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The seasonal variation of the temperature and salinity of the surface waters of the British Columbia… McLeod, Donald Cameron 1951

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(tri fix n*k Si THE SEASONAL VARIATION OF THE TEMPERATURE AND SALINITY OF THE SURFACE WATERSOOF THE BRITISH COLUMBIA COAST BI DONALD CAMERON McLIOD A THESIS SUHvETTED IN PARTIAL FULFIIMEKT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department o of Physics We accept this thesis as conf/oxming to the standard required from candidates for the degree of MASTER OF ARTS. Members of tne Department of Physics THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1951 ABSTRACT For a number of years d a i l y observations of surface temperature and s a l i n i t y nave been taken at ooeanographic stations (mostly lighthouses) on the B. C. coast. The present thesis i s the f i r s t attempt that has been made to systematically analyse t h i s data. The annual v a r i a t i o n i n temperature was seen to follow the general olimatological trend of the B. C. coast at each of the stations^ although a wide range i n the amplitudes of these periodic variations was noted. The faotors influencing the amplitude of the annual temperature curves were considered and such e f f e c t s as^ncoming r a d i a t i o n , the extend of turbulence, the degree of shelter and the phenomena of upwelling due to horizontal wind s t r e s s (West Coast of Vancouver Island) have been discussed for each of the stati o n s . Correlations were made between available meteorological i n f o r -mation and the sea temperature observations and an attempt has been made to determine temperature contours of the B. C. coastal waters during the summer when the surface temperature i s l e a s t uniform. The s a l i n i t y observations were treated i n an analogous manner to temperature and found to exhibit c h a r a c t e r i s t i c periodic annual v a r i a t i o n s . The stations were c l a s s i f i e d by means of these variations and the influences of p r e c i p i t a t i o n and fresh water runoff, evaporation and mixing were discussed and correlations with meteorological observations were again made. ACKNQWJiTCEMENT The author wishes to express his thanks and appreciation to Dr. G. L. Pickard for Ms continued interest and helpful critisisms during the writing of this thesis, and to Prof. W, M. Cameron for several interesting discussions. The data which enabled the author to prepare the thesis was made available through the efforts of Dr. J. P. Tully and his associates of the Pacific Oceanographic Group. TABLE OF CONTENTS Page I Introduction 1 I I Annual Variation i n Surface Temperature 4 I I I Variation i n Amplitude of Temperature Curves 9 IV Standard Deviation of Temperature 18 V Harmonic Analysis of Temperature Vari a t i o n 24 VI Correlation i n Temperature Between Stations 28 VII Correlation of Sea Water Surface Temperature with A i r Temperature . ..i.,.,- .. 32 VIII The E f f e c t of Cloud Cover on Surface Temperature... 38 IX Annual Variation i n Surface S a l i n i t y 40 X The Stations at which S a l i n i t y Increases to a Maximum during the Summer Months 44 XL The Stations at wni ch S a l i n i t y Decreases to a Minimum during Summer 59 XII The Stations at wnich S a l i n i t y remains Constant Throughout the Year 65 1 I INTRODUCTION For a number of years observations of the temperature and s a l i n i t y of the surface sea water have been made at stations on the B r i t i s h Columbia coast. The procedure adopted i s to take a sample of sea water d a i l y at a depth of three feet and to observe the water tempera-ture at the same time. The samples of sea water are sent, together with the temperature data, to the P a c i f i c Oceano-graphic Group at the P a c i f i c B i o l o g i c a l Station, Nanaimo, B.C. for analysis to determine the s a l i n i t y . The data obtained i n t h i s way i s c o l l e c t e d and published annually by the P a c i f i c Oceanographic Group as 'Observations of Sea Water; Temperature, S a l i n i t y and Density on the P a c i f i c Coast of Canada.' The present thesis gives an account of the f i r s t attempt which has been made to analyse this published data systematically to determine, and i f possible, account for the behavior patterns of temperature and s a l i n i t y . The analysis pertains to data available i n the period from January 1, 1935 to December 31, 1948, and consists -&£ 2 of approximately 4000 d a i l y observations of temperature and s a l i n i t y at each of the stations l i s t e d below. Records are available for Departure Bay (P a c i f i c B i o l o g i c a l Station) from 1914 and for New Westminster from 1927. The records for the majority of the stations how-ever are more recent. A l i s t of the stations for which extended series of observations are a v a i l a b l e follows: EXPOSED STATIONS Vancouver Island - West Coast Observations Commenced Amphitrite Pt. - Barkley Sound... August 1934 Nootka - Nootka Sound August 1934 Kains Island - Q,uatsino Sound.... January 1935 Georgia S t r a i t Race Rocks - Juan de Fuca S t r a i t May 1941 Entrance I s . - Georgia St. Central May 1936 Cape Mudge - Georgia St. North November 1936 Queen Charlotte Islands - West Coast Cape S t . James - Queen Charlotte I s . July 1934 Langara Island - Queen Charlotte I s . October 1936 Queen Charlotte Sound and Hecate S t r a i t Pine Island - Queen Charlotte Sound January 1937 Ivory Island - Milbanie Sound July 1937 Triple Island - Brown Passage November 1939 SHELTERED STATIONS Southern B. C. Coast Departure Bay - Georgia St. West Side September 1914 New Westminster - Fraser River February 1927 The geographical l o c a t i o n of the oceanographic stations i s indicated i n F i g . 1, together with the meteorological stations whose records have been used i n FIG.1 BRITISH COLUMBIA PINE PACIFIC O C E A N X LOCATION OF STATIONS MAKING DAILY SEAWATER OBSERVATIONS. O WEATHER STATIONS FROM WHICH METEOROLOGICAL PATfl HAS BEEN USED. this discussion. A l l but the last two oceanographic stations are at lighthouses and the observations are made by the lighthouse keepers. The temperature data have f i r s t been examined for periodic trends and for possible c o r r e l a t i o n with meteoro-l o g i c a l events and sea water dynamics. Following t h i s the s a l i n i t y data have been analysed i n an analogous manner. 4 II ANNUAL VARIATION IN SURFACE TEMPERATURE For the purposes of determining a t y p i c a l annual v a r i a t i o n i n temperature at each of the B. C. coastal stations the following procedure was used. The mean tempera-ture was calculated from d a i l y temperature observations throughout each p a r t i c u l a r month. This i s ref e r r e d to as the 'monthly mean;' The mean of the monthly means has been calculated over the entire period during whi ch observations have been carried on and i s referred to as the 'grand monthly mean.' F i g . 