37° 



T. C CHAMBERLIN 



the ice-covered tracts, where the precipitation and melting are con- 

 siderable, and where adjacent polar lands pour in much fresh water, 

 the surface layers are so much fresher than the average sea water 

 that the concentration of salinity by freezing does not overbalance 

 the original freshness. But in those polar regions where there is little 

 inflowage from the land, and where precipitation is slight and almost 

 wholly snow, which accumulates on a previously frozen surface and 

 absorbs most of its own summer melting, it is believed that a sufficient 

 degree of saline concentration combined with depression of tempera- 

 ture takes place to cause an effective downward movement. This 

 is believed to co-operate with diffusion and conduction in giving the 

 lower body of polar waters the superior gravity which actuates the 

 abysmal circulation. The sea immediately bordering Antarctica and 

 that lying northwest of Greenland seem to furnish these conditions. 

 Moss' and Krogh^ have found that at times of northwesterly winds 

 the air west of Greenland contains about double the usual content of 

 carbon dioxide. This, I have suggested, may come from waters 

 overcharged with it by the freezing of the overlying layer. 



To a large extent the polar ice is carried to lower latitudes, and 

 the waters arising from its melting do not redilute the concentrated 

 waters, which are thus left free to pursue an independent course. 



It is not to be inferred, however, that the deep-sea waters derived 

 from the polar regions are superior in salinity to the waters of the 

 evaporating tracts of low latitudes, but merely that by this concen- 

 tration, conjoined with low temperature and modified by diffusion 

 and mechanical mixture, water of superior gravity is derived, and 

 that this controls the abysmal circulation. 



Dr. Otto Pettersson, in an elaborate article, supports by experi- 

 ment and observation the theory of Bjerknes, that the melting of the 

 polar ice also promotes circulation, both superficial and deep-seated ; 

 but I can only make reference to this here.^ 



A survey of the existing temperatures and salinities of the ocean 



1 Moss, "Notes on Arctic Air," Proceedings of the Royal Dublin Society, Vol. 

 II (1880). 



2 Krogh, "Abnormal CO2 Percentage in the Air of Greenland, etc.," Meddeleher 

 om Gronland, Vol. XXVI (1804), pp. 409-11. 



3 "On the Influence of Ice-Melting on Oceanic Circulation," Geographical Jour- 

 nal, Vol. XXIV (1906), pp. 285-333. 



