This 3-D reconstruction of the topography hidden under Antarctica's two-mile-thick coating of ice was made using data from radar surveys.
Image: Stuart N. Thomson/UA department of geosciences
Like Alaska's mighty Yukon, a broad river once flowed across Antarctica, following a gentle valley shaped by tectonic forces at a time before the continent became encased in ice. Understanding what happened when rivers of ice later filled the valley could solve certain climate and geologic puzzles about the southernmost continent.
The valley is Lambert Graben in East Antarctica, now home to the world's largest glacier. Trapped beneath the ice, the graben (which is German for ditch or trench) is a stunning, deep gorge. But before Antarctica's deep freeze 34 million years ago, the valley was relatively flat and filled by a lazy river, leaving a riddle for geologists to decode: How did Lambert Graben get so steep, and when was it carved?
The key to Lambert Graben's history was found in layers of sediments just offshore, in Prydz Bay. In a new study, Stuart Thomson, a geologist at the University of Arizona (UA) in Tucson, looked into the past by decoding sands deposited by the river, and the messy piles left behind by the glacier. The river sands are topped with a thick layer of coarser sediment that signals the onset of glacial erosion in the valley, the researchers found. The erosion rate more than doubled when the glaciers moved in, Thomson said.
"The only way that could happen is from glaciers," he said. "They started grinding and forming deep valleys."
Understanding when glaciers first wove their way across Antarctica will help scientists better model the ice sheet's response to Earth's climate shifts, the researchers said.
"There's a big effort to model how glaciers flow in Antarctica, and these models need a landscape over which glaciers can flow," Thomson told OurAmazingPlanet. "Once these models can predict past changes, they can more accurately predict what will happen with future climate changes."
The sediments also hold clues to the tectonic evolution of East Antarctica, and a mountain range buried beneath the vast, thick ice sheet. [Album: Stunning Photos of Antarctic Ice]
The findings are detailed in the March 2013 issue of the journal Nature Geoscience.
History of the ice
Lambert Graben formed during the breakup of Gondwana, an ancient supercontinent, a process that happened in stages. Antarctica, India and Africa tore apart in the Late Cretaceous (about 80 million years ago). The split created long, linear valleys oriented perpendicular to the continental coastlines. At the time, Earth's climate was warmer than it is today, and as Antarctica moved southward, settling into its home over the South Pole, the continent teemed with plants and animals.
Scientists can partially reconstruct this past environment with fossils and through radar that peers beneath the ice to map the shapes of the rock below. A 3D map of Antarctica today shows chasms carved by glaciers, rugged mountains and other remnants of its warmer existence.
But the surveys tell nothing about how the landscape looked before the ice carved out all those features. "People have speculated when the big fjords formed under the ice," Thomson said. "But no one knows for sure until you sample the rocks or the sediments."
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8 Comments
Add CommentIt won't be long before will get a look at it again the way global warming is accelerating. Perhaps our grand kids grand kids anyway.
Reply | Report Abuse | Link to thisOne day there will be a mile of ice above NYC. It's citizens (our descendants) will have, long ago migrated to the rapidly expanding lands of Florida, as sea level drops by 50 meters. Problem is... nobody can say exactly WHEN that will happen... only that it is becoming overdue. GK
Reply | Report Abuse | Link to thisWTF? Not overdue, was possible, but not anymore.
Reply | Report Abuse | Link to thisModels of the globe Static and Dynamic www.mammoths.narod.ru prove, that the Earth casually appeared in Solar system (~800 thousand years), these models of the globe have proved, what changes in time II, III, IV stages have particularly taken place, millions years is a leisure fiction
Reply | Report Abuse | Link to thisNot just possible, but probable, and some humans actually believe that they can stop it by accident. That would be funny, if it weren't so sad.
Reply | Report Abuse | Link to thisSavov. Nice fun stuff on that link. No data of course, just lots of speculations. Where is the raw data that generated these speculations? Might be fun to try to recreate your conclusions from real data, maps, etc. Could you explain your methods a bit more?
Reply | Report Abuse | Link to thisem_always_right: When you say another ice age is not possible, you are most likely wrong. Warming changes salinity in water, which could cause Gulf Stream and Japan Current to stop the engine that keeps coastal regions moderate, triggering another ice age (like the mini-ice-age in 1600's). The Pilgrims of course did not say WTF when it was so cold in UK, they just headed out for warmer shores, or so I was told long ago.
Reply | Report Abuse | Link to thisTo mclayton200
Reply | Report Abuse | Link to thisThe past of a planet the Earth includes many millions years when this planet was in system of planets of other Galaxy, thickness of a firm environment was measured (thousand in km). At occurrence of the Earth in an orbit of the Sun practically all planet has fused, as consequence was proceeded with global tectonic changes, II stage has terminated in cardinal change of volume and a geographical kind of the planet, the escaped inhabitants now appeared on a flexible and thin environment of a planet (Ms). During III stage this environment repeatedly turned in an equatorial plane, this "work" was carried out by thermal energy of the Sun, at total weight of ice domes which changed in limits (150 - 450 million км3). On last site of the schedule the environment of a planet has burnt through, as result, the thermal stream of bowels has practically kindled all ice (except for 29 million км3), the level of Ocean thus has raised on size (~ 450 м), thus, “ the Bible flood ” it, unfortunately a reality. So, with the beginning of IV stage the water elements has tired out inhabitants of a planet on top (Ms), the present abnormal level of Ocean and abnormal weight of an ice dome obliges inhabitants to predict variants of events in which IV stage will terminate. However “ the Science about the past of a planet ” has taken very strange position in relation to Dynamic model of the globe of a planet the Earth