Antarctic Fossils Paint a Picture of a Much Warmer Continent

[...] At 14.1 million years ago, the Dry Valleys were relatively warm. By 13.9 million years ago, everything was different. The transition brought the Dry Valleys from a climate like that of South Georgia to one that has Mars as a close analog."

Tom Wagner, program director for Antarctic Earth Sciences in NSF's Office of Polar Programs, added that "Lewis, Marchant and Ashworth discovered the last bit of life on the Antarctic continent. It was hanging on by its fingernails--just a few simple plants and bugs in a small pond, everything else around them frozen over--and then, wham!, they went too. And it must have happened quickly because these fossils are literally freeze dried. When I visited the scientists in the field, they showed me how the moss was still green and leafy."

"It is one of the most dramatic and long-lasting changes that one can imagine," Marchant said. "I don't know of any other place on Earth where such an enduring change has been documented; the fact that it is associated with the extinction of tundra plants and insects helps provide quantitative estimates for the magnitude of this change."

The mean summertime temperatures would have dropped in that period by as much as 8 degrees Celsius. On average, the summertime temperatures in the Valleys during this temperate period would have been as much as 17 degrees warmer than the present-day average. What caused the change, Marchant said, "Is really a big unknown", though theories abound and include phenomena as different as the levels of carbon dioxide in the atmosphere and tectonic shifts that affected ocean circulation.

According to Lewis, the freshness of the crystals and glass in the volcanic ash and the preservation of cellular detail in the fossils argues that they have been permanently frozen since 13.9 million years ago. The climate changed during those millions of years but the temperatures in the mountains never rose high enough to allow groundwater to flow and microorganisms to become active.

This conclusion suggests that even when global atmospheric temperatures were warmer than they are now, as occurred--approximately 3.5 million years ago during the Pliocene Epoch--and as might occur in the near future as a consequence of global warming, there was no significant melting of the East Antarctic ice sheet inland of the Dry Valleys, nor were there dramatic changes in environmental conditions in the fossil region.[...]

Antarctic Fossils Paint a Picture of a Much Warmer Continent - 4 août 2008