According to researchers reporting in the journal Nature Geoscience, global warmings between 5 – 3 million years ago may have caused parts of the East Antarctic ice sheet to melt and sea levels to rise by about 33 feet (10 m).
Regional map of study area, including geology of outcrops and inferred subglacial geology. Areas above sea level are shown in pale gray with gray outlines, and ice shelves are shown in white. Red lines denote the spatial extent of modeled maximum East Antarctic ice sheet retreat for the Pliocene: line A – 3 m; line B – 10 m; line C – 16 m (Cook CP et al)
The East Antarctic ice sheet is the largest ice mass on Earth, roughly the size of Australia. The ice sheet has fluctuated in size since its formation 34 million years ago, but scientists have previously assumed that it had stabilized around 14 million years ago.
In the new study, Dr Carys Cook from the Grantham Institute for Climate Change and his colleagues studied mud samples to learn about ancient melting of the ice sheet.
They discovered that melting took place repeatedly between 5.3 – 3.3 million years ago, during a geological period called Pliocene Epoch, which may have caused sea levels to rise approximately 33 feet (10 m).
The team was able to determine that the East Antarctic ice sheet had partially melted during this period by analyzing the chemical content of mud in sediments recovered offshore of Adélie Land, East Antarctica.
“The Pliocene Epoch had temperatures that were 2 – 3 degrees higher than today and similar atmospheric carbon dioxide levels to today,” said study second author Dr Tina Van De Flierdt of Imperial College London.
“Our study underlines that these conditions have led to a large loss of ice and significant rises in global sea level in the past. Scientists predict that global temperatures of a similar level may be reached by the end of this century, so it is very important for us to understand what the possible consequences might be.”
The isotopic characteristics of the mud enabled the scientists to trace where it came from on the continent. They discovered that the mud originated from rocks that are currently hidden under the ice sheet. The only way that significant amounts of this mud could have been deposited as sediment in the sea would be if the ice sheet had retreated inland and eroded these rocks.
The scientists suggest that the melting of the ice sheet may have been caused in part by the fact that some of it rests in basins below sea level. This puts the ice in direct contact with seawater and when the ocean warms, as it did during the Pliocene, the ice sheet becomes vulnerable to melting.
“Scientists previously considered the East Antarctic ice sheet to be more stable than the much smaller ice sheets in West Antarctica and Greenland, even though very few studies of East Antarctic ice sheet have been carried out,” Dr Cook explained.
“Our work now shows that the East Antarctic ice sheet has been much more sensitive to climate change in the past than previously realized. This finding is important for our understanding of what may happen to the Earth if we do not tackle the effects of climate change.”
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Bibliographic information: Cook CP et al. Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. Nature Geoscience, published online July 21, 2013; doi: 10.1038/ngeo1889
