The Editor,
Journal of Glaciology
Sir, The glacial history of Antarctica
I very much appreciated Mr. Hollin’s paper on the glacial history of Antarctica (Reference HollinHollin, 1962), and in particular its “chief conclusion … that the greatest glacial fluctuations in Antarctica were produced by changes of sea-level” (p. 174) seems to me very important. However he makes another affirmation that I should like to oppose; it arises in his calculation of the time of accumulation of Antarctica.
Hollin takes the average annual accumulation to be approximately 14 g. cm.−2 and says that “ignoring ablation” an average thickness of 2,300 m. could be built up from ground level in less than 15,000 yr. (p. 175). He further assumes that the “gross ablation (sublimation, evaporation and run-off)” amounts to 1.5 g. cm.−2 at lat. 67° S. and 1 g. cm.−2 at lat. 85° S. Later on he points out that “the Antarctic Ice Sheet is not … ‘static’ or ‘sluggish’ or ‘passive’ but is in fact highly active. Indeed its mean velocity around its periphery of roughly 15,000 km. must be of the order of hundreds of meters per year.” All of this I agree with—but these facts mean that the figure of 15,000 yr. is not the time it actually takes the ice sheet to accumulate!
Let us suppose that at the periphery with a velocity of 100 m./yr. ice with a thickness of only 100 m. is driven into the sea. That would give 1.5 × 1017cm.3 of ice or 1.3 × 1017g. of water—7.2 per cent of the annual accumulation of 1.8 × 1018g. And the ice sheet may be some 300 m. thick, and its mean velocity much more than 100 m./yr. Indeed according to Reference HoinkesHoinkes (1961, p. 368–69) Mellor assumes all the annual ice losses in the mass balance of Antarctica (ablation plus export of ice) to be 9.45 × 1017g., while Kotlyakov even puts it as high as 1.32 × 1018g. of water.
Glacier movement starts when glaciers are some 30 to 60 m. thick in the temperate zones; it may be that in the Antarctic the ice had to get a little thicker due to the different temperature and bed conditions, but it cannot be neglected entirely when calculating the time of accumulation of an ice sheet of continental dimensions, which might easily need five times the time that Hollin has supposed.
