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Science

Antarctica Moved From Flat To Fjord 34 Million Years Ago

Often, understanding what the planet’s climate will do and why requires study into fields that we as laymen might consider irrelevant. Thankfully, there are those out there who have dedicated their lives to the sciences and are not so quick to discuss a particular field or aspect of science as irrelevant.

So when geoscientists from the University of Arizona tell me that understanding Antarctica’s topography underneath the two-mile thick ice sheet is helpful to understanding how that same ice sheet affects global climate and sea-level rise, I don’t question their expertise.

The results of their study, which was published in the March edition of the journal Nature Geoscience, explain that 34 million years ago Antarctica’s topography started changing from flat to fjord-filled.

Antarctica Went From Flat to Fjords
This 3-D reconstruction of the topography hidden under Antarctica’s two-mile-thick coating of ice was made using data from radar surveys. Glaciers started carving Antarctica into the current mountain-and-fjord landscape 34 million years ago, according to new findings from UA geoscientist Stuart N. Thomson and his colleagues.
Image Credit: Stuart N. Thomson/UA department of geosciences

“We have worked out how the landscape under the ice has changed through time,” said lead author Stuart N. Thomson. “People have speculated when the big fjords formed under the ice. But no one knows for sure until you sample the rocks or the sediments.”

So they sampled the rocks in East Antarctica.

“We use the sediments to trace what was happening under the ice in the past,” said Thomson, a research scientist in the UA department of geosciences.

What they found was that between 250 million and 34 million years ago, erosion from the region that is now covered by the huge Lambert Glacier was slow, which suggests that the region was relatively flat and drained by slow-moving rivers.

However, 34 million years ago — at the same time that the climate shifted and Antarctica was slowly becoming covered by a thick ice sheet — the rate of erosion more than doubled.

“The only way that could happen is from glaciers,” Thompson said. “They started grinding and forming deep valleys.”

“East Antarctica’s landscape changed dramatically when big glaciers appeared there,” co-author Peter W. Reiners, a UA professor of geosciences, said. “Glaciers can carve deep valleys quickly – and did so on Antarctica before it got so cold that the most of it got covered by one or two miles of thick, stationary ice.”

Source: University of Arizona




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