Research team advances knowledge of Antarctica's climate history

North Dakota State University researchers, Fargo, are among the leaders of a group of National Science Foundation-funded scientists who have discovered the last traces of tundra on the interior of Antarctica before temperatures began a relentless drop millions of years ago.

The collaboration's research, which resulted in a major advance in the understanding of Antarctica's climatic history, appears in the 4 August issue of the Proceedings of the National Academy of Sciences.

The international team of scientists headed up by NDSU geoscientists Allan Ashworth and Adam Lewis and David Marchant, an earth scientist at Boston University, combined evidence from glacial geology, palaeoecology, dating of volcanic ashes and computer modelling, to report a major climate change centred on 14 million years ago. The three scientists often spend months living in tents in the Transantarctic Mountains' Dry Valleys doing their research.

They have documented the timing and magnitude of the continent's shift from warm, temperate glaciers and fringing tundra to polar glaciers and polar tundra. 'The contrast couldn't be more striking,' Marchant said. 'It is like comparing Tierra del Fuego today with the surface of Mars - and this transition took place over a geologically short interval of roughly 200,000 years.'

According to Lewis, the discovery of lake deposits with perfectly preserved fossils of mosses, diatoms and ostracods is particularly exciting to scientists. 'They are the first to be found even though scientific expeditions have been visiting the Dry Valleys since their discovery during the first Scott expedition in 1902-03,' said Lewis.

For Ashworth, the fossils are a palaeoecological treasure trove. He notes that some ancient species of diatoms and mosses are indistinguishable from the ones today, which occur throughout the world except Antarctica.

'To be able to identify living species amongst the fossils is phenomenal. To think that modern counterparts have survived 14 million years on Earth without any significant changes in the details of their appearances is striking,' said Ashworth, the principal palaeoecologist in the research. 'It must mean that these organisms are so well-adapted to their habitats that in spite of repeated climate changes and isolation of populations for millions of years, they have not become extinct but have survived.'

The fossil finds and dating of volcanic ash show that roughly 14.1 million years ago, the area was home to tundra, 'wet' glaciers typical of those of the mountains of Tierra Del Fuego in the high southern latitudes and seasonally ice-free lakes. The beds of the long-gone lakes contain layers of sediments where dying plants and insects accumulated and were preserved.

The mean summertime temperatures would have dropped in that period by as much as 8 degrees Celsius. On average, the summertime temperatures in the Dry Valleys 14.1 million years ago would have been as much as 17 degrees warmer than the present-day average.

According to Lewis, the freshness of the crystals and glass in the volcanic ash and the preservation of cellular detail in the fossils indicate they have been permanently frozen since 13.9 million years ago.

The research conclusion suggests that even when global atmospheric temperatures were warmer than they are now, as occurred 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. According to Ashworth, if this conclusion stands the test of time, it suggests a very robust ice sheet in this sector of Antarctica, and emphasises the complex and non-uniform response of Antarctica's ice sheets to global change. He adds, 'The huge uncertainties regarding the inherently unstable marine-based West Antarctic ice sheet, however, make all predictions about the future based on past behaviour educated guesses at best.'

The National Science Foundation, in its role as the manager of the United States Antarctic Program, supported the work of Ashworth, Lewis and Marchant as well as United States researchers from Lamont-Doherty Earth Observatory, Ohio State University and the University of Montana.

The work of the research team in the field also appears in the documentary 'Ice People' by Emmy-award-winning director Anne Aghion. The film will be screened in science museums throughout Australia during the month of August and will air on SBS Australian Television on August 24. Ice People received support from the National Science Foundation's Antarctic Artists and Writers Program. It has been screened at international film festivals in New York, San Francisco and Jerusalem and is scheduled to air on the Sundance Channel in 2009.

Source: North Dakota State University