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dominant drifts and interchanges in the mid-strata of the ocean^^ 

 basins are only now crystallizing. This is especially true of one 

 vast and lonelv expanses of the Pacific, which have been traversed 

 by scientific expeditions only at long intervals, and along tracics 

 far aoart. Knowledr-e of the underlying circulation of the Paciiic 

 and of the Indian Ocean might be expected to lag far behind tnat of 

 the Atlantic, because of the great areas to be covered, and the ^ 

 expense involved, did not their closure to the north (complete lor 

 the Indian Ocean, nearly so for the Pacific), greatly simplify tneir 

 circulatory characters. The immediate need here is for the accuniu- 

 lation of the raw data. 



Vertical currents are not as apparent to the causal observer 

 as are the horizontal drifts. In fact, movements of thi,3 sort are, 

 as a rule, so slow that they are not to be detected by ordinary 

 instrumental observation, but only indirectly by their effects upon 

 the te^iperature and salinity of the surface waters of the regions 

 in question. Since they are not of direct interest to the navigator 

 (omitting the mythical or more actual whirlpools in narrow straits, 

 etc.) their existence vvas not recognized until theoretic discussions 

 of the circulatory systems of the oceans made clear the necessity 

 for assiining the existence of something of the sort. Moreover, 

 such vertical currents were later deduced from wind observations. 



Modern oceanograph3/ is, however, much concerned with the up- 

 wellings and sinkings that are now '-.nown to take place on a vast 

 scale, because it is certain that the presence of a thick stratuij 

 of water in the abyss, much colder than the mean temperature of the 

 underlying crust of the earth, is the resiilt of mass sinkings, near 

 the poles, of water cooled and so given a high specific gravity 

 at the surface. Conversely, we need more than our present sketchy 

 view of the corapensating up-wellings, known to prevail along the 

 coasts of Ilorocco; of Southwest Africa; of California; of Ecuador, 

 Peru, and Chile. From what depths do these chiefly draw? What are 

 their velocities, their seasonal fluctuations, the volumes of v/ater 

 involved? Just how do they control the physical characters of the 

 upper strata of v/ater, and what is their effect on the vital oconouy 

 of the seas where their physical effects are greatest? Only for 

 the California up-welling can v;e yet answer these questions even in 

 the roughest way. The South American up-welling offers perhaps the 

 most attractive problem in general Oceanography tode^y. 



Perhaps of first importance in this connection is the role of 

 these upwellings as conveyors to the surface, of water rich in 

 dissolved plant nutrients. It seems clear enough (in fact, n^jjierous 

 analyses of phosphates, nitrates, etc. establish) that an the car- 

 casses of animals and plants are constantly sinking, the chemical 

 compounds to T^hich they finally decay would tend to accumulate in 

 the deeper levels out of the reach of the photosynthetic plant world, 

 were there no such up-drafts, and no churnings of the water. That 

 planktonic plants have been found in some abundance at great depths 

 does not arg^ae against this, any ;aore than does the fact that vre can 

 grow rhubarb etc., in our cellars, because they have been found -aost 

 abundant under regions where the surface flora (hence the sinking 

 carcasses) are also most abundant, suggesting that this abyssal plant 

 Plankton really represents a saprophitic community. Diffusion in 



