CANADIAX FISHERIES EXPEDITION, 191'rlo 261 



From these experiments important conclusions may be drawn with regard to the 

 (}ult' Stream. The actual bottom water of the ocean does not participate in the cir- 

 culation of this current, which affects only water within the depth to which beat is 

 carried down by the vortex of the Sargasso sea. The Gulf Stream thus presents a 

 well-defined, closed circulation with a warm surface current from the tropics to the 

 Arctic ocean, and a cold, deep-water current in the opposite direction. It is at the 

 surface of the water in the Arctic, and at the bottom of the Sargasso vortex in the 

 south, that the physical changes take place which give rise to the circulation of the 

 entire current. From the experiments referred to it is seen that these changes act 

 in co-operation, the quantity of water heated in the tropics corresponding exactly to 

 the amount cooled in the Arctic. Even when the warm and cold centres are placed 

 at the same level, or the former at a higher level than the latter, this rule is strictly 

 complied with. (In the last case, the quantity of water cooled and heated is nil, the 

 centres being surrounded by water of their own respective temi)erature.) This remark- 

 able adaptation of the physical processes is perhaps the most important factor in 

 regulation of the condition of the sea. 



From fig. 44 b it will be seen that if the Sargasso vortex did not exist, and the 

 sea-water were only heated by the direct action of the sun's rays upon its surface, 

 then there woiild be no Gulf Stream, but only a very slight surface current. The 

 oblique strip in fig. 44 b corresponds to the lower surface of the Gulf Stream, -which 

 is likewise situated at a greater depth about its warm centre in the tropics than at 

 the cold centre in the Arctic. 



The experiments indicate, as a general rule, for the two complementary physical 

 changes, that the process whereby the specific gravity of the water is reduced must 

 take place at a greater depth than that which increases it, and that the greater this 

 depth the more easily will a current develop. If, however, the two processes take place 

 at the same level, or with the reduction of specific gravity at a higher level than the 

 reverse process, then no current will be produced thereby. It is thus not all physical 

 processes in the sea which give rise to ocean cui-rents. 



It may occasionally happen that two opposite physical processes at the same 

 level enter into co-operation, and thus set up a current. This is accomplished by a 

 massing of the products of the one process until the difference of level necessary for 

 the propulsion of a current is reached. The Labrador current is itself an instance of 

 a current originating in just this very way. The melting of the ice in the Arctic 

 basin produces a mass of brackish water, which has to be carried away. This water 

 therefore collects until it has formed a layer so deep as to be capable of forming a 

 current, the volume of the latter tlien corresponding to the further production of 

 Drackish water beyond that point. 



As to how far the Gaspe current should properly be considered as belonging to 

 this last category is a question whicb can only be determined by further investigation. 

 The physical process in which it originates is the mixing of St. Lawrence water with 

 sea-water outside the mouth of the river. It is possible that this mixing process 

 extends, owing to ebb and flow of the tide, down to a considerable depth. It may, 

 however, take place at the surface, in which case the mixed water would only by 

 accumulation attain a sufficient depth to give rise to a current, w'hen the amount of 

 water transported thereby would answer to the quantity of mixed water thereafter 

 produced outside the mouth of the St. Lawrence. 



The Gaspe current is one of the few ocean currents which may conveniently be 

 observed and studied, as regards cause and progress, by hydrographical measurements 

 at its point of origin, throughout its course, and at its termination. Such study is, 

 moreover, of the highest importance, not least as a means towards the better compre- 

 hension of similar problems which present themselves in the case of other currents 

 whose origin and progress are less easily discernible. The value of the Gaspe current 

 in this particular respect has, as a matter of fact, already been manifested, the investi- 



