194 MAEION EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



fourth of the total surface of the Nortli Athintic. Arctic Ocean in- 

 chuled, of whicli about one-sixth is iioriually frozen and meUed each 

 year, so that one-thirtieth of the entire surface of the Athintic is 

 annually exposed to the latent heat phenomena. A comparison of 

 vertical dimensions shows that only about 0.001 of the mean depth 

 of the Atlantic is ice filled and if volumes are matched, only 0.0005 

 of the entire ocean is given over to ice. It is obvious from this that 

 the proportions, horizontal to vertical, definitely prove the ice proc- 

 esses as wholly sui)erficial. 



The principal regions of ice production are the coastal seas of 

 Eurasia and the ofling of the latter, of east Greenland, and of 

 Arctic Xorth America. The principal regions of ice production are 

 also the general regions in whicli the ice melts in greatest amount 

 during summer. It follows that the life cycle of nearly all the ice 

 is spent in w^aters whose outer bounds are the continental edges, and, 

 although a certain quantity of ice is carried out into the deep 

 ocean basin, tJiis forms oidy an exceedingly small proportion of 

 the w hole. 



Therefore, the raw materials, so to speak, out of wdiich the great 

 mass of ice is created, and back to which it returns, are the great 

 reservoirs of shallow^ coastal waters of the north. During the colder 

 months of the year, depending upon the severity of the air tempera- 

 tures, these become readily chilled (from the top down to depths 

 of 100 to 200 meters) close to the freezing point and ice forms in 

 large amounts on the surface. Thus the actual appearance of the 

 ice marks the release of heat energy, partly to the atmosphere and 

 partly to the water, but the creation of the surface covering of ice 

 tends to insulate the deeper waters and thereby protects them from 

 further rapid freezing. The low temperature of the atmosphere, 

 therefore, produces over shelves and northern seas, at the end of 

 winter, a relatively deep frigid body of water, in the upper few 

 feet of which then floats a covering of ice. It is obvious that prac- 

 tically no melting, hence no withdrawal of heat energy from the 

 water, can take ])lace even on the undei'side of the ice, as some have 

 claimed, while it lies insulated in such boreal surroundings. 



With the approach of summer increased radiation from the more 

 perpendicular rays of the sun becomes applied to (a) the top of 

 the ice cover, and (&) to the surface water wdiere this is exposed. 

 The ice and water are thus w^armed simultaneously, but due to the 

 far greater ca|)acity of the water to absorb heat and also to spread 

 the heat rapidly downward to 10 to 25 meters, the ice is soon com- 

 pletely enveloped, even on its underside, by relatively warm water. 

 The sun-warmed surface layers, moreover, due to their great specific 

 heat, are much more efi'ective as a melting agency than are the 

 direct rays of the sun on the ice itself. The latent heat of melting, 

 it is true, tends to retard the ablation of the ice but continued solar 

 radiation striking its surface more than counterbalances this. As the 

 ice melts it loses draft and. floating higher and higher, it becomes 

 more and more confined to the shallowest and Avarmest stratum 

 which materially accelerates the rate of its dissipation. All this is 

 made evident by the shrinkage of the floes, by the expansion of the 

 areas of open water between the fields, and by the grow^th of char- 



