CONTROLLING FACTORS OF CIRCULATION IN ROSS SEA 189 



current normally setting from Cape Bird towards Cape Royds, that is, setting 

 southwards. 



There can be little doubt that the powerful blizzard winds which control the 

 water circulation on the west side of Ross Sea and McMurdo Sound tend to force 

 the water northwards along the shore of South Victoria Land from Cape Royds 

 towards Cape Adare. The easterly winds experienced by Captain Amundsen at the 

 Bay of Whales would obviously tend to drive the water of Ross Sea from the direc- 

 tion of King Edward VII. Land towards Ross Island. One may conclude, therefore, 

 that as the result of the action of these two strong prevalent winds, of which the 

 southerly and south-easterly blizzards characteristic of the Ross Island region are the 

 more powerful, is to cause a clockwise circulation in the waters of Ross Sea.* This 

 satisfactorily accounts for our observed directions of ocean current at Cape Royds, 

 viz. towards the north-west. One would expect from such a circulation, if the 

 deep-seated circulation be similar to the surface, that the warmer water would be 

 drawn down the eastern side of Ross Sea, and that it would exert its greatest 

 influence in thawing the sea ice in that region, and would be somewhat lowered in 

 temperature after passing under the Barrier, and emerging perhaps in part east of 

 Cape Crozier, in part in McMurdo Sound. On its northerly course it would be 

 further chilled by the strong plateau wind blowing from the west off the high plateau 

 on to the western waters of Ross Sea. Thus these western winds contribute another 

 component to control the general surface circulation of Ross Sea. One would expect 

 therefore, theoretically, that the maximum thaw effect exerted by the sea water 

 would be on the eastern side of Ross Sea. The recent observations of Captain 

 Amundsen are not inconsistent with this view. He found that to the north of his 

 winter quarters at the Bay of Whales the sea was constantly open, as indicated by 

 the rising of heavy cumulus clouds and strong water blink actually within about 8 

 miles of his camp. This open water persisted throughout the whole of the winter. 

 At Cape Royds we were unable during the months of winter darkness to decide 

 whether or not there was open water between us and the mountains of South Victoria 

 Land to the west. Occasional moonlight enabled us to see that apparently the 

 whole of McMurdo Sound during a considerable part of the winter was completely 

 frozen over. This suggests that the sea water temperature here is probably lower 

 than it is near the Bay of Whales. That the greater persistence of sea ice in 

 McMurdo Sound as compared with Ross Sea near the Bay of Whales is due rather 

 to difference of temperature of sea water than to that of surface air temperature is 

 rendered probable by the consideration that Captain Amundsen found that at the 

 Bay of Whales, even with 8 miles of this constant open water, the main air tempera- 

 ture at the surface was often lower than it was for the corresponding period at Cape 

 Evans on Ross Island. So far, therefore, as surface air temperatures are concerned, 



* A similar clockwise rotation on the whole dominates the circulation of the water in the 

 Weddell Sea. 



2 B 



