30 



motionless water takes place too slowly, and on too small a scale, 

 to account for the regeneration of dissolved food stuffs in the 

 uoper stratum that is known to occur. But in the sea upv.ellingis, 

 eddy motions, and turbulence of all sorts, by effecting interchanges 

 of water masses having different properties, produces an effect 

 agreeing with what would happen if the coefficient of diffusion were 

 very high. Empiric tests of the actual events are, hov/ever, ir.uch 

 needed, because theory has far outstripped observation in this field. 



Closely associated with the phenomena of mass upwellings and 

 sinkings are the problems of turbulence, in the shoal marginal seas 

 where most of the important sea fisheries are concentrated. In such 

 situations this type of circulation is a physical factor of tho very 

 first rank, because it there does the same work, in bringing rich 

 water up from the bottom to the surface, and in maintaining the 

 circulation of oxygen, that the great vertical currents do for the 

 ocean basins far from land. In high latitudes the interchange of 

 water between surface and bottom brought about by turbulence also 

 plays an active role in the thermal complex of shoal seas, by 

 bringing cold vvater from the deeps up within the direct influence 

 of the sun and carrying warm v/ater down in summer, while assisting 

 the loss of heat by radiation in the same way in winter. The 

 activity of turbulence at any given time and place is determined by 

 the interplay of many factors; strength of the tidal current; shape 

 of the bottom; contour of the coastline; strength of the wind; 

 height and shape of the x^aves; likewise by the degree of vertical 

 stability given to the water by the vertical distribution of 

 specific gravity prevailing at the time. 



Turbulence, moreover, varies from hour to hotir with changes in 

 the tide and wind. Thus wide regional and seasonal variations may 

 exist in this respect between stations only a few miles apart, ma.k- 

 ing local solution of the problems of turbulence extremely co:molex, 

 and the turbulent movements are of such a nature as to preclude 

 direct neasurem.ent , But interpretation of the local variations in 

 the thermal and haline cycles in shoal northern seas (where tho 

 greatest abundance of plants and animals are concentrated), and of 

 many events in the life histories of fishes and other animals, as 

 well as of the periods of multiplication for the Planktonic plants, 

 depend so directly on knowledge of the varying degrees of turbuJ.once 

 that this general subject deserves much more attention than it has 

 received. We see a striking example of turbulence as a determining 

 factor in the Bay of Fundy, 



The problem of the distribution of oxygen in the sea is so 

 closely associated with the general problems of vertical circulation 

 in the ocean that it is best mentioned here. The intake of oxygen 

 occurs exclusively at and near the surface, (l) in the surface film, 

 or within the upper few feet where air buboles are entrapped by 

 breaking v/aves, and (3) throughout the upper ill-urainated zone v;here 

 plants carry en photos3mthesis. Quantitative data as to the rapidity 

 with which any deficiency in oxygenis renewed from these sources 

 (particularly the efficiency of the latter out in the open sea) are 

 present desi d erata . There are no sources from y;hich the v/ator cm 

 absorb free oxygen in the deeper levels. On the contrary the deeps 

 are constantly being roboed of their dissolved oxygen, not only by 



