New study shows that unstable Antarctic Ice Sheet led to rapid sea-level rise in the past

Bremerhaven, 28 May 2014. At the end of the last glacial period, the Antarctic Ice Sheet lost a large amount of ice within a very short timespan. This led to a rapid global sea level rise of several metres. An international research team came to this conclusion in a study published in the latest edition of the scientific journal Nature. The joint project of geologists and climate scientists has shown that an unstable Antarctic ice sheet could precipitously change the climate of the Southern Hemisphere. At the same time it provides important evidence of how current climate change may affect the ice masses over the South Pole.

In the study, scientists provide the first evidence that massive ice loss from the Antarctic Ice Sheet significantly contributed to a rapid rise in sea levels at the end of the last glacial period. In the time period before 18,000 to 9,000 years ago, Antarctic glaciers repeatedly calved an unusually large number of big icebergs within just a few decades. One of these periods of iceberg flux was of special interest to the scientists. It took place 14,600 years ago, and thus at the very same time that the global sea level rose up to 16 metres in less than 500 years. Scientists have now been able to link half of this increase to sudden ice loss in the Antarctic.

What triggered this rapid, massive ice loss? To find this out, a team of scientists under the direction of geologist Dr Michael Weber from the University of Cologne examined two sediment cores. Both cores had been recovered from the Scotia Sea, a marine region situated between the Falkland Islands and the Antarctic Peninsula, which is considered the main route and melting area for drifting icebergs. “The icebergs carry debris from the mainland out into the ocean. If the ice melts, the small stones sink to the ocean floor and are deposited there, layer by layer. Samples allowed us to pinpoint the exact period in which an especially large number of icebergs drifted into this region,” Dr Gerhard Kuhn, geologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research and co-author of the study, explained.

Subsequently climate models were used to evaluate the iceberg data from the sediment cores. With their help, scientists were able to reconstruct which environmental changes at that time led to massive ice loss of the Antarctic Ice Sheet. They concluded that unusually warm masses of water flowed towards the Antarctic at the end of the last glacial period, which induced glacial discharge. The climate models also showed that deglaciation intensified the influx of warm water into the Antarctic – positive feedback that led to the discharge of even more icebergs from the ice sheet. This abrupt change in the ice sheet decay surprised the scientists. “The transition from the last glacial period to the subsequent interglacial period actually happened quite slowly. The models therefore suggest that the positive feedback significantly intensified what was at first only a slight change in climate. This means that the ice sheet became unstable much faster than previously supposed,” Prof Dr Gerrit Lohmann, climate modeller at the Alfred Wegener Institute and co-author of the study, explained.

The study makes it possible for scientists to understand which processes led to large-scale deglaciation of the Antarctic Ice Sheet in the past. However, the results are also key in developing scenarios for possible future changes. “Our data provide important reference values on how anthropogenic climate change may affect the Antarctic ice volume and the global sea level rise” Prof Dr Gerrit Lohmann said.

In order to carry out the investigations for their study, scientists of the Alfred Wegener Institute surveyed the region surrounding the Scotia Sea and took seafloor samples during three expeditions on the AWI icebreaker Polarstern. They could thus ensure that the deposits from this part of the ocean floor were of sufficiently high time resolution – that is, the individual sediment layers and thus geologic events could clearly be differentiated. The two sediment cores for this study were then recovered from the French research vessel Marion Dufresne with the financial support of the Deutsche Forschungsgemeinschaft (German Research Foundation).

American colleagues have lately observed the retreat of several glaciers in the West Antarctic. They suggest that a number of these may be on the brink of collapse. “These high rates of retreat are especially evident among glaciers flowing into the Amundsen Sea. Models have shown that this makes them potential candidates for collapse. In early 2015 we will take the Polarstern into this region to collect further data on the past behaviour of the West Antarctic Ice Sheet by drilling into the ocean floor,” Dr Gerhard Kuhn explained.

Note to editors:

This paper was published online on 28 May 2014 (Advance Online Publication) by the scientific journal Nature under http://www.nature.com/nature under the original title "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation" and in the 5 June 2014 print edition of Nature. DOI: 10.1038/nature13397.Please list Nature as the source.

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Your contact persons are Dr. Gerhard Kuhn (Tel.: 0471 4831 1204, E-Mail: Gerhard.Kuhn(at)awi.de) and Prof. Dr. Gerrit Lohmann (Tel.: 0471 4831-1758, E-Mail: Gerrit.Lohmann(at)awi.de), as well as Kristina Baer, Dept. of Communications and Media Relations (tel.: 0049 471 4831-2139; e-mail: kbaer(at)awi.de).

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The Alfred Wegener Institute conducts research in the Arctic, Antarctic and oceans of the high and mid-latitudes. It coordinates polar research in Germany and provides major infrastructure to the international scientific community, such as the research icebreaker Polarstern and stations in the Arctic and Antarctica. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.