Wednesday, February 2, 2011

East Antarctic Ice Sheet may not be as stable as previously thought

Macquarie University: The East Antarctic Ice Sheet (EAIS) holds enough ice to raise global sea level by about 60 metres. But because surface temperatures across East Antarctica are well below freezing point, this ice has long been thought to be relatively stable, and thus unlikely to contribute significantly to sea level rise during the next few centuries.

However, new field-based studies of ice sheet response to climate warming and sea level increase after the last ice age about 20,000 years ago suggest that parts of the ice sheet may respond more rapidly to global climate change than previously assumed. Most of the contribution to sea level from melted ice occurs along the coastal perimeter of East Antarctica, where the slow moving ice sheet meets the ocean. An alternative mechanism of ice sheet melt to sea level is via large outlet glaciers which stream through deep and extensive basins that act like drainage channels. Little is known about the relative amounts of these two mechanisms.

The research, by Dr Duanne White and Associate Professor Damian Gore of Macquarie University and Dr David Fink of the Australian Nuclear Science and Technology Organisation (ANSTO), is published in the most recent edition of the prestigious journal Geology.

In this publication, the authors describe their study of large ice streams that drain a large proportion of the snow that falls on the Antarctic Ice Sheet to the sea.

“These outlet glaciers can quickly move ice from the ice sheet to the coast through these basins and are thus a strong linkage between the ice sheet and the ocean, providing a means of more rapidly transferring changes in oceanic and atmospheric conditions to changes in the size of the ice sheet than would otherwise be expected,” explains White. “However, the large area, remoteness and complexity of the ice streams means they have been difficult to study before now.”

…The Intergovernmental Panel on Climate Change (IPCC) indicates that total sea level rise by the end of this century from all sources may range between 0.2 to 0.6 metres. However these IPCC climate change models do not include the accelerated discharge from dynamic ice sheet outlet glaciers documented in White’s Geology publication. The results of White and co-authors provide further urgency for the inclusion of ice streaming into future global earth system models.

Two massive icebergs drifted along the coast of East Antarctica in early March 2010. In mid-February 2010, the Rhode Island-sized Iceberg B-09B collided with the protruding Mertz Glacier Tongue along the George V Coast. The Mertz Glacier was already in the process of calving an iceberg when the arrival of the B-09B accelerated the process, leaving two icebergs the size of small states off this part of Antarctica’s coast. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this true-color image of Iceberg B-09B and the newly created iceberg off the Mertz Glacier. Between each iceberg and the coast floats a mélange of smaller pieces of ice. Farther out to sea, delicate white swirls indicate a relatively thin layer of sea ice. Occasional clouds floating overhead cast shadows on the ice surfaces below.

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