t a l l of the P water i n the column t o the t op of the l a y e r and the g r e a t e r the d e n s i t y (and hence the mass) of the l a y e r , the g r e a t e r the magnitude of E^. S ince the top of the l a y e r i s taken t o be the r e fe rence l e v e l , E p w i l l be a negat ive q u a n t i t y so t h a t decreases i n p o t e n t i a l energy r e s u l t i n a more negat i ve va lue of E^ (more work must be expended t o mix the c o l -umn) and i n c rea se s i n p o t e n t i a l energy r e s u l t i n a l e s s negat i ve va lue of Ep ( l e s s work must be expended t o mix the co lumn). The magnitude of Ep can decrease i n two wayss by m ix i ng the water column, i n c r e a s i n g the p o t e n t i a l energy (making E l e s s n e g a t i v e ) , o r by hav ing l e s s mass i n P the column by dec rea s i ng the d e n s i t y (by a d v e c t i o n , f o r example). The p o t e n t i a l energy d e n s i t i e s f o r d i f f e r e n t geographic l o c a t i o n s cannot be d i r e c t l y compared w i t h each o the r t o determine which a rea i s more mixed because the magnitude of depends d i r e c t l y upon the d e n s i t y . I n g e n e r a l , the 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 Georg ia has h i g h -e r d e n s i t i e s i n the sou th , lower d e n s i t i e s i n the c e n t r a l p o r t i o n and h i ghe r d e n s i t i e s a ga i n i n the no r t h ( F i gu re 28 ) , a t l e a s t f o r the s u r -f a ce l a y e r . S i nce E^ i s d e f i n e d a s a negat ive q u a n t i t y v a l ue s of E^ w i l l tend t o have an i n ve r s e r e l a t i o n s h i p t o the d e n s i t y d i s t r i b u t i o n , be i ng more negat ive i n the south , a r e g i o n of I n ten s i ve t i d a l m i x i ng and l e s s 16 negat i ve i n the C e n t r a l r e g i o n , the s i t e of the g r e a t e s t s t r a t i f i c a t i o n . Thus on ly changes i n the p o t e n t i a l energy d e n s i t y can be used t o e v a l u -a t e m ix i ng w i t h i n a g i ven geog raph i ca l l o c a t i o n . (b) M ix ing Energy Dens i t y One way t o compare mix ing and s t r a t i f i c a t i o n between d i f f e r e n t l o c a t i o n s i s by u s i n g a q u a n t i t y r e f e r r e d t o a s the m ix ing energy d e n s i -t y . I f the s t r a t i f i e d water column of F i g u r e ?a were comple te l y mixed t o homogeneity ( F i gu re 7b) i t would have a cons tant d e n s i t y "jF which would be g i ven by The p o t e n t i a l energy per u n i t volume r e f e r r e d t o the upper su r f ace ( z « 0) a s ze ro p o t e n t i a l energy i s now The mix ing energy d e n s i t y i s d e f i n e d a s the energy pe r u n i t volume need- ed t o mix the water column t o homogeneity. I n the example above i t would be the d i f f e r e n c e between the p o t e n t i a l energy d e n s i t y of water column •B* and water column 'A*? The mix ing energy d e n s i t y i s a p o s i t i v e q u a n t i t y f o r s t a b l e s t r a t i f i c a -t i o n ( p 2 p^) but g e n e r a l l y does not depend a s s t r o n g l y upon the a v -17 erage d e n s i t y a s the p o t e n t i a l energy d e n s i t y does. E m i s a measure of depar tu res from a t o t a l l y mixed s t a t e ; va lues of B m f rom d i f f e r e n t r e -g ions can be compared w i t h each o t he r . The mix ing energy d e n s i t y i s a l s o a measure of the s t r a t i f i c a t i o n of the water column ( the g r e a t e r the s t r a t i f i c a t i o n the g r e a t e r the work needed t o mix the co lumn). F o r an example assume t h a t t he re i s a cons tant v e r t i c a l d e n s i t y g r ad i en t such t h a t the d e n s i t y of the water column i s P - 0 - z i s p o s i t i v e V X O f>i f>T and z i s p o s i t i v e upwards). Then the average d e n s i t y , , of the column w i l l be 3.5 The mix ing energy d e n s i t y f o r t h i s example w i l l be .o ~- TT iTiU ^ . - H ^  L 3 * J 3.6 12-,3-Al though the d e n s i t y g r ad i en t w i l l g e n e r a l l y not be cons tant but a f u n c -t i o n of z , E w i l l s t i l l depend u p o n l £ and thus be a f u n c t i o n of the s t r a t i f i c a t i o n ( ^ ) . (c ) Two-Layer P o t e n t i a l Energy Dens i ty Whi le changes i n the p o t e n t i a l energy d e n s i t y r e f l e c t the work done by m ix i ng and the mix ing energy d e n s i t y i n d i c a t e s how much mix ing can s t i l l be done, n e i t h e r of these q u a n t i t i e s i n d i c a t e s how w e l l mixed the water column a c t u a l l y i s . One way t o e s t imate the t o t a l m ix ing (and t o t a l s t r a t i f i c a t i o n ) of the water column i s the c a l c u l a t e the depar tu re s 18 f rom a t o t a l l y unmixed s t r a t i f i c a t i o n . An a b s o l u t e l y s t r a t i f i e d water column would c o n s i s t of a Layer of f r e s h water over a homogeneous l a y e r of sea water w i t h oceanic s a l i n i t y . Such a two-Layer system would be a s •unmixed 1 a s p o s s i b l e ; the p o t e n t i a l energy d e n s i t y of the system would be the minimum p o s s i b l e and the d i f f e r e n c e between i t and the a c t u a l p o -t e n t i a l energy d e n s i t y i s a measure of the ab so l u t e amount of m ix i ng of the system. F o r a g i ven water column of u n i t a rea the t h i c kne s se s of the f r e s h and s a l t water l a y e r s a r e chosen t o conserve s a l t . The t h i c kne s se s of the l a y e r s depend upon the va lue chosen f o r the base s a l i n i t y . T u l l y and Dodimead (1957) suggested 31%0» the r e p r e s e n t a t i v e va lue f o r waters a t a 50 in depth i n the S t r a i t of Geo rg i a , but t h i s s tudy uses the same va lue a s Waldichuk;(1957)* 33«8%„, which i s r e p r e s e n t a t i v e of the most s a l i n e water a t the seaward mouth of the S t r a i t of Juan de Fuca . Fo r a water column of u n i t a r ea and t h i c k n e s s H w i t h a s a l i n i t y d i s t r i b u t i o n S ( z ) and w i t h the v e r t i c a l z - a x i s p o s i t i v e upwards, the con se r va t i on of s a l t r e q u i r e s t h a t 33.8 L - f S<0 O / E 3.7 where L g would be the t h i c k n e s s of the s a l t water l a y e r . The t h i c k n e s s of the f r e s h water l a y e r would be H - L g and the p o t e n t i a l energy d e n s i -t y would be g i v en by equat ion 3«1 where o ^ and p2 a r e the a p p r o p r i a t e d e n s i t i e s f o r the f r e s h and s a l t water l a y e r s r e s p e c t i v e l y and h^ and h 2 a r e the t h i c kne s se s of the f r e s h and s a l t water l a y e r s . The d i f f e r e n c e between the observed p o t e n t i a l energy d e n s i t y and the minimum t w o - l a y e r p o t e n t i a l e ne r g y l den s i t y i s a measure of how mixed the water column i s . To summarize, the p o s s i b l e p o t e n t i a l energy d e n s i t i e s can range from a minimum va lue g i v en by the t w o - l a y e r p o t e n t i a l energy d e n s i t y t o a maximum va lue determined by the mix ing energy d e n s i t y which i n t u r n depends upon the e x i s t i n g s t r a t i f i c a t i o n . 20 4. DATA DESCRIPTION Th i s s e c t i o n g i ve s the source and a b r i e f summary o f the da ta used i n t h i s s tudy. The a n a l y s i s of the da t a i s presented i n s e c t i o n 5» 4.1 Oceanographlc Data Oceanographic da ta r e f e r s t o any da ta t h a t i s used t o d e s c r i b e the p h y s i c a l c h a r a c t e r i s t i c s of the waters i n the S t r a i t o f Geo r g i a . (a) Hydrographic Data The bu l k of the data used i n t h i s s tudy was b a s i c hydrographic data taken i n the S t r a i t of Geo r g i a . Most of the hydrographic da ta came from a s e r i e s of c r u i s e s taken i n a pe r i od from l a t e I967 through I968 (Crean and Ages, 1971). The da ta were obta ined from the Marine E n v i r o n -mental Data S e r v i c e (MEDS) and was augmented by a d d i t i o n a l hydrographic da ta taken i n the pe r i od 1967-1970. A t o t a l of 970 oceanographic s t a -t i o n s were p rov ided by MEDS f o r l o c a t i o n s s c a t t e r e d throughout the S t r a i t of Georg ia from 4 8 ° 24*N t o 50° 04*N. Of these 970 s t a t i o n s 747 were taken d u r i n g 1968. The MEDS da ta were encoded on a n ine t r a c k magnetic tape and each s t a t i o n i n c l uded the geog raph i ca l l o c a t i o n ( l a t i t u d e and l o n g i t u d e ) , date and t ime of the sample ( f o r a d e s c r i p t i o n o f the MEDS da ta format see Sweers, 1970). The hydrographic da ta f o r each s t a t i o n i n c l uded d i s -so l ved oxygen c o n c e n t r a t i o n s , temperature, p re s su re , s a l i n i t y and s l gma-t f o r each sampled dep th . The d i f f e r e n t da ta va lues were a l s o i n t e r p o l a -ted f o r every 5 metres of dep th , from the su r f ace t o 150 m and f o r every 25 metres of depth from 150 m t o the maximum sample dep th . S ince most of the a v a i l a b l e data were taken d u r i n g I968 i t was dec ided t o choose I968 as a r e p r e s e n t a t i v e y e a r . Four months (February , May, August and November) were chosen t o be ana l yzed i n d e t a i l , r e p r e -21 s e n t i n g the c o n d i t i o n s i n the s t r a i t f o r w i n t e r , s p r i n g , summer and a u -tumn. 251 hydrographic s t a t i o n s were a v a i l a b l e f o r those f o u r months (F i gu re 8). These s t a t i o n s p rov ided the b a s i s f o r a d e s c r i p t i o n o f the water p r o p e r t i e s of the S t r a i t o f Georg ia and c a l c u l a t i o n s of the d i f f -e r en t mix ing parameters. (b) Other Oceanographic Data Photographs of bathythermographs taken d u r i n g the 1968 c r u i s e s of Crean and Ages (1971) were prov ided by A . Ages ( pe r sona l communicat ion). These bathythermograph s l i d e s were used t o prov ide q u a l i t a t i v e va l ue s of mixed l a y e r depths and the v e r t i c a l temperature s t r u c t u r e . E s t imates of I n t e r n a l wave ampl i tudes i n the southern S t r a i t of Georg ia were taken from Hughes (1969) and Garget t (1976). A e r i a l pho to -graphs and sketches of i n t e r n a l wave groups i n the southern s t r a i t which were taken i n May I968 were p rov ided by P. LeBlond ( pe r sona l communica-t i o n ) . Values of the B r u n t - V a i s a l a f requency f o r f o u r s t a t i o n s i n the S t r a i t of Georg ia f o r I968 were computed by J . H e l b i g (pe r sona l commun-i c a t i o n ) . 4.2 M e t e o r o l o g i c a l Data Mean va lue s f o r m e t e o r l o g i c a l v a r i a b l e s f o r each month o f 1968 were taken from the p u b l i c a t i o n Monthly Record - M e t e o r o l o g i c a l Observa- t i o n s i n Canada. Department of T ranspor t , M e t e o r o l o g i c a l B ranch. Meteor -o l o g i c a l data i n c l uded mean a i r temperatures, dew p o i n t temperatures , r e l a t i v e humid i t y , monthly i n s o l a t i o n va lues f o r d i r e c t sunshine and summaries of hou r l y wind measurements. Table I summarizes the da ta a -v a i l a b l e f o r the m e t e o r o l o g i c a l s t a t i o n s around the S t r a i t of Georg ia and F i gu re 9 shows t h e i r l o c a t i o n s . S t a t i o n coverage i s good i n the 22 S t a t i o n A i r D i r e c t Month Temperatures Wind Sunshine Ba l l ena s I s . Feb May Aug Nov X X X X X X X Comox A i r p o r t Feb May Aug Nov X X X X X X X X Departure Bay-Feb May Aug Nov X X X X Merry I s . Feb May Aug Nov X X X X X X Feb X P o i n t A t k i n s on May Aug Nov X X X Sandheads Feb May Aug Nov X X X X X X X X Saturna I s . Feb May Aug Nov X X Vancouver I n t . A i r p o r t Feb May Aug Nov X X X X X X X X X X X X V i c t o r i a I n t . A i r p o r t Feb May Aug Nov X X X X X X X X Table I M e t e o r o l o g i c a l da ta f o r s t a t i o n s around the S t r a i t of Geo rg i a . 23 southern S t r a i t o f Georg ia but r a t h e r sparse i n the no r the rn a rea o f the s t r a i t . Values of vapor pressure over sea water and psychometr ic r e d u c -t i o n formulae needed f o r e s t i m a t i n g evapora t ion r a t e s were taken from the Smithsonian Tab le s and the Handbook of Chemistry and P h y s i c s . 4.3 T i d a l Data Mean va lues of t i d a l v e l o c i t i e s f o r the t i d a l component and es t imates of bottom f r i c t i o n c o e f f i c i e n t s i n the s t r a i t were obta ined from P. Crean (pe r sona l communicat ion). The v e l o c i t y and f r i c t i o n va lue s were taken from a numer i ca l model of the t i d e i n the S t r a i t of Georg ia and the S t r a i t of Juan de Fuca (Crean, 1978). 4.4 Hydrometric Data Monthly va l ue s of d i s charge da ta f o r the F r a s e r R i v e r d u r i n g 1968 were taken from the p u b l i c a t i o n Sur face Water Data. B.C. 1268, Water Survey of Canada, I n land Waters Branch. The d i scharge da ta were measured a t the Po r t Mann r e c o r d i n g s t a t i o n on the F r a s e r l R i v e r . 4.5 Bathymetr ie Data Depths and depth contours f o r the S t r a i t of Georg ia were obta ined from standard hydrographic c h a r t s ( c ha r t numbers 3001, 3449, 3450, 3577» 3590 and 3591) pub l i shed by the Canadian Hydrographic S e r v i c e , Marine Sc iences D i r e c t o r a t e , Department of the Environment. 24 5. DATA ANALYSIS AND PRESENTATION In order t o eva lua te the s t a t e of m ix ing i n the S t r a i t of Georg ia s e v e r a l p h y s i c a l p r o p e r t i e s were ana l yzed f o r the f o u r r e p r e s e n t a t i v e months of February, May, August and November f o r the yea r 1968. The p r o p e r t i e s ana l yzed i n c l uded temperature, s a l i n i t y and d i s s o l v e d oxygen concen t r a t i o n f o r the d i r e c t l y observed p h y s i c a l v a r i a b l e s and p o t e n t i a l energy d e n s i t y , m ix ing energy d e n s i t y and t w o - l a y e r p o t e n t i a l energy d e n s i t y f o r c a l c u l a t e d v a r i a b l e s . Fo r purposes of showing the geographic v a r i a t i o n of p h y s i c a l v a r -i a b l e s , the S t r a i t of Georg ia was d i v i d e d by a r e c t a n g u l a r g r i d i n t o a number of compartments. F i gu re 10 shows the boundar ies of the su r f ace o f the s t r a i t approximated by the edges of the g r i d . The g r i d i s r e c t a n g u -l a r on a Mercator map p r o j e c t i o n w i t h each g r i d compartment hav ing d i -mensions of 5 minutes o f l a t i t u d e by 7 minutes, 45 seconds o f l ong i t ude which i s equa l t o a 5 by 5 n a u t i c a l m i l e square a t a l a t i t u d e o f 49° 48 'N. S ince the w id th of each compartment i n c rea se s l i n e a r l y w i t h l o n g i -tude,, t h e y a c t u a l w id th w i l l depend upon the l a t i t u d e of the compartment w i t h the widths v a r y i n g from 9*53 km (5»15 n a u t i c a l m i l e s ) a t a l a t i t u d e of 48° 24 fN t o 9.21 km (4.97 NM) a t a l a t i t u d e of 50° 04 'N w i t h a mean width of 9.37 km (5.O6 NM). The a rea of each g r i d compartment v a r i e s from 88.7 square k i l ome t r e s (25.7 NM 2) i n the south t o 85.4 km 2 (24.9 NM 2) i n the north> a d i f f e r e n c e of on ly 3% which was i gnored i n the a -n a l y s i s . A l l of the p h y s i c a l water p r o p e r t i e s s t ud i ed ( temperature, s a l i n -i t y , s igma-t and d i s s o l v e d oxygen concen t r a t i on ) were s p a t i a l l y averaged v e r t i c a l l y and h o r i z o n t a l l y . The S t r a i t of Georg ia was v e r t i c a l l y s p l i t i n t o 25 metre t h i c k l a y e r s from the su r f ace t o the bottom w i t h f o u r of these 25 metre l a y e r s ana l y zed i n t e n s i v e l y . Layer 1 (0 m t o 25 m) and 25 l a y e r 2 (25 m t o 50 m) were chosen t o rep resent the su r f ace l a y e r s , l a y -e r 7 (150 m t o 175 m) was chosen t o rep re sen t an Intermediate l a y e r and l a y e r 9 (200 m t o 225 m) was chosen t o rep resent a deep l a y e r . Each p h y s i c a l p roper ty was depth-averaged f o r these f o u r l a y e r s . F o r a v a r i -a b l e r3(z) t h a t i s dependent upon the v e r t i c a l d imens ion z , the depth a -veraged v a l u e , Q t w i l l be g i ven by e j 9(*)Jz 5.1 where z^ and a re the bottom and t op r e s p e c t i v e l y of the l a y e r of i n -t e r e s t and (zg - z^) • 25 m. The i n t e g r a l was eva lua ted n u m e r i c a l l y u -s i n g a S impson ' s r u l e method. S ince the data va lue s were i n t e r p o l a t e d f o r every 5 metres f o r the upper 150 metres of depth and f o r every 25 metres f o r depths g r e a t e r than 150 metres there were a t o t a l of 6 da ta po i n t s f o r each v a r i a b l e t o be n u m e r i c a l l y i n t e g r a t e d f o r l a y e r s 1 and 2 and two da ta po i n t s a v a i l a b l e f o r numer i ca l i n t e g r a t i o n f o r l a y e r s 7 and 9 . A f t e r depth -averag ing , a l l v a r i a b l e s were h o r i z o n t a l l y averaged f o r each of the f o u r r e p r e s e n t a t i v e l a y e r s . Each l a y e r was d i v i d e d by a r e c t a n g u l a r g r i d i n t o compartments a s de s c r i bed above w i t h the edges of ; the g r i d approx imat ing the depth contour a t the bottom of the l a y e r . The h o r i z o n t a l average of the depth-averaged v a r i a b l e s was found by comput-i n g the weighted mean f o r each g r i d i n t e r s e c t i o n u s i n g the e i g h t c l o s e s t da ta p o i n t s . The mean va lue f o r the j * t h g r i d i n t e r s e c t i o n f o r v a r i a b l e 0 i i s g i ven by w i t h the we igh t i ng f a c t o r WA equa l t o 1/R^ where ^ i s the d i s t a n c e ( i n a r b r i t r a r y u n i t s ) t o the i ' t h da ta p o i n t Q.. By u s i n g the i n ve r se 26 square of the d i s t a n c e t o the da ta po i n t s a s a we igh t ing f a c t o r , the h o r i z o n t a l mean i s weighted more h e a v i l y towards the c l o s e s t da ta p o i n t s . A r e p r e s e n t a t i v e va lue f o r each g r i d compartment was computed by t a k i n g the mean of the va lue s a t the f o u r co rner s of the compartment. The g r i d compartments were grouped i n t o the f o u r reg ions of F i gu re 2 and a mean va lue f o r each r e g i o n was computed. A f t e r ave rag ing h o r i z o n t a l l y each v a r i a b l e was c o n t o u r - p l o t t e d f o r the r e p r e s e n t a t i v e l a y e r s and months u -s i n g a computer program de s c r i bed by Gou l thard (1975)• The f o l l o w i n g s e c t i o n s q u a l i t a t i v e l y d e s c r i b e the average water p r o p e r t i e s i n l a y e r s 1, 2 , 7 and 9 f o r the months of February , May, A u -gust and November of 1968. An I n t e r p r e t a t i o n of the average f e a t u r e s w i l l be made i n s e c t i o n 7» 5.1 Observed P h y s i c a l P r o p e r t i e s (a) Temperature F i gu re s 11 through 14 show the d i s t r i b u t i o n s o f the dep th - a ve r -aged temperatures i n the S t r a i t of Georg ia f o r l a y e r s 1, 2 , 7 and 9 f o r the f o u r r e p r e s e n t a t i v e months. V e r t i c a l s e c t i o n s of temperature i n the s t r a i t a r e presented i n F i g u r e 64. The average temperature f o r each r e -g i on of the S t r a i t of Georg ia i s graphed f o r each l a y e r i n F i g u r e s 15 through 18. The main f e a t u r e s f o r each l a y e r a r e a s f o l l o w s : l a y e r l j 0 m - 25 mj Temperatures i n l a y e r 1 show a s t r ong s e a -sona l c y c l e w i t h the minimum va lues l n February r i s i n g t o maximums i n August and c o o l i n g by November. F i g u r e 15 shows the average temperatures f o r the f o u r reg ions of the S t r a i t of Georg ia graphed f o r the f o u r r e p -r e s e n t a t i v e months. In February ( F i gu re 11a), the average temperatures f o r l a y e r 1 a r e a lmost un i fo rm i n the Northern and C e n t r a l r eg i on s of the s t r a i t 27 with t y p i c a l values of 6.7° C to 6 . 8° G suggesting that the upper layer i s we l l mixed. Temperatures are s l i g h t l y higher i n the Southern and San Juan regions with values from 7*0° C to 7 . 1 ° C but again are f a i r l y u n i -form. The highest temperatures i n l ayer 1 are found a t the extreme northern end of the s t r a i t and are probably due to t i d a l mixing with warmer deep water as suggested by Figure 64a. By May (Figure l ib) with increasing s t r a t i f i c a t i o n due to runoff and increased i n s o l a t i o n , aver-age temperatures i n l ayer 1 have r i s e n by 2° C or more. There i s a rough trend i n the temperature d i s t r i b u t i o n with the lowest temperatures (A. 9 ° C) i n the San Juan region r i s i n g to the values i n the Northern region (^ 12° C ) . Average temperatures peak i n August (Figure 11c) with temper-atures approaching 15° C i n the Northern reg ion . As i n May the lowest temperatures are found i n the San Juan region with temperatures increas-ing towards the north (Figures 64b and 64c). In the Centra l region there i s an east-west temperature gradient with s l i g h t l y lower temperatures i n the eastern s t r a i t . This i s probably due to the inf low of cooler Fraser River water since s a l i n i t i e s (Figure 19c) are lowest i n the same area . Cooling and mixing processes have reduced temperatures to an average of < ~ 9 , 5 ° C by November (Figure l i d ) . Temperatures are f a i r l y uniform throughout the s t r a i t (Figure 64d) and there are no obvious trends or gradients. Layer 2$ 25 m - 50 m« Figure 16 i l l u s t r a t e s the average tempera-tures f o r l ayer 2 , The temperatures show a seasonal cycle s i m i l a r to l ayer 1 (Figure 15) wi th low values i n February r i s i n g to a peak i n A u -gust with a cool ing trend i n November. In contrast to l ayer 1 (Figure 15) temperatures i n the Centra l region of the s t r a i t increase more slow-l y during the spring and summer with Isotherms r i s i n g towards the sur-face i n May (Figure 64b). 28 In February (Figure 12a) temperatures are fairly uniform in the layer, running from 7.2° G to 7.5°C through most of the Strait of Geor-gia with a patch of higher temperatures of 7.6° G - 7,8° G in the north-ern end of the strait. Temperatures are slightly lower in the Southern and San Juan regions compared with the rest of the strait. The average temperature of the San Juan and Southern regions (7*1° C) is the same as layer 1 (there is l ittle vertical variation of temperature in these re-gions as shown by Figure 64a) while the average temperature of the Northern and Central regions (7 .4° C) is warmer than the average value of 7.1° C for layer 1. The main features of the average temperatures in May (Figure 12b) are the rapid change of temperatures from an average of 8.8° C in the Southern region to an average of 8.3° G in the Central re-gion and a pronounced east-west temperature gradient present throughout the Northern and Central regionsj temperatures are lower along the east-ern side of the strait (while salinities are higher as shown by Figure 20b). In August (Figure 12c) the east-west gradient is s t i l l present with much of the eastern part of the Central region a uniform 9.2° G rising to temperatures of 10.1° C - 10.3° C along the western side. A-verage temperatures are highest ln the Southern region (10.3° C) and a-long the western side of the northern strait (10.5° C - 10.9° C)« Tem-peratures have fallen by November (Figure 12d) with average values of 9.3° C - 9.5° C. Temperatures are again fairly uniform (Figure 64d) but there is s t i l l an east-west temperature gradient in the Central region. Layer 7» 150 m - 175 ms Figure 17 shows the average temperatures for each region in Layer 7* In contrast to the upper layers (Figures 15 and 16) the average temperatures do not show a simple cycle of warming in the summer and cooling in the winter. The Southern And San Juan re-gions have identical average temperatures that rise steadily from a low 29 of 7.3° C in February to a high of 8 . 8 ° C in November. The Central re-gion rises from 8.2° C in February to 9.2° C in November while the Northern region cools from 8 . 8 ° C in February to 8 . 4 ° C in May then r i s -es gradually to 9 . 1 ° C in November. The average temperatures of the strait for a l l regions converge to 8 . 4 ° C in May with uniform tempera-tures at intermediate depths (Figure 64b). In February (Figure 13a) temperatures are a uniform 7*3° C in the Southern and San Juan regions rising to 8.3° C - 8 . 4 ° C in the Central region and 9° C in the Northern region. Temperatures are fairly uniform in the Central region ( 8 . 4 ° C) with the most noticable feature the gra-dient between the Central and Southern regions of the strait . In May (Figure 13b) temperatures throughout the Strait of Georgia have reached a uniform 8.3° C - 8 . 4 ° C suggesting that the water in layer 7 had been replaced by an intrusion of a different water mass. By August (Figure 13c) temperatures have risen with warm water intruding from the southern strait along the eastern side of the strait (as suggested by the temper-ature distributions). An east-west temperature gradient is present in the Central region with the higher temperatures along the eastern side. Temperatures in the Northern region show l i t t l e variation from a mean of 8 .6° C (Figure 64c). In November (Figure 13d) the temperatures of layer 7 are again almost uniform with values in the 9 . 1 ° C - 9.2° C range as shown by Figure 64d. Layer 9I 200 m - 225 m: The average temperatures for each region of layer 9 are shown in Figure 18. The temperatures follow a similar pattern to that of layer 7 (Figure 17) with the temperature of the San Juan region rising from a low of 7.3° C in February to a high of 8.9° C in November. The temperatures of the Northern and Central regions do not vary greatly, decreasing from 8 . 7 ° C - 8.9° C in February to 8 . 