The researchers also analyzed the distribution of ancient membrane lipids from soil bacteria known as tetraethers, which correlate to temperature. The chemical structure of the fossilized tetraethers makes them highly sensitive to both temperature and acidity, or pH, said Ballantyne.
The last line of evidence put forward by the CU-Boulder-led team was a comparison of Pliocene ancient vegetation at the site with vegetation present today, providing a clear "climate window" showing the overlap of the two time periods. "The results of the three independent temperature proxies are remarkably consistent," said Eberle. "We essentially were able to 'read' the vegetation in order to estimate air temperatures in the Pliocene."
Today, Ellesmere Island is a polar desert that features tundra, permafrost, ice sheets, sparse vegetation and a few small mammals. Temperatures range from roughly minus 37 degrees F, or minus 38 degrees C, in winter to 48 degrees F, or 9 degrees C, in summer. The region is one of the coldest, driest environments on Earth.
"Our findings are somewhat disconcerting regarding the temperatures and greenhouse gas levels during the Pliocene," said Eberle. "We already are seeing evidence of both mammals and birds moving northward as the climate warms, and I can't help but wonder if the Arctic is headed toward conditions similar to those that existed during the Pliocene."
Elevated Arctic temperatures during the Pliocene -- which occurred shortly before Earth plunged into an ice age about 2.5 million years ago -- are thought to have been driven by the transfer of heat to the polar regions and perhaps by decreased reflectivity of sunlight hitting the Arctic due to a lack of ice, said Balla
|Contact: Ashley Ballantyne|
University of Colorado at Boulder