2 i l l u s t r a t e s the character of the annual tem-perature curves from the grand monthly means for the stations. I t i s seen that these curves are i n very close phase agreement, the temperature generally reaching a minimum i n February and r i s i n g to a maximum i n August, thus following the general c l i m a t o l o g i c a l trend of the B. C. coast. The minimum temperatures at the stations are f a i r l y uniform at 45° F. ± I F 0 i n February but there i s a notable v a r i a -t i o n i n the amplitude of the temperature curves. The smallest annual temperature range i s that for Pine Island, 4.7 F° while the largest Is that for Departure Bay, 19.7 F°„ m 11111 [ 1111111111111111111111 [ 111111111 [ [ 111 MI 1111111111 m a 11 M H 11111111 i 111111111111111111 rmn 111 II 111| II11 II 111 70 FIG 2 A M P H 1 T R I T E N O O T K A K f l l N S I N L A N D R A C E R O C K S E N T R A N C E " IS. C A P E M U D G E COPE ST. TAMES LANGBRB IS. PINE tSLOND I V O R Y I S L A N D T R I P L E ] S L P N P P E P A R T U R E B A Y MONTH OF THE YEAR TAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT OCT NOV PEC. ANNUAL VARIATION OF GRAND MONTHLY MEAN TEMPERATURE OF SFA W A T E R FROM DAILY OBSERVATIONS AT STATIONS ON THE JAN. _j : : • 6 The si g n i f i c a n c e of these annual temperatures was tested, using Pine Island as the appropriate test case. Applying the Student , t l test (Hoel p. 145) to the data yields a value f o r t of 10.8 which indicates that the difference between minimum and maximum tempera-ture i s h i g h l y s i g n i f i c a n t i n this case and, as the follow-ing discussion shows, w i l l be more so for the other stations which have larger ranges with approximately the same stand-ard deviations. Values of c S / ^ > the standard deviation of the grand monthly mean, are given i n Table I for each of the oceanographic stations. I f i t i s assumed that the sea water i s subject to no long range temperature variations of a period comparable to the period during which the data has been analysed, the monthly mean surface temperatures w i l l be normally d i s t r i b u t e d with a mean m and standard deviation <5~ . The monthly means for each year for which the oceanographic data i s a v a i l a b l e may be regarded as random samples of this normal d i s t r i b u t i o n , of size n where n i s the number of years i n which the data i s a v a i l a b l e . Then the sample mean x" w i l l be normally d i s t r i b u t e d with mean m and standard deviation <^/jy\ • The quantity i s the 'unbiassed' standard deviation of the monthly mean, cT~ = [IL(*i*J « \| n — I As the standard deviations of the grand monthly "means are i n a l l cases small compared with the annual TABLE 1 - Annual Tem Station Jan. Feb. Mar. Apr. May June July Aug.Sept. Oct. Nov. Dec. Mean Range i n Amphitrite .35 .42 .38 .44 .39 .44 .48 .31 .25 .29 .54 .46 .40 10.6 Nootka .45 .34 .44 .35 .27 .34 .43 .32 .30 .39 .41 .44 .37 16.2 Kains Island .51 .48 .38 .44 .24 .37 .45 .29 .36 .32 .45 .52 .40 10.1 Race Rocks .34 .30 .18 .18 .26 .20 .25 .12 .11 .11 .29 .28 .22 6.3 Entrance I s . .23 .24 .27 .39 .33 .49 .50 .50 .44 .38 .34 .35 .37 18.1 Gape Mudge .38 .36 .45 .42 .50 .24 .30 . .26 .31 .34 .37 .38 .36 14.1 Gape St.James.75 .71 .53 .45 .39 .41 .57 .57 .69 .63 .66 .59 .58 10.7 Langara I s . .60 .73 .52 .48 .42 .45 .37 .69 .43 .58 .52 .64 .54 9.5 Pine Island .35 .39 .34 .40 .32 .24. .23 .17 .22 .44 .54 .37 .33 4.7 Ivory Island .57 .49 .35 .49 .36 .30 .36 .22 .35 .20 .40 .53 .38 14.6 Triple Island .67 .53 .50 .53 .47 .43 .47 .32 .30 .21 .42 .65 .46 10.2 Departure Bay.28 .30 .28 .48 .49 .35 .60 .48 .43 .27 .35 .24 .37 19.7 Values of the standard deviation <5~/r— » a n d t n e annual range, of the temperature curves of F i g . 2. 8 temperature range (Table 1) then-the temperature curves of F i g . 2 may be regarded as representative of the annual v a r i a t i o n i n sea water surface temperature i n the l o c a l i t y of each s t a t i o n . are the same order of magnitude. Therefore as the Pine Island station exhibits the lea s t annual temperature range and an application of the student's t test to monthly mean tempera-tures i n February and August y i e l d s a value of t =10.8^ 'the annual temperature v a r i a t i o n at a l l twelve B. C. Coastal stations may be regarded as being highly s i g n i f i c a n t . Table I also shows that the values o f for a l l stations 9 I I I THE VARIATION IN AMPLITUDE OF TEMPERATURE CURVES The c y c l i c annual temperature v a r i a t i o n from a winter minimum to a summer maximum i s a t t r i b u t e d to v a r i a t i o n i n i n s o l a t i o n during the year. The large v a r i a t i o n i n ampli-tude requires explanation, and may possibly be at t r i b u t e d to some or a l l of the following: 1. The extent of turbulence and consequent mixing of cold subsurface water with warmer surface water. 2. The phenomena of upwelling of colder, more saline water due to horizontal wind stres s as observed on the west coast of Vancouver Island. 3. The comparative degree of shelter or exposure of the p a r t i c u l a r s t a t i o n . 4. Variation of i n s o l a t i o n with l a t i t u d e . For the purpose of discussion the twelve B. C. coastal stations are divided into three groups as follows: A - West Coast Area Amphitrite Nootka Kains Island B - Georgia S t r a i t Area ^ Entrance Island Departure Bay Cape Mudge Race Rocks 10 C - Northern Area Gape St. Jame s Langara Island Pine Island Ivory Island Tr i p l e Island The j u s t i f i c a t i o n for this grouping w i l l appear i n the following discussion. A West Coast Area During the summertime the p r e v a i l i n g winds along the west coast of Vancouver Island are directed from the north west, p a r a l l e l to the shoreline. The wind exerts a horizontal f r i c -t i o n a l s t r e s s on the water which is well known to r e s u l t i n a net transport of water i n the upper 50 - 200 meters, to the right of the wind di r e c t i o n i n the northern hemisphere (Sverdrup, Johnson, Fleming p.500). A net off shore mass transport i s pro-duced along the west coast and re s u l t s i n an upwelling of colder, more sa l i n e water from below the surface to s a t i s f y continuity requirements as i l l u s t r a t e d W A R M E R SURFACE W f t T E ^ S i n F i g . 3. The extent of ~ ^ ~ « — ^ / V ^ M this upwelling process i s y ^/ / |5. discussed in SectionX i n connection with the annual v a r i a t i o n of surface s a l i n i t y along the West Coast. Up-welling tends to l i m i t the maximum temperature attained during the summer here. FIG. 3 THE UPWELLING PROCESS ON THE WEST COAST OF VANCOUVER ISLAND. 11 Kains Island and Amphitrite are representative of general con-ditions along this coast. The temperature curves' for these stations show maximum surface temperatures of 56°. F and 55.7°]? o ' o and exhibit annual ranges of 10.1 F and 10.6 F respectively. Of the three west coast stations Nootka (Fig. 4) i s i n a more sheltered location than Kains Island and Amphi-t r i t e . I t s l o c a t i o n at the same time protects i t from north west winds and i t would not be affected by upwelling to the same extent as the l a t t e r . Therefore i t i s to be expected that Nootka w i l l a t t a i n a greater maximum temperature during the FIS/4- LOCATION OF NOOTKA STATION summer than Kains Island and Amphitrite. Inspection of F i g . 2 shows this to be the case. The maximum temperature at Nootka o o i s 60.4 F and the annual temperature range i s 16.2 F . Nootka i s therefore regarded as only being representative of i t s immediate l o c a l e i n Nootka Sound. As the colder water due to upwelling reaches the sur-face and i s transported toward the open ocean i t w i l l be heated due to i n s o l a t i o n . Therefore a d i s t i n c t temperature gradient would be expected perpendicular to the Vancouver Island shore-l i n e . Off shore temperature data i s avail a b l e as a result of an 12 oceanographic survey conducted by P a c i f i c Oceanographic Group during August, 1950 (Progress Reports, October 1950). A study of the temperature contours obtained i n d i c a t e the existence of t h i s temperature gradient and substantiate the described effect of upwelling. B Georgia S t r a i t Area The p r i n c i p a l factors influencing the maximum tempera-ture attained during the summer at the stations of the Georgia S t r a i t area are the degree of shelter and the extent of turbu-lence a t the pa r t i c u l a r s t a t i o n s . There i s a comparatively small l a t i t u d e v a r i a t i o n among these stations and no upwelling process analogous to that on the west coast of "Vancouver Island. Departure Bay which i s the mos t sheltered of the coastal stations also attains the greatest maximum temperature, o 64 F. Because i t i s sheltered to the extent that i t i s ef f e c t -i v e l y a harbor and i t s water i s shallow (approximately 20 fathoms on the average) i t s temperature curve may be regarded only as appropriate to the immediate l o c a l i t y and possibly to other harbors i n Georgia S t r a i t . Entrance Island should be more representative of expected conditions i n Georgia S t r a i t . I t i s an exposed s t a t i o n , although not exposed to the same degree as are Amphitrite and Kains Island since Georgia Straight i s almost e n t i r e l y land-locked. From F i g . 