190 GLACIOLOGY 



this would tend to reverse the actual conditions of the sea ice respectively in 

 McMurdo Sound and near the Bay of Whales. 



Obviously what is now urgently needed is a series of current observations at 

 various depths from the surface to the bottom of Ross Sea taken systematically at 

 frequent intervals. 



It should be noted that we observed on our ascent of Erebus that the surface 

 of Ross Sea in March froze over earliest under the western mountains, from which 

 one could see from day to day long tongues of ice spreading from the shore far 

 out into McMurdo Sound. After our subsequent experience of the strong cold 

 plateau winds which blow down the gaps in these ranges, especially at night time, 

 we venture to suggest that the very strongly indented shape of the growing ice 

 sheet in this region was due to corresponding tongues of cold air protruded from 

 the outlet glacier valleys allowing these cold air masses to descend fi-om the inland 

 plateau. Obviously this cold plateau wind and the proximity of such high land as 

 the west coast of Ross Sea accounts for this part of the sea freezing over first. 



That these ocean currents have a powerful influence in thawing the sea ice was 

 obvious from the slightly honeycombed character of the ice in McMurdo Sound 

 ill January and February of 1908. In landing our stores over the bay ice at Cape 

 Royds we frequently came upon what may be termed corrosion hollows, with only 

 a very thin covering of ice over them. These of course were not in any way to be 

 confounded with the seal holes. The fact that the Nimrod was able to make 

 some little progress in hammering her way through the ice late in January shows 

 that it must have been immensely weakened as compared with the strength it 

 must have possessed when it was a compact sheet of ice 7 to 8 feet in thickness, 

 as in the autumn. It is not of course certain that the whole of Ross Sea is frozen 

 over during the winter. It is certain that it freezes over, and is continuously 

 covered with ice for many miles eastwards from the coast of South Victoria Land, 

 but no attempt having as yet been made by any ship to penetrate the north-east 

 part of Ross Sea during winter, one cannot predict what its exact state is during 

 that time of the year. 



MECHANICAL DISRUPTION OF THE ICE 



On September 1 we observed a strong water sky with cumulus cloud over 

 McMurdo Sound, both clear indications of open water. The general appearance of 

 the ice-foot near Blacksand Beach and of the open water is shown on Plate LI. 

 Fig. 3. On the right-hand side is the pressure mound of ice slabs formed in the 

 preceding autumn. 



At the time when the Northern Party left Cape Royds on October 5 there was 

 already a long strip of open water in McMurdo Sound extending to within about 

 5- or 6 miles of the pinnacled ice, so that it was necessary for the party to make 



