DESCRIPTION OF THE ISLANDS 347 



the S. Atlantic caused by the fluctuating quantity of polar ice induces changes in the volume, direc- 

 tion, and temperature of the great ocean currents, which will in turn affect the pressure of the over- 

 lying air and lead to changes in the tracks of the cyclonic and anticyclonic systems which dominate 

 climatic conditions in Southern America.^ 



PACK-ICE2 



For a longer or shorter period every year, beginning as a rule before and extending 

 through and beyond the winter months, the South Orkneys are surrounded by pack- 

 ice.^ Even the comparatively short open season, how^ever, is sometimes interrupted by 

 the arrival of a broad stream of ice which may partially or wholly envelop the group. 

 Such streams as a rule are formed of loosely knit floes and their existence in the neigh- 

 bourhood of the islands is fleeting, although they have been known during the whaling 

 days to block the entrance to one of the harbours for as long as six days on end, even in 

 the height of summer, to the great inconvenience of the whale-catchers and floating 

 factories using it as a base. But the pack which approaches and eventually envelops 

 the South Orkneys in a more or less solid sheet throughout the winter arrives with 

 southerly winds. Drifting into the bays and straits as the temperature falls, the 

 floes gradually become cemented together by younger ice or jammed tightly against each 

 other by their own momentum, until with the advance of winter the group is completely 

 invested by a more or less compact and occasionally immovable ice-sheet. 



The main drift of the water in the neighbourhood of the South Orkneys is easterly, 

 and pack-ice, and especially icebergs, are known to be carried past the group in that 

 direction. Current, however, is a less important agent in the transport of pack than 

 wind, and it is in fact, as already noted, southerly winds that are responsible in the main 

 for driving the ice on to the southern coasts of the islands. Mossman describes how 

 after a hard south-easterly gale accompanied by a moderate sea — a sure sign of heavy 

 obstruction to the southward — pack-ice appeared in the south-east on April 30, 1904, 

 and, approaching rapidly, entered Scotia Bay on the same day. Thus with south-easterly 

 gales the eastern part of the South Orkneys, especially the south side of Laurie Island, 

 together with Washington and Lewthwaite Straits, is liable to become blocked at an 

 earlier date than the region to the westward. Within recent years the 'Discovery' and 

 'Discovery II', in the course of their several visits to these islands in late summer or 

 autumn, have been able to reach and obtain shelter on the east coast of Signy Island or 

 in Sandefjord Bay without any great difficulty, while farther to the eastward the south 

 coasts were unapproachable owing to the pack-ice which blocked them. 



1 Mossman, R. C, 1918, The Climate and Meteorology of the Antarctic and Sub-Antarctic Regions, Journ. 

 Scott. Met. See, XVIII, No. xxxv, p. 29. 



2 Except where otherwise stated this account is largely indebted to the observations of Rudmose Brown, 

 Mossman, and Pirie in The Voyage of the ' Scotia \ and to the ice summary in the first edition of The Antarctic 

 Pilot, p. 56; see also Annals of the Argentine Meteorological Office, vols, xvi, pp. 176-88, 1905 (Buenos 

 Aires), and xvii, part 2, pp. 163-9, '9^2 (Buenos Aires). 



3 A notable exception was the year 1908, which was abnormally open: the winter pack-ice never reached 

 the group and in its absence the bays froze over, a thin and level sheet of ice forming as the temperature fell. 

 This ice lasted only for 52 days during July and August (see also pp. 338-9). 