2 i t i s seen that the temperature curve for Entrance Island reaches a maximum of 63° F, only 1 F° i e 3 S than that of Departure Bay and about 7 F° greater than that of 13 Amphitrite and Kains Island. Because the temperature curve for Entrance Island shows a high maximum value i t may be concluded that mixing processes with subsurface layers of colder water during the summer are unimportant and that any mixing i s con-ducted only r e l a t i v e l y close to the surface i n this l o c a l i t y . Gape Mudge i n the northern section of Georgia S t r a i t a t t a i n s a maximum temperature of approximately 5 F° less than that a t Entrance Island which is considerably less than can be accounted for by variation of i s o l a t i o n with l a t i t u d e . The region to the south of Cape Mudge i s a region of convergence of the flood tides from passages to the north and south, but i t i s not apparent that this would cause mixing of surface waters with subsurface l a y e r s . However, because of i t s location at the southern entrance to Discovery Passage and Seymour Narrows i t i s suggested that i t s maximum temperature would be modified due to turbulence caused by the strong t i d a l currents which are a feature of t h i s region. I t i s notable that the temperature curve for Race Rocks, the southernmost st a t i o n , shows, one of the smallest ranges (only Pine Island being l e s s ) . As Race Rocks is located i n an area of violent turbulence this i s strong evidence of the important e f f e c t of turbulence i n modifying the maximum temperature a t t a i n -ed at a s t a t i o n . Turbulence i s a result of the i r r e g u l a r l a t e r a l boundaries of the Gulf Islands (Fig. I ) , and the strong t i d a l currents (4 to 6 knots) observed i n this area. Georgia S t r a i t water when being transported into Juan de Fuca Strait; mixes with 14 ocean water. Colder water from considerable depths i s raised to the surface and the mixing of t h i s colder water with sur-face water w i l l reduce the r i s e i n surface temperature due to i n s o l a t i o n . Race Rocks may be regarded as i l l u s t r a t i v e of a modification of temperature due to turbulence. C Northern Area The temperature curves here would be expected to show somewhat lesser amplitudes i n general due to a decrease of i n -solation i n the more northerly l a t i t u d e s . The v a r i a t i o n i n incoming r a d i a t i o n due to latitude v a r i a t i o n over the B. C. coast i s about 8%. This would be expected to cause, a v a r i a t i o n of annual temperature range from 1 to 2 F°. However a change i n l a t i t u d e may result i n a change i n climatological conditions and t h i s must al30 be taken in t o consideration. The temperature curve for Langara Island ( F i g . 2) reaches a maximum of 53° F. This i s 3F° less than the maximums for Kains Island and Amphitrite, the representative West Coast s t a t i o n s . There i s a decrease i n annual temperature range of about 1F° at Langara Island over these stations (Table 1 ) . However the l a t i t u d e e f f e c t i s probably somewhat more s i g n i f i c a n t here than a I F 0 difference i n range would indicate due to the absence of the West Coast upwelling process. A comparison with Entrance Island, representative of Georgia S t r a i t shows a de-crease i n temperature range of 8.6F 0 although the comparatively high degree of shelter at Entrance Island i n t h i s case would c e r t a i n l y be l a r g e l y responsible f o r this difference. 15 The temperature curves of the stations at Gape S t . James and Triple Island are observed to have approximately, the same ranges, with maximum temperatures of 54.8°F. A decrease i n i n s o l a t i o n at T r i p l e Island due to i t s more northerly l a t i t u d e may be counterbalanced by a higher degree of shelter i n comparison with Cape St. James. Ivory Island exhibits a temperature curve with a maximum of over 58°F. This i s considerably higher than the other stations of the Northern Area, and over 2F° higher than Amphitrite and Kains Island on the West Coast. Ivory Island, situated i n Milbanke Sound (Fig. 5) i s considerably more sheltered than the other northern stations and the temperature curve probably represents only the l o c a l i z e d area. The curve may t y p i f y the v a r i a -tion to be expected i n the inner passages of the Northern Area. F i g . 5 Location of Ivory Island Pine Island shows a temperature curve with the smallest range of any of the B. G. coastal stations which i s i n t e r e s t i n g as i t i s situated at an intermediate l a t i t u d e . I t s l o c a t i o n 16 at the northern extremity of Vancouver Island i n Queen Char-l o t t e Sound is analogous to that of Race Rocks at the southern extremity i n Juan de Fuca S t r a i t . I t i s suggested that turbu-lence r e s u l t i n g from i r r e g u l a r bottom topography (reference to charts of the area) and the mixing of the inner waters with the ocean waters would l i m i t the maximum temperature i n the manner described at Race Rocks s t a t i o n . In summarizing, Amphitrite and Kains Island may be regarded as representative West Coast stations and i l l u s t r a t i v e of the e f f e c t of upwelling on temperature curves. Entrance Island i s t y p i c a l of Georgia S t r a i t and shows the e f f e c t of a more enclosed and sheltered s t a t i o n . Langara Island i s a representative station of the Northern area and i t s temperature curve demonstrates a decrease i n i n s o l a t i o n with an increase i n l a t i t u d e . Race Rocks and Pine Island stations i l l u s t r a t e the importance of turbulence i n modifying the seasonal v a r i a t i o n i n temperature. In general the sea water surface temperature on the B.C. coast may be regarded as approximately uniform at 45° F i n February and at an annual temperature minimum during this period. The temperatures r i s e from the minimum, rounding to peak values i n August. In F i g . 6 an attempt has been made to show temperature contours for the month of August when the B, C. coastal waters have attained their, annual temperature maximum. Owing to the l i m i t e d number of stations from which data i s _ a v a i l a b l e i t must be emphasized that these contour l i n e s are only approximations. FIG.G 18 IV STANDARD DEVIATION OF TEMPERATURE The values of <s/fc i n Table 1 have been plotted for the stations of each area i n F i g . 7, 8, and 9. These give an estimate of the annual v a r i a t i o n i n standard deviation of the grand monthly means. The following general conclusions may be drawn: 1. As a l l values of <s/ff\ are small i n comparison 'with the amplitudes of the temperature curves of F i g . 2, then as discussed i n Section I I , the curves are representative of actual annual v a r i a t i o n i n sea water surface temperature at the s t a t i o n s . 2. As a l l values of <s/fa\ are of the same order of magnitude then the probable deviation from normal i n any par-t i c u l a r year i s approximately the same over a l l B. C: coastal waters. 3. I t appears from F i g . 7 that the temperatures a t . the stations of the northern area seem to vary with regard to <s/fr\ from a maximum i n the winter to a minimum i n the summer perhaps due to more variable meteorological conditions i n the winter. F i g . 8 shows that stations on the.West Coast n,2o  | | 11II11111 [ 11 i l l 11J1111[[111 III 11111111III 1111111[|11II1111| M ^  G.7 NORTHERN AREA THN FEB. MftR. APR. MAY TUNE XULY AUG. SePT. OCT. NOV. DEC. Xftf). 