4 ° C -30 8.5° C In May and rising to 8.8° C - 9,0° C in November. In February (Figure 14a) the temperature runs from 8.4° G in the Central region to 9»1° G in the Northern region with most of the Central region a uniform 8.7° C and the Northern region at 8.9° G. The tempera-tures in the Northern and Central regions have decreased slightly by May (Figure 14b) with temperatures higher along the western side of the strait (similar to layer 7). In August (Figure 14c) the Northern region shows a uniform 8.5° G with the highest temperatures of 9»0° G along the eastern side of the Central region. Temperatures in the southern part of the strait range from 8.9° C in the San Juan region decreasing to 8.4° C in the Southern region. . (b) Salinity Figures 19 through 22 show the depth-averaged salinities of the representative layers contour-plotted while Figures 23 through 26 show the average salinity for each region in those layers graphed for the representative months. Vertical sections of salinity through the Strait of Georgia for the months of February, May, August and November of 1968 are illustrated in Figure 6 5 . Layer 1| 0 m - 25 m: The average salinities for the four regions are graphed in Figure 23• Salinities for the Northern and Central re-gions are influenced by the runoff from the Fraser River, salinities in the San Juan region are influenced more by water from the Strait of Juan de Fuca while the average salinity of the Southern region will be influ-enced by both the Juan de Fuca water and the Fraser River. The average salinity in the Central region decreases from a high of 27,5%* 1 x 1 Feb-ruary to a low of 26.6%© in May rising slightly to 26.7%* in August and November. The salinity ln the Northern region stays at 28,0%, from Feb-ruary to May and decreases to 26.1%,, in August rising back to 27• 5°/oo in 31 November. The highest sa l in i t i e s are in the San Juan region (Figure 65) r i s ing from 29»3%« i n February to a high of 29 .9%* i n May decreasing to 29.7%, by November. The sa l in i ty in the Southern region decreased stead-i l y from a high of 28.4%, in February to a value of 27.9%* i n November. In February (Figure 19a) sa l in i t i e s are highest in the San Juan region with values of 29.4%* decreasing to values of 26.5%o - 2?,Q%> i n the Central region and r i s i n g to values of 29»0%o i n the Northern r e -gion. By May (Figure 19b) sa l in i t i e s have increased up to 30.6%> i n the San Juan region but have decreased to 24.3%o in the Central region of the s t r a i t . Sa l in i t i e s are lower (as are temperatures, Figure l i b and oxygen concentrations, Figure 32b) along the eastern side of the s t ra i t due to the Fraser River runoff. In August (Figure 19c) the lowest s a l i n -i t i e s are found near Texada Island i n the Northern region with values of 25»1%* with higher values of 2?,5%,a.t the western side of the s t r a i t . The highest values of average sa l in i ty (30.0%,) are found i n the San Juan region decreasing to values of 26 .7%* i n the Central region. The lower sa l in i t i e s i n the Northern region may be due to fresh water runoff from Jervis Inlet which empties into the eastern side of the s t r a i t near Texada Island or i t may-/be due to Fraser River water having been advec-ted northwards. By November (Figure 19d) sa l in i t i e s i n the Northern r e -gion have increased back to 26,7%, - 27.9%>with no obvious east-west sa l in i ty gradient. Sa l in i t i e s reach 30.8%o in the San Juan region and decrease to values of 26 .1%>in the Central region of the s t r a i t . Layer 2j 25 m - 50 m« Figure 24 i l lus trates the average s a l i n i -t ies for layer 2 for the four representative months for the regions of the s t r a i t . In contrast to layer 1 (Figure 23) a l l sa l in i t i e s r i se from February to May ref lect ing increasing sa l in i t i e s during this time i n the Stra i t of Juan de Fuca (Figure 65b) . Sa l in i t i e s i n the San Juan region 32 i n c r ea se from 29.6/^in February t o a h i gh of 30,k%oin May dec rea s i ng t o 30.1%* by November. A l l s a l i n i t i e s i n the Nor thern . C e n t r a l and Southern reg ions r i s e from February t o May and decrease from May t o No-vember. I n February (F i gu re 20a) t he re i s l i t t l e c o n t r a s t i n s a l i n i t i e s i n the Northern and C e n t r a l r eg i on s w i t h both reg i on s hav ing an average s a l i n i t y of 28.8%,. S a l i n i t i e s a r e h i ghe r a l ong the ea s t e r n s i d e of the s t r a i t i n these reg i on s wh i l e temperatures (F i gu re 12a) and oxygen c o n -c e n t r a t i o n s (F i gu re 33a) a r e l owe r . S a l i n i t i e s a r e h i ghe s t i n the s o u t h -e rn p a r t of the s t r a i t and the re i s a no r th - sou th s a l i n i t y g r ad i en t b e -tween the Southern r e g i o n and the C e n t r a l r e g i o n ( F i gu re 65a) w i t h the s a l i n i t y dec rea s i ng from t y p i c a l va lues of 29«3%o t o 28 .8%« . I n May (F i gu re 20b) the weak eas t -west s a l i n i t y g r ad i en t i s s t i l l p resent a l ong the ea s te rn s i d e of the S t r a i t of Geo rg i a . I n the Southern and San Juan r eg i on s the s a l i n i t y g r a d i e n t becomes o r i en t ed no r th t o south w i t h s a -l i n i t i e s i n c r e a s i n g f rom 29.6%<? i n the no r t h t o 3°.9%» i n the sou th . The s a l i n i t y p a t t e r n has not changed by August (F igure 20c) except f o r the presence of low s a l i n i t y water a l o n g the ea s te rn s i de of the Southern and San Juan r e g i o n s . I n November ( F i gu re 20d) l ower s a l i n i i t y . water i s found a l o n g the ea s t e r n s i de of the Southern and San Juan reg i on s a l -though the gene ra l s a l i n i t y g r ad i en t i s no r th t o south (F i gu re 65d) w i t h the h i ghe r s a l i n i t i e s a l ong the ea s te rn s i de of the s t r a i t i n c o n t r a s t t o the southern r eg i on s w i t h a gene ra l eas t -west s a l i n i t y g r a d i e n t . Layer 7$ 150 m - 175 m* The average s a l i n i t i e s of l a y e r 7 a r e shown i n F i gu re 25. The main f e a t u r e s of the seasona l changes i n s a l i n i -t y a re t h a t the Southern and San Juan r eg i on s show the same seasona l p a t t e r n and t h a t the Northern and C e n t r a l reg ions of the s t r a i t have a very s i m i l a r p a t t e r n t o each other t h a t i s ve ry d i f f e r e n t t o the one i n 33 the southern S t r a i t of Geo rg i a . S a l i n i t i e s f o r the Southern and San Juan reg i on s show an i n c rea se from February t o May, l i t t l e change from May t o August and then a decrease from August t o November. S a l i n i t i e s f o r the C e n t r a l r e g i o n i n c rea se s l i g h t l y from February t o November. In November the average s a l i n i t i e s f o r the Nor thern , C e n t r a l and Southern reg i on s a l l have s i m i l a r va lues near J0»5%o ( F i gu re 65d). I n February (F i gu re 21a) s a l i n i t i e s a r e f a i r l y un i fo rm i n the Northern and C e n t r a l r eg i on s w i t h va lues between 30.4%« t o 30.6%« w i t h s a l i n i t i e s lower a l o n g the ea s t e r n s i de of the s t r a i t . The lowest s a l i n -i t i e s a r e found i n the Southern r e g i o n w i t h va lues of 29»7&» t o 30»o2»© whi le s a l i n i t i e s i n the San Juan r e g i o n i n c rea se s t e a d i l y southwards from 30.1%o t o 30.9%> ( F i gu re 65a). I n May (F i gu re 21b) s a l i n i t i e s d e -crease s t e a d i l y northwards throughout the s t r a i t form 31.7&> i n the south t o 30.4%, i n the n o r t h . There i s a s l i g h t eas t -west s a l i n i t y g r a -d i e n t i n the C e n t r a l r e g i o n w i t h h i ghe r s a l i n i t i e s a l ong the western s i de of the s t r a i t . S a l i n i t i e s decrease r a p i d l y northwards i n the Sou th -e m r e g i o n from 31.4%, t o 30.7%> ( F i gu re 65b). I n August (F i gu re 21c) s a l i n i t i e s a r e f a i r l y un i fo rm (30.5%. - 30.7%>) throughout the Northern and C e n t r a l r eg i on s of the s t r a i t and i n c rea se r a p i d l y southwards ( F i g -ure 65c) from 30.7%, t o 31 «4/oo i n the Southern r e g i o n and from 3lA%e t o 31.8%<> i n the San Juan r e g i o n . I n November ( F i gu re 21d) the lowest s a l -i n i t y i s a g a i n i n the Southern r e g i o n w i t h a t y p i c a l va lue of 30.4%,. Values a re h i ghe r l n the Northern and C e n t r a l r eg i on s w i t h va lues of 30»?Z» and 30,8/C* S a l i n i t i e s i n c rea se r a p i d l y southwards l n the San Juan r e g i o n from 30.4%> t o 3 1 . 2& . Layer 9} 200 m - 225 m» F i gu r e 26 shows the average s a l i n i t i e s f o r the f o u r r e p r e s e n t a t i v e months (data were not a v a i l a b l e f o r the Southern r e g i o n f o r February i n l a y e r 9). The seasona l s a l i n i t y p a t t e r n 34 is similar to that of layer 7 (Figure 25) • Salinities in the San Juan region rise from February to May and decrease from August to November as they did in layer 7 while the salinities in the Northern and Central re-gions decrease slightly from February to May and increase slightly from May to November. In February (Figure 22a) salinities vary slightly throughout the strait with values from 30.6^, to 30.8%e> in the Northern and Central re-gions. The lowest salinities are in the Southern region and reach values of 30.4%» in the northern part of the San Juan region increasing rapidly southwards to 30.9%>. From May to November (Figures 22b to 22d) there are l i t t l e variations in salinity throughout the strait: higher salini-ties are in the southern strait decreasing northwards (Figures 65b to 65d). (c) Sigma-t Density in the Strait of Georgia is primarily determined by sa-linity and changes in the density closely follow changes in the salini-ty. Comparison of Figure 27 with Figure 19a and of Figure 67 with Fig-ure 65a shows that the same features described for the average salinity are also present in the sigma-t distributions. Therefore, only the aver-age density for each region will be described in this section. The variable sigma-t (<r^) is related to the density by the rela--3 -3 tionship 0 » 1 +10 where the density has the units of gm cm . In this section the terms sigma-t and density will be used interchangeably in describing the density features of the strait although sigma-t is the variable plotted. The average densities for each region are graphed in Figures 28 through 34 while Figure 67 shows a vertical section of sigma-t for February I968. Layer 1; 0 m - 25 m: Figure 28 illustrates the regional averages 35 f o r s igma-t i n l a y e r 1. S igma-t va l ue s i n the Nor thern , C e n t r a l and Southern r eg i on s decrease from February t o August due t o the decrease i n s a l i n i t y ( F i gu re 23) f rom f r e s h water r u n o f f and r i s e i n November a s r u n o f f decreases and m ix ing i n c r e a s e s . The s igma-t va lues of the San Juan r e g i o n r i s e s l i g h t l y f rom February t o May from 22.95 t o 23.20 t hen f a l l i n August t o 22.65, r i s i n g back t o 23.0 i n November. Layer 2j 25 ro - 50 ro: F i gu re 29 graphs the average s igma-t va l ue s f o r l a y e r 2 f o r the f o u r r e p r e s e n t a t i v e months. D e n s i t i e s f o r a l l r e -g ions i n the S t r a i t o f Georg ia i n c rea se from February t o May which i n d i -c a te s an i n f l o w of denser water from the S t r a i t o f Juan de Fuca s i n ce d e n s i t i e s decrease f o r the upper l a y e r . The i nc rea se i n d e n s i t i e s c ou l d be t i e d t o i nc rea sed deep e s t ua r i n e f l o w a s the f r e s h water r u n o f f i n the su r face l a y e r i n c r e a s e s . The i n f l o w of denser water i s i l l u s t r a t e d by the ex ten s i on of the 30.0%> and 30.5%a s a l i n i t y contours northwards i n t o the s t r a i t i n F i g u r e 65b. D e n s i t i e s decrease i n a l l r eg i on s from May t o August p o s s i b l y due t o mix ing w i t h l e s s s a l i n e water from l a y e r 1 or t o decreased e s t ua r i n e f l o w . I n November, d e n s i t i e s cont inued t o d e -crease i n the San Juan and C e n t r a l r eg i on s but i n c rea sed i n the Southern r e g i o n and remained cons tant i n the Northern r e g i o n . The i n c rea sed d e n -s i t y f o r the Southern r e g i o n may have been due t o c o o l i n g of the upper l a y e r s ( F i gu re s 15 and 16) wh i l e the s a l i n i t y decreased on l y s l i g h t l y (F i gu re 24). Layer 7; 150 m - 175 ms Average s igma-t va lues f o r the f o u r r e -g ions a re shown graphed i n F i gu re 30 f o r the f o u r r e p r e s e n t a t i v e months. The d e n s i t i e s i n the Northern and C e n t r a l r eg i on s were very c l o s e i n va lue and show the seasona l p a t t e r n (as d i d the average s a l i n i t i e s , F i g -u re 25). The average s igma-t of the C e n t r a l r e g i o n s l ow l y i n c rea sed from 23.68 i n February t o 23.83 i n November wh i l e the average s igma-t of the 36 Northern r e g i o n s l i g h t l y decreased from a va lue of 23.69 i n February t o 23.66 i n May then g r a d u a l l y i n c rea sed t o a va lue of 23.75 i n November. Average d e n s i t i e s i n the Southern r e g i o n a r e lower than those of the San Juan r e g i o n but both r eg i on s show a r e l a t i v e l y l a r g e i n c r ea se of d e n s i t y from February t o May, a s l i g h t decrease between May and August and then a l a r g e r decrease t o va lue s i n November t h a t a r e c l o s e t o the va l ue s of February j t h i s i s the same p a t t e r n shown by the average s a l i n i t i e s , F i g 7 u re 25* The lowest d e n s i t i e s a r e found i n the Southern r e g i o n i n both February and November and i n the Northern r e g i o n i n the o the r months. As was the case f o r the average s a l i n i t i e s , the changes i n d e n s i t y i n the Southern and San Juan reg i on s d i d not seem t o be c o r r e l a t e d w i t h changes of d e n s i t y i n the Northern and C e n t r a l r eg i on s of the s t r a i t . Laye r 9J 200 m - 225 mt F i g u r e 31 i l l u s t r a t e s the r e g i o n a l a v e r -ages of s igma-t f o r the f o u r r e p r e s e n t a t i v e months (data were not a v a i l -a b l e f o r the Southern r e g i o n i n Feb rua r y ) . The seasona l p a t t e r n of d e n -s i t y v a r i a t i o n s f o r the Nor thern , C e n t r a l and San Juan reg i on s i s the same as de s c r i bed f o r l a y e r 7 ( F i gu re 30) and f o l l o w s the s a l i n i t y v a r i -a t i o n s of F i gu re 25. Values of the average s igma-t f o r the Northern and C e n t r a l r eg i on s a r e v i r t u a l l y i d e n t i c a l t o those of l a y e r 7* D e n s i t i e s f o r the Southern r e g i o n of the s t r a i t show an Increase between May and August i n c o n t r a s t t o l a y e r 7 where va lues decreased. Values of s i gma-t i n the Southern r e g i o n decreased from August t o November a s they d i d f o r l a y e r 7* The h i ghe s t d e n s i t i e s f o r the s t r a i t were i n the San Juan r e -g i on w h i l e the Northern r e g i o n had the lowes t va lues f o r a l l months. (d) 1 D i s so lved ' - Oxygeri,C onceh t r a t i on The d i s s o l v e d oxygen content of the water can be used a s a t r a c e r t o i n d i c a t e water movement and m i x i n g . U n l i k e o the r q u a n t i t i e s such a s 37 temperature o r s a l i n i t y , d i s s o l v e d oxygen i s not a c on se r va t i v e q u a n t i -t y ; i t i s renewed by a e r a t i o n a t the su r f ace and by photosynthes i s and consumed by b i o chem i ca l a c t i v i t y . I n a d d i t i o n , the s o l u b i l i t y and s a t u r -a t i o n l e v e l of oxygen depends upon the water temperature w i t h the s a t u r -a t i o n va lue s i n c r e a s i n g w i t h dec rea s i n g temperature. I n g e n e r a l , d i s -so l ved oxygen concen t r a t i on s a r e h i g h e r i n the su r face l a y e r s where pho-t o s y n t h e s i s and gas exchange can occur and lower i n the deeper l a y e r s where oxygen i s s t e a d i l y dep l e ted by b i o l o g i c a l a c t i v i t y . Increases i n the d i s s o l v e d oxygen c o n c e n t r a t i o n a t depth u s u a l l y I n d i c a t e the i n t r u -s i o n of a d i f f e r e n t water mass. F i g u r e s 32 through 35 show contours of equa l oxygen concen t r a t i on s f o r l a y e r s 1, 2, 7 and 9* F i g u r e s 36 through 39 graph the average d i s s o l v e d oxygen c o n c e n t r a t i o n f o r each r e g i o n f o r each of the r e p r e s e n t a t i v e months wh i l e v e r t i c a l p r o f i l e s of oxygen c o n -c e n t r a t i o n a r e i l l u s t r a t e d i n F i g u r e 66. L a t e r l j 0 m ~ 25 m: F i gu re 36 i l l u s t r a t e s the average oxygen c o n c e n t r a t i o n f o r each r e g i o n i n l a y e r 1 f o r the months o f February , May, August and November. D i s s o l ved oxygen concen t r a t i on s i n the C e n t r a l r e g i o n decreased from February t o August. T h i s was p robab ly due t o the I n c rea s i n g s t r a t i f i c a t i o n due t o f r e s h water r u n o f f which I n h i b i t s m i x -i n g and t o i n c rea sed temperatures which lower the s a t u r a t i o n va lue of d i s s o l v e d oxygen. A e r a t i o n of the upper l a y e r by wind m ix ing and gas e x -change probably oxygenate the upper l a y e r more e f f e c t i v e l y than oxygen p roduc t i on through photosynthes i s s i n ce t he re i s more photosynthes i s i n the summer than i n the w i n t e r y e t an o v e r a l l decrease i n the average d i s s o l v e d oxygen c o n c e n t r a t i o n . Oxygen concen t r a t i on s f o r a l l r e g i on s reach t h e i r minimum i n August (when the average temperatures a r e a max-imum) then r i s e i n November. The oxygen concen t r a t i on s i n l a y e r 1 seem t o be i n v e r s e l y r e l a t e d t o the average temperature ( F i gu re 15) which i n -38 d i c a t e s t h a t the temperature determines the maximum oxygen c o n c e n t r a t i o n by f i x i n g the s a t u r a t i o n l e v e l . I n February ( F i gu re 32a) the h i ghe s t oxygen concen t r a t i on s a r e -1 found i n the C e n t r a l r e g i o n of the s t r a i t w i t h va lue s near 7,0 ml 1 , Concent ra t i on s decrease g r a d u a l l y southwards r e a ch i n g a va lue of 6.1 ml 1~* i n the San Juan r e g i o n . Concen t ra t i on s a l s o decrease t o the no r t h of the C e n t r a l r e g i o n , r a p i d l y dec rea s i ng a t the no r the rn end of the s t r a i t t o the minimum c o n c e n t r a t i o n of 4.9 ml 1 • The lower oxygen c o n c e n t r a -t i o n s seem t o be l o c a t e d i n the a rea s of h i gh t i d a l m i x i n g , i n the Southern and San Juan r eg i on s and a t the no r the rn end of the s t r a i t , p o s s i b l y because oxygen-poor deep water i s be i n g mixed w i t h the su r face water a s suggested by F i g u r e 66a. I n May ( F i gu re 32b) the l owes t oxygen -1 concen t r a t i on s a r e s t i l l i n the t i d a l m ix ing r e g i o n s ; 5«7 ml 1 i n the -1 no r the rn s t r a i t and 4.9 ml 1 i n the San Juan r e g i o n . I n a d d i t i o n , oxy -gen concen t ra t i on s a r e lower a l ong the ea s te rn edge of the Northern and C e n t r a l r eg i on s where l ower s a l i n i t i e s ( F i gu re 19b) may i n h i b i t mix ing and a e r a t i o n of the su r f ace l a y e r . The h i ghe s t d i s s o l v e d oxygen concen-t r a t i o n s a re a l o n g the western s i d e of the s t r a i t r each i ng a maximum —1 —1 va lue of 6.7 ml 1 i n the Northern r e g i o n and 6,5 ml 1 i n the C e n t r a l r e g i o n . I n August ( F i gu re 32c) the lowest d i s s o l v e d oxygen c o n c e n t r a -t i o n s a r e a g a i n near the t i d a l m ix ing a reas i n the Southern and San Juan reg ions (and a t the no r the rn end of the s t r a i t ) and a l ong the ea s te rn s i de of the Northern and C e n t r a l r e g i o n s . The h i ghe s t c oncen t r a t i on s a r e a l ong the western s i d e of the Northern and C e n t r a l r eg i on s of the s t r a i t . There i s a patch of low oxygen water l y i n g i n the Boundary Passage a r ea of the Southern r e g i o n . As b e f o r e , the lower oxygen concen -t r a t i o n s a re a s s o c i a t e d w i t h the lower s a l i n i t i e s i n the Northern and C e n t r a l r eg i on s and w i t h a rea s of t i d a l m i x i n g . The same p a t t e r n p e r -39 sists in November (Figure 32d) with and east-west oxygen gradient in the Northern and Central regions and a north to south gradient in the South-ern and San Juan regions. The lower oxygen concentrations are along the eastern side of the strait and towards the southern end of the San Juan region. Layer 2; 25 m - 50 m« The average dissolved oxygen concentrations for each region in layer 2 are graphed in Figure 37* The oxygen concen-trations for a l l regions decreased from February to August and increased between August and November. The seasonal variation of dissolved oxygen concentrations in layer 2 seems to be inversely correlated to the aver-age temperature of the layer (Figure 16) as i t was for layer 1. In February (Figure 33a) the lowest oxygen concentrations are found at the northern end of the strait (as in layer 1) near the north-ern tidal passages. Concentrations increase southwards with the maximum value of 6.36 ml 1~* in the Central region of the strait and decrease slightly to values of 6.0 ml 1 * in the San Juan region. Concentrations are somewhat lower along the eastern side of the strait but the gradient of oxygen concentration is generally north to south. In May (Figure 33b) the highest and the lowest oxygen concentrations are both in the North-em region of the strait. The maximum value of 5.46 ml 1~* is found at the extreme northern end while the minimum value of 4.63 ml 1 is lo-cated in Malaspina Strait along the eastern side of Texada Island. Oxy-gen concentrations in the Central region do not vary much having values -1 -1 between 4.95 ml 1 and 5»03 ml 1 with values decreasing southwards —1 into the San Juan region to 4.80 ml 1 • The gradient of oxygen concen-trations is east to west in the Northern region and north to south in the rest of the Strait of Georgia, a different pattern from that of lay-er 1. In August (Figure 33c) oxygen concentrations have decreased fur-4o t h e r w i t h the minimum va lue l o c a t e d t o the ea s t of Texada I s l a n d . Con--1 c e n t r a t i o n s decrease southwards from a va lue of 4.5 ml 1 l n the Cen -t r a l r e g i on t o a va lue of 4.0 ml 1 i n the San Juan r e g i o n . Oxygen c o n -c e n t r a t i o n s have i nc reased somewhat i n November (F i gu re 33d). There i s an ea s t t o west g r ad i en t of oxygen concen t r a t i on s i n the Northern and C e n t r a l reg ions w i t h lower va lues a l ong the ea s te rn s i de of the s t r a i t . The oxygen g r ad i en t i s no r th t o south i n the Southern and San Juan r e -g ions w i t h concen t r a t i on s dec rea s i ng southwards. Layer 7} 150 m - 175 m: F i gu re 38 i l l u s t r a t e s the r e g i o n a l a v e r -ages of d i s s o l v e d oxygen c o n c e n t r a t i o n f o r the r e p r e s e n t a t i v e months (data were not a v a i l a b l e f o r the Southern r e g i o n i n November). The Southern and San Juan reg ions show the same c y c l e as l a y e r s 1 and 2; a decrease of oxygen c oncen t r a t i o n from February t o August and an i n c r ea se from August t o November. Th i s suggests t h a t t i d a l m ix ing i n these r e -g ions mainta ins a f a i r l y homogeneous water column and changes i n oxygen c oncen t r a t i o n i n the upper l a y e r s a re r e f l e c t e d i n a l l l a y e r s . F i g u r e 66 shows t h a t v e r t i c a l changes o f oxygen concen t r a t i on s i n the southern s t r a i t a re much l e s s than those of the C e n t r a l o r Northern reg ions ( e x -cept a t the extreme nor thern end of the s t r a i t ) . The changes i n oxygen c oncen t r a t i o n f o r the Northern and C e n t r a l r eg i on s show a d i f f e r e n t p a t -t e r n than those of the other reg i on s of the s t r a i t . The average concen-t r a t i o n . f o r the C e n t r a l r e g i o n shows a s l i g h t decrease between February and May (but l e s s than the decrease f o r the Southern and San Juan r e -g ions ) wh i l e the oxygen c oncen t r a t i o n of the Northern r e g i o n i n c r e a s e s . The average oxygen concen t r a t i on s f o r both reg ions then decrease from May t o November. The i nc rea se of oxygen content f o r the Northern r e g i on (and the r e l a t i v e l y s m a l l decrease f o r the C e n t r a l r eg ion ) between F e b -rua r y and May suggests an i n t r u s i o n of water i n t o the no r the rn S t r a i t of 41 Georg ia occurred i n t h a t p e r i o d . Th i s i s a l s o suggested by the r a i s i n g of the 4.5 ml l " * contour towards the su r face i n May (F i gu re 66b). I n February (F i gu re 34a) the da ta a v a i l a b l e show a no r th t o south g r ad i en t of oxygen concen t r a t i on s w i t h the minimum va lue of 3»49 ml 1 a t the extreme no r the rn end of the s t r a i t and the maximum va lue of 5»6 ml 1~* a t the southern end. Much of the C e n t r a l and Northern reg i on s of the s t r a i t have a near un i fo rm d i s t r i b u t i o n w i t h concen t r a t i on s of 4.4 ml 1 * o f d i s s o l v e d oxygen. The d i s s o l v e d oxygen d i s t r i b u t i o n q u a l i t a -t i v e l y suggests a northward f l o w from the southern s t r a i t w i t h h i ghe r oxygen va lues a s s o c i a t e d w i t h •younger* water . Qu i te a d i f f e r e n t p a t t e r n e x i s t s i n May (F i gu re 34b). A mass of water w i t h a miximum c o n c e n t r a t i o n of 4.58 ml 1 * of d i s s o l v e d oxygen occupies most of the C e n t r a l r e g i o n o f the s t r a i t . There a r e a rea s i n the Northern r e g i o n w i t h c o n c e n t r a -t i o n s of 4.38 ml 1 * of d i s s o l v e d oxygen on the western and ea s te rn s i de s of Texada I s l a n d w i t h an a rea of 3*84 ml 1 o f d i s s o l v e d oxygen l y i n g between them. The minimum c o n c e n t r a t i o n o f 3•66 ml 1 * i s found a t the no r the rn end of Malaspina S t r a i t t o the ea s t of Texada I s l a n d . A t a depth of 150 metres t h a t pa r t of the s t r a i t i s a semi-enc losed b a s i n o -pen only a t the southern end and the re may not be much c i r c u l a t i o n w i t h -i n the b a s i n l e a d i n g t o lower concen t r a t i on s of oxygen. Concent ra t i on s of d i s s o l v e d oxygen decrease s l i g h t l y southwards from the C e n t r a l r e g i o n t o an Intermediate va lue of 4.29 ml 1 . The h i ghe r d i s s o l v e d oxygen concen t r a t i on s and gene ra l oxygen d i s t r i b u t i o n q u a l i t a t i v e l y suggest t h a t a d i f f e r e n t water mass has r ep l a ced the water mass t h a t occupied the s t r a i t i n February . I n August ( F i gu re 34c) d i s s o l v e d oxygen concen -t r a t i o n s have decreased throughout the S t r a i t of Geo rg i a . The h i ghe s t d i s s o l v e d oxygen concen t r a t i on s of 3.87 ml 1~* a r e found t o the n o r t h -west of Texada I s l a nd w h i l e the lowes t concen t r a t i on s of 2.91 ml 1 * a r e 42 in the basin to the east of that island. Most of the Central region has a value of 3.71 ml 1~* of dissolved oxygen increasing southwards to a patch with a concentration of 3*81 ml 1~* in the Southern region. Dis-solved oxygen concentrations decrease in the San Juan region to a value of 3.61 ml 1*"*. Dissolved oxygen levels have decreased further by Nov-ember (Figure 34d). As in February the maximum levels are in the San Juan region decreasing northwards. Most of the Central region has values -1 -1 between 3.40 ml 1 and 3*50 ml 1 with concentrations decreasing to 3.2 ml 1*"* near Texada Island. Values of dissolved oxygen concentration in the Northern region of the strait vary slightly between 3.2 ml 1 * -1 and 3.5 ml 1 . Layer 9} 200 m - 225 mi Regional averages of dissolved oxygen are shown in Figure 39. Data were not available for the Southern and San Juan regions but the seasonal cycle in those regions was probably simi-lar to that of shallower levels judging from the seasonal pattern of layer 7. The seasonal cycle of dissolved oxygen concentrations in the Northern and Central regions follows a similar pattern as layer 7.