Antarctic Glacier Threatens 2m Sea Level Rise

Sea Level RiseScientists predict extensive ice loss from the huge and unstable Totten Glacier in Antarctica ultimately leading to a sea level rise of more than 2m. Image shows the Totten Glacier seen from space. Courtesy: ESA.

Scientists predict extensive ice loss from a huge Antarctic glacier ultimately leading to a sea level rise of more than 2m. This is the result of a study into the history of the giant Totten Glacier, which drains one of the world’s largest areas of ice on the East Antarctic Ice Sheet (EAIS).

by Hayley Dunning, Imperial College

Current rates of climate change could trigger instability in a major Antarctic glacier, ultimately leading to more than 2m of sea level rise.

This is the conclusion of a new study looking at the future of Totten Glacier, a significant glacier in Antarctica. Totten Glacier drains one of the world’s largest areas of ice, on the East Antarctic Ice Sheet (EAIS).

By studying the history of Totten’s advances and retreats, researchers have discovered that if climate change continues unabated, the glacier could cross a critical threshold within the next century, entering an irreversible period of very rapid retreat.

Sea level rise

This would cause it to withdraw up to 300 kilometres inland in the following centuries and release vast quantities of water, contributing up to 2.9 metres to global sea level rise.

The EAIS is currently thought to be relatively stable in the face of global warming compared with the much smaller ice sheet in West Antarctica, but Totten Glacier is bucking the trend by losing substantial amounts of ice. The new research reveals that Totten Glacier may be even more vulnerable than previously thought.

The study, by scientists from Imperial College London and institutions in Australia, the US, and New Zealand is published today in Nature. Last year, the team discovered that there is currently warm water circulating underneath a floating portion of the glacier that is causing more melting than might have been expected.

Rapid repeat

Their new research looks at the underlying geology of the glacier and reveals that if it retreats another 100-150km, its front will be sitting on an unstable bed and this could trigger a period of rapid retreat for the glacier. This would cause it to withdraw nearly 300km inland from its current front at the coast.

Retreating the full 300km inland may take several hundred years, according to co-author Professor Martin Siegert, Co-Director of the Grantham Institute at Imperial College London. However, once the glacier crosses the threshold into the unstable region, the melting will be unstoppable – at least until it has retreated to the point where the geology becomes more stable again.

“The evidence coming together is painting a picture of East Antarctica being much more vulnerable to a warming environment than we thought,” he said. “This is something we should worry about. Totten Glacier is losing ice now, and the warm ocean water that is causing this loss has the potential to also push the glacier back to an unstable place.”

“Totten Glacier is only one outlet for the ice of the East Antarctic Ice Sheet, but it could have a huge impact. The East Antarctic Ice Sheet is by far the largest mass of ice on Earth, so any small changes have a big influence globally.”

To uncover the history of Totten Glacier’s movements, the team looked at the sedimentary rocks below the glacier using airborne geophysical surveys. From the geological record, influenced by the erosion by ice above, they were able to understand the history of the glacier stretching back millions of years.

They found that the glacier has retreated more quickly over certain ‘unstable’ regions in the past. Based on this evidence, the scientists believe that when the glacier hits these regions again we will see the same pattern of rapid retreat.

Abstract

Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion—enough to expose basement rocks—has occurred in two regions: the head of the Totten Glacier, within 150 kilometres of today’s grounding line; and deep within the Sabrina Subglacial Basin, 350–550 kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the ‘modern-scale’ ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200–250 kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat–advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9 metres in the modern-scale configuration, and exceeds 2 metres in the retreated configuration.

Citation

A. R. A. Aitken, J. L. Roberts, T. D. van Ommen, D. A. Young, N. R. Golledge, J. S. Greenbaum, D. D. Blankenship & M. J. Siegert; Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion; Nature 533, 385–389 (19 May 2016) doi:10.1038/nature17447

Source

Imperial College news release.

See also

Our previous report on this research.

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