Western Antarctic was ice-free during interglacials - Geological data signal dynamic developments of the ice shield three to five million years ago

The ice cap of the Western Antarctic has apparently deglaciated completely many times three to five million years ago. The periodical nature reports in its current issue (vol. 458) that these regular deglaciation phases have been caused by changes in the tilt of the Earth’s rotational axis in times of increased atmospheric carbon dioxide concentrations. This is the result of a sediment core drilled under German participation below the Antarctic Ross ice shelf in the framework of the international drilling project ANDRILL (ANtarctic geological DRILLing).

Five geoscientists from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association were involved in the examination of the drilling core. The group around Dr. Frank Niessen and Dr. Gerhard Kuhn reads from the data that open ocean conditions with algal bloom prevailed in the Antarctic over a time span of about 200.000 years about 3.5 million years ago. “An explosive issue is that the western Antarctic ice receded particularly in times when it was three degrees Celsius warmer than nowadays, with a higher atmospheric carbon dioxide concentration”, explains Niessen. “Given the expected global warming of up to 3° C until the end of this century, we have to take these results from the Antarctic as a warning: the ice cap of the western Antarctic with its offshore ice shelfs could behave unstable in the coming centuries”, Niessen continues.

The microorganisms found in the sediment by paleontologists indicate that water temperatures during the Antarctic summer were occasionally significantly above the freezing point. After this interglacial, the ice pushed forward periodically in cycles of 40.000 years with a thickness reaching down to the bottom of the sea, where we now have the Ross Ice Shelf, before it receded again in the next interglacial. “The sequences of algal relics and glacial accumulations from the last five million years found by us in the core coincide with worldwide results from corings of the deep-sea sediments which indicate fluctuations of the global Sea Level and coincide with changes of the Earth’s orbital parameter,” explains  Kuhn. “A deglaciation of the current ice masses in the West Antarctic would cause a global rise of the Main Sea Level of five to seven metres”, Kuhn continues. An ice shelf of eighty metres thickness floats today at the investigation area on the Ross Bay.

The reconstructions from the core are confirmed and concretized by means of model computations. Another paper published in the same issue of nature computes as the consequence of warm ocean temperatures at the ANDRILL drilling site a recurring collapses of the western Antarctic ice cap while the eastern Antarctic remained relatively stable.

The paper “Obliquity-paces Pliocene West Antarctic ice sheet oscillations” will be published on Thursday March 19th in the periodical nature (07867, doi: 10.1038, p. 322-328).

Notes for editors:

Your contact persons at the Alfred Wegener Institute are Dr Gerhard Kuhn(phone: +49 471 4831-1204;email: Gerhard.Kuhn@awi.de) and Dr Frank Niessen (phone: +49 471 4831-1216; email: Frank.Niessen@awi.de). Your contact person in the public relations department is Dr Ude Cieluch (phone: +49 471 4831-2008; email: Ude.Cieluch@awi.de).

The Alfred Wegener Institute has a share in the development of the technology for the project ANDRILL. It is a co-proprietor of the rig together with institutions from the USA, New Zealand and Italy. The German researchers are supported by scientific funds from the Helmholtz Association and the DFG (Deutsche Forschungsgemeinschaft).