80 hr A 3] I IV7. O W E S T COAST AREA •60 •oo J P N . FFfi,. MflR. fip MONTH OF THE YEAR Nwv X V N E ; OCT. NOV. DEC. XftN. I FIG1? GEORGIA STRAIT AREA J"AN. FITS. MflR. ftPR. 1^«Y T U N E T U L Y OCT. NOV. D E C . JAN. ANNUAL VARIATION IN THE STANDARD DEVIATION., (6~/jf\) OF THE T E M P E R A T U R E CURVES O F FIG. 2 E l have values of G/fo of the same magnitude throughout the year. From F i g . 9 Departure Bay and Entrance Island show temperature variations having minimum <s/(ffx values i n the winter and maximum values i n the summer. Mixing of surface water with water at appreciable depths w i l l oppose an extreme temperature deviation from the normal due to unusually high or low r a d i a t i o n income during any p a r t i c u l a r period. Therefore a comparison of the 'unbiassed' standard deviation of the monthly means, J ^ _ t" where X i s the monthly mean temperature, x" i s the grand monthly mean and n the number of years i n which the data was treated, should give a comparative i n d i c a t i o n of the extent of mixing at par-t i c u l a r stations. The calculated values of are shown i n Table E. These values are not necessarily i n the same r a t i o as the corresponding values of Table'1, as the value of n d i f f e r e d at several s t a t i o n s . A study of Table E shows Race Rocks to have s i g n i f i c a n t l y lower standard deviations throughout the year which i s a t t r i b u t e d to the described e f f e c t of mixing. The observed low values of standard deviation at Pine Island from June to August and perhaps those of T r i p l e Island from August to October may be due to the e f f e c t of mixing. However, i t i s d i f f i c u l t to draw conclusions when there i s no q u a l i t a t i v e basis of comparison. The importance of meteorological con-ditions i n governing the standard deviation i n the v i c i n i t y of the p a r t i c u l a r stations must be also taken into consideration. A study of v e r t i c a l temperature gradients would be necessary TABLE 2 Jan. Feb. Mar. Apr. May Amphitrite 1.3 1.6 1.4 1 .6 1 .4 Nootka 1.7 1.3 1.6 1 .3 1 .0 Kains I s . 1.9 1.8 1.4 1 .6 0 .9 Race Rocks 0.9 0.8 0.5 0 .5 0 .7 Entrance I s . 0.8 0.8 0.9 1 .4 1 .2 Cape Mudge 1.3 1.4 1.6 1 .4. 1 .7 Cape St.James 2.5 2.4 1.7 2 .0 1 .5 Langara I s . 1.8 2.0 1.6 1 .4 1 .2 Pine I s . 1.2 1.4 1.2 1 .4 1 .1 Ivory I s. 1.9 1.6 1.2 1 .6 1 .2 Tr i p l e I s . 2.0 1.6 1.5 1 .6 1 .4 Departure Bay 1.5 1.0 1.0 1 .7 1 .7 June July Aug. Sept. Oct. Nov. Dec. Mean 1.6 1.8 1.2 1.0 1.1 2.0 1.7 1.5 1.3 1.6 1.2 1.1 1.5 1.5 1.6 1.4 1.4 1.7 1.1 1.3 1.2 1.7 1.9 1.5 0.5 0.7 0.3 0.3 0.3 0.8 0.8 0.6 1.7 1.8 1.7 1.5 1.3 1.2 1.2 1.3 0.8 1.0 0.8 1.0 1.2 1.3 1.3 1.2 1.5 1.9 2.1 2.6 2.3 2.5 2.2 2.1 1.3 1.1 1.9 1.3 1.7 1.5 1.9 1.6 0.8 0.8 0.6 0.8 1.5 1.8 1.3 1.2 1.0 1.2 0.7 1.2 0.7 1.3 .1.8 1.3 1.3 1.4 0.9 0.9 0.6 1.3 2.0 1.4 1.2 2.1 1.7 1.5 0.8 0.9 0.8 1.3 Standard deviations of the monthly mean surface temperatures at the B. C coastal s t a t i o n s . 23 to further ascertain the extent of mixing. 24 V A HARMONIC ANALYSIS OF TEMPERATURE VARIATION I t i s apparent from F i g . 2 that a periodic annual v a r i a t i o n i n temperature exists at each s t a t i o n . To study the character of this periodic v a r i a t i o n a harmonic analysis was made of the observations at the d i f f e r e n t s t a t i o n s . To obtain the equation of a l i n e accurately representing the• observed temperature curve a t each of the stations a Fourier Series has been assumed, T ( X I - a 0 + a 1 # Cos X + a 2 Cos 2X +- a 3 Cos 3X + b i Sin X + b i Sin 2X + b 3 Sin 3X where T i s the temperature i n °F. and X i s a phase angle taken as 0° at January 1 and increasing by 30° each month. The c o e f f i c i e n t s a 0 .... a^ and bj_ .... b 3 have been evaluated by means of the twelve ordinate scheme IWhittaker and Robinson). The values of the c o e f f i c i e n t s are tabulated (Table 3) and graphs plotted comparing the observations a t each of the stations with the corresponding Fourier Series. F i g . 10 shows the type of f i t obtained for Ivory Island station using the c o e f f i c i e n t s of Table 3, and i s representative of the closeness of f i t ob-tained at the other stations. I t i s to be emphasized that the 25 ao> a l C ° s % a n < * D l Sin X terms predominate while the others are minor corrections to improve the f i t . TABLE 3 Station a 0 Amphitrite Pt. 50.58 Nootka Light 51.60 Kains Island 50.47 Race Rocks 48.28 Entrance I s . 52.29 Gape Mu.dge L t . 50 .90 Gape St.James 48.54 Langara I s . 48.00 Pine Island 47.72 Ivory Island 50.50 Triple Island 49.03 Departure Bay 52.81 a *>1 a2 -4 .62 -1.95 - .05 -8.15 -1.93 .38 -4.82 -2.17 .23 -2.97 -1.28 .13 -9.03 -2.62 1.55 -7.10 -0.90 .50 -4.10 -2.82 .80 -4.32 -2.50 .18 -1.97 -1.33 .10 -7.18 -2.32 .75 -4 .43 -2.44 .93 -9.90 -1.82 1.30 b2 a 3 b3 .13 .12 -.15 .73 .40 .07 .30 .22 .18 .01 .12 .12 .58 .23 -.12 .20 .05 .05 .68 .05 -.37 .35 .07 .20 .15 -.03 .07 .38 .28 .08 .03 -.12 .16 .63 .25 -.17 Fourier c o e f f i c i e n t s calculated from sea water surface temperature observations at B. C. coastal stations. lllllllllllllllllllllilllltlllMI'!rri!IM!IIIITTTTT 21 111 I I 111 11111 I [ 111 | | | IJJMp J | l I ^ j - L j ^ j - U ^ l l j j j II I | II | Ml CoO FIG. 10 OBSERVATIONS FOURIER SERIES NO NTH OF THE YEAR TAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. PEC. TAN. A COMPARISON OF T H E OBSERVED ANNUAL TEMPERATURE CURVE AT IVORY ISLAND AND IT5 CORRESPONDING FOURIER SERIES. 28 YI CORRELATION OF TEMPERATURE BETWEEN STATIONS It i s of i n t e r e s t to determine whether or not the temperatures at i n d i v i d u a l stations deviate from their mean temperature curves of F i g . 2 i n an i d e n t i c a l manner for a p a r t i c u l a r period. This can be determined s t a t i s i c a l l y by use of the corr e l a t i o n c o e f f i c i e n t r . Where X and y are the monthly mean temperatures of the stations being correlated, oT a n d Oy the i r standard deviations, and x" and y their grand monthly means for the pa r t i c u l a r month, during n years i n which observations have been made at the stations under consideration. Correlation c o e f f i c i e n t s were f i r s t calculated among stations i n each of the three main groups and are presented i n Table 4. The values of r indicate a good c o r r e l a t i o n among stations of the West Coast area and the Northern area, although rather poor correlation among the stations of Georgia S t r a i t area. 29 TAB IE 4 i a Nootka And January A p r i l July October West Coast Area Amphitrite Kains Island .63 .73 .85 .79 .93 .84 .80 .79 Entrance I s . And Georgia S t r a i t Area Departure Bay Cape Mudge .28 .34 .54 .56 .62 - .30 .83 .68 Race Rocks .65 .82 -.01 - .21 Ivory Island And * Northern Cape St.James .99 .43 .79 .58 Area Langara I s . .97 .67 .69 .28 Pine Island .92 .98 .78 .74 Tr i p l e Island ..97 .73 .91 .39 Correlation of monthly mean temperature between stations i n each o-f the three areas. 30 For purposes of comparison c o r r e l a t i o n c o e f f i c i e n t s have also been calculated between each s t a t i o n and Ivory-Island, which has a r b i t r a r i l y been selected as the reference s t a t i o n . These are given i n Table 5. The data has been treated from the period 1941 to 1948 as i t i s reasonably complete during this period and a comparison of r e s u l t s i s l i k e l y to be more s i g n i f i c a n t . As these c o r r e l a t i o n co-e f f i c i e n t s are i n general quite high we may conclude that the sea water surface temperatures over B. C. coastal waters tend to deviate from their long period mean values i n an i d e n t i c a l manner during a p a r t i c u l a r period. Cape Mudge i n July (Table 5) i s a notable exception, and the stations of Georgia S t r a i t i n general show comparatively poor cor r e l a t i o n amongst each other as indicated by the c o r r e l a t i o n c o e f f i c i e n t s at each s t a t i o n with reference to Entrance Island (Table 4). This may be due to the complex dynamics of Georgia S t r a i t . An inspection of Table 5 also indicates a better c o r r e l a t i o n between stations i n winter, as represented by January, than i n summer, as represented by Ju l y . 