(Fig-ure 38). Dissolved oxygen concentrations rose between February to May then decreased from May to a minimum in November. The increase of oxygen in the deep waters of the strait in May suggests that an intrusion of water occurred between February and May. In February (Figure 35a) the maximum oxygen concentrations were in the southern strait and the minimum concentrations were at the north-ern end. There was a patch with a concentration of 4.0 ml 1 in the Northern region but in general dissolved oxygen concentrations decreased steadily from the south towards the north (Figure 66a). By May (Figure 35b) the maximum oxygen concentrations were in the Central region with values up to 4.29 ml l""*. Concentrations in the Northern region of the 43 -1 s t r a i t were h i ghe r a l o n g the western s i de w i t h va lues up t o 3*9 ml 1 . The s m a l l e s t c oncen t r a t i on s were i n the b a s i n i n the e a s t e r n s i de of the Northern r e g i o n w i t h va lue s down t o 3»07 ml 1 There was a patch of low oxygen concen t r a t i on s i n the northwestern co rne r of the C e n t r a l r e -g i on w i t h a va lue down t o 3«3 ml 1 . I n August (F igure 35c) the minimum d i s s o l v e d oxygen c o n c e n t r a t i o n was s t i l l i n the ea s te rn b a s i n of the Northern r e g i o n a t 2.8 ml 1 • Concent ra t i ons i nc rea sed southwards t o 3.6 ml 1 i n the C e n t r a l r e g i o n . The h i ghes t oxygen concen t r a t i on s were i n the western s i de of the Northern r e g i o n w i t h a maximum va lue of 3«75 -1 -1 ml 1 dec rea s i ng t o 3*3 ml 1 towards the e a s t . D i s s o l ved oxygen c o n -c e n t r a t i o n s decreased f u r t h e r by November (F i gu re 35d) w i t h the h i ghe s t -1 va lue of 3«46 ml 1 i n the C e n t r a l r e g i o n . In the Northern r e g i o n d i s -so l ved oxygen concen t r a t i on s were lower than i n the south w i t h va lues of -1 -1 3.2? ml 1 t o 3 « H ml 1 a l ong the western s i d e . The minimum d i s s o l v e d oxygen c oncen t r a t i o n was i n the b a s i n a l ong the ea s t e r n s i de of the -1 Northern r e g i o n w i t h a va lue of 2.71 ml 1 • 5.2 Der ived P h y s i c a l P r o p e r t i e s (a) P o t e n t i a l Energy Dens i ty F o r a water column of u n i t a r ea and w i t h the bottom of the l a y e r a t z = z^ and the top of the l a y e r a t z « Zg ( the v e r t i c a l z a x i s i n -c reases upwards) the g r a v i t a t i o n a l p o t e n t i a l energy of the column per u -n i t volume i s g i ven by z % where the r e fe rence l e v e l of ze ro p o t e n t i a l energy i s a t the t op ( z «• z 2 ) of the l a y e r . I f z^ - -H and z g - 0, equat ion 5*3 s i m p l i f i e s t o e -qua t i on 3.1• The d e n s i t y , P , can be expressed i n terms of cr. by 44 3 5.4 and equat ion 5«3 can be r e w r i t t e n a s T^Z,[f 3^'^^ I*'Vjfz-Zx)^] 5.5 The f i r s t i n t e g r a l i n equat i on 5.5 i s approx imate l y the c o n t r i b u -t i o n due t o the mass of f r e s h water ( a t 4° G) i n the l a y e r wh i l e the s e -cond i n t e g r a l i s approx imate l y the c o n t r i b u t i o n due t o the s t r a t i f i c a -t i o n from s a l i n i t y and thermal e f f e c t s . F o r t y p i c a l s igma-t va lues i n the S t r a i t of Georg ia the f i r s t i n t e g r a l w i l l be approx imate ly 50 t imes l a r g e r than the second and w i l l c o n t r i b u t e most t o the t o t a l p o t e n t i a l energy d e n s i t y . Except f o r v a r i a t i o n s i n g , the a c c e l e r a t i o n due t o g r a v i t y , over the S t r a i t of Georg ia the f i r s t p a r t of equa t i on 5.5 i s cons tant f o r a 25 metre, l a y e r ( z 2 - z^ •* 25 metres) and a t a l a t i t u d e of 48° 24*N has a va lue of -1.226 X 10^ e rgs per c ub i c c e n t i m e t r e . F o r t h i s s tudy, the p o t e n t i a l energy d e n s i t y , E^, was d e f i n e d u s i n g s igma-t p l u s the c o n t r i b u t i o n from the f i r s t i n t e g r a l of equat i on 5*5 due t o changes i n g(^?) f rom changes i n the l a t i t u d e Thus E^ was d e f i n e d as Ef • ^ ^ 5.6 where Zg - z^ «• 25 metres and Ag i s the d i f f e r e n c e between the va lue of g a t the l a t i t u d e of the da ta s t a t i o n and g a t the r e fe rence l a t i t u d e of 48° 24*N. The l a s t term of equa t i on 5«6 c o n t r i b u t e s a maximum of 186 ergs per c ub i c cent imet re t o the t o t a l p o t e n t i a l energy d e n s i t y . S i nce the u n c e r t a i n t y of the p o t e n t i a l energy d e n s i t y due t o the i nhe ren t e r -r o r s i n the va lue of s i gma-t ( p l u s o r minus 0.02 s i gma-t u n i t s ) i s on l y 25 ergs cm"^ the c o n t r i b u t i o n due t o the changes of g w i t h l a t i t u d e can not be i gno red . Values of E were computed f o r l a y e r s 1, 2, 7 and 9 f o r the months of February , May, August and November of 1968. The va lue s of E p were c o n t o u r - p l o t t e d f o r those l a y e r s and months and a r e shown i n F i g -u res 40 through 43• An average va lue of E^ was computed f o r each g r i d compartment f o r each l e v e l . The t o t a l p o t e n t i a l energy due t o s i gma-t f o r each g r i d compartment was computed by t a k i n g the product of the mean p o t e n t i a l energy d e n s i t y and the volume of the g r i d compartment (approx -i m a t e l y 2.14 k n r ) . The average va lues of p o t e n t i a l energy p e r g r i d com-partment f o r the f o u r r eg i on s of the s t r a i t a r e graphed i n F i g u r e s 44 through 47. An i n c rea se i n E f o r a l a y e r was due t o r a i s i n g the c e n t e r of g r a v i t y of the l a y e r . T h i s c ou l d be accompl i shed by dec rea s i ng the mean d e n s i t y of the l a y e r o r by m ix ing w i t h i n the l a y e r . I n e i t h e r case changes i n the d i s t r i b u t i o n of E^ w i l l r e f l e c t changes i n the d e n s i t y d i s t r i b u t i o n , e i t h e r v e r t i c a l l y o r h o r i z o n t l a l l y . Layer l j 0 m - 25 m: F i g u r e 44 i l l u s t r a t e s the average p o t e n t i a l energy per g r i d compartment due t o s igma-t i n each r e g i o n f o r l a y e r 1. The San Juan r e g i o n ma inta ins a f a i r l y cons tant va lue of p o t e n t i a l e n e r -12 gy, w i t h a va lue near -6.2 X 10 J o u l e s . I t s energy content i n c rea se s s l i g h t l y between February and August and then decreases from August t o November. The Southern r e g i o n shows the oppos i te behav i o r , dec rea s i ng from February t o August then i n c r e a s i n g from August t o November. The S t rong t i d a l m ix i ng i n the San Juan r e g i o n i s probably s u f f i c i e n t t o ma in ta i n the near - cons tant p o t e n t i a l energy l e v e l . The decrease of p o -t e n t i a l energy i n the Southern r e g i o n of the s t r a i t i s probably due t o i n c r e a s i n g s t r a t i f i c a t i o n due t o f r e s h water r u n o f f which c ou l d be i m -po r tan t i n the no r the rn h a l f of the Southern r e g i o n where t i d a l m ix ing i s not a s s t r o n g . P o t e n t i a l energ ie s i n the C e n t r a l r e g i o n decrease from 46 February t o May but then i n c r e a s e s l i g h t l y from May t o November i n d i c a t -i n g e i t h e r m i x i n g o r a decrease i n the mean d e n s i t y of the l a y e r ( p r o b -a b l y the l a t t e r a s i n d i c a t e d by F i g u r e 2 8 ) . The p o t e n t i a l energy i n the Nor thern r e g i o n i n c r e a s e s from February t o August then decreases between August and November. These changes a re p robably due t o changes i n the a -verage d e n s i t y ( F i g u r e 28) be s ides m i x i n g . I n February (F igu re 40a) the s m a l l e s t va lue s o f E ^ a r e i n the e x -treme nor the rn and southern ends of the s t r a i t (where s igma- t has the g r e a t e s t v a l u e s ) w i t h a minimum va lue of - 2 . 8 5 X 10^ e rgs cm~^. I n gen -e r a l , Ep and the average s igma- t w i l l be i n v e r s e l y r e l a t e d w i t h E ^ d e -c r e a s i n g as s igma- t i n c r e a s e s , a l t h o u g h E ^ w i l l a l s o depend upon the d i s t r i b u t i o n of s igma- t w i t h d e p t h . Values i nc r ea se s l i g h t l y from the h nor th i n the C e n t r a l r e g i o n t o an a r ea w i t h a va lue o f - 2 . 6 X 10 e rgs cm then decrease a g a i n southwards i n the San Juan r e g i o n o f the s t r a i t . The e x c e p t i o n t o t h i s p a t t e r n i s the a r ea o f maximum energy d e n s i t i e s i n the Boundary Bay a rea of the Southern r e g i o n w i t h a h i g h va lue o f 4 -3 - 1 . 7 X 10 ergs cm • T h i s f ea tu re was not apparent i n the con tours o f depth-averaged s a l i n i t y ( F i g u r e 19a) and i s probably due t o the p a r t i c u -l a r d e n s i t y d i s t r i b u t i o n w i t h d e p t h . P o t e n t i a l energy d e n s i t i e s i n May (F igu re 40b) i n the C e n t r a l r e g i o n a re f a i r l y un i fo rm and do not show 4 -3 any g r a d i e n t s . The maximum va lue o f -2 .17 X 10 e rgs cm J i s found i n two pa tches , one i n the Nor the rn r e g i o n and one i n the Southern r e g i o n 4 -3 w i t h ano ther h i g h va lue o f -2 .31 X 10 e rgs cm J i n the e a s t e r n s i d e of the San Juan r e g i o n . P o t e n t i a l energy d e n s i t i e s have i n c r e a s e d over most of the San Juan r e g i o n and i n the Southern r e g i o n . The patchy d i s t r i b u -t i o n of p o t e n t i a l energy d e n s i t i e s may be due t o l o c a l wind m i x i n g but does not seem t o be c o r r e l a t e d w i t h f r e s h water r u n o f f (as i n d i c a t e d by the average s a l i n i t y d i s t r i b u t i o n , F i g u r e 1 9 b ) . I n August (F igu re 40c) 47 there exists a rough north to south gradient of potential energy density with isopleths usually running across the strait from east to west* En-ergy densities are low at the extreme northern end of the strait (cor-responding to larger values of sigma-t and salinity, Figure 65c) then increase to the greatest values in the strait, -2*04 X 10 ergs cm , in the Northern region. Energy densities decrease southwards from typical 4 - 3 4 values of -2.4 X 10 ergs cm J in the Northern region to -2.67 X 10 -3 ergs cm in the Central region of the strait. There is a band of higher potential energy densities in the Southern region with a value of -2.58 4 -3 X 10 ergs cm but then the energy densities decrease southwards to the 4 -3 minimum value of -2.95 X 10 ergs cm J in the San Juan region, values are higher along the eastern side of the San Juan region where the den-sity is somewhat lower. In November (Figure 40d) as in February the high-est energy densities are near Comox in the Northern region and Boundary 4 -3 Bay in the Southern region with values of -2.13 X 10 ergs cm J . Most of the Northern and Central regions have fairly unifrom energy density dis-4 -3 tributions with a typical value of -2.61 X 10 ergs cm decreasing as usual southwards to the minimum value. Although values of E can not be P directly compared with each other since the sigma-t (and salinity) dis-tribution is not horizontally uniform, the presence of maxima at Comox and Boundary Bay which were present in May and partially present in Feb-ruary and August seem to indicate these are local areas where mixing takes place. Layer 2} 25 m - 50 ms Figure 45 shows the average potential ener-gy due to sigma-t for layer 2 graphed for the representative months. En-ergies in the Southern region decrease from February to May, increase from May to August then decrese from August to November. The potential energies for the Northern, Central and San Juan regions of the Strait of 48 Georgia a l l show a decrease from February to May then an increase from May to November. In a l l cases the changes in potential energy are rela-tively small. In February (Figure 41a) the distributions of the potential ener-gy density closely follow those of sigma-t and salinity (Figure 20a) un-like layer 1. This would indicate that the vertical distribution of sig-raa-t with depth in layer 2 did not vary greatly from the average sigma-t. Lower values of E^ correspond with higher values of sigma-t as stated above. There is a gradient of potential energy density running east to west in the Northern and Central regions and north to south in the Southern and San Juan regions of the strait. In the Northern and Central regions, values of potential energy density are lower along the eastern 4 -3 side of the strait with typical values of -2.8 X 10 ergs cm J to -2.82 4 -3 X 10 ergs cm and higher along the western side with a maximum value 4 -3 of -2.74 X 10 ergs cm . Potential energy densities decrease southwards 4 -3 in the Southern and San Juan regions from -2.78 X 10 ergs cm in the 4 -3 northern part to -2.89 X 10 ergs cm ^  at the southern end and values are slightly higher along the eastern side in the San Juan region. The same pattern persists in May (Figure 41b) with an east to west potential energy density gradient in the Northern and Central regions and a north to south gradient in the southern strait. Values of potential energy density are lower than those of February throughout the Strait of Geor-4 -3 gia with the lowest values of -2.84 X 10 ergs cm along the eastern side of the Northern and Central regions and the minimum value of -2.94 -3 ergs cm in the southern part of the San Juan region. The distribution of potential energy density in August (Figure 41c) closely follows that of salinity (Figure 20c) for layer 2. As in May the lower values of po-tential energy density are along the eastern side of the Northern and 49 Central regions of the strait and along the western side of the San Juan 4 -3 region with the lowest value of -2.96 X 10 ergs cm J at the southern end of the strait . In the Northern and Central regions there is an east to west gradient of potential energy density while in the San Juan re-ion the gradient is from the south to the north. There is a band of higher potential energy densities in the Southern region causing a •sad-dle* in the contour lines. Potential energy densities are generally higher throughout the strait than May although energy densities are low-er at the southern end of the strait . In November (Figure 41d) areas of higher energy density have appeared along the western side of the strait 4 in the Northern and Central regions with a maximum value of -2.7 X 10 -3 ergs cm # There is s t i l l an east to west potential energy density gra-dient in those regions. As before the gradient of potential energy den-sity changes from east to west to north to south in the Southern and San 4 -3 Juan regions with the minimum value of -2.93 X 10 ergs cm J at the southern end. Layer 7$ 150 m - 175 m« The average potential energy per grid compartment for each region of the strait is shown in Figure 46. The po-tential energies for the Southern and San Juan regions show a similar seasonal patternj a decrease from February to May, l i t t l e change from May to August then an increase from August to November (data were not a-valiable for the Southern region in November). This pattern reflects the changes in salinity (Figure 25) with an Increase in salinity leading to a decrease in the potential energy. The potential energy in the Northern region shows a different pattern than the Southern and San Juan regions, increasing from February to May, decreasing from May to August and show-ing l i t t l e change from August to November. As in the Southern and San Juan regions the variations of potential energy in the Northern region 50 show an inverse relationship to the variations of the average salinity (and density) for that region. The average potential energy for the Cen-tral region also had an inverse relationship to the average salinity, showing a slight decline in energy from February to November. In February (Figure 42a) the highest potential energy densities 4 are in the Southern region with the maximum value of -2.86 X 10 ergs _3 cm J decreasing towards the north and south of that region. Unlike the upper layers potential energy densities are slightly higher along the eastern side of the Northern and Central regions, decreasing slightly towards the western side of the strait. The potential energy densities show more of an east to west gradient in the Northern and Central re-gions than the average salinities (Figure 21a). In the Southern and San Juan regions of the strait potential energy densities closely follow the same distribution of salinity. Potential energy densities in May (Figure 42b) are very uniform in the Northern and Central regions with values of 4 - 3 4 - 3 -2.93 X 10 ergs cm J increasing slightly to -2.91 X 10 ergs cm at the northern end of the strait. There is a strong north to south gradi-ent of potential energy density ln the Southern and San Juan regions 4 -3 with the potential energy density decreasing from -2.93 X 10 ergs cm ' 4 -3 in the Southern region to the minimum of -3.03 X 10 ergs cm J at the southern end of the San Juan region. Potential energy densities remain fairly uniform in the Northern and Central regions by August (Figure 4 — 3 42c) with values near -2.94 X 10 ergs cm . The maximum energy densi-ties are in the southern part of the Central region with values up to 4 -3 -2.9 X 10 ergs cm . Values decrease southwards to the minimum value of 4 -3 -3.05 X 10 ergs cm J at the southern end of the San Juan region. In No-vember (Figure 42d) the distribution of potential energy density is sim-ilar to the one of salinity (Figure 2ld). Values are slightly higher in 51 the North r e g i o n than i n the C e n t r a l r e g i o n , then i n c rea se t o the m a x i -mum p o t e n t i a l energy d e n s i t y i n the Southern r e g i o n . There i s a s t r ong no r th t o south p o t e n t i a l energy d e n s i t y g r ad i en t i n the San Juan r e g i o n L ..3 w i t h va lues dec rea s i ng southwards from -2.91 X 10 e rgs cm v t o -2.96 X 4 -3 10 ergs cm . Layer 95 200 m - 225 F i gu re 47 shows the average p o t e n t i a l e n -ergy due t o s igma-t f o r the reg ions o f the S t r a i t o f Georg ia graphed f o r the f o u r r e p r e s e n t a t i v e months. Data were not a v a i l a b l e f o r the Southern r e g i o n i n February . The p o t e n t i a l ene rg ie s o f Layer 9 show an i n ve r s e r e l a t i o n s h i p t o the average s a l i n i t i e s (and d e n s i t i e s ) which have been graphed i n F i gu re 26. Changes i n the p o t e n t i a l energy f o r l a y e r 9 seem t o be due t o changes i n the average d e n s i t y r a t h e r than changes i n the v e r t i c a l d e n s i t y s t r u c t u r e . Whi le v e r t i c a l mix ing might be r e s p o n s i b l e f o r changing the average d e n s i t y i t i s more l i k e l y t h a t a t the depth of l a y e r 9 a d v e c t i o n phenomena a re more important i n de te rm in ing the a v e r -age d e n s i t y d i s t r i b u t i o n which i n t u r n determines the p o t e n t i a l energy d e n s i t y d i s t r i b u t i o n and the average p o t e n t i a l energy i n the l a y e r . I n February (F i gu re 43a) va lues of p o t e n t i a l energy d e n s i t y a l -4 - 3 4 - 3 t e r na te between -2.93 X 10 e rg s cm J and -2.94 X 10 ergs cm i n a patchy d i s t r i b u t i o n over the Northern and C e n t r a l r eg i on s of the s t r a i t . I n the San Juan r e g i o n the re i s a no r t h t o south g r ad i en t where p o t e n t -4 -3 -3 i a l energy d e n s i t i e s decrease from -2.93 X 10 e rgs cm J e rgs cm J i n 4 -3 the no r th o f the r e g i o n t o -2.96 X 10 e rgs cm J a t the southern end. The main f e a t u r e i n May (F i gu re 43a) i s the r e l a t i v e l y l a r g e d i f f e r e n c e 4 i n p o t e n t i a l energy d e n s i t y i n the C e n t r a l r e g i on (-2.94 X 10 e rgs —3 4 —3 cm ) compared w i t h the San Juan r e g i o n (-3.02 X 10 e rgs cm J ) » Mean va lues of p o t e n t i a l energy d e n s i t y have not changed by August ( F i gu re 43c) over the Northern and C e n t r a l r eg i on s but have decreased somewhat 4 -3 In the San Juan region to a minimum of -3.07 X 10 ergs cm J . There is a north to south potential energy density gradient in the San Juan region but unlike February or Kay values increase towards the south instead of 4 - 3 / decreasing reaching a value of -3.04 X 10 ergs cm . In November (Fig-ure 43d) potential energy densities in the San Juan region have increas-4 -3 ed to -2.98 X 10 ergs cm . Potential energy densities have decreased slightly in the Northern and Central regions with a mean value of -2.95 4 -3 X 10 ergs cm . There are no obvious gradients of potential energy den-sity in those regions. (b) Mixing Energy Density If a water column was mixed to homogeneity its density would be Xi 5 m 7 the depth-averaged density, J5 , of that column given by where z^  and z^ would be the bottom and top of the column respectively. The gravitational potential energy per unit volume of the homogeneous column would be ^ If = 7~^, f f^(t-2x)clz 5.8 and would be the maximum potential energy possible for the column. The difference between the maximum potential energy density and the observed potential energy density was defined in section 3 as the mixing energy density, E , given by 5.9 where ^ is defined by equation 5.7 and ^(z) is the observed vertical density distribution. E^ is a measure of the departure from a totally 53 mixed s t a t e o r t o s t a t e i t s l i g h t l y d i f f e r e n t l y , a measure o f the energy needed t o mix the column t o homogeneity. The depth-averaged d e n s i t y , can be expressed i n terms of s i g -ma-t ass where cr^ i s the depth-averaged s i gma- t . Equat ion 5*10 f o l l o w s d i r e c t l y from equat ions 5»4 and 5*7• Us ing s igma-t and the average s i gma- t , equa-t i o n 5*9 reduces to» , -3. ^ 1 2 - 2 / 1 + ^ M * / d Z 5 . U 7 A couple of examples can h e l p i l l u s t r a t e the d i f f e r e n c e between Ep and E m . F i r s t , c o n s i d e r a l a y e r w i t h a un i form g r ad i en t of d e n s i t y w i th ,depth so t h a t there i s a change o f one u n i t of s igma-t over the l a y e r ; t h a t i s z K - °z ~ ^  The average s igma-t of the l a y e r i s (see equat ion 3*5)« and the p o t e n t i a l energy d e n s i t y can be c a l c u l a t e d ( n e g l e c t i n g changes i n g) from equat ion 5»6 t o be: - ' H P 7. 4 F o r a t y p i c a l va lue of 20.0 f o r cr , E w i l l have a va lue o f -2 .4 X 10 o p ergs cm ^ . The mix ing energy d e n s i t y i s (equat ion 3*6): ip'*} H which i s approx imate ly 204 ergs cm or 0.9$ of the p o t e n t i a l energy d e n s i t y . The mix ing energy d e n s i t y (and a l s o E^) depends upon the exac t form of the s t r a t i f i c a t i o n . F o r another example c o n s i d e r a sudden s tep i n the v e r t i c a l s igma-t d i s t r i b u t i o n a t the depth z =» -H/2 S O t h a t : - H / x f Z ^ + 1 - H f z ± " H / z . The average s igma-t of the l a y e r w i l l be the same a s the f i r s t example, The p o t e n t i a l energy d e n s i t y , E^, i s now: lo'3a H r ^ ' E , - l > * ( < r * ' L ) which f o r a va lue f o r C T q of 20.0 l e ad s t o a va lue of -2.5 X 10 e rgs -3 cm . The mix ing energy d e n s i t y f o r t h i s s tep d i s t r i b u t i o n of i s » F = 3 which has a va lue of 306 ergs cm or 1.2/5 of the p o t e n t i a l energy d e n -s i t y . The mix ing energy d e n s i t i e s w i l l depend more s t r o n g l y upon the d e n s i t y d i s t r i b u t i o n w i t h depth than the p o t e n t i a l energy d e n s i t y . In the above examples changing the d e n s i t y d i s t r i b u t i o n from a cons tant g r ad i en t t o a sudden s tep changed the p o t e n t i a l energy d e n s i t y by k% wh i l e the mix ing energy d e n s i t y changed by 50$. Values o f the mix ing energy d e n s i t y , E m , were computed f o r l a y e r s 1, 2, 7 and 9 f o r the f o u r r e p r e s e n t a t i v e months of February, May, A u -gust and November. A mean va lue of E^ was computed f o r each g r i d com-partment i n each l a y e r and the g r i d s were c o n t o u r - p l o t t e d , F i gu re s 48 55 through 51 show the contour p l o t s i f E^ f o r the ana l yzed l a y e r s . The t o -t a l energy needed t o mix each g r i d compartment t o a cons tant d e n s i t y was computed by t a k i n g the product of the mean mix ing energy d e n s i t y f o r each g r i d compartment and the volume of the compartment. The average mix ing energ ie s per g r i d compartment a r e graphed f o r the reg i on s of the s t r a i t i n F i gu re s 52 through 55* Layer 1; 0 m - 25 m« F i gu re 52 i l l u s t r a t e s the average mix ing e n -ergy per g r i d compartment f o r each r e g i o n f o r l a y e r 1. G e n e r a l l y , the g r e a t e r the va lue of mix ing energy the more the r e g i o n i s s t r a t i f i e d . F re sh water r u n o f f and buoyancy e f f e c t s from hea t i n g and p r e c i p i t a t i o n w i l l i n c rea se the s t r a t i f i c a t i o n (and mix ing energy d e n s i t y ) w h i l e m i x -from winds o r t i d e w i l l tend t o break down the s t r a t i f i c a t i o n and d e -c rease the mix ing ene r g i e s . The C e n t r a l r e g i o n r e c e i v e s the r u n o f f of the F r a s e r R i v e r and has h i ghe r mix ing energ ie s than the o the r r e g i o n s . The mix ing energy f o r the C e n t r a l r e g i o n reaches a peak i n May ( f o r the months s tud ied ) and then d e c l i n e s from May t o November. I n the Northern r e g i o n mix ing ene rg ie s reach a peak i n August and then decrease from A u -gust t o November. The average mix ing ene rg ie s f o r the Southern and San Juan reg ions a r e s m a l l e r than those of the o ther reg i on s because t i d a l m ix ing i n those reg i on s breaks down the s t r a t i f i c a t i o n and l ead s t o s m a l l e r mix ing ene r g i e s . M i x i ng energ ie s f o r both the Southern and San Juan reg i on s i n c rea se from February t o May then decrease s l i g h t l y from May t o November. I n February (F i gu re 48a) the h i ghe s t energy d e n s i t i e s a r e found i n the Northern r e g i o n near J e r v i s I n l e t and i n the C e n t r a l r e g i o n near the F r a s e r R i v e r mouth. The lowest va l ue s a r e i n the Southern and San Juan reg ions and a l ong the western s i de of the Northern r e g i o n i n the northwestern S t r a i t of Geo rg i a . I n the Northern and C e n t r a l r eg i on s the 56 higher mixing energy densities are along the eastern side of the s t r a i t , corresponding to the areas of lower sa l i n i t y (Figure 19a). There i s an area of lower mixing energy densities ( < 106 ergs cm J ) i n Boundary Bay in the Southern region corresponding to an area of high potential energy densities (Figure 40a). In May (Figure 48b) the highest mixing energy-densities are found i n two areas of the Central region with values up to 3 -3 3.6 X 10^ ergs cm J. Generally, i n both the Northern and Central regions mixing energy densities continue to be higher along the eastern side of the s t r a i t . The minimum mixing energy densities are i n the San Juan re--3 glon decreasing to 17 ergs cm i n the southern end, and i n the Northern region along the northwestern side of the s t r a i t . Mixing energy densi-ties are closely correlated with the sigma-t distribution (and s a l i n i t y , Figure 19b) with a low salinity (high stratification) corresponding to a high mixing energy density. In August (Figure 48c) the maximum mixing energy densities are s t i l l i n the Central region but have decreased 3 -3 somewhat from those of May to 2.5 X 10^ ergs cm . Mixing energy densi-ties have increased i n the Northern region from those i n May, with v a l -3 - 3 3 - 3 ues ranging from 1.2 X 10^ ergs cm J up to 1.92 X 10^ ergs cm while i n —3 3 —3 May the range was 756 ergs cm J to 1.0 X 10^ ergs cm . In the Northern and Central regions there i s a definite east to west gradient of mixing energy density with the higher values along the eastern side of the st r a i t . This changes i n the Southern region with the lower mixing energy densities i n the east as well as a band of higher mixing energy densi-ties near Boundary Passage. Mixing energy densities decrease southwards in the San Juan region and are somewhat lower along the eastern side of that region. By November (Figure 48d) mixing energy densities have de-creased i n both the Northern and Central regions but have increased slightly i n the Southern region. The maximum value of mixing energy den-57 3 -3 sity, 2.09 X 10 ergs cm J is found in a patch in the Southern region extending northwards into the Central region which is probably associ-ated with the Fraser River outflow. As in other months the higher mixing energy densities are along the eastern side of the Northern and Central regions and towards the south of the strait in the Southern and San Juan regions. Layer 2; 25 m - 50 m: The average mixing energies for the regions of the strait are shown in Figure 53• The increases in mixing energy for the Southern and San Juan regions between May and August seem to be cor-related with a decrease in the average salinity (Figure 24) for those regions. The total mixing energy per grid compartment for the Central region decreases from February to May (corresponding with an increase in salinity) then increases from May to November. The average mixing energy for the Northern region shows a large Increase from May to August then a decline from August to November. This pattern of mixing energy varia-tions does not seem to be correlated the variations of salinity in layer 2 but rather with the salinity variations of layer 1 (Figure23) although this may be a coincidence. Throughout the Northern and Central regions mixing energies are smaller than those of layer by an order of magnitude. This indicates that most of the stratification is in the upper 25 metres of the strait. In February (Figure 49a) the maximum mixing energy densities are in the Central region (up to 200 ergs cm ^ ) and in the Northern region (up to 160 ergs cm ^ ). Mixing energy densities are higher along the eastern side of the Northern region and in patches in the Central re-gion. The patchy distribution of mixing energy densities extends from the Central region into the Southern and San Juan regions. Unlike layer 1 mixing energy densities decrease slightly towards the southern end of 58 the San Juan r e g i on r a t h e r than i n c r e a s i n g . In May ( F i gu re 49b) the d i s -t r i b u t i o n of m ix ing energy d e n s i t i e s i s q u i t e u n l i k e t h a t of s a l i n i t y ( F i gu re 20b) . The maximum mix ing energy d e n s i t i e s (128 ergs cm J ) a r e found i n patches a l o n g the ea s t e r n s i de of the Northern r e g i o n w i t h a •r idge* of h i gh mix ing energy d e n s i t i e s ex tend ing southeastwards i n t o the C e n t r a l r e g i o n reach ing a va lue of 105 e rgs cm . I n the Northern r e g i o n the h i ghe r mix ing energy d e n s i t i e s a re g e n e r a l l y found a l ong the ea s te rn s i de of the s t r a i t (a l though the minimum va lue i n the s t r a i t , 45 ergs cm""^, i s found i n the no r thea s te rn c o r n e r ) . There i s a band of low mix ing energy d e n s i t i e s runn ing ea s t t o west a c ro s s the s t r a i t no r t h of Texada I s l and w i t h h i ghe r energy d e n s i t i e s t o the no r th and s ou th . I n the C e n t r a l r e g i o n the h i ghes t m ix ing energy d e n s i t i e s a re near the c e n -t e r of the r e g i o n dec rea s i ng towards the western and ea s te rn s i d e s . Most of the C e n t r a l r e g i o n l y i n g southwards from the maximum ' peak ' has v a l --3 ues near 70 ergs cm w i t h s l i g h t l y l ower va lues a l ong the western s i d e . In the Southern r e g i o n the re i s an ea s t t o west mix ing energy d e n s i t y g r ad i en t w i t h the h i ghe r energy d e n s i t i e s a l ong the western s i de d e -c r e a s i n g towards the e a s t . There i s a patch of h i ghe r mix ing energy d e n -—3 s i t i e s (81 ergs cm ) i n the San Juan r e g i o n but i n gene ra l the energy d i s t r i b u t i o n shows a no r th t o south g r a d i e n t . The minimum mix ing energy d e n s i t i e s (9*5 e rg s cm ^) a r e near the c e n t e r of the San Juan r e g i o n and energy d e n s i t i e s a r e h i ghe r a l o n g the ea s te rn s i de r each i n g va lue s of 57 ergs cm 3, i n August (F igure 49c) m ix ing energy d e n s i t i e s have i nc rea sed f o r a l l r eg ions of the s t r a i t (a l though the minimum va lue found i s s m a l l e r than the one found i n May). The maximum mix ing energy d e n s i t y o f _3 620 ergs cm i s found i n a patch a t the no r the rn end of the s t r a i t . A -way from t h a t patch most of the energy d e n s i t i e s i n the Northern r e g i o n -3 _3 l i e between 180 ergs cm and 250 e rgs cm . Most of the C e n t r a l r e g i o n 59 shows l i t t l e v a r i a t i o n w i t h most mix ing energy d e n s i t i e s "being g r e a t e r than 