Antarctica’s Giant Totten Glacier Unstable

Totten glacier unstableTotten Glacier, East Antarctica's largest outlet of ice, is unstable and has contributed significantly to rising sea levels in the past, according to new research. Courtesy: The University of Texas at Austin.

Totten Glacier, East Antarctica’s largest outlet of ice, is unstable and has contributed significantly to rising sea levels in the past, according to new research. Evidence of repeated rapid retreat of the East Antarctic ice sheet is reported in a paper published by Nature.

From the University of Texas at Austin

Research published in the journal Nature on May 19, 2016 has revealed that vast regions of the Totten Glacier in East Antarctica are fundamentally unstable and have contributed significantly to rising sea levels several times in the past.

Totten Glacier is the most rapidly thinning glacier in East Antarctica, and this study raises concerns that a repeat scenario could be underway as the climate warms.

An international consortium led by The University of Texas at Austin’s Institute for Geophysics (UTIG), a unit at the university’s Jackson School of Geosciences, led the research and data collection for the study. Alan Aitken of the University of Western Australia’s School of Earth and Environment was lead author.

Totten Glacier is East Antarctica’s largest outlet of ice and a key region for understanding the large-scale and long-term vulnerabilities of the Antarctic Ice Sheet. Until now, knowledge of the region’s glacial history has been very limited. While other studies have indicated that this region of the ice sheet may have retreated in the past, this study reveals direct linkages between the modern Totten Glacier and the eroded landscape currently buried in ice hundreds of kilometers inland.

“We now know how the ice sheet evolves over the landscape in East Antarctica and where it is susceptible to rapid retreat, which gives us insight into what is likely to happen in the years ahead,” said ICECAP lead Principal Investigator Donald D. Blankenship, Senior Research Scientist at UTIG.

Totten Glacier’s catchment is a collection basin for ice and snow that flows through the glacier.

“Totten Glacier’s catchment is covered by nearly two-and-a-half miles of ice, filling a California-sized sub-ice basin that reaches depths of over one mile below sea level,” Blankenship said. “This study shows that this system could have a large impact on sea level in a short period of time.”

The UTIG-led ICECAP (International Collaboration for Exploration of the Cryosphere through Aerogeophysical Profiling) project collected the data over five Antarctic field campaigns using an aircraft equipped with instruments to assess the ice and measure the shape of the landscape and rocks beneath it. The airplane was outfitted with radar that can measure ice several miles thick, lasers to measure the shape and elevation of the ice surface, and equipment that senses the Earth’s gravity and magnetic field strengths, which are used to infer the sub-ice geology.

The study used ice-penetrating radar, magnetic and gravity data to determine the thickness of the ice-sheet and the sediment thickness under the ice sheet. These were used to map glacial erosion beneath the ice and find two unstable zones where the ice sheet is prone to rapid collapse.

“By examining the characteristic patterns of erosion left by past ice sheet advance and retreat, revealed through mapping the topographic surface and the thickness of sedimentary rocks beneath, this paper demonstrates direct evidence of past changes in the ice sheet in the Totten region,” Aitken said.

The study found the transition between the stable and unstable states has occurred repeatedly during the life of the ice sheet.

“If this was to happen again, with a warmer climate than today, it could lead to a rapid rise in sea level of over a meter,” Aitken said.

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

University of Texas at Austin news release via EurekAlert!

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