31 TABLE 5 1 Ivory Island And Jan. i 1 > A p r i l July Oct. Station Mean Amphitrite Pt. .84 . .87 .84 .77 ,83 Nootka Light .94 .98 .80 .64 .84 Kains Island .93 .97 .75 .74 .85 Race Rocks .77 .52 .38 .46 .54 Entrance Island .35 .92 .75 .54 .64 Gape Mudge .96 .95 -.02 .71 .66 Cape S t . James .99 .43 .79 .58 .70 Langara Island .97 .67 .69 .28 .65 Pine Island .92 .98 .78 .74 .85 Tr i p l e Island .97 .73 .91 .39 .75 Departure Bay .93 .92 .72 .86 .86 Mean for Month .87 .81 .68 .61 Correlation c o e f f i c i e n t s for monthly mean temperatures at B. C. coastal stations with reference to Ivory Island s t a t i o n during the period 1941 to 1948. 32 VII CORRELATION OF SEA WATER SURFACE TEMPERATURE WITH AIR TEMPERATUR E I t i s apparent from the temperature curves of F i g . 2 that the surface sea water temperature follows very clos e l y the general c lima to l o g i c a l trend of the B. C. Coast. To determine th i s c o r r e l a t i o n more cl o s e l y , a i r temperature curves have been determined and plotted for weather stations corresponding to each of the three groups of oceanographic stati o n s . The data on a i r temperatures was obtained from the Monthly Records, Department of Transport, Meteorological D i v i s i o n and has been treated i n a si m i l a r manner to the sea water temperature data. The weather stations selected as representing cl i m a t o l o g i c a l conditions are as follows: 1. Esteftan Point West Coast Area 2. Departure Bay Cape Lazo Georgia S t r a i t Area 3. Langara Island Prince Rupert Northern Area Owing to the l i m i t e d number of meteorological stations from which data was avail a b l e , i t was not possible to selec t ' weather stations that coincided with the oceanographic stati o n s . However the above stations, while they may not 33 give a true representation of weather data applicable to the oceanographic stations, should give a s u f f i c i e n t approximation. The geographical l o c a t i o n of these weather stations i s indicated i n F i g . 1. The procedure followed i n t r e a t i n g the data was to average the d a i l y recorded maximum and minimum a i r tem-peratures over each month and then take the average of the two mean values. This temperature i s r e f e r r e d to as the monthly mean. The data was treated from 1938 - 48 and the monthly means averaged over t h i s period. The values are referred to as the grand monthly means. They have been plotted i n Fig.'s 11, 12,and 13 along with the sea tempera-ture curves o f the oceanographic stations and indicate the character of the annual v a r i a t i o n i n a i r temperature i n the v i c i n i t y o f the weather s t a t i o n s . These curves are seen to be i n complete phase agreement with the temperature curves at the oceanographic stations suggesting that the annual v a r i a t i o n i n i n s o l a t i o n i s the chief factor i n c o n t r o l l i n g the annual v a r i a t i o n of sea temperatures. The amplitudes of the a i r temperature curves are considerably larger than the sea temperature curves. In the winter the minimum a i r temperature i s less than the sea temperature and i n the summer the maximum a i r temperature exceeds that of the sea. Insolation primarily controls the c y c l i c v a r i a t i o n of both a i r and sea but because i l l i n i u m I r I I II I I ITTTI l l l l l l l l l l l l l l l l l l 3^ 1111111111 m m FIG. 11 A M P H I T R I T E N O O T K A KAINS ISLAND — E S T E B A N POINT ( A I R T E M P ) MONTH OF THE YEAR WW -1 '[ 1 : JAN. FEB. MAR APR. MAY JUNE JULY AUG. SEPT OCT NOV. DEC. JAN. ANNUAL SEA A N D AIR TE IMPERATURE VARIATIONS A T S T A T I O N S OF T H E W E S T C O A S T AREA . 66 FIG. 12 R A C E R 0 C K 5 E N T R A N C E IS . C A P E M U D G E D E P A R T U R E B A Y C A P E L A Z O (AIR T E M P ) D E P A R T U R E B A Y ( A I R T E M P ) J A N . F E B . M A R . A P R . M A Y J U N E J U L Y A U G . 5EPT O C T N O V . D E C J A N . A N N U A L SETA A N D A I R T E M P E R A T U R E V A R I A T I O N S A T S T A T I O N S O F T H E G E O R G I A S T R A I T A R E A jjjlijljjjn 4 ' ! 11 [4J444TTTTT1 1111 [ [ 11111111 [ | m | [ | [ [4444444444444444^^^^ ^ 4 4 + 0 4 4 4 4 4 4 . FIG. 13 C A P E S T J A M E S L A N G A R A I S L A N D P I N E I S L A N D I V O R Y I S L A N D T R I P L E I S L A N D LANGARA ISLAND (AIR TEMR) PRINCE RUPERT (AIR T E M R ) T A N F E B . M A R . A P R M A Y J U N E J U L Y A U G . S E P T O C T N O V D E C . J A N A N N U A L S E A A N D A I R T E M P E R A T U R E V A R I A T I O N S A T S T A T I O N S O F T H E N O R T H E R N A R E A . sea water has a much larger thermal capacity than a i r the time rate of change of temperature i s considerably l e s s . The temperature difference a t the boundary o f the two media results i n an exchange of heat. During the winter months thermal energy i s transferred from sea water to a i r through processes of radiation, conduction and evaporation. During the summer months heat may be conducted from a i r to sea water, although eddy conductivity i s then greatly reduced (Sverdrup, Johnson, Fleming, p. 114) and transfer is very much les s e f f i c i e n t . The oceanographic stations selected as representa-t i v e of general conditions i n each of the three areas are seen to conform clo s e l y to thi s pattern as i l l u s t r a t e d i n Fig.'s 11, IE and 13. Notable exceptions to the above de-s c r i p t i o n are Nootka (Fig. 11) and Ivory Island (Fig. 13) at which the sea temperatures throughout the year exceed the a i r temperatures at the weather stations selected to represent their respective areas. This supports the argument put for -ward i n Section I I I that, because of the comparatively high degree of shelter of these stations, they do not t y p i f y the conditions of t h e i r surrounding area but only represent t h e i r immediate l o c a l e . To i l l u s t r a t e the influence of a i r and sea tempera-ture on each other c o r r e l a t i o n c o e f f i c i e n t s have again been calculated. The corr e l a t i o n c o e f f i c i e n t has been applied here to determine whether or not i f the a i r temperature was 36 > observed to deviate from i t s temperature curve i n a p a r t i c u l a r period the corresponding sea temperature would follow this deviation. The values of r have been calculated between the monthly means for a i r and sea water throughout the period 1938-48 i n c l u s i v e . They are given i n Table 6. The values found for the correlation c o e f f i c i e n t s are i n general quite high. This indicates that the primary source of heat i s the same for both a i r and sea water and emphasizes the importance of the influence of one on the other. I t should be pointed out that i n the case of Cape St. James, January and A p r i l , (Table 6) the readings of 1940 spoiled the co r r e l a t i o n and suggest possible instrument error here. When the corr e l a t i o n was made neglecting the 1940 readings calculations of r gave values of .84 and .53 respectively. There are however other discrepancies, p a r t i c u l a r l y in the Georgia S t r a i t area which may be attributed to the complex dynamics of the area. 37 TABLE 6 •i ••. i Lighthouse T . 1 Station Jan •. Apr. July Oct. West Coast Area Amphitrite .91 .88 .89 .88 Isteban Pt • Nootka .66 .77 .89 .89 A i r Temp. Kains Island .88 .75 .91 .92 Georgia Race Rocks .79 .70 .32 .43 S t r a i t Area Entrance I s . .15 .67 .73 .70 Cape Lazo Cape Mudge' .28 .88 - .35 .81 A i r Temp. Departure Bay .75 .95 .76 .85 Cape St. .26 .15 Northern James (.84) (.53) .63 .52 Area Langara I s . .92 .86 .62 .72 Pine Island .81 .72 .74 .38 Langara I s . Air Temp. Ivory Island .70 .84 .24 .69 Tr i p l e Island .90 .82 .92 .05 , Values of the corr e l a t i o n c o e f f i c i e n t s of monthly mean a i r and sea temperatures at the B. C. coastal stations during the period 1938 - 48. 