126 ergs cm"^ but l e s s than 180 ergs cm"^. In the Southern r e g i o n there a re a reas of h i gh mix ing energy d e n s i t i e s (>300 ergs cm J ) near Boundary Pass . M i x i ng energy d e n s i t i e s decrease i n the San Juan r e g i o n -3 t o a minimum of 2 e rgs cm i n d i c a t i n g thorough mix ing of the water c o l -umn. In November (F i gu re 49d) m ix ing energy d e n s i t i e s have decreased f o r most of the reg ions a l though energy d e n s i t i e s a re h i ghe r f o r the C e n t r a l r e g i o n . There i s a rough eas t t o west g r ad i en t of mix ing energy d e n s i t y i n the Northern and C e n t r a l r eg i on s w i t h the g r ea t e s t va lues a l ong the ea s te rn s i de of the s t r a i t . I n the Southern r e g i on the h i ghe s t energy d e n s i t i e s a re i n an a rea i n the middle of the s t r a i t dec rea s i ng towards the ea s t and the west. M i x i ng energy d e n s i t i e s decrease southwards i n t o the San Juan r e g i o n reach ing t h e i r minimum va lue a t the southern end of the s t r a i t . Layer 7; 150 m - 175 m» F i gu re 54 i l l u s t r a t e s the average mix ing energ ie s f o r the reg i on s of the s t r a i t . U n l i k e the ene rg ie s of the upper l a y e r s , the mix ing energ ie s f o r l a y e r 7 a r e not c o r r e l a t e d w i t h the mean d e n s i t i e s of the l a y e r ( F i gu re 30). The mix ing energ ie s f o r the Northern and C e n t r a l reg ions seem t o be i n v e r s e l y r e l a t e d ; when mix ing ene rg ie s i n the C e n t r a l r e g i o n i n c rea se those i n the Northern r e g i o n dec rease . M i x i ng energ ie s f o r the C e n t r a l r e g i o n decrease from May t o August wh i l e m ix ing energ ie s f o r the o ther reg i on s i n c r e a s e . The C e n t r a l and Southern r e g i o n mix ing ene rg ie s i n c rea se from August t o November wh i l e those of the Northern and San Juan reg i on s decrease . I n February (F igure 50a) the s m a l l e s t mix ing energy d e n s i t i e s a r e i n the Northern and Southern r e g i o n s . M i x i n g energy d e n s i t i e s a r e below 40 ergs cm over most of the Northern r e g i o n except f o r one a rea i n the _3 southern p a r t where energy d e n s i t i e s a re 48 ergs cm or g r e a t e r . M i x i n g 60 energy d e n s i t i e s a r e g r e a t e r i n the C e n t r a l r e g i o n w i t h one a rea of 72 -3 -3 ergs cm and a patch w i t h va lues g r e a t e r than 84 e rgs cm . Minimum mix ing energy d e n s i t i e s i n the C e n t r a l r e g i o n a r e near 48 e rgs cm which a re g r e a t e r than the maximum energy d e n s i t i e s i n the Northern r e -g i o n . M i x i ng energy d e n s i t i e s reach t h e i r minimum i n the Southern r e g i o n -3 wi th va lues down t o 25 e rgs cm . I n c o n t r a s t t o the upper l a y e r s the maximum mix ing energy d e n s i t i e s a re i n the Southern r e g i o n w i t h va l ue s _3 up t o 146 e rgs cm • M ix ing energy d e n s i t i e s i n the Southern r e g i o n d e -.3 crease northwards t o a va lue of 36 e rgs cm J a t the C e n t r a l r e g i o n . I n May (Figure>50b) m ix i ng energy d e n s i t i e s have i nc rea sed i n the Northern r e g i o n but have decreased i n the o the r r e g i o n s . M i x i ng energy d e n s i t i e s -3 -3 i n the Northern r e g i o n range from 20 ergs cm t o 43 ergs cm w i t h most -3 -3 of the r e g i o n hav ing va lues between 35 ergs cm and 40 e rgs cm • There i s a no r th t o south g r a d i e n t of m ix ing energy d e n s i t y i n the C e n t r a l r e -_3 g i on w i t h va lues i n c r e a s i n g southwards from 43 ergs cm t o a maximum of -3 -3 82 ergs cm J then dec rea s i ng t o va lue s near 50 ergs cm . M i x i ng energy „3 d e n s i t i e s i n the Southern r e g i o n decrease southwards from 66 e rgs cm J -3 t o the minimum .value i n the s t r a i t , 20 ergs cm . Energy d e n s i t i e s i n _3 the San Juan r e g i o n va ry from a h i gh of 7^ e rgs cm J i n the no r the rn -3 pa r t of the r e g i o n t o a minimum of 35 e rg s cm i n the c e n t e r . M i x i ng energy d e n s i t i e s r i s e southwards i n the San Juan r e g i o n from the minimum i n the c e n t e r t o the maximum of 97 ergs cm"^ , i n August ( F i gu re 50c) mix i ng energy d e n s i t i e s have decreased over most of the western s i d e of .3 the Northern r e g i o n t o 34 e rgs cm but have i nc rea sed i n the e a s t e r n -3 s i de t o over 90 e rgs cm . M ix ing energy d e n s i t i e s show l i t t l e v a r i a t i o n -3 i n the C e n t r a l r e g i o n of the s t r a i t w i t h va lue s near 34 e rg s cm i n -c r e a s i n g towards the south t o 60 e rgs cm J . M ix ing energy d e n s i t i e s i n -_3 crease t o a maximum of 146 e rgs cm J i n the Southern r e g i o n dec rea s i ng 61 t o 60 ergs cm J a t the southern p a r t of the r e g i o n . The d i s t r i b u t i o n of m ix ing energy d e n s i t i e s i n the San Juan r e g i o n v a r i e s c on s i de r ab l y f rom the no r th of the r e g i o n t o the sou th . Values va ry from a maximum of 230 -3 ergs cm i n the no r the rn p a r t of the r e g i o n t o a minimum of l e s s than —3 —3 30 ergs cm J i n the c e n t e r then r i s e t o another maximum of 286 e rgs cm a t the southern end. I n November (F i gu re 50d) m ix ing energy d e n s i t i e s a r e f a i r l y un i fo rm i n the Northern r e g i o n w i t h most va lues near 30 e rgs -3 cm . M ix ing energy d e n s i t i e s i n c rea se southwards i n the C e n t r a l r e g i o n -3 -3 from 30 e rgs cm ' i n the no r the rn p a r t of the r e g i o n t o 78 e rgs cm J a t the southern end. The no r t h t o south g r a d i e n t of m ix ing energy d e n s i t y cont inues i n t o the Southern r e g i o n w i t h energy d e n s i t i e s i n c r e a s i n g -3 .3 southwards from 78 ergs cm J t o 200 e rgs cm . I n the San Juan r e g i o n the mix ing energy d e n s i t y g r ad i en t r eve r se s w i t h va l ue s dec rea s i ng i n -s tead of i n c r e a s i n g . The maximum mix ing energy d e n s i t y of the s t r a i t , _3 248 ergs cm , i s a t the no r the rn end of the San Juan r e g i o n and mix ing energy d e n s i t i e s decrease r a p i d l y towards the south w i t h the minimum _3 va lue of 6 e rgs cm J a t the southern end. l a y e r 9} 200 m - 225 m» The average mix ing energ ie s f o r the Nor thern , C e n t r a l and San Juan reg ions a r e graphed i n F i g u r e 55* M i x i n g energ ie s l n l a y e r 9 do not seem t o be c o r r e l a t e d w i t h the energ ie s i n l a y e r 7 ( F i gu re 5*0 o r the average d e n s i t i e s f o r l a y e r 9 ( F i gu re 31)• The mix ing ene rg ie s f o r the Northern and San Juan reg i on s seem t o be i n -v e r s e l y r e l a t e d , ;<with the energy f o r one r e g i o n i n c r e a s i n g wh i l e the e n -ergy f o r the o ther r e g i o n dec reases . M i x i ng energ ie s f o r the San Juan r e g i o n i nc rea se from February t o August then decrease from August t o No-vember wh i l e the energ ie s f o r the Northern r e g i o n show the oppos i te p a t -t e r n . M i x i n g energ ie s f o r the C e n t r a l r e g i o n decrease between February and May but then show a s l i g h t i nc rea se from May t o August then a s l i g h t 62 decrease between August and November. In February (F i gu re 51a) the minimum and maximum mix ing energy d e n s i t i e s a re both i n the Northern r e g i o n . The minimum mix ing energy „3 d e n s i t y of 6 ergs cm J i s found a t the no r the rn end of the s t r a i t and -3 energy d e n s i t i e s i n c rea se t o over 30 e rgs cm J near the western s i de of Texada I s l a n d . The maximum mix ing energy d e n s i t i e s a r e i n the b a s i n a -l ong the ea s te rn s i de of the Northern r e g i o n ( l n the a r ea of minimum ox -ygen concen t r a t i on s ) w i t h va lues r each i n g 89 ergs cm . M i x i ng energy d e n s i t i e s decrease southwards a l o n g the ea s t e r n s i de of the Northern r e --3 g i o n t o va lues near 50 e rgs cm J and cont inue t o decrease i n the C e n t r a l -3 r e g i o n t o minimum va lues near 22 ergs cm i n two a r e a s , one a t the western s i de of the s t r a i t and one a t the ea s t e r n s i d e . M i x i ng energy d e n s i t i e s i n c rea se towards the southern end of the C e n t r a l r e g i o n t o a -3 h i gh va lue near 50 e rg s cm . M i x i ng energy d e n s i t i e s a re l ower i n the San Juan r e g i o n , 15 e rg s cm o r l e s s . I n May (F i gu re 51b) mix ing energy d e n s i t i e s have decreased over the Northern and C e n t r a l r e g i on s but have i nc reased i n the San Juan r e g i o n . There i s a l a r g e d i f f e r e n c e i n energy d e n s i t i e s between the western and ea s t e r n ba s i n s of the Northern r e g i o n . The minimum mix ing energy d e n s i t y of 6 ergs cm J i s a t the no r the rn end o f the Northern r e g i o n and v a l ue s i n c rea se towards the southeas t , up t o _3 24 ergs cm a t the western s i de of Texada I s l a nd which separates the two bas in s of the r e g i o n . I n the ea s t e r n h a l f of the Northern r e g i o n the g r ad i en t of m i x i ng energy d e n s i t y goes the oppos i te way w i t h va lue s i n --3 —3 c r e a s i n g northwards from 24 ergs cm J t o a maximum of 43 e rgs cm J a t the no r the rn end of the b a s i n . The d i s t r i b u t i o n of m ix i ng energy d e n s i -t i e s i n the C e n t r a l r e g i o n c o n s i s t s of •peaks* of h i gh energy d e n s i t i e s separated by • v a l l e y s * of low energy d e n s i t y . There a r e two peaks w i t h va lues of Jk- ergs cm , one a t the nor thern end of the r e g i o n and one 63 near the c e n t e r , separated by a band of lower energy d e n s i t i e s (down t o 15 e rgs cm~^). There i s another a rea of h i gh m ix ing energy d e n s i t i e s ( a -pprox imate ly 43 e rgs cm"^) a t the southern end of the r e g i o n . There i s a s t r ong no r th t o south g r ad i en t of m ix i ng energy d e n s i t y i n the San Juan -3 r e g i on w i t h va lues I n c rea s i n g southwards from 42 e rgs cm J t o the m a x i --3 mum i n the s t r a i t of 97 e rgs cm J a t the southern end. M i x i n g energy d e n s i t i e s have i nc rea sed from May i n the San Juan r e g i o n by August ( F i g -u re 51c) but have g e n e r a l l y decreased over the r e s t of the s t r a i t . I n the Northern r e g i o n energy d e n s i t i e s i n c rea se southwards from the m i n i -—3 —3 mum va lue o f 6 ergs cm J t o 26 e rgs cm • Most of the C e n t r a l r e g i o n has -3 —3 va lues near 26 e rgs cm J except f o r an a rea of 46 e rg s cm J a t the southern end of the r e g i o n . The San Juan r e g i o n cont inues t o have a s t r ong no r t h t o south g r ad i en t of m ix i ng energy d e n s i t y w i t h va lues —3 —3 rang ing from 46 e rgs cm t o the maximum i n the s t r a i t , 206 e rgs cm , a t the southern end. The d i s t r i b u t i o n of m ix ing energy d e n s i t i e s has changed a g a i n by November (F i gu re 5id) f o r most of the s t r a i t . I n the Northern r e g i o n energy d e n s i t i e s a r e h i ghe r i n the e a s t e r n h a l f than i n the western h a l f where va lues range from the minimum of 6 e rgs cm J a t the nor thern end t o 15 e rgs cm J near Texada I s l a n d . I n the ea s te rn b a -s i n of the Northern r e g i o n mix ing energy d e n s i t i e s i n c rea se towards the -3 -3 ea s t from 30 ergs cm J t o 40 ergs cm . I n the C e n t r a l r e g i o n the d l s --3 t r i b u t l o n of energy d e n s i t i e s c o n s i s t s of a peak of 40 e rg s cm near -3 the c e n t e r of the r e g i o n w i t h va lue s dec rea s i ng t o 14 e rgs cm J towards -3 the west and 23 e rgs cm J towards the sou th . I n the San Juan r e g i o n —3 there i s an a rea of low mix ing energy d e n s i t y (30 e rgs cm J ) i n the c e n -t e r of the r e g i o n w i t h va lues i n c r e a s i n g towards the no r t h t o 57 ergs -3 -3 cm and i n c r e a s i n g towards the south t o 91 e rgs cm . 64 (c) Two-Layer P o t e n t i a l Energy Dens i t y As a way of q u a n t i t a t i v e l y e v a l u a t i n g the s t a t e of m ix ing and e s -t i m a t i n g changes i n m ix ing due t o changes of f r e s h water c on ten t , the p o t e n t i a l energy d e n s i t y was computed f o r the water column d i v i d e d i n t o two s u b - l a y e r s , one of f r e s h water and one of s a l t water . The r e l a t i v e t h i c kne s se s of the f r e s h and s a l t l a y e r s w i l l depend upon the base s a l -i n i t y of the s a l t water l a y e r . As d i s cu s sed i n s e c t i o n 3«3 the base s a l -i n i t y was chosen t o be 33*8%,, the average s a l i n i t y of the deeper waters a t the seaward end of the S t r a i t of Juan de Fuca . I n o rder t o conserve s a l t , the t h i c kne s s of the s a l t water l a y e r , L , i s g i ven by: s z„ i 5.12 where S ( z ) i s the v e r t i c a l s a l i n i t y d i s t r i b u t i o n of the t o t a l l a y e r and z^ and Zg a r e the bottom and t op of the t o t a l l a y e r r e s p e c t i v e l y ( the t o t a l l a y e r of i n t e r e s t c on t a i n s both the s a l t water and f r e s h water s u b - l a y e r s ) . S ince the depth-averaged s a l i n i t y , S, i s g i ven by : 5 = vz, / Si-£)Xz 2. equat ion 5*12 can be r e w r i t t e n a s _ 5.13 5.14 where H • z^ ~ * 25 metres . The f r e s h water t h i c k n e s s , L^., w i l l then be : 5.15 The f r e s h water t h i c kne s s depends d i r e c t l y upon the average s a l -i n i t y of the l a y e r . S ince a l a y e r of f r e s h water over a l a y e r of water 65 w i t h oceanic s a l i n i t y would r ep re sen t ab so l u te s t r a t i f i c a t i o n the p o -t e n t i a l energy d e n s i t y of such a system would be the minimum p o s s i b l e ; any mix ing of the l a y e r s cou l d on ly r a i s e the p o t e n t i a l energy of the water column. The d i f f e r e n c e between the observed p o t e n t i a l energy d e n -s i t y and the t w o - l a y e r p o t e n t i a l energy d e n s i t y w i l l r e f l e c t changes i n the average d e n s i t y of the l a y e r . Whi le the mix ing energy d e n s i t y d e -pends s t r o n g l y upon the s t r a t i f i c a t i o n of the l a y e r the t w o - l a y e r po -t e n t i a l energy d e n s i t y does no t ; i t i s a f u n c t i o n of the average s a l i n -i t y and temperature of the l a y e r which determine the t h i c kne s se s and d e n s i t i e s of the f r e s h and s a l t water s u b - l a y e r s . The t w o - l a y e r p o t e n t i a l energy d e n s i t i e s were c a l c u l a t e d f o r each s t a t i o n by f i r s t c a l c u l a t i n g the t h i c kne s se s of the f r e s h and s a l t water l a y e r s u s i n g equat ions 5»1^ and 5»15» S i gma - t ' s were computed from the UNESCO fo rmula f o r the 3 3 s a l t water l a y e r and the 0%„ f r e s h water l a y e r u s i n g the average temperature f o r the e n t i r e l a y e r . F o r a l a y e r w i t h the bottom a t z = Z j and the t op a t z «• Z g , which has been s u b - d i -v i ded i n t o a s a l t water s u b - l a y e r w i t h a t h i c k n e s s of L g and s i gma- t , and a f r e s h water l a y e r w i t h t h i c k n e s s L .^ and s i gma- t , cr^, so t h a t Zg - z^ = L g + L^, the p o t e n t i a l energy per u n i t volume from equat ion Two- layer p o t e n t i a l energy d e n s i t i e s were computed f o r l a y e r s 1, 2, 7 and 9 f o r the r e p r e s e n t a t i v e months. Mean va lue s were computed f o r each g r i d compartment and the average t w o - l a y e r p o t e n t i a l energ ie s pe r g r i d compartment f o r each r e g i o n were c a l c u l a t e d . The average t w o - l a y e r 66 p o t e n t i a l energ ie s f o r the reg i on s of the s t r a i t a r e graphed i n F i g u r e s 56 through 59• The f o l l o w i n g s e c t i o n s d e s c r i b e the main f e a t u r e s f o r the average t w o - l a y e r ene rg ie s i n the S t r a i t of Geo rg i a . Layer 1; 0 m - 25 m: F i gu re 56 i l l u s t r a t e s the average t w o - l a y e r p o t e n t i a l energ ie s f o r l a y e r 1 graphed f o r the f o u r r e p r e s e n t a t i v e months. The seasona l v a r i a t i o n s f o r the No r the rn , C e n t r a l and San Juan reg ions a re s i m i l a r t o those of the observed p o t e n t i a l energ ie s ( F i gu re 44). The t w o - l a y e r energ ie s f o r the San Juan r e g i on show l i t t l e v a r i a -t i o n , i n c r e a s i n g s l i g h t l y from February t o August then dec rea s i ng s l i g h t -l y from August t o November. The mean va lue of the t w o - l a y e r p o t e n t i a l 10 energy i n the San Juan r e g i o n , -682 X 10 J o u l e s , i s c l o s e i n va lue t o the observed p o t e n t i a l energy, -619 X 10 10 J o u l e s . Two- layer p o t e n t i a l energ ie s f o r the Northern.and C e n t r a l reg ions a r e approx imate l y 70 X 10 10 J ou l e s l e s s than the observed ene r g i e s . Two- layer ene rg ie s f o r the Northern and C e n t r a l r eg i on s i n c rea se between February and August and decrease between August and November, a p a t t e r n s i m i l a r t o t h a t of the observed p o t e n t i a l ene rg ie s i n the Northern r e g i o n . I n c o n t r a s t t o the other r e g i o n s , the v a r i a t i o n s of the t w o - l a y e r p o t e n t i a l ene rg ie s and of the observed p o t e n t i a l energ ie s of the Southern r e g i o n va ry i n v e r s e l y . Two- layer energ ie s f o r the Southern r e g i o n show the same p a t t e r n a s the other r e g i o n s ; an i n c rea se from February t o August and a decrease from August t o November, wh i l e the observed p o t e n t i a l ene rg ie s show the oppo-s i t e p a t t e r n . Layer 2; 25 m - 50 m» Average t w o - l a y e r p o t e n t i a l ene rg ie s f o r the s t r a i t i n l a y e r 2 a r e graphed i n F i g u r e 57• The t w o - l a y e r energ ie s f o r the Nor thern , C e n t r a l and San Juan reg i on s a l l va ry i n a way s i m i l a r t o the observed p o t e n t i a l energ ie s (F i gu re 45); no r e g i on shows any l a r g e v a r i a t i o n s . Two- layer energ ie s f o r the Nor thern , C e n t r a l and San 67 Juan r e g i o n s show a n i nc r ea se from February t o August and a decrease from August t o November, s i m i l a r t o the v a r i a t i o n s o f l a y e r 1 ( F i g u r e 56). Two- laye r ene rg ie s f o r the Southern r e g i o n show a s i m i l a r p a t t e r n t o t h a t o f the o ther r e g i o n s w h i l e the observed p o t e n t i a l ene rg ie s show the oppos i te p a t t e r n (F igu re 45)» d e c r e a s i n g from February t o August then i n c r e a s i n g from Ausus t t o November. L a y e r 7; 150 m - 175 m: F i g u r e 58 shows the average two-Layer p o t e n t i a l ene rg ie s f o r l a y e r 7» Ene rg ie s f o r the Southern and San Juan r eg ions show very l i t t l e v a r i a t i o n between months a l t h o u g h the San Juan r e g i o n shows a s l i g h t i nc r ea se i n t w o - l a y e r p o t e n t i a l energy between February and November. There does not seem t o be any c o r r e l a t i o n between the t w o - l a y e r ene rg ie s and the observed p o t e n t i a l ene rg i e s (F igu re 46) f o r the Southern and San Juan r e g i o n s . Two-Layer ene rg ies f o r the C e n -t r a l r e g i o n show an i nc r ea se between February and November co r re spond ing w i t h a decrease i n observed p o t e n t i a l ene rg ie s w h i l e t w o - l a y e r ene rg i e s f o r the Nor thern r e g i o n show a decrease between February and May and an inc rease from August t o November. L a y e r 9j 200 m - 225 m: F i g u r e 59 i l l u s t r a t e s the average two-l a y e r ene rg i e s f o r l a y e r 9« The t w o - l a y e r ene rg i e s f o r the San Juan r e -g i o n show a s i m i l a r p a t t e r n t o t h a t o f Layer 7 (F igu re 58) w i t h a s l i g h t i nc rease i n va lue between February and November, a d i f f e r e n t p a t t e r n than t h a t o f the observed p o t e n t i a l ene rg ie s (F igu re 47). Two-Layer p o t e n t i a l ene rg ie s f o r the Nor the rn n and C e n t r a l r e g i o n s show a s i m i l a r p a t t e r n ; a s l i g h t decrease from February t o May then a s l i g h t i n c r e a s e from May t o November. T h i s seasona l p a t t e r n i s a l s o s i m i l a r t o the observed p o t e n t -i a l e n e r g i e s . I n a l l cases the t w o - l a y e r ene rg i e s a r e s m a l l e r than the observed p o t e n t i a l e n e r g i e s . 68 (d) Heat Content E s t imates of the average heat content of the r e p r e s e n t a t i v e l a y -e r s were made a s an i n d i c a t o r of m ix i ng (and advec t i on ) i n the S t r a i t of Geo rg i a , F o r a g i ven l a y e r , the t o t a l heat content (above a r e fe rence temperature of 0° C) was computed f o r each g r i d compartment. The heat content of the n * th g r i d compartment i s g i ven by : H, = C r f - X v h 5.17 where C^ i s the s p e c i f i c heat o f sea water , ^ n i s the mean dep th - a ve r -aged d e n s i t y f o r the g r i d compartment, T r i s the mean temperature o f the g r i d compartment and V i s the g r i d compartment volume. Values of the s p e c i f i c heat o f sea water were taken from Mamayev (1975)» the s p e c i f i c heat depending upon the temperature and s a l i n i t y . The average heat c o n -t e n t above 0° C f o r each r e g i on was computed and i s l i s t e d i n Table I I . Layer l j 0 m - 25 m: The average heat content of l a y e r i s a f f e c t -ed s t r o n g l y by the t o t a l i n s o l a t i o n r e ce i v ed by the S t r a i t of Geo rg i a . A l l r eg ions show an i nc rea se i n heat content from February through May t o August c o i n c i d i n g w i t h the i nc rea sed s o l a r r a d i a t i o n and a decrease i n heat content between August and November as s o l a r r a d i a t i o n d e c r e a s -e s . The Northern and C e n t r a l reg ions c o n t a i n more heat than the Southern o r San Juan reg i on s d u r i n g May and August. Th i s c ou l d be due t o the g r e a t e r s t r a t i f i c a t i o n i n the Northern and C e n t r a l r eg i on s a l l o w i n g the upper l a y e r t o reach h i ghe r temperatures than the Southern and San Juan reg i on s where t i d a l m ix ing can mix the warm su r face water w i t h c o o l e r deep water . Laye r 2; 25 m - 50 m: Much of the s o l a r r a d i a t i o n has a l r e a d y been absorbed before i t reaches l a y e r 2 and temperatures i n the l a y e r a re g e n e r a l l y l ower than those of l a y e r 1 ( F i gu re s 15 and 16). One e x -HEAT CONTENT (X 10 1 j) ' San Juan Region  Month Layer 1 Layer 2 Layer 7 Layer 9 H AH H AH H AH H AH Feb 6.4 6.4 6.6 6.6 +29% +25% +15% +12% May 8.3 8.1 7.5 7.4 +16% +11% +7% +8% Aug 9.6 9.0 8.0 8.0 -13% -7% +2% +1% Nov 8.4 8.4 8,2 8.1 Southern Region Month Layer 1 Layer 2 Layer 7 Layer 9 H AH H AH H AH H AH Feb 6.3 6.4 6.5 — +39% +23% +15% May 8.8 7.9 7.5 7.4 +17% +17% +9% +3% Aug 10.2 8.5 8.2 7.6 -18% -8% 0 +6% Nov 8.4 7.8 8.2 8.1 Central Region  Month Layer i Layer 2 Layer 7 Layer 9 H 4H H AH H H AH Feb 6.0 6.6 7.3 7.7 +57% +12% +2% -3% May 9.5 7.4 7.5 7.5 +12% +15% +6% +h% Aug 10.6 8.5 7.9 7.8 -19% 0 +k% +3% Nov 8.6 8.«i 8.2 8.0 Northern Region Month Layer 1 Layer 2 Layer 7 Layer 9 H AH H AH H AH H AH Feb 6.0 +18% 6.5 +21?? 7.8 -5% 7.9 -k-% May 10.0 +19% 7.9 +11% 7.4 +2% 7.6 0 Aug 12.0 8.8 7.6 7.6 -30% -5% +6% +3% Nov 8.4 8,3 8.0 ? T 8 Table II Average heat contents (and per cent variations) i n joules over a reference temperature of 0° C, 70 ception i s i n February when cooling of layer 1 results ln a smaller heat content than layer 2 for the Northern and Central regions. The heat con-tent of a l l regions shows an increase between February and August but the heat content of the Northern and Central regions i s appreciably smaller than that of layer 1 i n May and August. In November, heat con-tents of a l l regions match those of layer 1 Indicating that the two sur-layers are well mixed at that time. Heat contents for the Southern and San Juan regions i n layer 2 are close i n value to those of layer 1 ( a l -though they are slightly smaller i n May and August) indicating that t i -dal mixing keeps these regions well mixed throughout the year. Layer 7t 150 m - 175 m: Heat contents of a l l regions are gener-a l l y smaller than those of the surface layers i n May and August and l a r -ger i n February and November. The heat content of the San Juan region shows an increase for a l l months from February to November while the Southern region shows increases of heat content between February and Au-gust and no change between August and November. The heat contents of the Northern and Central regions converge from February to a similar value in May. The heat content of the Northern region decreased from February to May while that of the Central region Increased during the same peri-od. The heat contents of both regions showed a gradual increase between May and November. The pattern of heat content variations for the north-ern s t r a i t suggests that an intrusion of a different water mass took place between February and May (increasing the heat contents of a l l re-gions except the Northern region) and that another intrusion occurred between August and November (causing the increases i n heat content i n the Northern and Central regions). The 1968 data seem to be similar to the 1931 data used by Tully and Dodimead (1957) who noted that there seemed to be a three month lag i n the heat content of the deep water of 71 the Strait of Georgia compared to the heat content of the surface layer. Layer 9? 200 m - 225 The variations i n the heat content of layer 9 are similar to those of layer 7 for most of the regions. The heat content of the San Juan region shows a slight increase from Febru-ary to November but the difference i s very small, less than any of the other layers. The heat contents for the Northern,and Central regions show the same patterns a slight decrease between February and May and a gradual increase between May and November, a similar pattern to that of the Northern region i n layer 7. (e) Salt Contents Besides the average heat content of the Strait of Georgia, the average salt content of the s t r a i t was computed for layers 1, 2, 7 and 9 for the representative months (Table I I I ) . The salt content of the d i f f -erent regions of the s t r a i t w i l l depend upon sources of fresh water as well as upon the processes of mixing, advection and diffusion. The total salt content was estimated for each grid compartment u-sing the mean values of density and salini t y for that compartment. For the n'th grid compartment i n a layer the total salt content, Sa n» i s es-timated by: 5.18 where ^ n and S^ are the average density and salini t y of the grid com-partment and i s the volume of the compartment. Layer l j 0 m - 25 m« Table III illustrates the average salt con-tent for the regions of the s t r a i t . The Southern and San Juan regions do not show any relatively large variations i n the total salt content from month to month. The salt contents of the Southern and San Juan regions SALT CONTENT (X 1 0 1 U KG) San Juan Region Month Layer 1 Layer 2 Layer 7 Layer 9 S _AS S JiS_ S AS S AS Feb 6.58 6.65 6.91 6.92 +2A% +2,9% +3,0% +3*5% May 6.74 6.84 7.12 7.16 -1,3% -0,1% +0,1% +0,1% Aug 6.65 6.83 7.13 7.17 +0,6% -0,9% -2,0% -1,7% Nov 6.69 6.77 6.99 7.05 Southern Region  Month Layer 1 Layer 2 Layer 7 Layer 9 S j4S S ASn S AS S_ AS_ Feb 6.35 6.50 6.70 -0.8?? +1,8% +k,0% May 6.30 6.62 6.97 7.01 -0,8% -0,5% -2,2% +1,V% Aug 6.25 6.59 6.82 7.08 -0,2% 0 +0,3% -1,6% Nov 6.24 6.59 6.84 6.97 Central Region  Month Layer 1 Layer 2 Layer 7 Layer 9 S J\S S jAS S 4S S j i S _ Feb 6.09 6.38 6.75 6.81 -3,k% +2,h% +0,k% 0 May 5.88 6.53 6.78 6.81 +0,5% -0,3% +0,6% +0,k% Aug 5.91 6.5I 6.82 6.84 -0,2% -0,3% +0,3% +0,3% Nov 5.90 6.49 6.84 6.86 Northern Region  Month Layer 1 Layer 2 Layer 7 Layer 9 S _4_S S AS S ^S S 4S_ Feb 6.15 6.32 6.71 6.75 -0,2% +1,9% -0,3% -0,3% May 6.14 6.44 6.69 6.73 -6,8% -1,1% +0,k% +0,3% Aug 5.72 6.37 6.72 6.75 +5,6% 0 +0,3% +0,3% Nov ,6.04 6s22! 6*74 6.77 Table III Average salt contents (and seasonal varia-tions i n per cent) per grid compartment. 