TEMPERATURE AND SPECIFIC GRAVITY VARIATIONS 35 



III. 



Temperature and Specific Gravity Variations in the 

 Surface Waters of Departure Bay, B.C. 



BY 



C. MoLean Fraser. 



An earlier paper provided some preliminary notes on the variations in temperature 

 and density in coast waters, based on observations made during the summer of 1914^. 

 In continuation of one phase of the work then begun, the daily record of the tempera- 

 ture and tlie specific gravity of the surface water at the station landing float in Depar- 

 ture bay, has since been kept. This paper deals with the record for five years ending 

 May 31, 1919. 



It is fully realized that temperature readings taken once a day and specific gravity 

 readings taken with an hydrometer do not give sufficiently accurate data for getting 

 any light on such problems as diurnal migration but in a location such as this where 

 there is so much variation during the year, certain general conditions of value may 

 be de4uced which at least may form the basis for more accurate observations by one 

 who may put his whole time on the work. It is true also that in the waters of a 

 sheltered bay the conditions are somewhat special, but, although they cannot be con- 

 sidered as truly oceanic, by any means, they are typical of hundreds of situations along 

 the north Pacific coast, where there are such extensive areas protected in a similar way, 

 while at the same time they are directly connected with the open ocean and hence 

 share to some extent the oceanic conditions. 



In considering the temperature records, it will be noted that there is a definite 

 relation between the temperature of the surface Avater and that of the air. Since the 

 readings were taken but once a day, there is nothing to show coincidence throughout 

 the day, but although the water does not show the variation in temperature during 

 the twenty-four hours that the air does, it is probable that there is a certain amount 

 of coincidence. As the water readings were -taken at a definite time of the day, 

 at or near 8 a.m., and the air records were not taken at a definite time, since only the 

 maximum and minimum temperatures were recorded, there are no records exactly 

 comparable. Since the water varies comparatively little during the day, the mean 

 of the maximum and minimum temperatures each day shows a better parallelism witli 

 the water temperature from day to day than either the maximum or the minimum 

 temperature does, hence the mean readings are considered here and it is these that are 

 given in the table of air temperature. 



While there are many small fluctuations in each record that are not found in the 

 other, practically all the larger fluctuations are common to both, although the water 

 variation is not so extreme as the air variation. Thus when graphs are made of the 

 daily readings, many differences show up, whereas, when averages are taken for more 

 extended periods (the periods taken for the graph appearing in the plate are of ten, 

 days), the correlation is very distinctly marked. 



The curves for the different years are similar in a general way but each has its own 

 special features and these may have much to do with changing conditions from year 

 to year for the inhabitants of the sea. This is noticeably true in the hatching out of 



1 Fraser, C. M., and Cameron, A. T. Variations in density and temperature in the coastal 

 waters of British Columbia, Contr, to Can, Biol, for 1914-1915, 1916, p. 133-143. 



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