38 VIII THE EFFECT OF CLOUD COVER ON SURFACE TEMPERATURE In an e f f o r t to determine more s p e c i f i c a l l y the i n -fluence of meteorology on surface temperature the e f f e c t of cloud cover was investigated. A high percentage cloud cover i s expected to reduce the incoming r a d i a t i o n reaching the sea surface. However with the sun penetrating through scattered clouds the incoming r a d i a t i o n may be increased due to re-f l e c t i o n from the clouds. Also e f f e c t i v e back r a d i a t i o n may be decreased i n the presence of clouds due to an increase i n radi a t i o n from the atmosphere (Sverdrup, Johnson, Fleming; p. 101). I t i s therefore not apparent that a dire c t r e l a t i o n -ship between cloud cover and surface temperature would e x i s t . Data on cloud cover was obtained from the Monthly Records of the Department of Transport, Meteorological D i v i s i o n . Observations of the cloud cover i n tenths are taken a t spec i f i e d times (usually three or four observations spaced s i x hours apart). The Monthly Records provide the monthly mean o f the da i l y observation time. The values were averaged andL:assumed to represent the monthly mean percentage cloud cover i n the v i c i n i t y o f the p a r t i c u l a r s t a t i o n . To investigate a possible d i r e c t r e l a t i o n s h i p the co r r e l a t i o n was calculated between monthly mean percentage cloud cover and monthly mean sea 39 temperature at Amphitrite (Esteban Pt. weather sta t i o n cloud cover data) and Langara Island (Langara Island weather sta t i o n cloud cover data). Calculations however gave no evidence of a c o r r e l a t i o n and i t i s concluded that more extensive data on cloud cover i s necessary to determine the effect of cloud cover on surface temperature . 40 IX ANNUAL VARIATION IN SURFACE SALINITY Before discussing further meteorological influences such as p r e c i p i t a t i o n , evaporation and wind force a general analysis of s a l i n i t y data i s necessary. S a l i n i t y i s defined as the t o t a l amount of s o l i d material i n grams contained i n one kilogram of sea water when a l l the carbonate has been con-verted to oxide, the bromine replaced by chlorine, and a l l organic matter completely oxidized. I t i s always expressed i n parts per thousand for which the symbol °/0o i s used. The manner i n which the data has been treated i s analogous to that described i n the preceding discussion on temperature. A mean s a l i n i t y was calculated from d a i l y s a l i n i t y observa-tions throughout each month and i s re f e r r e d to as the monthly mean. The mean of these monthly means was calculated over the e n t i r e period i n which observations have been carried on and i s again referred to as the grand monthly mean. The grand monthly mean s a l i n i t i e s have been plotted for each month i n F i g . 14. These curves describe the annual variation i n s a l i n i t y i n the v i c i n i t y of each of the oceanographic stations. | | ! l l l [ | i | | i | | | | | i | i i | [ m p HA l l i Mll i l l l l l l l l l l lHI I! l [ l i l l l lMlM! l l l l l l ' i | | ! l l [ l l l l | l | l [ l |Mi| | I . i: 11! I f 11 FIG. 14 3500 H z 35-00 >-A M P H I T R I T r N O O T K A K A I N 5 I S L A N D RACE ROCKS E N T R A N C E K. CAPE MUME C A F E ST. TAMES L A N S A R A IS. 3300 Z U9 flNE ISLAND IVORY ISLAND T R I P L E r S L A N O DEPARTURE B « T 2240 2100 2 0 0 0 — M O N T H O F T H E Y E A R J A N FEB MAR APR MAY JUNE JULY AUG SEPT OCT. NOV. DEC. J A N . ANNUAL VARIATION OF GRAND MONTHLY MEAN SA L I N I T Y A T S T A T I O N S O N T H E B C . C O A S T " 42 A study of F i g . 14 indicates that the s a l i n i t y curves catagorize the stations into three d i s t i n c t groups as follows: A Those stations a t which the s a l i n i t y increases to a maximum during the summer months: Amphitrite Nootka Kains Island B Those stations at which the s a l i n i t y decreases to a minimum during the summer months: Entrance Island Departure Bay Cape Mudge Ivory Island Triple Island C Those stations at which the s a l i n i t y remains f a i r l y constant throughout the year: Langara Island "Cape St. James Pine Island Race Rocks The surface s a l i n i t y i s mainly determined by three processes. 1. Decrease of s a l i n i t y by p r e c i p i t a t i o n on the sea and fresh water run o f f from the land. 43 2. Increase of s a l i n i t y by evaporation, 3. Change of s a l i n i t y by processes o f mixing The following sections give a discussion of the mechanisms involved i n cont r o l l i n g the annual v a r i a t i o n of surface s a l i n i t y for each of the above three groups of oceanographic sta tions. 44 X THE- STATIONS AT WHICH SALINITY INCREASES TO A MAXIMUM DURING THE SUMMER MONTHS I t i s notable that those stations at which there i s an increase i n s a l i n i t y during the sumner months (Fig.15) are the stations on the West Coast of Vancouver Island. To v e r i f y the significance of the s a l i n i t y curves the standard deviation ( ^ n ) of the grand monthly means have been c a l c u l a -ted for Amphitrite. This' treatment i s simi l a r to that d i s -cussed i n section I I with temperature, and the quantity c f i s again the 'unbiassed 1 standard deviation <5~ = &~*) V r i - i where X now represents monthly mean surface s a l i n i t y and n i s the number of years during which the data has been treated. Calculations y i e l d the following values of cT/^n f o r Amphitrite. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov.Dec, .21 .23 .20 .26 .23 .26 .25 .13 .22 .22 .33 .18 Since the annual range of s a l i n i t y at Amphitrite i s 2.5 °/oo the above values for  <s/(fr\ i n d i c a t e that the change from winter to summer i s s i g n i f i c a n t . As the standard deviations for the other stations are simi l a r to those at Amphitrite their annual changes may al s o be considered s i g n i f i c a n t . 3500 3280 35-00 o< b 2 3100 < to 30-00 m | | | | | | | | i i i | [ i | i i | | l | | | i | | i i | | | i | m [||[||||||||||||[|[|[[[|[[||[i||i[||[i!||[|[||!![;|!HI|[[|: X h z o Z > ui I «J Z PIG. 16 z o I 20 I W E S T COAST NCRTH W E S T C O A S T M O N T H OF THE YEAR D JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. JAN. AVERAGE A N N U A L VARIATION IN PRECIPITATION ON THE W E S T COAST OF VANCOUVER I S L A N D DURING T H E YEftRS W4-I, 2 , t-, 5 A N D 6 . 33 47 The character of the s a l i n i t y curves ( F i g . 15) i s a t t r i b u t e d to annual, v a r i a t i o n i n p r e c i p i t a t i o n and the up-welling process which was previously discussed (Sec. I I I ) . P r e c i p i t a t i o n here includes both that which f a l l s d i r e c t l y on the sea and that which f a l l s on the land and then runs off the land into the sea. The l a t t e r i s r e f e r r e d to i n the following discussion as ' r u n o f f . The p r e c i p i t a t i o n (Fig.16) varies from 15 inches, per month during the winter to a minimum of 2 or 3 inches per month during the summer. Evidence would indicate that along the West Goast the time lag between pre-c i p i t a t i o n f a l l i n g on land and the resultant runoff i s small. Therefore the runoff i s expected to follow approximately the same form of annual v a r i a t i o n as p r e c i p i t a t i o n and substan-ti a t e s the importance of p r e c i p i t a t i o n i n determining annual v a r i a t i o n i n s a l i n i t y . To examine the importance of p r e c i p i t a t i o n i n con-t r o l l i n g the s a l i n i t y on the West coast c o r r e l a t i o n c o e f f i c i e n t s have again been calculated. The c o r r e l a t i o n c o e f f i c i e n t has been used to determine whether i n a p a r t i c u l a r period when monthly mean p r e c i p i t a t i o n deviated from the grand monthly mean the corresponding s a l i n i t y showed an inverse deviation. The values obtained are shown i n Table 8. These values are i n general high indicating correla-t i o n although there are several anomalies present. P r e c i p i t a -tion during preceding months would a f f e c t a monthly mean 48 TABLE VIII Amphitrite Nootka Kains Island January- - .01 » .98 - .88 February - .65 - .80 - .79 March - .08 - .35 - .17 A p r i l - .98 - .94 - .99 May - .77 - .02 - .09 June - .91 - .75 - .66 July - .49 - .85 - .53 August - .09 - .09 - .30 September - .63 - .52 - .96 October - .92 - .75 - .70 November - .53 - .82 - .34 December - .62 - .83 - .87 Correlation c o e f f i c i e n t s between monthly mean p r e c i p i t a t i o n on the West Coast of Vancouver Island and monthly mean s a l i n i t y at the oceanographic stations on the West Coast during the years 1941, 2, 4, 5, and 6. 