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The Middle Miocene Mystery. CAS Assistant Professor of Earth Sciences David Marchant is investigating whether global climate changes are affecting the East Antarctic ice sheet, and if so, how those changes may be affecting the rest of the world.

The recent discovery by Marchant and colleagues of Miocene-age volcanic ash embedded in Antarctic sediment will allow scientists for the first time to reconstruct its precise climate and glaciological conditions 14 million years ago.

"This data is crucial to understanding the conditions that led to abrupt global cooling back then, as well as the emergence of the East Antarctic ice sheet itself," says Marchant. "This in turn will shed light on the implications of current climate changes."

Additional data will be supplied by another, unexpected discovery by Marchantís team: the oldest fossil glacier ice in the world, formed more than 8.1 million years ago in the Dry Valleys region of Antarctica.

"The presence of Miocene-age ice less than 20 inches below the surface implies that temperatures have never warmed enough during the last 8.1 million years to allow significant melting in this area," he says. "It calls into question the view that during part of the Pliocene Epoch of three to four million years ago, East Antarctica was largely free of glacier ice, but rather points to the development of a polar ice sheet by Middle Miocene time."

The ice also holds samples of the earthís Miocene-age atmosphere trapped within bubbles. This will enable Marchant to compare the Miocene atmosphere with todayís atmosphere and see how atmospheric chemistry over Antarctica has evolved. He says this will likely be the only data set on earth that records an ancient atmosphere.

Marchantís work is funded by the National Science Foundationís Office of Polar Programs.

"Research Briefs" is written by Joan Schwartz in the Office of the Provost. To read more about BU research, visit


15 May 2003
Boston University
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