73 show small fluctuations but essentially remain at a constant level from February to November. The salt content of the Central region shows a de-crease from February to May matching the increase i n fresh water runoff (Figure 4) then changes very l i t t l e between May and November. The aver-age salt content of the Northern region shows a slight decrease from February to May and then the largest change of any region, decreasing a-ppreciably between May and August. The salt content of the Northern re-gion then increases between August and November to levels near that of May. The low value of the average salt content for the Northern region i n August i s due to the greatly lowered s a l i n i t i e s observed at that time (Figure 23). Layer 2} 25 m - 50 m» Most of the regions show more variations i n their average salt contents than those of layer 1 except for the North-em region. The average salt contents of the Southern and San Juan re-gions increase between February and May then remain at the higher value from May to November (the San Juan region has a slight decrease between August and November and the Southern region declines slightly between May and August). The salt contents for the Northern and Central regions also increase between February and May but then gradually decrease from May to November. The increase may be due to increased estuarine flow and entrainment or higher s a l i n i t i e s i n the Juan de Fuca water (or both). Layer 7j 150 m - 175 mt The average salt contents for the San Juan and Southern regions show a similar pattern to that of layer 2« an increase of salt between February and May then small decreases between May and November. The salt contents of the Northern and Central regions show a pattern similar to that of the heat content (Table I I ) . The salt content of the Central region increased between February and May while the salt content of the Northern region decreased during the same peri-74 od. Salt contents for both regions then increased gradually from May to November. The increase of salt i n the intermediate layer seems to be due to the same intrusion that increased heat contents i n the Central re-gion. Layer 9; 200 m - 225 m: Salt levels f o r the regions did not change by a large amount but did follow the same pattern as the salt contents i n layer 7. The salt content for the San Juan region shows an increase between February and May and a decrease between August and No«= vember. The average salt content of the Northern region decreased s l i g h t -l y between February and May and then increased slowly from May to Novem-ber. While the average salt contents of the upper layers seem to be a-ffected most by the fresh water runoff into the s t r a i t and by mixing of the upper layers, the salt contents of the lower layers seem to be i n -fluenced most by advection and diffusion. The salt contents of the Southern and San Juan regions show the least variations indicating that t i d a l mixing processes tend to maintain a nearly homogeneous water c o l -umn throughout the year. 75 6. MIXING PROCESSES If a water column i s not already homogeneous any mixing of that column w i l l increase i t s potential energy. In order to estimate the im-portance of the various mixing processes, estimates were made of the en-ergy available for mixing by some of the more important mixing processes as well as some important mixing parameters such as the depth of the wind mixed layer. This section br i e f l y describes the main features of some of the more important or obvious mixing processes i n the Strait of Georgia. An interpretation of the various mixing parameters and effects and a discussion of the relative Importance of each mixing process w i l l be made i n section 7. 6.1 Wind Mixing The mixing of the surface layer by the wind i s one of the most important contributions to the total mixing of the Strait of Georgia es-pecially away from the t i d a l passages at the northern and southern ends of the s t r a i t . As the wind blows i t drives motions i n the surface layer and creates turbulence. The turbulent surface layer tends to he well mixed with a uniform temperature. As the wind continues to blow the mix-ed layer deepens, entraining water from the deeper non-turbulent Layer and increasing the potential energy of the water column. There have been several studies of the deepening of the wind mix-ed layer both theoretical (Kraus and Turner, 1967$ Denman, 1973* Pollard, Rhines and Thompson, 1973J N i i l e r , 1975) and experimental (Kato and P h i l l i p s , 1969* Linden, 1975)* Denman (1973) related the energy a v a i l -able for mixing of the Layer to the input of kinetic energy from the surface wind stress. Pollard, Rhines and Thompson (1973) showed that the maximum depth of the wind mixed layer w i l l depend upon both the i n f l u -76 ence of the Goriolis parameter ( i n e r t i a l forces) and the s t r a t i f i c a t i o n of the underlying water. This study used a theoretical model by N i i l e r (1975) to estimate the energy available for mixing of the upper Layer and the depth of the wind-mixed layer. The model assumes that the rate of change of the potential energy of the water column i s proportional to the rate of input of kinetic energy at the surface although laboratory experiments by Linden (1975) indicated this was not exactly true. Energy estimates used the mean monthly values of wind speed from meteorological stations around the Strait of Georgia (Table I ) . This tends to underes-timate the energy available for mixing since i t does not take into ac-count the mixing done by storms which can effectively mix the water c o l -umn more deeply than the mean wind speed would indicate. The energy es-timates ignored the effect of increasing the kinetic energy of the upper layer (by feeding energy into the mean wind-driven circulation of the strait) or losses of energy due to radiation of internal waves along the bottom boundary of the mixed layer. Ignoring losses due to internal waves leads to overestimating the energy available for mixing while u-sing mean wind speeds leads to underestimating the available energy but the relative importance of each error i s not known. For a wind stress T acting upon a surface of a layer with den-sity pQ, the energy flux (energy per unit area) available for mixing stress T~ i s related to the wind blowing over the surface, U, bys w i l l bej 6.1 where mQ i s an order-one quantity (Niiler sets raQ » 15/12). The wind 6.2 77 where i s the drag coefficient of the wind at an altitude of 10 met-res (C^ 0 - 0.0013) and where c i a i s the density of the a i r . As the wind continues to blow i t w i l l rapidly deepen the mixed layer to a depth given by: 6.3 where N i s the buoyancy frequency and f the Goriolis parameter. If the wind continues to blow there w i l l be a slow erosion of the stably strat-i f i e d lower layer. If there i s heating of the surface layer (or an input of lower density water from fresh water runoff) leading to a negative buoyancy flux (see equation 6.5) the slow erosion w i l l be halted at a depth near the Monin-Obukhov length, L^, given by (P h i l l i p s , 1966): - - „ 6.* where X © i s ***e K a 1 ™ ^ constant (0.4) and where B i s the buoyancy flux. If B ^ 0, then < 0 and the mixed layer w i l l not extend much beyond J L p I * If there i s cooling of the surface layer (or an excess of salt due to evaporation), B ^ 0 and there can be free convection past the Monin-Obukhov length and the mixed layer depth can extend to large depths. Values of the energy flux from the wind were calculated for each grid compartment for the Strait of Georgia i n layer 1 along with e s t i -mates of the mixed layer depth and the Monin-Obukhov length (the Monin-Obukhov length i s discussed further i n section 6.2). The maximum comput-ed mixed layer depth was 18 metres with most values ranging between 6 metres and 12 metres. This indicates that most of the mixing energy pro-vided by the wind i s i n i t i a l l y confined to the upper 25 metres (layer 1) although internal mixing may s t i l l occur and Increase the potential en-ergy at deeper depths. 78 Figure 60 illustrates the average energy per grid compartment a-vailable for mixing f o r the regions of the s t r a i t . A l l regions show an increase i n the energy flux from August to November corresponding to a rise i n the mean speed. The Southern and Central regions show a decrease in wind mixing energies from February to a minimum i n May then an i n -crease to the maximum i n November. The Northern region shows a slight increase i n wind mixing energy between February and May but otherwise follows the same pattern as the Central and Southern regions. The San Juan region shows a different pattern with a rise i n wind mixing energy between February and May, a decline i n August and then a rise i n wind mixing energy i n November. This could be attributed to a different wind pattern i n the Strait of Juan de Fuca compared with the southern Strait of Georgia. 6,2 Buoyancy Flux and Gravitational Instability Another process that can be important i n mixing the waters of the st r a i t i s convection brought on by gravitational i n s t a b i l i t y . Conversely, increasing the s t a b i l i t y of the water column can be important i n inhib-i t i n g mixing (Turner, 1973). The s t a b i l i t y of the water column i s close-l y tied to the net rate of generation of buoyancy (or net buoyancy flux) at the surface. A positive buoyancy flux indicates unstable conditions and convective mixing may occur while a negative buoyancy flux denotes increasing s t a b i l i t y of the water column and consequently increasing re-sistance to mixing. Buoyancy may be generated at the surface of the s t r a i t by resid-ual salt l e f t behind by evaporation or by cooling of the upper layer (Phillips, 1966). If E i s the net rate of evaporation and S the s a l i n i -ty, ES w i l l represent the rate at which salt i s l e f t behind by evapora-79 tion. I f Q i s the heat flux, the net loss or gain of heat of the surface layer, the layer w i l l expand or contract at a rate of OL. Q/p o G p f where ot i s the thermal coefficient of expansion and the heat capacity of sea water. The net buoyancy flux, B, w i l l be given byi Br [Q^ - f 5 ~] 6.5 If there i s a buoyancy flux i n a layer of thickness h, the layer w i l l gain (or lose) energy at a rate given by where i s the energy per unit area gained or lost by the layer. A pos-it i v e buoyancy flux corresponds to an excess of mass i n the upper layer which would lead to unstable conditions and convective mixing (with a gain of potential energy density). The positive buoyancy flux could be due to either cooling of the layer (Q <^  0) or to excess salt through e-vaporation. A negative buoyancy flux due to warming (Q "> 0) or to d i l u -tion of the layer (ES < 0) w i l l cause increasing s t a b i l i t y and a loss of potential energy density. One measure of the depth at which buoyancy forces become impor-tant i s the Monin-Obukhov length, L^, defined by equation 6.4, It repre-sents the depth at which the energy terms from wind mixing and the buoy-ancy flux are of the same order (Phillips, 1966). If the buoyancy flux i s positive, > 0, and buoyancy effects continue to be important at depths greater than the Monin-Obukhov length. Bathythermographs taken o-ver the Strait of Georgia during November 1968 show uniform cold temper-atures down to a depth of 150 metres indicating convective mixing had created a mixed layer deeper than any Ekman type layer due to wind mix-ing alone. If the buoyancy flux i s negative, <( 0, the density struct-80 ure i s stable and below depths of the order of turbulence i s damped out: the wind mixed layer does not extend far past the Monin-Obukhov length and convection i s not Important. In order to estimate the buoyancy flux estimates had to be made of the heat flux, Q, into the top Layer of the s t r a i t . For the purposes of this study, the heat flux Q was defined by: a = % - Q b - Q € -Qu 6.7 where Qg i s the contribution from solar radiation, i s the loss from back radiation, Qg i s the loss from evaporation and i s the exchange of sensible heat. No estimates were made of the contribution to the to-t a l heat flux by heat transport through currents. Waldichuk (1957) found that there was a net annual loss of heat from the Strait of Georgia due to advection so that ignoring losses due to advection leads to overesti-mating the heat flux. The back radiation flux was estimated from the temperature of the water and the relative humidity estimated from shore stations. The evaporative heat loss was estimated by multiplying the l a -tent heat of vaporization by the evaporation rate, E, which was estimat-ed by the vapor pressures at the sea surface and the mean wind speed. The evaporative heat loss and sea and a i r temperatures can also be used to estimate the sensible heat transfer Q^. Waldichuk (1957) discusses more f u l l y the procedure for estimating the heat fluxes. Using the estimates of Q, E and the monthly mean of the wind speed, values of the buoyancy flux, the potential energy change due to the buoyancy flux and the Monin-Obukhov length for each grid compartment were computed for each grid compartment of layer 1. Since only limited meteorological data were available the estimates are rough and mainly indicate whether convection could be important and give order of raagni-81 tude estimates of the energy changes due to buoyancy. Figure 61 i l l u s -trates the estimates of the energy per grid compartment generaged per month from the buoyancy flux. The magnitude of E^ w i l l depend upon the depth h over which the buoyancy flux i s integrated. The depth used i n this study was chosen to be the estimated mixed layer thickness given by equation 6.3. The Northern, Central and Southern regions a l l had a net negative buoyancy flux from February to August due to heating of the up-per layer and fresh water runoff. The negative buoyancy flux caused a net loss of potential energy density with minimum values of E^ for the Northern, Central and Southern regions i n August when surface heating i s a maximum. The San Juan region had a positive buoyancy flux i n February indicating convective mixing and gained i n potential energy density. The San Juan region had a negative buoyancy flux from May to August and a loss of potential energy density. A l l of the regions of the s t r a i t show-ed a positive buoyancy flux i n November with increasing potential energy densities. The average Monin-Obukhov lengths for each region are illustrated i n Figure 62. In February only the San Juan region had a positive value indicating buoyancy effects were important at depths greater than 10 metres. The other regions had negative values i n February Indicating stable conditions. The Central region had the largest magnitude, -19 metres, which would be the limiting depth of the mixed layer. The Monin-Obukhov length was negative for a l l regions i n May and August with a magnitude less than 6 metres reflecting increasing s t a b i l i t y due to warming of the surface layer and fresh water runoff. The Monin-Obukhov length was positive for a l l regions i n November Indicating convection was important. The Southern and San Juan regions had magnitudes near 10 metres, the Northern region had a magnitude near 20 metres and the Cen-82 t r a l region had a value near 30 metres. The increased magnitudes mean a deeper mixed layer depth with buoyancy effects important below the Monin-Obukhov length. 6.3 Tidal Mixing One of the more important (and obvious) mixing processes i s t i d a l mixing especially i n the southern Strait of Georgia. Strong t i d a l mixing i n the San Juan Archipelago and other t i d a l passages can result i n a near homogeneous water column as illustrated i n Figure 67. Elsewhere i n the s t r a i t t i d a l mixing i s less important except at the extreme northern end where there are narrow t i d a l passages. There may however be a t i d -a l l y mixed layer along the bottom of the s t r a i t . Garrett, Keeley and Greenburg (1978) discuss the importance of the buoyancy flux upon t i d a l mixing and show that the boundary bwtween well mixed and s t r a t i f i e d conditions should correspond to a c r i t i c a l value of BH/U^, where B i s the buoyancy flux, H the mean water depth and U the mean t i d a l current speed. A transition from well mixed to s t r a t i -fied conditions during the summer occurred i n a numerical model when H/lr 70 m s . Garrett et a l . found this corresponded to a mixing efficiency of only 0.3$, much less than the 6% to 8% efficiency from wind mixing (Kato and P h i l l i p s , 1969). As a means of determining how important t i d a l mixing Is to the total mixing, estimates were made of the energy available f o r mixing from the t i d a l energy dissipated from f r i c t i o n . It was estimated that a-pproximately 5% of the t i d a l energy dissipated by f r i c t i o n went into mixing and raising the potential energy of the water column. The figure of 5% was chosen since the kinetic energy of the t i d a l flow approximate-l y equals the dissipation and i n a number of phenomena ; such, as/.internal 83 waves (Thorpe, 1973) and penetrative convection (Farmer, 1975) approxi-mately 5% of the kinetic energy goes into increasing the potential ener-gy by mixing. I f the t i d a l current has the form u =» U Qcosa;t, the rate of energy dissipation per unit area averaged over a t i d a l period w i l l be (Officer, 1976): where ^ i s the mean density and k the bottom f r i c t i o n coefficient. Es-timates of the total t i d a l energy (0.05W) for each grid compartment were made for the representative months. The energy estimates were made for the lowest layer that information was available for, either layers 2, 7 or 9 depending upon the total depth at each grid compartment. The values of the mean current, U , and the bottom f r i c t i o n coefficient k were t a -o ken from a numerical model of the Mg tide developed by P. Crean (1976). Table IV l i s t s the average amount of t i d a l energy per grid compartment available per month for mixing for the regions of the s t r a i t . The San Juan and Southern regions have the greatest t i d a l veloci-t i e s and hence the greatest dissipation of t i d a l energy. The f r i c t i o n coefficient, k, for the Southern and San Juan regions i s also greater than i n the other regions with a value of 0.03 compared with 0.003 f o r the Central and Northern regions. While the estimates of t i d a l mixing are rough they indicate that t i d a l mixing i s quite large i n the southern st r a i t compared to the northern area of the s t r a i t . 6.4 Internal Waves Near-surface internal waves are observed i n many coastal areas of the oceans (Shand, 19531 Curtin and mooers, 1975) and i n some cases are 84 Region San Juan Southern Central Northern Layer 2 1.3 X 10 4 . 2 X 10 ,13 12 2.0 X 10 1.1 X l o -l l ENERGY (J) Layer 7 1.6 X 10 1 3 4 . 0 X 10 12 2.7 X 10 1.1 X 10S 1 1 Layer 9 1.6 X 10 5.3 X 10 2.5 X 10 1.5 X 105 1 3 12 10 Table IV Average t i d a l energy available for mixing per month per grid compartment. even detectable from s a t e l l i t e photographs (Apel et a l . , 1975). Such coastal areas usually have a strong near-surface pycnocline so that i n -terfacial waves are visible from the a i r through their surface manifes-tations, either slick formation (Ewing, 1950), interactions with short surface waves (Gargett and Hughes, 1972), or variations i n the color of the sea-surface. Groups of such waves have been observed i n the Strait of Georgia (Shand, 1953) and i t has been observed (Gargett, 1976) that the wave groups are generated by the scattering of the barotropic tide over the s i l l s that l i e between the Islands of the San Juan Archipelago and the Gulf Islands (Figure 6). Observations indicate that the internal wave groups seen i n the st r a i t are generated mainly by topographic scat-tering of the flood tide over the s i l l lying between East Point (on Sa-turna Is.) and Patos Island, at the northern end of Boundary Passage and propagate northwards into the southern Strait of Georgia. Any wave groups generated by the ebb tide tend to be swept out of the s t r a i t and do not contribute to wave groups seen i n the southern s t r a i t . As the internal wave groups travel northwards into the s t r a i t they can break and do mixing along the pycnocline. Estimates of the en-ergy content of the internal waves can help establish the importance of the waves to the total mixing. During a flood tide cycle of 6 hours the internal waves propagate northwards with a group velocity given approxi-mately by (Samuels and LeBlond, 1977): c,. ( * where h^ i s the depth of the upper low-density layer and where and r_) g a r e the mean densities of the upper and lower layers respectively. With a mean density contrast (^ 2 - ^ j ) / ^ m 1 0 (typical of the southern strait) and h. «• 10 m, G » 1.0 m s~*. Adding to this a mean flood current of about 0.25 "» s i n the southern Strait of Georgia means that a wave group can travel away from i t s generation area i n Boundary Passage a distance of about 25 km (15 nautical miles) in a six-hour flood. Thus internal wave wave mixing w i l l only affect the Southern region and the southern part of the Central region. The energy content of interfacial waves w i l l depend upon the den-sity stratification and the wave amplitudes. The energy density per unit area of interfacial waves of amplitude a may be written E = 1 ( f x - p , ) j ^ F(T;} v ) 6.10 where F i s a function of the wave amplitude (a/h^) and of other non-di-mensional parameters, such as the actual shape of the density transi-tion. For the rough estimates of this study F was taken as unity, cor-responding to small amplitude waves. Even though the linear approxima-tion (F =» 1) i s invalid over much of the wave f i e l d (since the internal waves can have amplitudes comparable to the upper layer thickness), by taking a sufficiently large range of wave amplitudes the energy e s t i -mates may be made to encompass the effects of non-linearity. The data on the internal wave groups i n the southern Strait of Georgia were gathered by P. LeBlond who took photographs of the groups during a series of fl i g h t s along a line joining Point Roberts and East Point on Saturna Island. The time of passage over these landmarks was clocked i n both directions and photographs of the most prominent visible internal wave groups were taken at measured times. It was then possible to calculate the position at which everyvphotograph was taken and to construct sketches of the internal wave trains i n the area covered (Fig-ure 6). Hydrographic observations taken on the day following the f l i g h t by Crean and Ages (1971) show the relative contrast between the density 87 rj at a depth of 10 m and that of the surface water p^, defined as (^2 ~ ^1^2' 7 3 x 1 6 8 ^ r o m 0*015 near the Fraser River mouth to 0.007 near Boundary Passage. No direct measurements of internal wave ampli-tudes were made at the time of the flights. Observations under similar conditions (Hughes, 1969; Gargett, 1976) have shown that isothern dis-placements of up to 6 metres are common. The observed areas of the internal wave groups varied from 5*9 X 107 m2 to 1.1 X 108 m2 with an average total area of 8.5 X 107 m2. Tak-ing a range of estimates of stratification and wave amplitudes led to o i o estimates of wave energy from 1.6 X 107 J to 1.1 X 10 J during each o flood tide cycle with a mean energy content of 5*4 X 107 J . With two flood tide cycles per day for the tide, in one month (30 days) the southern Strait of Georgia has an estimated flux of internal wave energy on the order of 3.2 X 10 J . Laboratory experiments by Thorpe (1973) indicate that only 5% of the turbulent energy dissipated by breaking in-ternal waves finds its way into gravitational potential energy of strat-10 ification leading to an estimate of 1.6 X 10 j of Internal wave energy available for mixing each month. For comparison, this is about an order of magnitude less than the energy from tidal mixing for one grid com-partment in the Central region and two orders of magnitude less than the tidal energy in one of the grid compartments in the Southern region (Ta-ble IV) although it should be noted that Internal wave mixing occurs in the surface layer while tidal mixing occurs along the bottom. The area 7 2 covered by the wave groups, 8.5 X 10 m , is comparable to the area of 7 2 one grid compartment, 8.6 X 10 m . If the energy of the internal wave groups is dissipated in a greater area than that of the wave groups themselves (which seems likely) the average internal wave energy avail-able for mixing in each grid compartment is even smaller than that esti-88 mated. Thus i n spite of their spectacular and ubiquitous nature, i t ap-pears that the near-surface internal waves observed i n the Strait of Georgia play an insignificant role l n the mixing energy balance of the local waters. 6.5 Entrainment Mixing The southern Strait of Georgia exhibits a s t r a t i f i e d estuarine flow: a brackish upper layer flowing seawards and a lower layer of more saline water flowing into the s t r a i t (Waldichuk, 1957J Schumacher et a l . , 1978). There Is an upward movement of the deep water into the top layer, or entrainment, with a vertical entrainment velocity w much smaller than the velocity i n either layer. The water from depth i s mixed into the up-per layer and contributes to the to t a l flow i n that layer. Prom some simple theoretical considerations an order of magnitude estimate can be made of the increase of potential energy due to entrainment mixing. A f u l l e r summary of the theory of entrainment mixing can be found i n O f f i -cer (1976). Gordes et a l . (1979) i n a study of the Fraser River plume found that the vertical entrainment velocity, w, was proportional to the mean speed of the upper layer, U, so that where k equals 2 X 10 . I f the thickness of the brackish layer i s h, the velocity of the upper Layer w i l l be related to the upper layer flow by: 6.11 where q i s the discharge per unit width i n the upper layer. Therefore 89 the entrainment velocity w i s related to the discharge per unit width by w = TT ^  6 , 1 2 Waldichuk (1957) made estimates of the flows into and out of the Strait of Georgia that Schumacher et a l . (1978) found to be basically correct (within 18$). While there was considerable variation from month to month (flows ranged from 29 krn^  to 231 km^) Waldiehuk's figures lead 3 to an estimate of 121 knr flowing out of the s t r a i t each month plus or 3 minus 60 km . This figure would represent the maximum discharge leaving the s t r a i t through the southern channels, while the minimum upper-layer flow would be that of the river discharge (Figure 4 ) . Using river d i s -charge data and the estimates for the t o t a l flow out of the s t r a i t , es-timates were made of the vertical entrainment velocity using equation 6.12. The upper-layer thickness was chosen to be 7 metres leading to es--2 -1 -2 -1 timates ranging from 1.2 X 10 cm s plus or minus 0.7 X 10 cm s -1 -1 at the Fraser River mouth to 0.15 cm s plus or minus 0.08 cm s at the southern t i d a l passages. In a layer of thickness h the rate of increase of potential ener-gy per unit volume due to the upwelling w i l l be given by 4 < - h / * « I Z 6.13 Making the assumption that p i s constant and that w decreases linear-a l l y to zero at the surface leads to estimates of approximately 6 ergs -3 -1 -3 -1 cm s at the river end ant to 75 ergs cm s at the southern end for the rate of increase of potential energy i n the layer. For a single grid compartment (25 NM2) the increase of potential 15 energy per month due to entrainment mixing i s approximately 1 X 10 J plus or minus 0.5 X 10 J J for grid compartments near the river mouth and 1 X 10 J plus or minus 0.5 X 10 J for grid compartments at the southern passages. These estimates are considerably larger than those for t i d a l mixing ( — 101-3 J) or wind mixing 10 1 0 J) and ill u s t r a t e s that even a small entrainment velocity could lead to large changes i n the potential energy in one month. It should be noted that while en-trainment mixing acts to increase the potential energy of the upper lay-er i t i s driven by the fresh water runoff which increases the s t r a t i f i -cation and hence decreases the potential energy so that the net change of energy may be quite small. 91 7. INTERPRETATION AND DISCUSSION The physical oceanographic features of the Strait of Georgia were described i n section 5 to i l l u s t r a t e the seasonal changes that occur i n the waters of the s t r a i t . The physical characteristics of the waters change in response to the mixing mechanisms described i n section 6 plus other processes such as estuarine flow and seasonal intrusions of d i f -ferent water masses. In this section the changes of the physical ocean-ography of the Strait of Georgia w i l l be discussed both qualitatively and quantitatively with reference to the physical mechanisms that are responsible for the changes. 