49 salinity to some extent but there are other factors which must be taken into consideration. The most important of these is upwelling which will be discussed later. A.comparison of the salinity curves and annual variation in precipitation indicates the possible existence of an inverse proportionality relation. Observed grand monthly mean values of salinity °/ 0 0 at Amphitrite have been plotted against the corresponding values of precipitation (inches per month) in Fig. 17. The smoothed curve has been extrapolated so that when.precipitation P = 0, salinity S = 31,70. A re-lation P = IT - C has been assumed where K and C are constants to be evaluated. Calculations from the observed values of P and S indicate an average value of K : 4620 and C - - — = - 146. 31.70 r-n- r. 4 6 2 0 S in o/ Then S = B 1 X 1 0 / oo P - 146 , P in inches/month Calculations of salinity from the observed monthly mean precipi-tation along the West coast using this idealized representation in which precipitation alone is assumed to control salinity re-sults in a salinity curve for. Amphitrite as illustrated by the dotted line in Fig. 18. Objections to this idealized treatment are: 1. It neglects the effect of upwelling of more saline water during the summer due to horizontal wind stress. 2. It neglects the effect of evaporation in increas-"=' ing salinity. so 51 3. I t neglects the effect of p r e c i p i t a t i o n during preceding months on monthly mean s a l i n i t y . 4.. There may be an appreciable time l a g between p r e c i p i t a t i o n and runoff i n ce r t a i n cases and the j u s t i f i c a t i o n of treating runoff as c o i n c i -dent with p r e c i p i t a t i o n i s then questionable. 5. The assumption that average, p r e c i p i t a t i o n as observed along the West coast i s representative of a par t i c u l a r l o c a l i t y i s questionable. .The neglect of evaporation seems j u s t i f i e d to a f i r s t approximation. Values of energy used for evaporation i n the Eastern North P a c i f i c (Jacobs; 1942) give an average value of 77 gram calo r i e s per square centimeter per day at o 50 N. lat.'which would produce an average evaporation of 1.6 inches per month. This w i l l be balanced by p r e c i p i t a t i o n i n the summer when p r e c i p i t a t i o n i s at an annual minimum and throughout the rest of the year w i l l be small i n comparison with p r e c i p i t a t i o n . upwelling as previously explained (Sec. I l l ) can .only occur when the p r e v a i l i n g wind d i r e c t i o n i s north west, i . e . from May to September as shown i n Eig. 19. F i g , 17 shows the s a l i n i t y curves for Amphitrite and Kains Island to be increas-ing s i g n i f i c a n t l y before the period i n which upwelling can be expected to occur and supports the importance of p r e c i p i t a t i o n i n c o n t r o l l i n g s a l i n i t y . However as the maximum rate of i n -crease of observed s a l i n i t y has a time l ag of approximately 53 two weeks behind the calculated values (Fig. 18), this would indicate that upwelling must be considered. The s a l i n i t y curve for Kains Island i s of the same form as that for Amphitrite and the mechanisms involved i n c o n t r o l l i n g s a l i n i t y are regarded as s i m i l a r . In general, s a l i n i t y i s s l i g h t l y higher throughout the year at Kains Island. This i s attributed to a lower p r e c i p i t a t i o n on the north-west coast, as shown i n Fig. 16. Reference to F i g . 15 shows the' s a l i n i t y at Nootka to be lower than that at Amphitrite and Kains Island through-out the entire year although the annual range i s greater. The more sheltered location of Nootka would prevent fresh water runoff from being dissipated from the surface through mixing processes to the same extent as at Amphitrite and Kains Island. Consequently during the winter when p r e c i p i t a t i o n i s heavy the surface s a l i n i t y would be expected to be lower as i s observed from the s a l i n i t y curves. I f i t i s assumed that a t Nootka an inverse propor-t i o n a l i t y r e l a t i o n s h i p exists similar to that at Amphitrite an empirical r e l a t i o n S _ 2210 Sin o/bQ P - 76.3 P i n inches/month i s derived from the observations. Calculation here results i n a s a l i n i t y curve described by the dotted l i n e i n Fig. 20. This curve, shows obvious discrepancies from the observed s a l i n i t y . The most apparent disagreement i s i n the rate of increase of . 55 s a l i n i t y between May and August . The observed increase i s much greater; than that predicted by a decrease i n p r e c i p i t a -tion alone. In the case o f Nootka st a t i o n the mean a i r tem-perature i s always less than that of the sea (Fig. 11) and, although r e l a t i v e humidity i s high, evaporation may become important during, the summer when p r e c i p i t a t i o n i s low. Up-welling may further contribute to th i s increase although because of the sheltered l o c a t i o n of Nootka (Fig. 4) and i t s protection from north west winds i t i s probable that evapora-tion may be of more consequence than upwelling i n contributing to an increase i n s a l i n i t y . In a further attempt to determine the importance of upwelling, c o r r e l a t i o n between wind and s a l i n i t y has been de-termined from May to September when the p r e v a i l i n g wind i n north west. Coef f i c i e n t s have been calculated between the monthly mean wind velocity component i n the north west d i r e c t i o n .(Monthly Records of the Department of Transport, Meteorological Division) and monthly mean s a l i n i t y for the years 1941, 2, 4, 5, and 6* Values of the c o r r e l a t i o n c o e f f i c i e n t s are shown i n Table 9. These indicate a c o r r e l a t i o n during May, June and July although the lack of c o r r e l a t i o n during August and September seems su r p r i s i n g . F i g . 21 shows the e f f e c t i v e wind vel o c i t y component to be r e l a t i v e l y small i n September although comparatively high i n August. However the deviations from the mean s a l i n i t y curve become small i n August and this may have 56 57 TABLE I I Amphitrite Nootka Kains Island May .36 .34 .87 June .90 .95 .86 July .73 .30 .64 Augus t -.75 ' - .47 -.10 September -.46 -.21 .19 Correlation c o e f f i c i e n t s between monthly t o t a l wind mileage i n north west d i r e c t i o n on the West coast of Vancouver Island and monthly mean s a l i n i t y at the oceano-graphic stations on the West coast during the years 1941, 2,4,5, and 6. 