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East Antarctic Ice Sheet

Global Meltdown?

How is global climate change affecting the huge East Antarctic Ice Sheet, and how will changes in the ice sheet affect the rest of the world? Is the ice sheet in danger of collapse due to "greenhouse" warming? These are some of the critical questions that David Marchant, professor of earth science is investigating with support from the National Science Foundation.

It is known that one of the largest global climate shifts occurred between about 15.6 and 12.5 million years ago (Middle Miocene time). During this time, dramatic global cooling and major reorganization of ocean circulation patterns occurred. This dramatic and permanent shift set the stage for modern oceanic and atmospheric circulation and ushered in the bipolar ice ages that have dominated climate records for the last 2.5 million years. How did Antarctica respond to the great climate shift at about 14 million years ago? Did growth of the Antarctic Ice Sheet in fact initiate this shift?

The recent (and unexpected) discovery by Marchant and his colleagues of Miocene-age volcanic ash embedded in sediment in southern Victoria Land will allow scientists, for the first time, to reconstruct the precise climate and glaciological conditions of this era on the Antarctic continent. It is a rich source of data crucial to address key questions about the conditions that led to abrupt global cooling 14 million years ago and the emergence of the East Antarctic ice sheet itself. This, in turn, will shed light on the implications of current climate changes Antarctica and what impact fluctuations in the volume of East Antarctic ice will have on our lives.

A related discovery by Marchant's team of the oldest fossil glacier ice in the world, formed earlier than 8.1 million years ago in the Dry Valleys region of Antarctica, will provide additional data. The presence of Miocene-age ice less than twenty inches below the surface implies that temperatures never warmed enough during the last 8.1million years to allow significant melting in this area. It calls into question the view that, during part of the Pliocene Epoch (three to four million years ago), East Antarctica was largely free of glacier ice and supports evidence pointing to the development of a stable, polar ice sheet by Middle Miocene time. Significantly, the ice holds samples of the earth's Miocene-age atmosphere trapped within bubbles. This will enable Marchant to compare the Miocene atmosphere with today's atmosphere and see how atmospheric chemistry, at least over Antarctica, has evolved. This may very well be the only data set on earth that records such an ancient atmosphere.

Marchant's work is funded by the National Science Foundation's Office of Polar Programs.

24 August 1999
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