8 GEORGE V SESSIONAL PAPER No. 38a A. 1918 



XV 



HYDROGRAPHY IN PASSAMAaUODDY BAY AND VICINITY, NEW 



BRUNSWICK. 



(By Professor Alexander Vachon^ B.A., L.Ph., etc., Laval University, Quebec.) 



The laws that regulate the distribution of the plankton in the sea furnish a 

 problem of paramount importance in the progressive industry of fisheries. Qualitative 

 and quantitative determinations of the plankton are made at selected hydrographic 

 stations, since the plankton is followed by multitudes of fishes which live on it, and 

 those fishes are followed by others which serve as food for men. 



As the plankton, which regulates, to a great extent, the migrations of the fish, is 

 itself at the mercy of the chemical, physical and mechanical conditions of the sea, it 

 is easily understood of what economical importance a correct knowledge of those con- 

 ditions will prove. We speak of the migrations of the herrings and sardines; they are 

 the same as those of the plankton which serve as food for them, and the presence of 

 the plankton is ruled by depth, light, temperature, salinity, pressure and density. 



TEMPERATURE. 



The heat of the atmosphere, emanating from the sun, penetrates the water, and is 

 attenuated according as the depth increases. At the surface, the temperature of the 

 water is almost as changeable as that of the air adjoining it, the variations of which 

 find their repercussion in the contiguous liquid, although somewhat mitigated. Cold 

 in winter, warmer in summer, the surface water expresses the alterations in the tem- 

 perature of the air. Therefore, in summer, the sun's rays heat the water at the surface, 

 and to a depth of a few meters. The difi^erence between the temperature of the day and 

 that of the night ceases to be perceptible at a small depth; in order to find the region 

 which is insensible to summer and winter variations, we must go down further. At 

 about one thousand metres, the secular variations are imperceptible. Then begins the 

 zone where the temperature never varies; by a slow and regular progression, the tem- 

 perature grows colder and colder until it is only about one or two degrees above zero. 

 This low temperature is found even in the tropical regions, where the scorching rays 

 of the sun beam constantly upon the surface. 



Ordinarily, the water gradually becomes cooler , from the surface to the bottom, 

 because, apart from the effect of the sun's heat at the top, cold water is more dense 

 and goes to the bottom; but, in the polar regions, and where there are cold currents, 

 we sometimes find an area of colder water between two warmer regions, and this state 

 of unstable equilibrium, where the water is cooler, more salt and more dense, affords 

 very interesting information. 



Light does not penetrate into the water further than two or three hundred metres 

 from the surface, hence, no green plants are found at such depths, as light is neces- 

 sary for the decomposition of carbon dioxide which is the bread of the vegetable kingdom.. 



When water is heated, it goes to the surface; if it be concentrated, it seeks a 

 lower level; should it cool for some reason or other, by the atmosphere or by evapora- 

 tion, it also descends. Everything influences the temperature of the superficial water, 

 the cold, polar currents as well as the hot currents coming from the equatorial regions. 



We understand why it is that the water is so cold at the bottom of the ocean, 

 since cold water descends, and being free from the heating influence of the sun in 

 those depths, where the light of day never reaches, and. on accgunt of the fe(^ble power 

 of water to conduct heat, the temperature of the lower regions of the ocean never 

 varies. Kelvin and Wegemann made calculations concerning the conduction of heat 

 through water and came to the conclusion that this conduction is practically negli- 

 gible. With a temperature of 30° C. at the surface and the water perfectly still, it 

 would take one hundred years for any heat to be perceived at a depth of a hundred 



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