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In a paper published in Nature, a large international research team has examined the status of the Antarctic ice sheets during the early Miocene, approximately 18 to 16 million years ago, that alternated between cold and warm periods. During warmer periods sea levels would rise up to 60 metres. “With this study we were able to prove that the West Antarctic Ice Sheet used to cover a much larger area and it contributed more to past sea level rise than previously thought. Because of this, we can now improve our predictions of the future of the West Antarctic Ice Sheets”, says co-author Francesca Sangiorgi of Utrecht ľ�ϸ���Ӱ��.

The relative contributions of the East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS) to the past sea level rise was uncertain. In this new study, scientists working as part of the International Ocean Discovery Program (IODP) show that the WAIS used to be much larger than previously thought during the colder periods of the early Miocene. This means that the WAIS played a larger role in the sea level rise during warm periods than previously thought. This insight will help researchers predict the future of the WAIS more accurately as the earth’s temperatures continue to rise.

If the Antarctic ice sheets melt, the sea levels rise to an alarming 55 metres

In the past, the WAIS was assumed to be relatively small before the late Miocene, about 10 million years ago, and that the sea level rise during the warmest period of the last 23 million years was mainly the consequence of the larger EAIS possibly completely melting. However, while geological data show a major rise in sea levels, ice sheet models suggest that parts of the EAIS were still present even during the warmest periods of the Miocene 23-5 million years ago.

Sediment drillings in the Ross Sea

Main author , of the Department of Earth Science and Engineering at Imperial College London, states: “Our observations of the past will help predict how the West Antarctic Ice Sheet, which is considered to be particularly vulnerable to loss of ice mass, will respond to various future global warming scenarios.”

The team of researchers drilled into sediments in the Ross Sea, Antarctica, in search of layers that corresponded to the warmest and coldest periods of the past ~ 20 million years. Francesca Sangiorgi was the only person from the Netherlands to join this expedition. She is an expert in fossils of dinoflagellates, an important group of single-cell plankton: “The sediments drilled far at sea contained microfossils and other trace material that must have been deposited by the WAIS. The WAIS must have been much bigger than we previously thought.” This was possible because in the past a much larger part of the land mass below the WAIS used to be situated above sea level, which is why there was more ice on the continent compared to today. This is clearly visible in the large amount of eroded material that was recovered in the sediment core. Later in the Miocene, due to geographical changes, the base of the ice sheet went largely underneath the sea levels, where it still resides today. This is why the West Antarctic Ice Sheet is very vulnerable to ocean warming.

Very vulnerable

The WAIS is currently considered highly vulnerable to the warming of the oceans and atmosphere. This new study confirms this notion and contributes to improve predictions on how Antarctica will react to changes in the future, on both short term and the longer term, hundreds to thousands of years.  

The results also show the effects of climate change on the Antarctic ice sheets will continue if there aren’t any important measures taken to lower the emissions of greenhouse gasses. “The past provides the opportunity to see what the planet may be up to in the future at certain levels of warming. The Antarctic ice sheets are of great importance to the earth, when they melt the sea levels will rise to an alarming 55 metres, the more vulnerable Western Antarctic Ice sheet contributing to 3-4 m”, explains Sangiorgi. “The big ice sheets react relatively slow to environmental changes. This means that if we intervene quickly, we can still prevent large-scale ice loss. However, the low-lying areas of the ice sheet have a melting ‘tipping point’, and we are still not sure when we get to this. The target of keeping warming below 1.5-2 degrees requires to halve emission by 2030, but we need to get there”

Future research will need to concentrate to rapid changes occurred in the most vulnerable parts of both ice sheets.

Scientists from Utrecht on sea expeditions

Sangiorgi: “It was an honour to be part of this oceanic drilling expedition.” Three geoscientists of Utrecht ľ�ϸ���Ӱ�� took part in three expeditions in 2.5 years. The IODP program is financed mainly by the United States and Japan, and the participation of The Netherlands is financed by the Dutch Research Council (NWO).

Publication

Marschalek J.M., Zurli L., Talarico F., van de Flierdt T., Vermeesch P., Carter A., Beny F., Bout-Roumazeilles V., Sangiorgi F., Hemming S.R., Pérez L.F., Colleoni F., Prebble J., van Peer T.E., Perotti M., Shevenell A.E., Browne I., Kulhanek D.K., Levy R., Harwood D., Sullivan N.B., Meyers S.R., Griffith E.M., Hillenbrand C.-D., Gasson E., Siegert M.J., Keisling B., Licht K.J., Kuhn G., Dodd J.E., Boshuis C., De Santis L., McKay R.M., and the Expedition 374 scientists, 2021, A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude. Nature, 600, 450–455 (2021)