The Eurasian Arctic During the Last Ice Age

A vast ice sheet once covered the Barents Sea. Its sudden disappearance 100 centuries ago provides a lesson about western Antarctica today

Anders Elverhøi, Martin Siegert, Julian Dowdeswell, John-Inge Svendsen

Implications for Western Antarctica

During the last ice age, the west Antarctic ice sheet was considerably larger than it is today. Grounded ice was probably in place across the whole continental shelf, just as it was in the Barents Sea. Yet the decay of this enlarged west Antarctic ice sheet was different from the decay of ice in the Barents Sea in two ways. For one, deglaciation in Antarctica began much later than in the Barents Sea. Also, ice decay resulted in the formation of large floating ice shelves between the open ocean and the grounded ice sheet. The Filchner-Ronne and Ross ice shelves, for example, are each now about 500,000 square kilometers in area.

These differences suggest two important conclusions about the stability of the west Antarctic ice sheet. First, the ice shelves may be influential in maintaining the stability of the ice sheet because they act as buttresses to support the grounded margin of the ice sheet, whereas in the Barents Sea they were absent and the grounded margin was actively calving icebergs. Second, given the buttressing effect of the ice shelves on the ice sheet, the present changes in sea level are not large enough to encourage ice decay in western Antarctica to the extent witnessed in the Barents Sea. One reassuring note relating to the latter conclusion is that during the last interglacial, sea level was several meters higher than it is at present, yet the west Antarctic ice sheet did not decay. The majority of the water responsible for the higher sea level at that time probably came from Greenland.

The west Antarctic ice sheet is clearly capable of resisting substantial rises in sea level—but why? The answer could well be that the floating ice shelves in western Antarctica help maintain the grounded ice upstream. If that is true, one should therefore be concerned with the stability of the ice shelves in western Antarctica. Their decay will not in itself raise sea level (just as the melting of a floating ice cube does not raise the water level in a glass). But if they do melt, the west Antarctic ice sheet will look much more like the former Eurasian ice sheet just before it broke apart.

What might cause the ice shelves to decay? The answer lies in the ocean. Melting from the bottom causes much of the mass lost from ice shelves. So if the ocean around Antarctica warms, the rate of melting will increase. If this is not balanced by the increase in evaporation and snowfall that would accompany warming of the Southern Ocean, the ice shelves will thin, and ultimately they will disappear. The west Antarctic ice sheet would then be poised to collapse rapidly. People must not ignore this possibility—and the rise in global sea level that would ensue.

Mercer called the present situation a "threat of disaster." Understanding the glacial history of the Eurasian ice sheet suggests that the threat will not be acute unless the existing ice shelves disappear. Still, this research makes it abundantly clear that such a disaster has taken place in the opposite hemisphere in the not-so-distant past, and people must be on guard for it recurring in the future.

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