7.1 Discussion of the Physical Oceanography of the Strait of Georgia For both the observed physical properties (temperature, sal i n i t y , density and dissolved oxygen concentration) and the derived quantities (potential and mixing energy densities, heat and salt contents) the sea-sonal changes are quite different between the upper layers of the s t r a i t (layers 1 and 2) and the lower layers (layers 7 and 9). Throughout most of the s t r a i t different physical processes are at work between the upper arid lower layers causing different responses i n the physical character-i s t i c s . For this reason the upper and lower layers w i l l be discussed separately. (a) Upper layers (Layers 1 and 2) The most important factors governing the surface layers of the s t r a i t (outside of the t i d a l mixing passages) are meteorologicalt warm-ing or cooling of the surface, wind mixing and fresh water runoff. The seasonal change of the a i r temperatures over the Strait of Georgia i s plotted i n Figure 63 i l l u s t r a t i n g the average a i r temperature over each region as interpolated from the meteorological stations around the 92 s t r a i t . Comparison of the a i r temperatures with the average temperatures of layers 1 and 2 (Figures 15 and 16) shows a similar seasonal cycle of increasing temperatures from February to maximums i n August followed by cooling between August and November. Another important factor, fresh wa-ter runoff, i s plotted i n Figure 4 which shows the output of the Fraser River for the representative months of the year 1968. The average s a l i n -i t i e s of the Southern and Central regions i n layer 1 (Figure 23) corre-spond closely to the runoff cycle of low flow i n winter increasing to a maximum i n summer. In February runoff i s low (Figure 4) leading to reduced s t r a t i f i -cation as shown by lower values of mixing energy i n layer 1 (Figure 52). Low a i r temperatures caused cooling of the surface layers (Figures 15 and 16) and possibly convective mixing i n the San Juan region (Figure 61). The mean wind energy available for mixing was higher i n February (Figure 60) than i n the spring or summer and, as a result of the low stra t i f i c a t i o n and wind mixing, temperatures were horizontally uniform in the Northern and Central regions for both layers 1 and 2 (Figures 11a and 12a). Because of surface cooling temperatures i n layers 1 and 2 were lower than deeper layers and t i d a l mixing with warmer deep water i n the Southern and San Juan regions caused temperatures i n the upper layers to be higher i n those regions. Figure 64 shows that temperatures were uni-form with depth i n the southern s t r a i t (the Southern and San Juan re-gions). Tidal mixing i n the southern Strait of Georgia also led to the highest s a l i n i t i e s for the upper layers (Figures 23 and 24 and Figure 65a). Salinities i n the Northern and Central regions are lower along the eastern side of the s t r a i t i n layer 1 but higher i n layer 2. This i s probably due to Fraser River runoff and estuarine entrainment. The Fra-ser River flows into the eastern part of the Central region leading to 93 lower s a l i n i t i e s i n layer 1 for the Northern and Central regions. As the fresh water flows to the sea i t entrains deeper, more saline water as described i n section 6.5 leading to higher s a l i n i t i e s i n layer 2 along the eastern side of the s t r a i t . In February dissolved oxygen concentra-tions were higher i n the upper layers than any other part of the year (Figures 36 and 37). This may have been due to wind mixing which would helpaerate the layers and to the low temperatures which would increase the solubility of oxygen in the water. The lowest dissolved oxygen con-centrations are i n regions of t i d a l mixing where oxygen-poor deep water i s mixed with the surface waters. These areas are i n the Southern and San Juan regions and the extreme northern end of the Northern region (Figure 35a and 36 a, Figure 66a). In May, runoff has increased (Figure 4) while wind mixing has de-creased (Figure 60) for most of the s t r a i t . The increased runoff and i n -creasing temperatures (Figures 15 and 16) led to Increased s t r a t i f i c a -tion i n layer 1 as shown by an increase of mixing energies for a l l re-gions (Figure 52). Temperatures were lower i n the Southern and San Juan regions of layer 1 due to t i d a l mixing with relatively cooler deep wa-ter. With increased runoff from the Fraser River, estuarine flow was i n -creased and estuarine entrainment led to upwelling of cooler water along the eastern side of the Northern and Central regions, illustrated i n Figure 12b. Upwelling i s also indicated by the rise of the 8.5° C i s o -therm towards the surface i n the Central region (Figure 64b) which caus-es the average temperature of the Central region to be lower than that of any other region i n layer 2. The increase of runoff led to decreases of salin i t y for the Southern, Central and Northern regions l n layer 1 (Figure 23). However, the average salinity increased for the San Juan region and for a l l regions of layer 2 due to an intrusion of higher sa-94 Unity water from the Strait of Juan de Fuca into the Strait of Georgia. This is indicated by the advance of the 31*0%, contour between February and May in Figures 65a and 65b. The highest salinities in the upper lay-ers are in the Southern and San Juan regions due to tidal mixing of deep water and the lowest in layer 1 are along the eastern side of the Cen-tral region due to Fraser River inflow. Upwelling of deep water due to estuarine entrainment leads to an east-west gradient of salinity in the Northern and Central regions of layer 2 with higher salinities (and den-sities) along the eastern side. By May, dissolved oxygen concentrations have decreased in layer 1 (except for the Northern region) and layer 2 (Figures 36 and 37). This is probably due to increasing temperatures which decrease the solubility of oxygen and reduced wind mixing which lowers aeration of the surface layer. The lowest oxygen concentrations were in the tidal mixing areas and in areas of higher stratification where wind mixing would be inhibited. These areas are at the eastern side of the Northern and Central regions of layer 1 where runoff is im-portant and the eastern side of the Northern region of layer 2 (Figures 3?b and 33b). These higher stratification areas are also areas of high mixing energy density as shown in Figures 48b and 49b. In August, fresh water runoff was slightly lower than in May (Figure 4) and wind mixing had increased (Figure 60). While this would tend to break down the stratification, increasing temperatures would work to increase the stratification. Thus, values of mixing energy de-creased only slightly or actually increased (Figures 52 and 53). Temper-atures were higher in August than in the other months (Figures 15 and 16) with the lowest temperatures in layer 1 in the tidal-mixing areas (Figure 64c). There was an east-west temperature gradient in the Central region for both layers 1 and 2 (Figures 11c and 12c) with cooler temper-95 atures along the eastern side of the s t r a i t . As before i n May this was probably due to inflow of Fraser River water and upwelling of cooler wa-ter i n response to estuarine entrainment. Average s a l i n i t i e s had de-creased for a l l regions (except the Central region) f o r both layers (Figures 23 and 24). The low sal i n i t y (and density) for the Northern re-gion i n layer 1 seems to be due to Fraser River water having been ad-vected northwards at the time of sampling. 'Blobs* of low sal i n i t y water are visible i n Figure 65c and in Figure 19c i n the Northern region along the eastern side of the s t r a i t . Dissolved oxygen concentrations reached a minimum for a l l regions due to higher s t r a t i f i c a t i o n which inhibited mixing and higher temperatures which reduced the solubility of oxygen i n the water. As i n May the higher mixing energies and the lower oxygen concentrations were found along the eastern side of the Northern and Central regions. In November, the str a t i f i c a t i o n of the Strait of Georgia began to break down as indicated by decreases of mixing energy for layers 1 and 2 for most of the regions (Figures 52 and 53). Reduced runoff (Figure 4) and cooling of the surface (Figures 15 and 16) would lead to the reduced st r a t i f i c a t i o n . Wind mixing (Figure 60) was at a maximum and rapid cool-ing probably led to convective mixing as indicated by the buoyancy flux energies (Figure 61). As a result, temperatures were very uniform for both layers throughout the s t r a i t (Figures l i d , l2d and 64d). Salinities increased for the Northern region of layer 1 but decreased for the other regions (Figures 23 and 24). This seemed due to a deepening of the iso-hallne lines i n the surface layers and a shift of the contours south-wards bringing less saline water into the Southern and San Juan regions (Figure 65d). This was possibly caused by a reduction of estuarine up-welling due to reduced fresh water runoff. There was s t i l l some entrain-96 ment upwelling present as shown by higher s a l i n i t i e s along the eastern edge of the Central region of layer 2 (Figure 20d). With lower tempera-tures increasing the sol u b i l i t y of oxygen and convective overturning, dissolved oxygen concentrations increased for a l l regions i n the surface layers (Figures 36 and 37)• As before, the lower oxygen concentrations are i n the t i d a l mixing areas and i n areas of higher s t r a t i f i c a t i o n (and higher mixing energy densities)J the eastern side of the Northern and Central regions of layer 1 (Figures 32d and 48d) and the eastern side of the Northern region of layer 2 (Figures 33d and 49d). To summarize, the physical characteristics of the upper layers of the s t r a i t are dominated by heating and cooling of the surface, fresh water runoff and by wind, tide and entrainment mixing. February and No-vember were characterized by higher wind mixing and lower fresh water runoff than the other months. This, along with low a i r temperatures, led to uniform cold temperatures for the entire s t r a i t (in the surface lay-ers) and increased dissolved oxygen concentrations. In May and August, increased fresh water runoff and higher temperatures and decreased wind mixing led to increased s t r a t i f i c a t i o n . Temperatures and s a l i n i t i e s showed the influence of the inflow of the Fraser River and estuarine up-welling which were mainly confined to the eastern side of the Northern and Central regions. Tidal mixing i n the San Juan and Southern regions and at the northern end of the Northern region maintains f a i r l y homogen-eous conditions with warmer temperatures i n February and November, cool-er temperatures in May and August and higher s a l i n i t i e s and lower d i s -solved oxygen concentration throughout the year. (b) Lower Layers (layers 7 and 9) In contrast to the upper layers the lower layers of the s t r a i t 97 respond much more slowly to different surface conditions. They are iso-lated from the direct influence of the heating and fresh water runoff cycles that alter the properties of the upper layers. Tidal mixing and advection processes are the most important factors that influence the physical characteristics of the deeper layers, although convection due to gravitational instability may occasionally alter the temperature of the deep waters. In February, tidal mixing maintained a uniform temperature in the Southern and San Juan regions both horizontally (Figures 13a and 14a) and vertically (Figure 64a). Temperatures were fairly uniform in the Central and Northern regions for both layers and warmer than the other regions. Remnants of warm summer water remained in the deep areas of the strait causing the average temperatures of the Northern and Central re-gions of layer 9 to be warmer than those of layer 7 (Figures 17 and 18). Tidal mixing of the deep water with brackish surface water caused the a-verage salinity of the Southern region to be lower than in the other re-gions (Figures 25 and 26). Salinities increased southwards into the San Juan region with a strong gradient that tidal mixing caused to be almost vertical (Figures 65a, 21a and 22a) while salinities were almost uniform throughout the Central and Northern regions. Tidal mixing of the deep water with surface waters also maintained higher dissolved oxygen con-centrations in the Southern and San Juan regions with concentrations de-creasing northwards (Figures 66a, 34a and 35a) and decreasing with depth. With the near uniform salinities in the Northern and Central re-gions stratification was small and values of mixing energy were smaller than in the upper layers (Figures 54 and 55)» a situation that existed during a l l months. The area to the east of Texada Island (Malaspina Strait), which forms a semi-enclosed basin at the depth of layer 9 (225 98 m), appeared to be a stagnant area of l i t t l e mixing (or advection) with higher values of mixing energy density (Figure 5ia) and low dissolved oxygen concentrations (Figure 35a)• By May, there appeared to be an intrusion of a different water mass into the Strait of Georgia from the Strait of Juan de Fuca. This was most apparent by the increase of s a l i n i t y i n the Southern and San Juan regions (Figures 25 and 26) shown by the advance of the 31,0%o i s o -haline into the s t r a i t (Figure 65b) and by an increase of dissolved oxy-gen at the bottom of the s t r a i t (Figures 66b and 39)• The average tem-perature for a l l regions converged to a value near 8.4° G with a uniform distribution (Figure 64b). While oxygen concentrations rose i n the Northern and Central regions of layer 9 and i n the Northern region of layer 7 (Figures 38 and 39) they f e l l i n the Southern and San Juan re-gions. This might have been due to t i d a l mixing but may also have been due to an intrusion of high s a l i n i t y and oxygen poor water from the Strait of Juan de Fuca as suggested by Figure 66b. The highest values of mixing energy density which were associated with areas of low mixing were found i n the basin to the east of Texada Island (Figures 54b and 55b) along with low values of dissolved oxygen concentration. In August, the deep waters had become warmer (Figures 64c, 17 and 18) and s a l t i e r (Figures 65c, 25 and 26). This appeared to have been due to an intrusion of warm, salty water as described by Waldichuk (1957) although dissolved oxygen concentrations dropped for a l l regions (Fig-ures 38 and 39). The intruding waters seemed to have entered along the eastern side of the s t r a i t since temperatures were higher there i n the Northern and Central regions (Figure 13c). As i n the other months the t i d a l mixing areas separated the lower s a l i n i t i e s of the Northern and Central regions from the high s a l i n i t i e s of the Strait of Juan de Fuca. 99 As in May, the highest values of mixing energy density (Figures 50c and 51c) and the lowest oxygen concentrations (Figures 34c and 35c) were a-long the eastern side of the Northern region. In November, the temperatures for a l l regions and the salinities for the Northern and Central regions continued to rise from the values of August although the salinities of the San Juan and Southern regions fe l l . This indicates that the intrusion of warm, salty water continued in the northern strait spread perhaps by diffusion processes. Oxygen concentrations (Figures 38 and 39) continued to decline except in the San Juan region. Temperatures (Figures 13d and 14d) and salinities (Fig-ures 2ld and 22d) were fairly uniformly distributed in the Northern and Central regions with the greatest change southwards through the tidal mixing areas. Cooling of the surface, causing convective mixing, may have been responsible for the vertically uniform temperature and salini-ty in the San Juan region (Figures 64d and 65d) plus the increase in oxygen concentration (Figure 66d). To summarize, tidal mixing is the most important factor in deter-mining the physical characteristics of the deep waters of the San Juan and Southern regions. The tidal mixing areas of the southern strait also mark the boundary between the deep waters of the northern Strait of Georgia (the Central and Northern regions) and the waters of the Strait of Juan de Fuca. Intrusions of different water masses into the northern strait are the main factors in changing the physical characteristics of the deep waters of the strait. Two separate large scale intrusions were noted in the 1968 data: an intrusion of cold, low salinity water (but with higher oxygen concentrations) between February and May and an in-trusion of warm, salty water with a low oxygen concentration between May and November. 100 7.2 Exchange Processes Besides the vertical mixing processes described i n section 6 l a t -eral exchange processes and advection act to a l t e r the physical proper-ties and to renew the waters of the Strait of Georgia. Horizontal advec-tion of foreign water masses can a l t e r the vertical density structure and introduce errors i n the estimates of vertical mixing effects. Possi-ble advection phenomena acting in the Strait of Georgia are t i d a l advec-tion, estuarine flow, advection by wind-driven circulation and seasonal intrusions of different water masses (as discussed i n section 7.1). Of these, wind-driven advection i s probably confined to the brackish layer in the upper part of layer 1, while the other processes can influence the entire water column. Schumacher et a l , (1978) found l i t t l e correla-tion between the mean wind and the mean near-surface currents during February i n the southern Strait of Georgia except along the eastern side. Lateral wind-driven advection i n the s t r a i t i s probably not as im-portant i n altering the vertical density structure as i s vertical mix-ing. Tidal advection i s the most obvious late r a l exchange process act-ing i n the Strait of Georgia. As the flood phase of the semidiurnal tide enters the s t r a i t (chiefly through the southern passages) the water c o l -umn i s mixed and fresh water i s removed with the ebb tide. One simple concept of t i d a l advection (and mixing) i s the t i d a l prism method. This assumes that the volume:of sea water entering the s t r a i t has oceanic sa-l i n i t y and i s completely mixed with a corresponding volume of fresh wa-ter. The entire quantity of mixed water i s then completely removed from the s t r a i t on the ebb tide. It can be shown (Officer, 1976) that the time to replace the existing fresh water i n an estuary at a rate equal to the river discharge (the t i d a l flushing time) i s given byj 101 7.1 where V i s the volume of the estuary, P the volume of the t i d a l prism and T the period of the semidiurnal tide. The volume of the estuary was chosen to be the volume of the s t r a i t lying with the bounds of the max-imum t i d a l excursion. Typical t i d a l excursions from Boundary Passage (Tully and Dodimead, 1957) are 18 km (11 miles) for the flood tide and 40 km (25 miles) for the ebb tide. The estimated volume of the s t r a i t lying within this range i s 379 knr^  while Waldichuk (1957) gives the mean volume of the t i d a l prism as 23*1 knr leading to an estimate of 8.2 days for the t i d a l flushing time. Since there i s not complete mixing during each t i d a l cycle and since some of the mixed water i s returned on the succeeding flood tide the calculated flushing time w i l l be less than the actual time. Nonetheless, t i d a l flushing should be important i n the Cen-t r a l and South regions i n removing fresh water (and pollutants) on time scales of the order of weeks. Estuarine circulation i s another advection process occuring i n the Strait of Georgia. The outflow of fresh water to the sea and the i n -flow of deep saline water tends to displace and renew the waters of the s t r a i t . Estimates of the efficiency of the removal of fresh water can be made by calculating the flushing time given by where V f i s the freshwater volume of the s t r a i t and R the runoff river flow. I f the total freshwater volume of the s t r a i t i s used flushing times on the order of 400 days are obtained. However, the flow of brack-ish water i n the s t r a i t i s for the most part confined to the upper 50 metres. As discussed by Waldichuk (1957) the total amount of fresh water 7.2 102 depends upon the value chosen for the base salinity. The percentage of fresh water in the upper layers will be (100)(SB - S)/SB with S the av-erage salinity of the layer and the base salinity (chosen to be 33.8%,). The estuarine flow will be more important in the Northern and Central regions where tidal mixing is small. Table V gives the average salinity of the upper 50 metres for the Northern and Central regions, the volume of fresh water in the layer, the volume of river runoff and the flushing times for the months of February, May, August and November of 1968. Flushing times vary from 80 to 180 days and give the time scale for removal of fresh water from the strait due to estuarine flow. The deep flow of saline water into the strait in response to the removal of fresh water can also work to alter the waters of the strait. Using Waldichuk*s 1957 estimates of the volume flowing into the strait, the time scales needed to completely renew the waters of the strait were estimated to be of the order of 10 months. Estimates were also made of the changes of potential energy due to the inflow of denser water from estuarine flow. The average density of layer 2 increased when fresh wa-ter runoff Increased in response to the increased estuarine circulation. Table VI shows the changes in sigma-t and corresponding changes of po-tential energy per grid compartment for layer 2 of the Northern and Cen-tral regions. While much of the changes of density in that layer was due to vertical entrainment mixing and not horizontal advection, the calcu-lated estimates of potential energy would represent the maximum effects of advection. In addition to the flow of denser water into the strait as part of the general estuarine circulation another advection process is the formation and intrusion of seasonal water masses. As described in sec-tion 7.1 the intrusions of different water masses followed the pattern 103 Month Runoff (km3) Region S F.W. (km3) t (days) Central 28.13 21.3 91 Feb 6.5 Northern 28.38 20.4 88 Central + Northern 28.3 41.7 179 Central 27.99 21.9 44 May 15.3 Northern 28.63 19.5 40 Central + Northern 28.3 41.3 84 Central 28.02 21.7 5k Aug 12.6 Northern 27.5^ 23.6 58 Central + Northern 27.8 ^5.3 112 Central 27.9^ 22.0 79 Nov 8.4 Northern 28.20 21.1 75 Central + Northern 28.1 43.1 154 Table V Fraser River runoff and average s a l i n i t i e s for the upper 50 m (Layers 1 and Z) of the Northern and Central regions plus fresh water contents (F.W.) and flushing times. Region Layer Feb - May May - Aug Aug - Nov Ao- A E (J) ACT A E (J) ACT A E (j) 2 +0.39 -10 X 10 1 0 -0.23 +6 X 10 1 0 -0.09 +2 X 10 1 0 Central 7 +0.09 -2 X 10 1 0 +0.05 -1 X 10 1 0 +0.01 -3 x lo 9 Northern 2 +0.24 -6 X 10 1 0 -0.33 10 +9 X 10 i U -0.01 +3 x lo9 Table VI Average changes of the mean density and potential energy for grid compartments i n the Northern and Central regions. 104 described by Waldichuk (1957) with the exception that the formation of a cold Intermediate Water in the Northern region was not observed. One o-ther slight difference was that the intrusion of warm and saline water in summer did not form an Intermediate Water but advanced along the bot-tom and so should more properly be labeled summer Deep Water. To b r i e f l y recap the description of seasonal Intrusions there i s the formation and intrusion of two different masses that in turn form the deep waters of the s t r a i t . In winter, cold water with a slightly lesser salin i t y d i s -places the warm water l e f t from the previous summer. In 1968 this o-ccurred between February and May. In summer and autumn warm saline water intrudes and forms the new deep water mass. This happened between May and August in I968 and continued through November. Both intrusions en-tered the s t r a i t through the San Juan region and moved northwards. A l -though the average density density of the Northern region In layers 7 and 9 showed a slight decline from February to May, the average density of the Central region increased i n the same period and the average den-s i t i e s for both regions increased between February and November (Figures 30 and 31)• This indicates that the deep waters of the s t r a i t were re-placed by advection of denser water. Table VI shows the increases of sigma-t for layer 7 of the Central region plus the decreases of potenti-a l energy in a grid compartment due to the Increases of density. While changes i n density were small the seasonal intrusions were important in altering the physical properties of the deep waters i n the absence of other mechanisms. 7.3 Mixing Energies This section deals with the actual 'budget' of mixing in the Strait of Georgia. The numerical estimates of mixing i n each region were 105 made by calculating the average potential and mixing energies for one of the grid compartments. These estimates are presented in Tables VII through X for layers 1, 2, 7 and 9. The columns marked Eg represent the total potential energy for a grid compartment that has been divided into a fresh water layer and a salt water layer with a salinity of 33«8%0 (as discussed in section 5•2c) while the columns marked E^ represent the total observed potential energies for one grid compartment. AE is the difference between Eg and Ep and represents an estimate of the total amount of mixing done on the water column and the amount of change from a totally stratified state. The magnitude of AE depends quite strongly upon Eg which in turn de-pends upon the value chosen for the base salinity of the two-layer sys-tem. For instance i f the value of the base salinity was chosen to be 32.8%, instead of 33* 8%*, values of Eg would be increased (AE would be 10 decreased) by approximately 16 X 10 J . Eg also depends upon the aver-age salinity of the entire layer (which determines the thicknesses of the fresh and salt sub-layersas given by equations 5»1^ and 5»15)» Since Eg and E^ are negative quantities, any decreases in value mean a corresponding increase in the absolute value. A decrease of 1% in the a-verage salinity would lead to an increase of Eg of 14 X 10*° J . The en-ergy required to mix a grid compartment from the observed density struc-ture to homogeneity is given by E m # In general, E m will also give a mea-sure of the stratification since the more stratified a layer is the more energy is needed to mix i t to a uniform density. The sum of E^ plus A E represents the total energy needed to mix the grid compartment from a totally stratified state to homogeneity. It can be shown from the defin-itions of the two-layer potential energy density (equation 5«16) and the mixing energy density (equation 5«H) that the sum of AE and E (which 106 would be the mixing energy for the totally s t r a t i f i e d state) i s given by AE + E„ = x L~rrf 7.3 where V i s the total volume of the grid compartment (approximately 2 . 1 4 knr). rT" depends only upon the base salini t y (assuming a constant temp-s erature) and L and L_ depend only upon the average s a l i n i t y of the lay-er plus the base s a l i n i t y . Thus assuming no changes i n the average temp-erature or sali n i t y , A E + E^ w i l l remain constant. Of course the aver-age temperatures and s a l i n i t i e s do not remain constant for any grid com-partment or layer but within the accuracy of the calculations the sum of A E plus E^ remains essentially constant for many of the regions of the s t r a i t . For example, for the months of February, May, August and Novem-ber the sum of A E plus E^ for the Central region of layer 1 (Table VII) was respectively 9 9 . 9 , 100.2, 96 .5 and 103.3 (X 10 1 0 J ) , a variation of only 2,8% from the mean while the sum of A E plus E m for the San Juan region of layer 1 was 73 .4 , 70.2, 61.7 and 6 1 . 8 (X 10 1 0 j ) , a variation of 8,9%, Since sigma-t does not depend as strongly upon temperature as upon sa l i n i t y for the range of temperature and sal i n i t y found i n the st r a i t , changes i n the average temperature tend to change the calculated densities of the fresh and salt sub-layers by the same amount so that the term cr - <r> i n equation 7*3 remains constant for many variations of S X temperature. Therefore, changes i n the average temperature of a layer may change the magnitudes of the potential energies but have a much smaller effect upon the total amount of energy needed to mix a layer from a totally s t r a t i f i e d state. The total magnitude of A E plus E de-m pends most strongly upon the average salin i t y of the layer. This can be seen by using equation 5 . 