5 8 obscured c o r r e l a t i o n . In summarizing the factors controlling annual v a r i a -tion of s a l i n i t y here i t i s concluded that v a r i a t i o n i n pre-c i p i t a t i o n and upwelling are both important. Because they are acting approximately co i n c i d e n t a l l y i t i s d i f f i c u l t to obtain an estimate of their r e l a t i v e orders of importance i n c o n t r o l l i n g the observed increase of s a l i n i t y to i t s summer maximum. Evidence indicates no appreciable time lag between p r e c i p i t a t i o n and runoff here and the runoff has been regarded as varying i n the same manner as the p r e c i p i t a t i o n observations (Pig. 16) . However the runoff may be of greater importance than p r e c i p i t a t i o n f a l l i n g d i r e c t l y on the sea i n influencing s a l i n i t y a t the West coast stations. At present there i s no data available on fresh water runoff to obtain a quantitative comparison of p r e c i p i t a t i o n on sea water and runoff and determine t h i s . 59 21 THE STATIONS AT WHICH, SALINITY DECREASES ' 1; iTO.A MINIMUM DURING SUMMER The stations at which there i s a decrease i n s a l i n i t y during the summer, months are situated along the coastline, com-paratively close to the mainland. Fig. '21 shows the annual variation of grand monthly mean sali n i t y at these stations. Precipitation on the sea and evapora ti on, Jiaving opposing influences on salinity could not be expected to account for the observed large annual range i n s a l i n i t y . I t must be there-fore assumed that the sharp decrease i n surface salinity dur-ing the early summer i s due to fresh water runoff from the mainland as i t i s at a maximum discharge rate during this period • ' • Evidence of the importance of fresh water discharge from the Fraser River i s shown in the salinity curves for c Entrance Island, Departure Bay and Gape Mudge (Fig. 21). The stations are a l l situated i n Georgia Strait which acts as a catch basin for runoff from the Fraser River. During the winter the heavy precipitation i s stored i n the mountainous areas of interior British Columbia, and i n the spring and early summer when air temperatures become warmer i s transported by i[ Hill 11| 1!; 11;; I III 111||[ UU IIII111IIIIIIIIIHI11 IIIIIHiq 60 H | 1111 |i 111111111111 in 11 in M ;| i1111111 | i | 1111| 3500 is 3T00 5 FIG. 21 20-DO M O N T H OF T H E Y E A R FEB. MAR. APR. MAY TUNE J U L Y AUG AVERAGE ANNUAL VARIATION OF SALINITY AT THE STATIONS HICH SHOW A MINIMUM SALINITY DURING THE SUMMER MONTHS. 61 the Fraser River i n t o Georgia S t r a i t . F i g . 22 i l l u s t r a t e s the average annual v a r i a t i o n of t h i s Fraser River runoff from observations made a t Hope, B.G. from 1935 - 41 with corrections applied as reoommended by the Water Resources D i v i s i o n o f the Department of Re-sources and Development i n order that the data be a p p l i c -able to discharge in t o Georgia S t r a i t . The discharge i s seen to increase from a minimum of approximately 0.7 X 10" oubic feet per month i n March to a maximum of 9.2 X 10" cubic feet per month i n June; an increase of 13 times the March minimum. A comparison of the s a l i n i t y curves of F i g . 23 and the annual v a r i a t i o n of Fraser River runoff i n F i g . 22 indicates a time l a g of approximately 25 days between the peak discharge rate of the Fraser River and the corres-ponding minimum s a l i n i t i e s at Entrance Island and Departure Bay. S i m i l a r l y the time l a g a t Cape Mudge i s approximately 30 days. Examination of the records for the i n d i v i d u a l years supports these values although the d a i l y observations are sub-je c t to anomalies due to p r e c i p i t a t i o n , evaporation and mix-ing processes and tend to obscure a d e f i n i t e value of t i me l a g . However the time l a g appears to vary over a considerable range from year to year. I t i s i n t e r e s t i n g that the time l a g at Cape Mudge i s only 30 days i n comparison to 25 days at Entrance Island • i land Departure Bay) when i t i s noted that the distance from €.2 63 Sandheads Lightship, at the mouth of the Fraser River to Cape Mudge is 90 nautical miles as compared with 20 nautical miles to Entrance Island. The apparent inconsistency is attributed to the influence of the runoff of the preceding months on the minimum salinity observed. A comparison of the time at which the runoff (Fig.22) first starts to rise significantly and the corresponding time when each of the oceanographic stations f i r s t shows a significant decrease in salinity should be more consistent with the dynamics of Georgia Strait because runoff during preceding months may be disregarded. The time lags observed i n this manner are 17 days to Entrance Island, 25 days to Departure Bay and 48 days to Cape Mudge. The ratio of the linear distances from the mouth of the Fraser River to Entrance Island and Cape Mudge is 1 to 4.5 and the ratio of the corresponding time lags is 1 to 3. Recent oceanographic surveys have indicated the existence of a prevailing anti clockwise circulation in Georgia Strait but i t is not known that this circulation acts as far north as Cape Mudge. However horizontal mixing must be considered and i t must be remembered that i t i s not yet definitely established that i t i s Fraser River water that influences salinity at Cape Mudge. The fresh water from the Fraser River on reaching Georgia Strait will be dissipated from the surface through mixing processes, the dissipation increasing with distance 64 from the r i v e r . Therefore assuming Cape Mudge to be i n -fluenced by Fraser River water i t i s to be expected that the annual range i n s a l i n i t y w i l l be considerably less at Cape Mudge than a t Entrance Island and Departure Bay. The s a l i n i t y curves v e r i f y t h i s , showing an average annual range of 2.00$oat Cape Mudge as compared with 5.20%aand 5.10%oat Entrance Island and Departure Bay r e s p e c t i v e l y . The location of Tr i p l e Island ( F i g . l ) i s such that i t s surface s a l i n i t y w i l l - b e influenced by v a r i a t i o n i n the f r e s h water discharge o f the Nass and Skeena Rivers which are of the same phase as that of the Fraser River (Fig.22). I t s s a l i n i t y curve i l l u s t r a t e s t h i s influence and shows an average-annual range of 2.80$»with a minimum of 28.95$*in June. Ivory Island, while not located near any large r i v e r s is close to the mainland and at a l a t i t u d e where pre-c i p i t a t i o n i s observed to be p a r t i c u l a r l y heavy. I t i s suggested that the c o l l e c t i v e runoff of the area causes the observed decrease i n s a l i n i t y to a summer minimum here • 65 •XII THE STATIONS AT WHICH SALINITY REMAINS CONSTANT . . THROUGHOUT THE YEAR The remaining stations show no marked annual v a r i a t i o n i n s a l i n i t y . The locations of Cape S t . James, Langara Island and Pine Island are such that there are no major influences to cause an annual v a r i a t i o n i n s a l i n i t y and they are only subject to small, short term fluctuations due to p r e c i p i t a t i o n , evaporation and wind induced mixing. In the case of Race Rocks one migit expect the Fraser River to influence surface s a l i n i t y but as previously discussed the intense mixing of the area probably reduces the effect.. 66 BIBLIOGRAPHY G i l l e s , B.C., The Temperature and S a l i n i t y of the Sur fa ee.. Waters of the I r i s h Sea f o r the Period  1935-46« Roy. Astron. S o c , Geophys. Supp. Vol.5, No. 9, 1949. Hoel, P.G., Introduction to Mathematical S t a t i s t i c s , Wiley, 1948. Jacobs, W. C., The Energy Exchange between Sea and Atmosphere. Journ. Mar* Res. V o l . 5. p. 37-66. Sverdrup, H. V., 'Johnson, M.W., Fleming, R.H., The Oceans. Prentice-Hall,1946. Tullay, J . P., Ooeanography of Nootka Sound. Journal of the B i o l . Board of Can., V o l . I l l , No. 1, p. 43-69. Waldie, R. J . , L.A.E. Doe and Assoc., Oceanographic Discovery, Prog. Rep. of th9 Pac. Coast Stns., No. 84, Oct. 1950, p. 59. Whittaker, E. T. and Robinson, G, Calculus of Observations. London, 1932, 

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