14 and 5.15 to rewrite equation 7.3 as: 107 which has the form of a parabola with a maximum at S/33.8 » i , or S -16.9%, • Since a l l of the average s a l i n i t i e s for the different regions were i n the range between 16.9/L and 33»8%> i n general the greater the average sa l i n i t y the smaller the value of AE + E • m Table VII presents the estimates of the various energy terms that are important i n mixing layer 1. E w and E^ represent the total energy input or loss due to wind mixing and buoyancy fluxes respectively. A l l energy estimates are f o r a single grid compartment in each region and are the average value f o r the entire region. The sum of E w plus E^ was negative f o r a l l regions for the months of May and August indicating losses of potential energy due to increasing s t r a t i f i c a t i o n . Values of fcE decreased between February and May with relative declines from Q% to 33$ for the various regions with corresponding increases of E^. However, ^ E increased between May and August for the Northern and Central re-gions even though E^ reached a minimum. E^ also showed an increase dur-ing this period and was probably responsible for the increase i n ^ E . Wind mixing seemed to be more important than buoyancy losses i n the Northern and Central regions than the energy estimates indicate. A l l values of &E increased between August and November as E^ turned posi-tive (indicating convective mixing) and as E increased. The sum of w plus E m remained f a i r l y constant (within the accuracy of the calcula-tions) for layer 1 escept for the Southern region. The Southern region was also anomalous in having the greatest values of ^ E + E^ when equa-tion 7*4 suggests that since the average sa l i n i t y l i e s between that of the San Juan and Central regions the sum of AE plus E for the Southern m region should also have an intermediate value between those of the San 108 Mixing Energies (X 10 J) E 2 E n E m nE+E m E w Ew'*,Eb San Juan Region Feb -691.9 72.0 -619.8 1.4 73.4 1.4 2.2 3.3 May -683.9 65.5 -618.3 4.7 70.2 4.7 -23.0 -21.6 Aug -672.O 57.6 -614.4 4.1 61.7 1.0 -11.3 -10.3 Nov -682.1 59.3 -622.8 2.5 61.8 2.4 3.2 5.6 Southern Region Feb -683.7 140.7 -543.0 2.7 143.4 1.1 -2.7 -1.6 May -667.0 97.3 -569.7 17.9 115.2 0.1 -3.4 -3.3 Aug -653.9 67.6 -586.3 13.0 80.6 1.2 -17.9 -16.7 Nov -667.1 103.9 -563.3 11.5 115.^ 6.3 9.2 15.5 Central Region Feb -674.2 90.6 -583.6 9.3 99.9 2.6 -3.6 -1.0 May -644.5 60.4 -584.1 39.8 100.2 1.9 -12.2 -10.3 Aug -638.7 67.0 -571.1 29.5 96.5 3.3 -27.2 -23.9 Nov -652.1 83.1 -568.9 20.2 103.3 6.5 5* 11.8 Northern Region Feb -672.5 86.1 -586.5 4.3 90.4 1.0 -0.9 0.1 May -646.5 72.9 -573.7 14.3 87.2 1.1 -14.2 -13.1 Aug -616.8 84.6 -532.2 21.5 106.1 2.4 -36.6 -34.2 Nov -654.4 89.7 -564.7 7.3 97.0 5.0 7.0 12.0 Table VII Estimates of mixing energies per grid compartment for Layer 1 (0 m - 25 m). 109 Juan and Central regions. The explanation could be that since the South-ern region was the smallest region averaging may not have smoothed out the variations between the s t r a t i f i e d conditions at the northern bound-ary of the region and the t i d a l l y mixed conditions i n the rest of the region and that the average sa l i n i t y of the region does not correctly indicate the possible ranges of potential energies. In general, consid-ering the uncertainty of using monthly estimates of wind speed and heat fluxes (which both could have errors of a factor of 2 or more) the changes of A E and seem to agree with expected changes from meteoro-logical changes. It should be noted that since none of the grid compart-ments of layer 1 were on the bottom of the s t r a i t no estimates were made of t i d a l mixing i n layer 1. However since t i d a l mixing energies are so large for deeper layers i n the Southern and San Juan regions (Tables VIII, IX and X) i t seems l i k e l y that t i d a l mixing i s also important for layer 1 i n those regions. Table VIII shows the mixing energy estimates for layer 2. There was some uncertainty on which energy terms should be included. Tidal en-ergy estimates were included because some grid compartments of layer 2 were on the bottom of the s t r a i t i n each region and subject to t i d a l mixing. While wind mixing was probably confined to layer 1 ( a l l calcu-lated mixed layer depths were less than 25 metres) convective mixing may be important for layer 2 besides ve r t i c a l entrainment mixing. Table VI contains estimates of potential energy changes i n layer 2 due to estuar-ine advection and entrainment. The average s a l i n i t i e s of layer 2 were higher than those of layer 1 and the values of ( AE + E ) were corre-m spondingly lower. Values of E^ i n layer 2 were also smaller than those of layer 1 indicating smaller s t r a t i f i c a t i o n . Values of A E declined for a l l regions between February and May, by Zk% i n the San Juan region and Mixing Energies (X 1CTU j) E 2 A.E E n E m E+E m E t San Juan Region Feb -693 .5 67.8 -625.8 0.7 68.5 1250 May -687.7 51.0 - 6 3 6 . 6 0.7 51.7 1340 Aug -681.3 48.5 -632 .8 2.1 50.6 1390 Nov -684.4 55.4 -629.1 0.8 56.2 1340 Southern Region Feb -687.5 74.1 -613.3 1.2 75.3 394 May -681.3 63.4 -617.8 1.0 64.4 423 Aug -671.8 60.2 -611.6 3.0 63.2 437 Nov -677.2 63.7 -613.5 2.0 65.7 404 Central Region Feb -680.2 77.1 -603 .1 2.0 79.1 20.9 May -679.5 66.3 -613.1 1.4 67.7 14.3 Aug -671.9 64.2 -607.7 2.2 66.4 23.1 Nov -671.5 65.1 -606.4 3.2 68.3 22.4 Northern Region Feb -674.6 77.8 -596.9 1.5 79.3 0.1 May -669.4 65.9 -603.5 1.6 67.5 0.1 Aug -662 .4 64.5 -597.9 4.6 69.1 0.1 Nov -665.1 68.6 -596.5 3.5 72.1 0.1 Table VIII Estimates of mixing energies per grid compartment for layer 2 (25 m - 50 m). I l l and by approximately 15$ i n the other regions. AE declined further by August by 2% to k% while E reached maximum values indicating maximum m str a t i f i c a t i o n . Values of increased between August and November by \2% i n the San Juan region, 2% i n the Central region and 6% i n the Southern and Northern regions. This was probably due to convective mix-ing since values of calculated f o r layer 1 were at a maximum. In gen-eral, values of E m were smallest i n the Southern and San Juan regions where t i d a l mixing kept any s t r a t i f i c a t i o n to a minimum. Tidal mixing energies (E^) were quite large i n the San Juan and Southern regions and relatively small elsewhere. The calculated t i d a l energies are for grid compartments that were on the bottom of the strait» some grid compart-ments were not on the bottom so that the total amount of energy expend-ed i n layer 2 of the southern s t r a i t may not be as large as Indicated. Nonethless, the estimated t i d a l mixing energies for the southern s t r a i t are so large that even near the surface some areas of the Southern and San Juan regions should be mixed to homogeneity (as indicated by Figures 64 and 65). Mixing energy estimates for layer 7 are shown in Table IX. The average s a l i n i t i e s for the layer have increased over layers 1 and 2 and the sum of 4 E plus E i s even smaller than that of layer 2. Variations m of temperature and s a l i n i t y are smaller i n the deep layers than i n the upper layers and this accounts for the smaller variations i n Eg, the two-layer potential energy. Changes i n physical properties mainly resulted in changes i n the observed potential energy ( E p ) . The Southern and San Juan regions show different variations i n potential energies than the o-ther regions. AE shows a decrease between February and May and an i n -crease between August and November for the southern s t r a i t while AE declines steadily from February to November for the Northern and Central Mixing Energies (X 1 0 1 U J) E_ AE E E /\E+E E. 2 fj E "» "> t San Juan Region Feb -6988G 47.5 -650.5 2.0 49.5 1450 May -695.3 30.7 -664.6 1.4 32.1 1560 Aug -692.4 28.2 -664.2 2.2 30.4 1560 Nov -689.5 39.9 -649.6 1.6 41.5 1560 Southern Region Feb -691.8 61.4 -630.4 0.8 62.2 369 May -690.7 40.0 -650.5 0.9 40.9 352 Aug -686.7 36.8 -659.9 2.0 38.8 364 Nov -684.0 45.6 -638.4 3.5 49.1 526 Central Region Feb -684.2 51.6 -632.7 1.2 52.8 25.6 May -683.8 48.9 -634.9 1.2 50.1 27.4 Aug -681.8 45.7 -636.1 1.1 46.8 28.3 Nov -680.3 43.7 -636.6 1.1 44.8 27.4 Northern Region Feb -675.9 48.2 -627.7 0.7 48.9 0.1 May -677*7 50.4 -627.4 0.8 51.2 0.1 Aug -677.3 47.8 -629.5 0.9 48.7 0.1 Nov -675.0 45.6 -629.5 0.8 45.7 0.1 Table IX Estimates of mixing energies for layer 7 (150 m - 175 m). 113 regions. The energy changes are mainly due to changes of the average den-sity (and salinity) illustrated by Figure 30 which i n turn seem to be due to advection of different water masses (as discussed i n the previous section). Mixing energies (E m) are small throughout the layer indicating l i t t l e s t r a t i f i c a t i o n . They are larger i n the t i d a l mixing areas of the southern s t r a i t because t i d a l mixing actually causes a larger v e r t i c a l change in density than i n the northern s t r a i t as i t t i l t s the sigma-t lines (and those of s a l i n i t y as shown i n Figure 65). Layer 9 mixing energy estimates (Table X) are almost identical to those of layer 7 since the vertical change of properties i s small i n the deep layers of the s t r a i t . Values of E are somewhat smaller than those m of Layer 7. It i s l i k e l y that the deep water of the Strait of Georgia i s relatively homogeneous so that any mixing done on the water column does not a l t e r the average density structure and change the potential energy. Instead, the potential energies of layers 7 and 9 respond to gradual changes of density caused by seasonal intrusions of deep water masses. The main vertical mixing process acting upon the deep layers i s t i d a l mixing. Tidal mixing energies are more than sufficient to mix the layers i n the Southern and San Juan regions and negligible i n the Northern re-gion. Tidal mixing may be important i n the Central region but i t i s pos-sible that the energy estimates have been overestimated so at present i t i s uncertain how much the tide contributes to the total mixing of the Central region. To summarize, most of the variation of the different mixing ener-gies occurs i n layers 1 and 2 which receive the effects of wind, tide, convective and entrainment mixing and st r a t i f i c a t i o n through fresh water runoff and surface heating. Away from the t i d a l mixing areas of the southern s t r a i t the deeper layers (layers 7 and 9) have energies that Mixing Energies (X i 0 l u j) E 2 AE E E m AE+E m 1 t San Juan Region Feb -697.9 48.6 -649.3 0.3 48.9 1530 May -696.4 27.2 -669.2 1.2 28.4 1640 Aug -692.8 25.1 -667.6 1.8 26.9 1690 Nov -690.6 34.8 -655.8 1.2 36.0 1640 Southern Region Feb - - - - mm -May -691.1 36.3 -654.9 0.9 37.2 526 Aug -690.7 29.4 -661.3 1.3 30.7 544 Nov -686.7 37.4 -649.3 1.1 38.5 526 Central Regi .on Feb -682.5 46.3 -636.1 0.8 47.1 2.4 May -683.8 46.6 -637.2 0.6 47.2 2.5 Aug -682.5 43.8 -638.7 0.6 44.4 2.6 Nov -681.2 42.0 -639.2 0.6 »i«ri L — • • nt mnm 42.6 2.5 Northern Region Feb -675.9 45.7 -630.2 0.7 46.4 0,1 May -677.6 48.0 -629.6 0.4 48.4 0.2 Aug -678.0 46.2 -631.8 0.3 46.5 0.2 Nov -676.6 44.6 -632.0 0.5 45.1 0.2 Table X Estimates of mixing energies for layer 9 (200 m - 225 m). 115 chiefly respond to variations of the average density caused by horizont-a l exchange processes, 7 . 4 Errors The estimates of potential and mixing energies are subject to a number of errors and uncertainties that make i t d i f f i c u l t to reach an exact balance i n the mixing budget. The data used to calculate the aver-age properties of the different layers and the estimates of the contri-butions from the different mixing mechanisms have various degrees of sampling errors arising from the various approximations that were made. One possible source of error i n calculating the potential energy and mixing energy densities i s due to neglecting the adiabatic compres-sion of the water column. The water of the Strait of Georgia (or any-where else) i s not incompressible and adiabatic compression causes a vertical gradient i n the density that i s not due to st r a t i f i c a t i o n . For-tunately, the effect of the adiabatic compression i n a layer can be ea-s i l y estimated. The ver t i c a l gradient of density i n the water column due to compression,if I i s given by (Karaenkovich, 1 9 7 3 ) » p o i s the average density of the column, c the speed of sound and ^ the ratio of the specific heats of sea water. These quantities can be assumed to remain essentially constant over a layer with a thickness of 25 metres so that the potential energy per unit volume, E . due to adia-St batic compression over a depth H i s i 7 . 6 116 The speed of sound i n sea water i s approximately 1500 m s""\ (Y - 1) i s approximately (Dorsey, 1940) 2 X 10~ 2, p Q i s 1.02 X 1(P kg m"3 and g i s -2 "3 9.8 m s so for a layer with a thickness of 25 metres, E = 0.2 J m . cL 3 For one grid compartment with a volume of 2 km the potential energy due Q to adiabatic compression i s 4x10 J which i s only 0.007$ of the po-tential energy due to sigma-t alone. Since the observed variations of potential energies are on the order of 1 X 10*° J the effect of adiabat-i c compression may be safely neflected. There i s a certain amount of error i n the calculated potential energies due to sampling uncertainties i n the density data. It was e s t i -mated that the interpolated values of sigma-t used in the calculations haderrors of plus or minus 0.02 sigma-t units (approximately 0.09$). An error of this magnitude meant there was an uncertainty i n the total po-ol tential energy of a grid compartment of approximately 6 X 10 J so that any variations of potential or mixing energies below this value were be-low the •noise* l e v e l . There were also errors associated with the numer-i c a l analysis of the potential energy Integral. A l l integrations were a-pproximated by a Simpson's rule method. This method has an inherent err-or given by (McGracken and Dorn, 1964): where f^\\ ) i s the fourth derivative of the function being integrated and Ax i s the width of the subinterval which the range of the integral has been divided into. The potential energy integrals depended upon the function C(z)z which varied most rapidly i n the surface layer near the pycnocline. To a reasonable approximation 0~(z) could be represented by a third order function CT + Az^ near the pycnocline and by lower order polynomials elsewhere. Examination of vertical density profiles led to 117 an estimate of 1 X 10 7 sigma-t units cm for the constant A so that the fourth derivative of cr(z)z was 24(A) (24 X l o" 9 <r cm"3) near the pycnocline and zero elsewhere. Using equation 7*7 the intrinsic error in using Simpson's rule was estimated and the total error in potential en-o ergy for one grid compartment is approximately 1 X 10 J for the surface layers and zero for the deeper layers. Thus the error due to the numeri-cal method used was less than the sampling error and could be ignored. There were also, unfortunately, Large errors in the estimates of mixing energies by wind, tide and buoyancy forces. The estimates of wind and tidal mixing depend upon the cube of wind and tidal velocities (e-quations 6.4 and 6.8) so that the uncertainties in the mixing energies are three times those of the velocities. This is not as important in the tidal mixing estimates because of the large difference in velocities and mixing energies between the San Juan and Southern regions (the southern strait) and the Northern and Central regions, resulting in large energy estimates in the southern strait and relatively small mixing energy es-timates in the northern strait. The difference is so large that a rela-tive error of 100?? in the mean tidal velocities would not change the conclusion that can be drawn from Tables VIII through Xt tidal mixing energies are more than enough to mix the southern strait but are usually too small to contribute to the mixing budget of the Northern region and probably the Central region as well. The errors in the estimates of wind mixing are probably not trivial however. The estimates of wind mixing were made using the monthly mean of wind speeds as estimated from mete-orological stations that were on the shore. This ignored the possibility that a strong wind may have been more effective in mixing the surface layers than a weak one. Also there may have been large (but.unavoidable) errors in estimating wind speeds over the Strait of Georgia from scat-118 tered stations that may have been located far from the area of interest (as i n the Northern region). A doubling of the mean wind speed would lead to increasing the wind mixing energy estimates by a factor of four and i t i s possible that the wind mixing energy estimates of Table VII are off by 300$ for the higher values (but probably not by so much as an order of magnitude). Buoyancy flux estimates may have had relative err-ors on the order of 100$. It was not intended that monthly averages of solar radiation taken at only two stations be considered to accurately reflect conditions over the entire s t r a i t or that the buoyancy flux c a l -culated from equation 6.5 remained constant over the upper layer. None-theless, there seemed to be rough agreement between changes of the buoy-ancy flux energy and the potential energies of the water column. Other uncertainties i n the mixing budget were due to changes of the density structure due to l a t e r a l advection. Changes i n the calculat-ed potential energy of the s t r a i t that were not due to ve r t i c a l mixing processes could be attributed to advection. The advection processes var-ied from the large such as t i d a l advection with excursions of the water column of kilometres within hours to the small such as estuarine flow -1 and seasonal intrusions with velocities less than 1 cm s . Much of the horizontal variations of the physical properties from month to month could be attributed to the effects of t i d a l advection which displaces the waters of the s t r a i t twice a day. Unless hydrographic surveys were made at the same phase of the tide each month there could be considerable differences i n the calculated energies due to displacement of the water by the tide. Averaging the physical properties over an entire region of the s t r a i t tended to minimize t i d a l differences but longer period advec-tion processes such as estuarine flow and seasonal intrusions were re-sponsible for much of the v a r i a b i l i t y of the average properties and ener-119 gies especially i n the deep waters of the s t r a i t . Comparison of Table VI with Tables VIII and IX indicates that many of the changes of Eg, E^ and A E were due to changes of density caused by advection instead of v e r t i -c a l mixing processes. While much of the change of potential energy f o r layer 2 may be due to estuarine entrainment (a ver t i c a l mixing process) and not to horizontal estuarine flow, vi r t u a l l y a l l of the variations of the potential energies for layers 7 and 9 may be attributed to advec-tion. To summarize, the errors i n estimating the contributions from the different mixing processes prevent reaching an exact balance i n the mix-ing budget. Uncertainties i n the magnitudes of the potential energies due to sampling errors and the numerical analysis are small and are much smaller than the changes caused by horizontal advection. 120 8. CONCLUSION The state of mixing i n the Strait of Georgia i s a four dimension-a l problem with variations depending upon depth, geographic location and time of year. The greatest geographic variations are between the southern s t r a i t (the Southern and San Juan regions) and the northern s t r a i t (the Central and Northern regions). Tidal mixing i s the most important (and obvious) mixing process i n the southern s t r a i t and tends to maintain a vertica l l y homogeneous water column (Figures 64, 65 and 66) with mixing energies in excess of what i s needed for to t a l mixing (Tables VIII, IX and X). Although t i d a l mixing minimizes ve r t i c a l differences of physical properties i n the southern s t r a i t the average properties such as temper-ature and s a l i n i t y do show seasonal variations. This i s due to seasonal changes of the waters of the Strait of Juan de Fuca and the Strait of Georgia since the water mass of the Southern and San Juan regions i s a mixture of the surface waters of the northern Strait of Georgia and the deep water of the Strait of Juan de Fuca. The northern s t r a i t can be divided into the surface layers and the deep layers. The surface layers of the northern (and to some extent the southern) Strait of Georgia are affected by fresh water runoff, i n -flowing sea water (estuarine flow) and meteorological conditions. In the late f a l l and winter convective mixing due to gravitational i n s t a b i l i t y i s the most important mixing mechanism closely followed by wind mixing (Table V i i ) , Fresh water runoff and surface heating leading to a nega-tive buoyancy flux decreases the total amount of mixing (with an increase of t o t a l stratification) i n the spring and summer for layer 1 but i n -creased estuarine flow and upwelling tends to offset the increased str a t i f i c a t i o n i n layer 2 although the to t a l amount of mixing does de-121 crease. The deep waters of the northern s t r a i t constitute a third regime that responds to different mixing mechanisms. Exchange processes predom-inate i estuarine flow i n the intermediate layers and the formation of deep water masses i n summer and winter. Deep flow originates i n the southern s t r a i t and travels northwards. The northern area of Malaspina Strait forms a stagnant basin with higher s t r a t i f i c a t i o n than other ar-eas of the northern s t r a i t as evidenced by oxygen data indicating deep flow passes to the west of Texada Island. Tidal mixing i s a more eff i c i e n t mechanism i n removing fresh wa-ter from the s t r a i t than estuarine circulation with t i d a l flushing times on the order of weeks while estuarine circulation flushing times"are*on the order of months (see section 7.2). There are large uncertainties i n calculating mixing energies by using monthly averages of meteorological conditions. However, using monthly averages leads to estimates that are correct to an order of mag-nitude and which help to indicate the relative importance of wind mix-ing versus convective mixing or Increasing s t r a t i f i c a t i o n . In conclusion the Strait of Georgia i s an extremely dynamic sys-tem with large variations of physical properties from onth to month or indeed from t i d a l period to t i d a l period. More refined measurements of mixing can certainly be made but the apparently random changes that occur i n the s t r a i t may make prediction of a l l but the gross features of the waters d i f f i c u l t i f not impossible. 1 2 2 LONGITUDE Figure 1 The Strait of Georgia showing the main geographic features. 123 Figure 2 The four regions of the Strait of Georgia. BOUNDARY JUAN DE F U C A ST. P A S S S T - 0 F GEORGIA Figure 3 M O •8 Hj 3 o 3 c+-CT (0 0.0 N F R A S E R R I V E R RUNOFF 4.0 8.0 12.0 (KM3J 16.0 20.0 m C D I D a -I v a «r 01 CD H -< vO ON OO D C T CD CO m o —I £21 JUAN DE FUCA ST. BOUNDARY PASS ST. OF GEORGIA F i g u r e . % Schematic i l l u s t r a t i o n of the winter formation of deep water masses i n winter (from Waldichik, 1957) JUAN DE F U C A ST. BOUNDARY P A S S ST. OF GEORGIA Figure 5b Schematic of the summer formation of deep water masses (from Waldichuk, 1957) 128 Figure 6 Internal wave groups i n the southern Strait of Georgia. The lines drawn delineate the areas of the wave groups photo-graphed during a f l i g h t i n May of I968. The f l i g h t line be-tween Point Roberts and East Point i s also shown, (from Samuels and LeBlond, 1977) 129 H •z=0 • uif/uh ///////II mi 11 a iiiiuinir/in / nii//ufUi/J/i///i/iiiii/iiii/iui/j A B F i gu re 7a Schematic i l l u s t r a t i o n of a s t r a t i f i e d water column. z=-H F i gu re 7o Schematic i l l u s t r a t i o n of a homogeneous water column. 130 L O N G I T U D E Figure 8 Locations of the hydrographic data stations i n the Strait of Georgia for the four representative months. 131 Merry I. ^Ballenas I. Sandheads Pt. Atkinson Vancouver Saturna I. \2$ 00* 224? 40* 124^  20* 124^  00' 323b 40' 123^  20' 3234 00* L O N G I T U D E Figure 9 Locations of the meteorological data stations around the Strait of Georgia. 132 LONG ITUDE Figure 10 Illustration of the grid system used to approximate the outline of the Strait of Georgia. 133 o L O O LO 3" o ro o . 3 O CM § 3 Q o -Q L O cn a . 6 . 8 • G 4 0 S T R A I T OF G E O R G I A TEMPERATURE O 1M F E B R U A R Y 1 9 6 8 LAYER 1 0 -25 METRES MIN. VALUE 5.98 MAX. VALUE 7.83 CONTOUR INTERVAL 0.40 6 . 8 . - . 6 . 8 125* 00' 124" 40" 1 2 4 » 2 0 ' 124° 00' 123" 40" 123^  20' 1234 00 LONG ITUDE Figure 11a Layer 1 average temperatures for February. o LO O LO o Q o . 3 O 9 Q § 3 C D o 9 LO O 1 9 6 8 MAY LAYER 1 0 -25 METRES MIN. VALUE 8.93 MAX. VALUE 12.50 CONTOUR INTERVAL 3.00 S T R A I T OF G E O R G I A TEMPERATURE 0 I . i * i 125»00' 124^ 40' 124*20' 124*00' 123'40' 123*20" 123» 00' LONG ITUDE • Figure l i b Layer 1 average temperatures for May. 135 o-O m a • O o . Q <D o . Q C\J L U 0 . C 3 in Q Q 1 3 , 114.5 1 9 6 8 RUGUST LRYER 1 0 -25 METRES M1N. VRLUE 9 . 6 3 MRX. VALUE 15.30 CONTOUR 1NTERYRL 1.50 S T R R I T OF GEORG IR TEMPERRTURE 1 0 129s 00' 124*41)' 124»20" 124*00* 123» 40' 1235* 20' 123fc 00" L O N G I T U D E Figure 11c Layer 1 average temperatures for August. 125s 00' 124" 40' 124* 20* 124° 00' 123" 40' 123° 20' 123» 00* LONGITUDE Figure l i d Layer average temperatures for November. 137 J . I I I I I L 125* 00' 124° 40' 124* 20' 1246 00' 1231 40' 123° 20' 123'00* L O N G I T U D E Figure 12a Layer 2 temperatures for February. 138 o LO LO o , o . $ Q fO o . O O LO o . \r o cn o _ LAYER 2 25 -50 METRES MIN. VALUE 7.98 MAX. VALUE 9.81 CONTOUR INTERVAL 0.40 S T R A I T OF G E O R G I A TEMPERATURE 125* 00' 124* 40' 124* 20' 124° 00' 123' 40' 123*20" 123* 00' L O N G I T U D E Figure 12b Layer 2 temperatures for May. 139 125^  OO* 124 40' 12^20- 12^00; 123^40- 123" 20' 123'OO-LONG ITUUE Figure 12c Layer 2 temperatures f o r August. 140 O LO L O 3" C 3 C O 3 o CM § 3 C 3 8 o LO a cn Q NOVEMBER 1 9 6 8 LAYER 2 25 -50 METRES M3N. VRLUE 9.08 MAX. VALUE 9.79 CONTOUR 1NTERVRL 0.20 S T R A I T OF G E O R G I A TEMPERATURE Q 125s 00* 124° 40V 124s 20' 124° 00" 123» 40" 123d 20* 123* 00* Figure I2d L O N G I T U D E Layer 2 temperatures for November. 141 CD-O LO C D L O C D X T o . 3 3 C D C M . C D 5 3 C D C D o LO C D v $ C D C O o . F E B R U A R Y 1 9 6 8 LRYER 7 350-175 METRES M3N. VRLUE 7.22 MRX. VALUE 9.06 CONTOUR INTERVAL 0.50 S T R A I T OF G E O R G I A TEMPERATURE 7 . 5 / 125»00' 124° 40' 1246 20' 124° 00* 123' 40' 1238 20' 123* 00' LONG ITUDE Figure 13a Layer 7 temperatures for February. 142 co-ca o m CO in a . % \r Q C D o -o CM o 3' o in o O ro S T R A I T OF GEORG IA TEMPERATURE MAY 1 9 6 8 LAYER 7 150-175 METRES M1N. VALUE 8.24 MAX. VALUE 8.62 CONTOUR INTERVAL 0.10 IS) 83 125^00' 224*40' 124»20' 1245* 00* 123" 40' 123° 20' 123* 00' LONG ITUDE Figure 13b Layer 7 temperatures for May. 143 co-ca a o L O o . 3 O 3 co o • O CM C D C 3 3 C D L O O o cn * 1 RUGUST 1 9 6 8 LRYER 7 250-175 METRES MIN. VRLUE 8.37 MRX. VRLUE 9.53 CONTOUR 1NTERVRL 0.30 S T R A I T OF G E O R G I A TEMPERATURE .8 4 125*00' 124" 40' 124*20" 124*00* 123* 40" 123*20* 123* 00* L O N G I T U D E Figure 13c Layer 7 temperatures for August. 144 o ir? o in w O \r o $ O CO a * o CM o <7 9 o m o o oo S T R A I T OF GEORG IA TEMPERATURE NOVEMBER 1 9 6 8 LAYER 7 150-175 METRES M3N. VRLUE 8.83 MRX. VALUE 9.27 CONTOUR INTERVAL 0.10 . 9 . 1 12^00* 124* 40* 124*20* 124*00* 123» 40* 123*20' 123-00 LONG ITUDE Figure 13d Layer ? temperatures for November. 1*5 o in Q to C D o . C 3 C O 5 Q O J § 3 ' C D C 3 C 3 3 LO O "\T Q ( O o . 8.8 FEBRUARY 1 9 6 8 LRYER 9 200-225 METRES MIN. VRLUE 7.21 MRX. VALUE 9.30 CONTOUR INTERVAL 0.20 S T R A I T OF G E O R G I A TEMPERATURE 8.4 125* 00* 124° 40' 124* 20' 124* 00' 123» 40' 123° 20' 123' 00* Figure 14a LONG ITUDE Layer 9 temperatures for February. 146 LO o L O o ro O CM § 3 C D Q 9 L O O Q ro a . 8 . § J 8.8 o 8.4 8,6 MAY 1968 LAYER 9 200-225 METRES M3N. VRLUE 8.01 MAX. VALUE 8.83 CONTOUR INTERVAL 0.20 STRAIT QF GEORGIA TEMPERATURE 8.2 125* 00* 124° 40' 224* 20" 124* 00' 323* 40" LONGITUDE Figure 14b Layer 9 temperatures for May. 123* 20* 123k 00* 147 o-Q o O to Q to o _ Q \r o _ Q CM o Q o . 3 O LO Q © -o -8 . 6 RUGUST 1 9 6 8 LRYER 9 200-225 METRES MIN. VRLUE 8.26 MRX. VALUE 9.08 CONTOUR INTERVAL 0.20 N . 8 . 6 S T R A I T OF G E O R G I A TEMPERATURE 7€T 8 . 8 8 , 4 8 , 8 8 , 6 125* 00' 124° 40' 124* 20' 124* 00' 123" 40' 123° 20' 323» 00' LONG ITUDE Figure 14c Layer 9 temperatures for August. 148 o -CD LO O LO o -O •vT a . ro O -O CM L U o _| § 3 9 O LO Q \r Q ro O . 8.8 NOVEMBER 1 9 6 8 LAYER 9 200-225 METRES M3N. VALUE 8.68 MAX. VALUE 9.14 CONTOUR INTERVAL 0.10 8.9 S T R R I T OF G E O R G I R TEMPERATURE 125* 00 * 324*40* 124*20' 124*00' 123* 40' 123° 20" 323* 00* LONG ITUDE Figure 14d Layer 9 temperatures for November. CD U J Q Q u_u. ZD I— cc L U Q _ LAYER 1 0 -25 METRES SAN JUAN REGION-• SOUTHERN REGION- A CENTRAL REGION - + NORTHERN REGION- X a 03' in I D ' " 1 MAR" Figure 15 T FEB T APR ' MAY ' JUN " JUL Regional temperature averages f o r layer 1. AUG SEP OCT NOV LAYER 2 « 25 -50 METRES °~] SflN JURN REGION-• SOUTHERN REGION- A FEB ' MRR ' RPR 1 MRY ' JUN ' JUL ' RUG ' SEP ' OCT ' NOV Figure 16 Regional temperature averages f o r layer 2 in LRYER 7 150-175 METRES SRN JURN R E G I O N - • SOUTHERN REGION- A CENTRRL REGION - + NORTHERN REGION- X 07 CD LU a CE03 I— d Ld Q_ in r-' FEB MRR Figure 17 T T T T RPR ' MRY ' JUN ' JUL ' RUG Regional temperature averages for layer 7» SEP OCT NOV LRYER 9 200 -225 METRES LO —»a CD L d a ZD f— CE 2 a . SRN JURN REGION-CQ SOUTHERN R E G I O N - A CENTRRL REGION - + NORTHERN REGION- X in a FEB MRR Figure 18 RPR ' MAY ' JUN ' JUL ' RUG Regional temperature averages for layer 9« S E P OCT NOV 153 a _| O LO O LO o . 3 CD CD CO o . $ CD CM U J o . CD CD 9 CD LO CD "\T Q CO ' 2 8 F E B R U A R Y 1 9 6 8 LRYER 1 0 -25 METRES MIN. VRLUE 25.86 MRX. VALUE 29.64 CONTOUR INTERVAL 1.00 S T R A I T OF G E O R G I A S A L I N I T Y 27 6 125s 00* 124s 40' 124*20' 124° 00* 123* 40' 123° 20' 123k 00' L O N G I T U D E Figure 19a Layer 1 average s a l i n i t i e s for February. 15** Q O LO O LO O O CO a . a CM as? C 3 9 LO o co 28.5 26.5 28.5 28.5 1 9 6 8 MAY LAYER 1 0 -25 METRES MIN. VALUE 23.60 MAX. VALUE 30.74 CONTOUR INTERVAL 2.00 S T R A I T OF GEORG IA S A L I N I T Y 26 5 28.5 30.5 125*00' 124° 40' 124* 20' 1243 00' 123» 40" 123*20' 123» OO-LONG I T U D E Figure 19b Layer 1 average s a l i n i t i e s for May. 155 J 1 I I I L ?__ rn r" I 30 I I I 125* 00' 124" 40' 124*20' 124* 00' 323* 40' 123*20' 123* 00' LONGITUDE Figure 19c Layer 1 average s a l i n i t i e s for August. 156 o LO O LO Q . o % ro o • O CM L U o . § 3 C D C D CD LO C D Q ro o . '28 0 " L 26.5 NOVEMBER 1 9 6 8 LAYER 1 0 -25 METRES M3N. VALUE 24.38 MAX. VALUE 30.80 CONTOUR INTERVAL 1.50 S T R A I T OF G E O R G I A S A L I N I T Y 26.5 125° 00' 124*40' 124* 20* 124*00' 123* 40' 123*20' 123» 00' LONG ITUDE Figure I9d Layer 1 average s a l i n i t i e s for November. 157 125* 00' 124° 40* 124* 20' 124*00' 123'40" 123* 20' 123* 00' LONGITUDE Figure 20a Layer 2 s a l i n i t i e s for February. 158 co-ca o - i LO Q LO o -•\T a -0 0 a • Q CM LLl„ _j ° 9 C D C D \ 2 9 . 4 9 LO co *1 1 : 29.4 1 9 6 8 MRY LAYER Z 25 -50 METRES M1N. VRLUE 29.03 MRX. VALUE 30.96 CONTOUR INTERVAL 0.40 S T R R I T OF G E O R G I R S R L I N I T Y ,29.8 30 6 V 125* 00* 124° 40* 124*20' 124° 00' 123» 40' 123* 20' 123» 00* LONGITUDE Figure 20b Layer 2 s a l i n i t i e s for May. 159-Cr L O O LO o . \r o • Q f O o . Q CM LUo _| «—O C 3 3 LO O O CO 1 9 6 8 flUGUST LRYER 2 25 -50 METRES MIN. VRLUE 27.50 MRX. VALUE 31.30 CONTOUR JNTERYRL 1.00 STRRIT OF GEORGIA SRLINITY 125* 00' 124° 40* 124* 20' 124° 00' 323'40' LONGITUDE Figure 20c Layer 2 s a l i n i t i e s f o r August. 123° 20* 123' 00* 160 o . O LO O LO o . Q M o -O ro o . Q C M o LO O *1 o ro 28.5 J 29 NOVEMBER 1 9 6 8 LATTER 2 25 -50 METRES M1N. VRLUE 28.43 MRX. VALUE 30.9L CONTOUR INTERVAL 0.50 S T R R I T OF G E 0 R G I R S R L I N I T Y 125* 00" 124*40* 124*20* 124* 00' 123* 40* 123*20' 123* 00* L O N G I T U D E Figure 20d Layer 2 salinities for November. 161 o o -LO O LO o -T o -ro o -O CM LLlc, . C 3 9 O LO O O CO o . FEBRURRY 1 9 6 8 LRYER 7 150-175 METRES MIN. VRLUE 29.71 MRX. VALUE 30.99 CONTOUR INTERVAL 0.20 5 T R R 1 T OF GEORG IR 5 R L I N I T Y 6 f30,3 30.1 29.9 30.5 30,1 \]30,9 125* 00' 124° 40' 124° 20' 124*00' 323* 43' 123* 20* 123* 00' LONG ITUDE Figure 21a Layer 7 s a l i n i t i e s for February. 162 co-ca o -I O m o LO C D o . 5 C D ro 5 C D CM U J 0 . § 3 C D C D 8 O LO C D XT C D ro o . V 30.4 30.4 v30,6 MAY 1 9 6 8 LRYER 7 350-175 METRES M3N. VRLUE 30.32 MftX. VRLUE 33.71 CONTOUR 3NTERYRL 0.20 S T R A I T OF G E O R G I A S A L I N I T Y P0.6 \^0, 0.8 31 31. 4 ^ 3 1 . 4 31. 6 125* 00* 124* 40* 124* 20" 124* 00' 323* 40' 123* 20* 323* 00' LONG ITUDE Figure 2lb Layer 7 s a l i n i t i e s for May. 163 o-o o . o LO O LO o . O T o . O CO o . Q CM UJo . Si?' o LO o CO 30.5 30.5 RUGU5T 1 9 6 8 N LRYER 7 150-175 METRES MIN. VRLUE 30.40 MRX. VALUE 31.80 CONTOUR INTERVAL 0.20 S T R R I T OF G E 0 R G I R S A L I N I T Y 04 30.9 31 3 131.5 125s 00* 124° 40' 124* 20* 124° 00' 1231 40" L O N G I T U D E 31.7 123* 20' 123» 00' Figure 21c Layer 7 salinities for August. 164 co-ca o to o LO C O o . C D ro o . O CM U J „ . § 3 C O C O 3 o LO O Q CO 30. 7 NOVEMBER 1 9 6 8 LRYER 7 150-175 METRES M3N. VRLUE 30.32 MRX. VALUE 31.19 CONTOUR INTERVAL 0.20 S T R A I T OF G E O R G I A S A L I N I T Y .30.5 pi i 125* 00' 324* 40' 124*20- 124* 00' 3231 40' 123* 20* 323* 00* LONG ITUDE Figure 2ld Layer 7 salinities for November. 0 165 C D -C D C D L O O LO o . C D \r a . o -C D CM U J 0 . ° 3 C D C D 3 C D L O O \r Q CO 2 30.6 F E B R U R R Y 1 9 6 8 LRYER 9 200-225 METRES MIN. VRLUE 30.42 MRX. VRLUE 30.88 CONTOUR INTERVAL 0.10 5 T R R I T OF G E 0 R G I R S R L I N I T Y 30.5 30.8 125*00' 124*40' 124* 20" 124° 00" 323» 40' 123° 20' 123* 00' L O N G I T U D E Figure 22a Layer 9 s a l i n i t i e s for February. 166 o L O O LO o -3 C O C D ro 3" o CM § 3 5? o LO o r o MRY 1 9 6 8 LRYER 9 200-225 METRES MIN. VRLUE 30.46 MRX. VALUE 32.03 CONTOUR INTERVAL 0.20 S T R R I T OF G E 0 R G I R S A L I N I T Y 3 1 . 6 3 1 8 3 2 125° 00' 124° 40* 124*20' 124° 00' 123* 40' LONG ITUDE 1238 20' 123' 00' F i g u r e 22b Layer 9 s a l i n i t i e s for Kay. 167 co-co co L O C D L O 3 C O a , o ro 5 CO CM UJ, ° 3 C O C O 3 o L O C D Q ro o -30 7 RUGU5T 1 9 6 8 LAYER 9 200-225 METRES M3N. VRLUE 30.56 MRX. VALUE 32.09 CONTOUR INTERVAL 0.20 S T R R I T OF G E O R G I A S A L I N I T Y TT 30.9 31.9 125* 00* 324* 40' 124* 20* 124° 00* 323* 40' 123d 20' 323* 00* LONG ITUDE Figure 22c Layer 9 s a l i n i t i e s for August. 168 C D -C D C D m C D L O *1 C D C D ro o . C D C M UJo -I C D C D 9" C D L O *1 C D *1 C D ro 3 0 . 8 _ NOVEMBER 1 9 6 8 LAYER 9 200-225 METRES M1N. VALUE 30.70 MAX. VALUE 31.37 CONTOUR INTERVAL 0.10 S T R A I T OF G E O R G I A S A L I N I T Y 31 125* 00' 124*40' 124*20' 124* 00' 123* 40' L O N G I T U D E 123° 20' 123» 00' Figure 22d Layer 9 s a l i n i t i e s for November. in r-LAYER 1 0 -25 METRES SflN JUAN REGION- LB SOUTHERN REGION-A CENTRAL REGION - + NORTHERN REGION- X FEB 1 MAR Figure 23 7 7 7 APR " MAY ' JUN JUL Regional s a l i n i t y averages for layer 1. AUG SEP OCT NOV * CO in <Oo)_| CM CD. CM in LRYER 2 25 -50 METRES 5RN JURN REGION-• SOUTHERN REGION-A CENTRAL REGION - * NORTHERN REGION- X FEB MRR Figure 24 RPR • MRY / JIJN JUL Regional s a l i n i t y averages for layer 2. RUG SEP OCT NOV o L A Y E R 7 1 5 0 - 1 7 5 M E T R E S SAN J U A N R E G I O N - C D SOUTHERN R E G I O N - A C E N T R A L REG ION - 4> NORTHERN R E G I O N - X F E B 1 MAR" Figure 25 T T APR ' . MAY ' J U N ' J U L Regional s a l i n i t y averages for Layer 7. AUG S E P OCT NOV 0 7 in *07 a . 01 cc=» 07 in r-a. 07 in a . oi LRYER 9 200-225 METRES 5RN JURN REGION- • SOUTHERN REGION-A CENTRRL REGION - + NORTHERN REGION- X FEB 1 MRR~ Figure 26 RPR ' MRY ' JUN 1 JUlT Regional s a l i n i t y averages for layer 9« RUG SEP OCT NOV 173 j 1 CO L O C D L O o . 5 3 C O ro o . CO CM L U o ° f 5 C O C O 3 o L O C D Q C O F E B R U A R Y 1 9 6 8 LRYER 3 0 -25 METRES MIN. VRLUE 20.35 MRX. VALUE 23.22 CONTOUR INTERVAL 0.80 S T R A I T OF G E O R G I A S I G M A - T 20.4 o -'22 8 125* 00' 124° 40* 124* 20 Figure 27 124* 00' 323* 40* 123* 20* 123' 00' L O N G I T U D E Contours of average sigma-t for layer 1 in February. FEB ' MAR 1 APR ' MAY ' JUN ' JUL ' AUG ' SEP ' OCT ' NOV Figure 28 Regional density averages for layer 1. NORTHERN REGION-X FEB ' MAR 1 APR ' MAY ' JUN ' JUL ' AUG ' SEP ' OCT ' NOV 1 Figure 29 Regional density averages for layer 2. I T ) . CM CM LAYER 9 200-225 METRES SAN JUAN REGION-• SOUTHERN REGION- A CENTRAL REGION - + NORTHERN REGION-X FEB ' MAR Figure 31 APR ' MAY. ' JUN ' JUL Regional density averages for layer 9. AUG SEP OCT NOV ^3 o L O o LO O : w b a . $ O ro % O CVI U J o . -4 Ji 3 Q L O Q O ro 5 ^ 5.5 6 1 6 .5 ' FEBRUARY 1 9 6 8 LRYER J 0 -25 METRES M1N. VALUE 4.92 MAX. VALUE 7.01 CONTOUR INTERVAL 0.50 S T R A I T OF G E O R G I A OXYGEN I M L / U 6.5 6.5 L - 6 125*00* 124° 40' 124*20- 124> 00* 1231 40" 123° 20* 323* 00* L O N G I T U D E Figure 32a Layer 1 oxygen concentrations for February. 179 CD o -I CD CD LO o -o -% CD CO o . CD CM U J o . § 3 CD CD 5 CD LO CD CD CO 6 . 5 6 , 5 6 . 5 1 9 6 8 MAY LRTER I 0 -25 METRES MIN. VRLUE 4 .94 MRX. VALUE 6.76 CONTOUR INTERVAL 0.50 STRAIT OF GEORGIA OXYGEN lMl_/U 6 . 5 o 1251* 00' i24b40' 124* 20* 124° 00* 123» 40' 123° 20' 123* 00* LONGITUDE Figure 32b Layer 1 oxygen concentrations for May. 180 CD-CO o L O O L O o -o . C O C O a . % C O C M L U o 4 s s CO CO (3 9 C D L O C O C D C O 1 9 6 8 RUGUST LRYER 1 0 -25 METRES MIN. VRLUE 4.20 MRX. VALUE 6.21 CONTOUR INTERVAL 0.50 S T R R I T OF G E O R G I A OXYGEN I ML/L ) 4.5 125* 00* 124* 40' 124° 20' 124*00' 123" 40" 123° 20' 123* 00' D L O N G I T U D E Figure 32c Layer 1 oxygen concentrations for August. 181 S S o 3 Q LO CO NOVEMBER 1 9 6 8 LRYER 3 0 -25 METRES MIN. VRLUE 4.53 MRX. VALUE 6.55 CONTOUR INTERVAL 0.40 S T R A I T OF G E O R G I A OXYGEN I M L / U 125" 00' 324* 40* 124* 20* 124* 00* 123* 40' 123* 20* 123* 00* L O N G I T U D E Figure 32d ' Layer 1 oxygen concentrations for November. 182 O LO Q LO 3 3 O CO a . O CM U J o . 3 O LO o c o 5.4 5.8 1 5.8 si 3$> F E B R U A R Y 1 9 6 8 LAYER 2 25 -50 METRES MIN. VALUE 4.85 MAX. VALUE 6.36 CONTOUR INTERVAL 0.40 S T R A I T OF G E O R G I A O X Y G E N I M L / L ) 1 2 5 * 0 0 * 3 2 4 * 4 0 - 124* 2 0 * 1 2 4 * 0 0 * 3 2 3 » 40* 1 2 * 2 0 ' 3 2 3 * 0 0 LONGITUDE Figure 33a Layer 2 oxygen concentrations for February. 183 o -C 3 L O O LO o . O XT 3 ro 3 Q CO § 3 O 3 O LO XT O fO 5.3 1 9 6 8 MAY LRYER 2 25 -50 METRES MIN. VRLUE 4.53 MRX. VALUE 5.46 CONTOUR INTERVAL 0.20 S T R A I T OF G E O R G I A OXYGEN I M L / U ' 4 . 9 5 . 1 125* 00* 324b40* 124*20' 124*00' 123* 40' 123° 20* J23fc 00* 122* L O N G I T U D E Figure 33b Layer 2 oxygen concentrations for May. 184 4.4 A.7\ •*3 4 .2 1 9 6 8 AUGUST LRYER 2 25 -50 METRES MIN. VRLUE 3.72 MRX. VALUE 4.80 CONTOUR INTERVAL 0.20 STRAIT OF GEORGIA OXYGEN tML/L) 0 t 4 .2 125* 00* 124^40* 124° 20' 124° 00* 123* 40' 123*20* 123*00 LONGITUDE EL Figure 33c Layer 2 oxygen concentrations for August. 185 125* 00' 124* 40' 124* 20* 124° 00* 123* 40" 123* 20' 123* 00' LONGITUDE Figure 33d Layer 2 oxygen concentrations for November. 186 czr O o in O LO a -CD a . O CM o 5 ' O LO O XT O CD F E B R U A R Y 1 9 6 8 LRYER 7 150-175 METRES MIN. VRLUE 3.49 MRX. VALUE 5.64 CONTOUR INTERVAL 0.50 S T R A I T OF G E O R G I A O X Y G E N I M L / U 4 . 5 5 . 5 5 . 5 125* 00' 124* 40' 124*20' 124° 00' 323* 40* 123* 20* 123*00 L O N G I T U D E Figure 34a Layer 7 oxygen concentrations for February. 187 C D -C D o -I O L O O L O a . o . % CO a • O C V L L)Q § 3 o 9 Q in o MRY LAYER 7 350-175 METRES MIN. VRLUE 3.66 MAX. VALUE 4.58 CONTOUR 3NTERVRL 0.20 STRRIT OF GEORGIA OXYGENIML/L) 42) .4.3 125* 0 0 * 324* 4 0 ' 124* 20" 124* 0 0 * 1 2 3 ' 40* 123* 2 0 * 3 2 3 * 0 0 * LONGITUDE Figure 34b Layer 7 oxygen concentrations for May. 188 Figure 3*c Layer 7 oxygen concentrations for August. 189 o Q o , o LO Q L O C D CO o C\J L U o 4 O CD 3 o L O O 3.2 3 4 NOVEMBER 1968 LAYER 7 150-175 METRES MIN. VRLUE 3.03 MAX. VALUE 4.34 CONTOUR INTERVAL 0.20 3 4 STRAIT OF GEORGIA OXYGEN t M L / U . 3 6 - 3 . 8 .4 2 125* 00' 124° 40* 124* 20' 124*00' 123* 40" 123* 20' 123* 00' LONGITUDE Figure 34d Layer 7 oxygen concentrations for November. 190 CD o . o LO o . a . $ CD fO o . $ CD CM L U o . § 3 CD CD 3' O LO CD XT o -CD CO 3.21 3.4 / 3.6 FEBRUARY 1968 LRYER 9 200-225 METRES MIN. VRLUE 3.19 MRX. VALUE 4.27 CONTOUR INTERVAL 0.20 STRAIT OF GEORGIA OXYGENtML/LJ 0 3.8 3.8 J 0 4.2 125* 00' 124* 40' 124* 20* 124* 00' 123* 40* 123* 20* 123* 00' LONGITUDE Figure 35a Layer 9 oxygen concentrations for February. 191 o -O LO o 10 • O XT a . ro a . O C U UJo . o o 3 o LO 8 o 3.9 3.9 L \ V 3.3 13.6 MAY 1 9 6 8 LRYER 9 200-225 METRES MIN. VRLUE 3.07 MRX. VALUE 4.29 CONTOUR INTERVAL 0.30 STRAIT OF GEORGIA OXYGEN tML/L'J 125*00' 124* 40* 124* 20* 124* 00* 123* 40' 123*20* 123* 00' LONGITUDE Figure 35b Layer 9 oxygen concentrations for Hay. 192 3.5 3,5 AUGUST 1968 LRYER 9 200-225 METRES MIN. VRLUE 2.80 MRX. VALUE 3.75 CONTOUR INTERVRL 0.20 STRAIT OF GEORGIA OXYGENtML/LJ 125" 00' \2$ 40' 124° 20" 124° 00* 123» 40* 123° 20' 323* 00' LONGITUDE Figure 35c Layer 9 oxygen concentrations for August. 193 CD-CD O LO O LO o . * a -ro a . O CM § 3 3 O in 9 ro 2.8 3.2 _L2 NOVEMBER 1968 LRYER 9 200-225 METRES MIN. VRLUE 2.71 MAX. VALUE 3.46 CONTOUR INTERVAL 0.20 STRAIT OF GEORGIA OXYGENIML/L) 3.2 3 . 4 • 3 . 4 125* 00' 124s 40* 124* 20' 124° 00* 123fc 40* 123° 20* J23l 00* LONGITUDE Figure 35d Layer 9 oxygen concentrations for November. SOUTHERN REGION- A CENTRAL REGION - 4> NORTHERN REGION- X FEB ' MAR ' APR....' MAY ' JUN ' JUL ' AUG ' SEP ' OCT ' NOV ' Figure 36 Regional oxygen averages for Layer 1. in I D ' - a - I D * -<X Odin &>*• UJ C J O 0 u j i n C D >— X o m M*' a LRYER 2 25 -50 METRES 5RN JURN REGION-• SOUTHERN REGION-A CENTRRL REGION NORTHERN REGION-X FEB ' MRR Figure 3? T T RPR MRY JUM JUL Regional oxygen averages for layer 2. RUG SEP OCT NOV 3.0 OXYGEN CONCENTRATION (ML / U 3 .2 3.4 3.6 3.8 4.0 -I I I I I -n m CD 3 3 5? CO 3 2 9 -\ CO CO Hj 8 3 vO X) c r CD CO m C3 O CD CO ca x> cz z — i X c_ rn cz X) X) rn rn G l CT) z Q o i i ro (— o x> 0 - < 1 rn ro :XJ ro cn CD rn rn 16\ 198 co-ca o . O LO CO LO o . CO \r o . CO CO o . % CO oo S W O CO Q LO CO CO CO 2 8 FEBRURRY 1968 LRYER 3 0 -25 METRES MIN. VRLUE -2.85 MRX. VALUE -1.67 CONTOUR INTERVAL 0.30 5 T R R I T OF GEORGIR POTENTIRL-ENERGY -2.5 2 8 1 2 5 * 0 0 ' 1 2 4 ° 4 0 ' 1 2 4 * 2 0 ' 1 2 4 ° 0 0 ' 123* 40" 1 2 3 d 2 0 ' 1 2 3 1 00* LONGITUDE Figure 40a Layer 1 potential energy densities (X 10^ ) for February. 199 125* 00' 124* 40* 124* 20' 124* 00' 123* 40' 123* 20' 123* 00' LONGITUDE Figure 40b Layer 1 potential energy densities (X 10 ) for May. 200 co-ca co LO Q LO a . a . CO CO o . o CM L U 0 . § 3 S ^ CO CO CD LO O co -2.4 o -2 4 "L -2.4 L D 1968 RUGUST LAYER 1 0 -25 METRES MIN. VALUE -2.95 MAX. VALUE-2.04 CONTOUR INTERVAL 0.20 STRRIT OF GE0RGIR POTENTIRL-ENERGY •2.6 -2.8 -2.8 -2.6 ML 125" 00* 324* 40* 124* 20* 124* 00* 123'40' 123° 20' 123* 00* LONGITUDE Figure 40c Layer 1 potential energy densities (X 10 ) for August. •2.8 201 cr Q s o LO o • 3 3 Q CO o . x? O CM U_J«, §<? O LO XT O CO O C NOVEMBER 1968 LRYER i 0 -25 METRES MIN. VRLUE -2.92 MAX. VALUE -2.13 CONTOUR INTERVAL 0.20 -2.6 STRAIT OF GEORGIA POTENTIAL-ENERGY 2.6 "2.6v 125* 00' 124s 40' 124*20' 124*00' 123* 40" 123* 20' 123* 00' LONGITUDE Figure 40d layer 1 potential energy densities (X 10 ) for November. 202 125* 00' 12^ 40* 124* 20' 124* 00* 123* 40' 123* 20* 123* 00' usruu W H U LONGITUDE Figure 41a Layer 2 potential energy densities (X 10 ) f o r February. 203 204 125* 00* 124*40' 124* 20* 124* 00' 123* 40* 123*20' 123* 00* LONGITUDE Figure 41c Layer 2 potential energy densities (X 10 ) f o r August, 205 125* 00* 124* 40' 124* 20' 124* 00' 123k 40' 123*20' 123» 00* LONGITUDE Figure Wd Layer 2 potential energy densities (X 10 ) f o r November. 206 c r o in o t o a _ % \r a -CD fO a _ CM L U o -I— I — o . O <7 — 9 O LO o CO • 2.93 (-2.93 FEBRURRY 1968 LRYER 7 350-175 METRES MIN. VRLUE -2.99 MRX. VALUE -2.86 CONTOUR INTERVAL 0.03 5TRRIT OF GEORGIA POTENTIRL-ENERGY -2.9 T g 7 -2.93 •2.9 •2.96 12^00' 124*40' 124*20' 124* OO' 123* 43' 123* 20' 123* 00' 125*00 124* 4U l&ti L 0 N G I T U D E Figure 42a Layer 7 potential energy densities (X 10 4) for February. 207 LONGITUDE Layer 7 potential energy densities (X 10 ) f o r May. 208 o in o in *3 -ro o . x? Q CO L U 0 . § 3 O o 3 o in ro AUGUST 1968 LRYER 7 350-175 METRES MIN. VRLUE -3.05 MAX. VALUE -2.90 CONTOUR INTERVAL 0.03 STRAIT OF GEORGIA POTENTIAL-ENERGY 2 93 -2,93 -2,96 3.027 ^J-2.9S r •3,05 125* 00' 324* 40* 124*20' 124*00' 323* 40* 123* 20V 323* 00' i ^ u u i * r LONGITUDE Figure 42c Layer 7 potential energy densities (X 10 ) for August. 209 o CM S 3 Q Q LO CD O CO STRRIT OF GEORGIR POTENTIRL-ENERGY NOVEMBER 1968 LRYER 7 150-175 METRES MIN. VRLUE-2.95 MRX. VALUE -2.90 CONTOUR INTERVAL 0.01 125* 00' 124* 40' T5$-iF~Ti?0D- 123* 40' 123* 20* 123* 00' LONGITUDE Figure 42d Layer 7 potential energy densities (X 10*) f o r November. 210 co-ca o LO o LO e . a . CO CO o . O CM CD CO 3 CD LO CO XT CD CO • 2 . 9 3 • 2 . 9 4 6 V 2 . 9 4 FEBRUARY 1968 LRYER 9 200-225 METRES MIN. VRLUE -2.96 MAX. VALUE -2.92 CONTOUR INTERVAL 0.01 STRAIT OF GEORGIA POTENTIAL-ENERGY - 2 , 9 3 - 2 , 9 4 \ jC^93\ •2 .94 •2.96 125* 00' 324* 40* 124* 20* 124* 00' 123> 40* 123* 20" 123* 00* LONGITUDE Figure 43a Layer 9 potential energy densities (X 10 ) for February. 211 o LO CO LRYER 9 200-225 METRES MIN. VRLUE -3.07 MAX. VRLUE -2.92 CONTOUR INTERVAL 0.02 STRRIT OF GE0RGIR POTENTIRL-ENERGY -3.04 - 3 . M 125* OO' 12*40' 12*20" 12*00' 123*40' 123*20' 12*00' LONGITUDE Figure 43b Layer 9 potential energy densities (X 10 ) f o r May. 212 Q O LO 8 O -a . Q fO o . o CM L U o 4 S S o Q O LO CO -2.94, 2,95 RUGUST 1968 1RYER 9 200-225 METRES MIN. VRLUE -3.07 MRX. VALUE -2.93 CONTOUR INTERVAL 0.01 STRRIT OF GEORGIR POTENTIRL-ENERGY -2.94 •3,05 •3.03 H-3.05 125* 00' 124*40' 124° 20" 124* 00' 123*40* 123*20' 123» 00' LONGITUDE Figure 43c Layer 9 potential energy densities (X 10 ) for August. e • O LO a 3 O \r 3 O CO o . * o C M L U „ . § 3 S 3 O o 3' o LO O Q CO - 2 9 4 NOVEMBER 1968 LAYER 9 200-225 METRES MIN. VRLUE -2.98 MAX. VALUE -2.93 CONTOUR INTERVAL 0.01 STRRIT OF GEORGIA POTENTIRL-ENERGY •2.97 125* 00' 124° 40* 124* 20* 124° 00' 123* 40* 123*20* 123*00' LONGITUDE Figure 43d Layer 9 potential energy densities (x 10^ ) for November. I T ) . I CD <X ^4 ' Q I — I D . £3 • Q _ o 1—4 Cr:0-L D . I LD. t LAYER 1 - 2 5 METRES SAN JUAN REGION- • SOUTHERN REG ION -A CENTRAL REGION - + NORTHERN REGION- X FEB ' MAR Figure 44 1 APR ' MAY ' J U N _ ' JUL ' AUG Regional potential energy averages for layer 1. SEP OCT NOV Q O) L O . 1 CD a >-CD ceo U J Q * LU<0-C X a Z -L U ^ I — L D . f£D I a. a •—4 I D . I 9 ID. I LRYER 2 25 -50 METRES SAN JURN R E G I O N - • SOUTHERN REG ION-A CENTRRL REGION NORTHERN REGION- X FEB MRR RPR MAY JUN JUL AUG Figure 45 Regional potential energy averages for layer 2. SEP OCT NOV LRYER 7 150-175 METRES X-SRN JURN REGION- • SOUTHERN REG ION-A CENTRRL REGION - 4> NORTHERN REGION- X FEB MRR Figure 46 RPR MRY JUN JUL RUG Regional potential energy averages for layer 7. SEP OCT •Xr I D . >-CD z • t—LO. €D I a . a •—i c z ° r~-ID. I LRYER 9 200 -225 METRES SRN JURN R E G I O N - • SOUTHERN REG ION -A CENTRRL REGION - + NORTHERN R E G I O N - X T T FEB MRR Figure k-7 T RPR ' MRY ' JUN ' JUL ' RUG Regional potential energy averages for layer 9. SEP OCT NOV 218 125*00' 124* 40* 124* 20* 124*00* 323' 40* 123* 20* 123* 00' LONGITUDE Figure 48a Layer 1 mixing energy densities for February. 219 cr C 3 o -• o in o • 3 o • 3 O CO a . 3 * O CM L U o -I S 3 o Q 3' 8 o O CO LRYER 1 0 -25 METRES MIN. VALUE 17.70 MRX. VALUE 3635.76 CONTOUR INTERVAL 750.00 STRRIT OF GEORGIR MIXING-ENERGY 5 0 0 5 0 0 125* 00* 124*40' 124* 20* 124*00- 123* 40' 123*20' 123' 00* LONGITUDE Figure 46b Layer 1 mixing energy densities for May. 220 125*00' 124* 40* 124* 20" 124*00* 123* 40* 123* 20* 3.23* 00* LONGITUDE Figure 48c Layer 1 mixing energy densities for August. O o LO 8 3 Q o CO 3 O CM S W O Q o • 3 O LO O O CO 250. NOVEMBER 1968 LRYER 3 0 -25 METRES MIN. VRLUE 13.65 MRX. VALUE 2092.87 CONTOUR INTERVAL 500.00 .750 STRRIT OF GEORGIR MIXING-ENERGY 125" 00* 124*40' 124* 20' 124* 00* 123* 40* 123" 20* 123* 00' LONGITUDE Figure 48d Layer 1 mixing energy densities for November, 222 co-ca 8 Q LO O XT O CO CM UJ, O O 3 o LO O XT *' o CO 25 FEBRURRY 1968 LAYER Z 25 -50 METRES MIN. VALUE 8.02 MAX. VALUE 200.31 CONTOUR INTERVAL 50.00 5TRRIT OF GE0RGIR MIXING-ENERGY V 125*00* 124* 40' 124* 20* 12* 00' 323* 40* 123*20* 323* 00 LONGITUDE Figure 49a Layer 2 mixing energy densities for February. 223 Figure 49b Layer 2 mixing energy densities for May. 224 Figure 49c Layer 2 mixing energy densities for August. 225 o k o C O o -* o 4X1 • § 9 O O 3 8 o co 150 STRAIT OF GEORGIA MIXING-ENERGY NOVEMBER 1968 LRYER 2 25 -50 METRES MIN. VRLUE -23.11 MRX. VALUE 379.18 CONTOUR INTERVAL 300.00 5 0 100 125*00' 124* 40* 124*20* 124* 00* 123* 40" 123* 20* 323* 00' LONGITUDE Figure 49d Layer 2 mixing energy densities for November. 226 co-ca « . o L O 8 <3 -« O CO a . 3 O CM § 9 O Q 3 O LO 3 o CO 25 FEBRURRY 1968 LAYER 7 150-175 METRES MIN. VALUE 24.59 MAX. VALUE 146.16 CONTOUR INTERVAL 25.00 STRRIT OF GEORGIA MIXING-ENERGY 50 u I 75 £ 0 75V ^3 Cos 125* 00* 324* 40* 124* 20* 124* 00* 123* 40* 123* 20' 123* 00* LONGITUDE Figure 50a Layer 7 mixing energy densities for February. 227 o-Q 9 -o 8 o . CO o . 3 o CM § 3 °=0 a o CO 40 7 40 STRRIT OF GEORGIR MIXING-ENERGY MRY 1968 l. OYER 7 350-175 METRES MIN. VALUE 19.72 MAX. VALUE 97.38 CONTOUR INTERVAL 20.00 5" 4 0 4 0 ) 60 80 125*00* 124*40- 124*20' 124*00* 123'40" 123° 20' 123* 00* LONGITUDE Figure 50b Layer 7 mixing energy densities f o r May. 228 Figure 50c Layer 7 mixing energy densities f o r August. co-ca e • 10 3 8 o CM £ ° * o CO o • Q O •cr o ro 50 NOVEMBER 1968 LRYER 7 350-175 METRES MIN. VRLUE 6.35 MAX. VALUE 248.43 CONTOUR INTERVAL 50.00 STRAIT OF GEORGIA MIXING-ENERGY 150 10( 200 — 1 5 0 50 50 125*00* 324* 40' 124*20' 124* 00' 323* 40' .123* 20' 123* 00' LONGITUDE Figure 50d Layer ? mixing energy densities for November. 230 o o LO o LO 3 a • o co e . 3 O CM o 3 o LO 3 o CO 10 \1 10 30 2. 5 0 3a rS0 77 JiL_ k 3 0 FEBRURRY 1968 LAYER 9 200-225 METRES MIN. VALUE 6.21 MAX. VALUE 89.68 CONTOUR INTERVAL 20.00 STRRIT OF GEORGIR MIXING-ENERGY 30 30 125* 00* 124* 40- 124* 20* 124* 00* 123* 40* 123° 20* 123* 00' LONGITUDE Figure 51a Layer 9 mixing energy densities for February. 231 o -o o LO 8 o • CD XT a . O CO C7 . x? O CM , § 3 3 o LO CD XT O CO 1 S 35 MAY 1968 LRYER 9 200-225 METRES MIN. VRLUE 6.18 MRX. VALUE 97.49 CONTOUR INTERVAL 25.00 STRAIT OF GEORGIA MIXING-ENERGY 35 35 60 / 8 5 125* 00* 12 * 40' 124* 2 ^ \ ^ ^ ^ 4 0 ' 2 ° ' 1 2 3 * ° 0 ' Figure 5ib Layer 9 mixing energy densities for May. 232 3 8 o o cn LAYER 9 200-225 METRES MIN. VALUE 6.17 MAX. VALUE 206.57 CONTOUR INTERVRL 50.00 STRAIT OF GEORGIA MIXING-ENERGY 75 175 125" 00' 1249 40* 124* 20' 124* 00' 123k 40* 123° 20* 123k 00' LONGITUDE Figure 51c Layer 9 mixing energy densities for August. 15 15 \ 30 I NOVEMBER 1968 LRYER 3 200-225 METRES MIN. VRLUE 6.20 MAX. VALUE 91.13 CONTOUR INTERVAL 15.00 STRRIT OF GEORGIA MIXING-ENERGY r 3 0 XT O 15 45 T60, 4 5 60 125*00' 12*40' 124*20' 12*00* 123* 40* 123*20' 123* 00' LONGITUDE Figure 5id Layer 9 mixing energy densities f o r November. GRID MIXING ENERGY 15.0 22.0 IX 10 29.0 10 J ) 36.0 o i n ' o .—< X CD ^ r o ' LU CD X CD LAYER 2 25 - 50 METRES SAN JUAN R E G I O N - • SOUTHERN R E G I O N - A CENTRAL REGION - + NORTHERN R E G I O N - X a CD ' T T FEB ' MAR Figure 53 T APR MAY JUN JUL Regional mixing energy averages for layer 2* AUG SEP OCT NOV FEB ' MflR ' RPR ' MAY ' JUN. ' JUL ' AUG ' SEP ' OCT ' NOV Figure 54 Regional mixing energy averages for layer 7. Figure 55 Regional mixing energy averages for layer 9. FEB MRR ' RPR 1 MRY ' JUN 1 JUL 1 RUG 1 SEP 1 OCT 1 NOV 1 Figure 56 Regional averages of two-layer potential energy for layer 1 . ~ ID ID CD. I O .—I o ° to. X I >— CD >-CDS. a •— i K Q . C D o CO CD. I LD a? to. 1 LRYER 2 25 - 50 METRES SRN JURN REGION- • SOUTHERN REGION- A CENTRRL REGION - + NORTHERN REGION- X T FEB ' KRR Figure 57 T T RPR ' MRY ' JUN ' JUL ' RUG ' SEP OCT Regional averages of two-layer potential energy for layer Z» NOV ro w vo Figure 58 Regional averages of two-layer potential energy f o r layer ?. Figure 59 Regional averages of two-layer potential energy for layer 9» -40.0 BUOYANCY FLUX ENERGY -30.0 -20.0 -10.0 J I I (X I 0 1 0 J ) 0.0 10.0 _ _ J I m DD 2: H* XJ 2 X> C Z • 2 : CO s _ Q c r . CD CO m o 2 n (/) o a rn a x> z c= z — i — i :E xi x <_ m D m c T O (— T D X ) Z 2 2 X) m 33 X) m CD m m CD < CD CD • M I 1 • 2 • a I I I I > * - » ! > • C. FLATTERY —JUAN DE FUCA STr BOUNDARY C. MUDGE STATION 75 [-HARO-1 -PASSr ST. 62 59 56 -SI OF GEORGIA-o to 46 I0O-200-30 C+-400 IFRASER I RIVER 42 39 27 2 3 6 9 J Ij2 14 16 Figure 64a Temperature distribution f o r February (from Crean and Ages, 1971). C. FLATTERY JUAN DE FUCA STr BOUNDARY C. MUDGE STATION 75 t-HARO-j -PASS.-ST. FRASER RIVER 59 56 46 42 39 -ST OF GEORGIA-CD lOCh 206-30 W-400 Figure 64b Temperature distribution f o r May. (from Crean and Ages, 1971) C. FLATTERY •JUAN DE FUCA STr BOUNDARY C. MUDGE lod-2 20O-30 Of 400 Figure 64c Temperature distribution for August, (from Crean and Ages, 1971) ro .C. FLATTERY -JUAN DE FUCA STr BOUNDARY -HARO-t-PASS.-C. MUDGE ST. 59 -ST OF GEORGIA-in CO 46 FRASER RIVER 42 39 27 O Oi 2 3.6 9 12 14 16 tr U l 0. Ul o 20C*-30 Ok 9.5-:__;_j ;. 400 Figure 64d Temperature distribution for November, (from Crean and Ages, 1971) £ NO Figure 65a Salinity distribution for February, (from Crean and Ages, 1971) D E P T H , M E T E R S Figure 65c Salinity distribution for August, (from Crean and Ages, 1971) ro Figure 65d Salinity distribution for November, (from Crean and Ages, 1971) C. FLATTERY JUAN DE FUCA STr BOUNDARY C. MUDGE STATION 75 r-HAROi -PASS.-ST. -ST. OF GEORGIA-FRASER RIVER 2 3 6 9 12 14 16 IOCF 2 UJ t-UJ a i t-o. UJ o 200-30 C f 400 Figure 66a Oxygen distribution for February, (from Crean and Ages, 1971) Figure 66b Oxygen distribution f o r May. (from Crean and Ages, 1971) Figure 66c Oxygen distribution for August, (from Crean and Ages, 1971) Figure 66d Oxygen distribution for November, (from Crean and Ages, 1971) Figure 67 Density (sigma-t) distribution f o r February (from Crean and Ages, 1971). 259 REFERENCES Apel,J.R., H.M, Byrne, J.R. Proni and R.L. Chamell (1975) Observations of oceanic internal and surface waves from the Earth Resources Technology S a t e l l i t e . J . Geophys. Res. 80 865-88I. CaraeronjW.M^ and D.W. Pritchard (I965) Estuaries. The Sea Volume II ed. by M.H. H i l l John Wiley, New York 306-324. Chang,P., S, Pond and S. Tabata (I976) Subsurface currents i n the Strait of Georgia, west of Sturgeon Bank. J . Fish. Res. Board Can. 22 2218-2241. Cordes.R.E. (1977) Measurements of the velocity f i e l d i n the Fraser River plume. M. Sc. Thesis, Inst, of Oceanography, University of British Columbia. Cordes,R,E., S. Pond, B.R. de Lange Boom, P.H. LeBlond and P.B. Crean (I979) Estimates of entrainment i n the Fraser River plume, B r i t -ish Columbia. Submitted to Atmosphere-Ocean, Coulthard,W,J. (1975) UBC CNTOURi contouring a grid. Documentation by the Computing Centre, University of B r i t i s h Columbia, Crean,P.B. (19?8) Numerical model studies of the tide between Vancouver Island and the mainland coast. J . Fish. Res. Board Can. 22 2340-2344. Crean,P.B. (1978) A numerical model of barotropic mixed tides between Vancouver Island and the mainland and i t s relation to studies of the estuarine circulation. Hydrodynamics of Estuaries and F.iords ed. by J.C.J. Nihoul Elsevier, New York 283-314. Crean,P.B, and A.B. Ages (1971) Oceanographic records from 12 cruises in the Str a i t of Georgia and Juan de Fuca S t r a i t , I968, Dept. Energy, Mines and Resources, Victoria. Curtin,T,B. and C.N.K. Mooers (1975) Observation and interpretation of a high frequency internal wave packet and surface s l i c k pattern. J, Geophys. Res. 80 872-894. de lange Boom,B.R. (I976) Mathematical modelling of the chlorophyll distribution i n the Fraser River plume, B r i t i s h Columbia. M. Sc. Thesis, Inst, of Oceanography, University of B r i t i s h Columbia. Denman,K.L. (1973) A time-dependent model of the upper ocean. J . Phys. 0c. 2. 173-184. Denman,K,L. and M. Miyake (1973) Upper layer modification at Ocean Sta-tion Papaj observations and simulation. J . Phys. 0c. 3_ 185" 196. Dorsey,N.E. (1940) Properties of Ordinary Water-Substance. Reinhold, New York 673 PP» i 260 Ewing,M. (1950) Slicks, surface films and internal waves. J. Mar. Res. 2 161-187. Farmer,D,M. (1975) Penetrative convection i n the absence of mean shear. Quart. J. R. Met. Soc. 101 869-891. Gargett,A.E. (1976) Generation of internal waves in the Str a i t of Geor-gia, B r i t i s h Columbia. Deep-Sea Res. 2J. 17-32. 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Linden,P.F. (1975) The deepening of a mixed layer i n a s t r a t i f i e d f l u -i d . J. Fluid Mech. 21 385-405. McCracken,D.D. and W.S. Dorn (1964) Numerical Methods and FORTRAN pro- gramming. John Wiley, New York 457 pp. Mamayev,O.I. (1975) Temperature-Salinity Analysis of World Ocean Wa- ters. Elsevier, New York 374 pp. Niiler,P.P. (1975) Deepening of the wind-mixed layer. J . Mar. Res. 3J. 405-422. 0fficer,C.B. (1976) Physical Oceanography of Estuaries (and Associated  Coastal Waters).John Wiley, New York4 6 5 p p . Phillips,O.M. (I966) The Dynamics of the Upper Ocean. Cambridge at the University Press. 261 pp. Pollard,R.T., P.B. Rhlnes and R.O.R.Y. Thompson (1973) The deepening of the wind-mixed layer. Geophys. Fluid Dyn. 2. 381-404. 261 Samuels,G. and P.H. LeBlond (1977) The energy of near-surface internal waves i n the Strait of Georgia. Atmosphere X5. 151-159• Schumacher,J.D., C.A. Pearson, R.L. Charnell and N.P. Laird (1978) Re-gional response to forcing i n southern Strait of Georgia. Estua-rine and Coastal Mar. S c i . 7_ 79*91 • Shand,J.A. (1953) Internal waves i n Georgia St r a i t . Trans. Amer. Geo-phys. Union 34 849-856. Sweers,H.E. (1970) Oceans IVi a processing archiving and retrieval sys-tem for oceanographic station data. Dept. Energy, Mines and Re-sources, Marine Sciences Branch Manuscript Report Series No. 15, 137 PP. Thompson,R.E. (1976) Tidal currents and estuarine-type circulation l n Johnstone S t r a i t , British Columbia. J . Fish. Res. Board Can. 33 2242-2264. Thorpe,S.A. (1973) Turbulence i n stably s t r a t i f i e d f l u i d s j a review of laboratory experiments. Bound. Layer Meteor. 5. 95~H9« Tully,J.P. and A.J. Dodimead (1957) Properties of the water ln the Strait of Georgia and influencing factors. J. Fish. Res. Board Can. 14 241-319. Tumer,J.S. (1973) Buoyancy Effects in Fluids. Cambridge at the Uni-versity Press. 366 pp. Waldichuk,M. (1957) Physical oceanography of the Strait of Georgia, B r i t i s h Columbia. J. Fish. Res. Board Can. 14 321-406. 

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