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Reporting this week in the journal Nature, an international team of researchers led by NERC's British Antarctic Survey (BAS) explains that wind-driven incursions of warm water forced the retreat of glaciers in West Antarctica during the past 11,000 years. These new results enable researchers to better understand how environmental change may impact future sea-level rise from this climate-sensitive region.

BAS Twin Otter aircraft on the Antarctic ice sheet.

By studying tiny shells in seafloor sediment cores retrieved from Pine Island Bay in West Antarctica, the team has reconstructed the interactions between the ice and ocean from 11,000 years ago until present. They describe the West Antarctic Ice Sheet (WAIS) as having experienced significant and sustained ice loss until 7,500 years ago, driven by warm water incursions. The influx of warm water then subsided for several thousands of years until it was reinvigorated in the 1940s, driving further retreat.

The WAIS is of great interest to researchers as two of its largest glaciers, Thwaites and Pine Island, are draining into the sea and contributing to sea-level rise. The big questions are why, and by how much, and what may happen in the future under climate change.

Lead author Dr Claus-Dieter Hillenbrand, Senior Marine Geologist at BAS, says:

This ten-year study has yielded some exciting results. By understanding the mechanisms that caused the retreat of the WAIS over the past several thousand years, we can begin to build a clearer picture of what is happening today.

Data collected over the last 20 years have shown that the present ice loss in West Antarctica results from the relatively warm water from the deep ocean flowing on to the shallow continental shelf. This warm water reaches the coastline in places, where it triggers substantial melting of the floating parts of glaciers and leads to thinning of the ice upstream.

Dr Hillenbrand continues:

Our reconstruction shows that warm deep water flooded Pine Island Bay at the end of the last ice age. It forced the ice to retreat but stopped at about 7,500 years ago, when the belt of westerly winds driving the deep water onto the shelf shifted northwards.

Ice loss from this part of West Antarctica is already making a significant contribution to sea-level rise - around 1mm per decade, and is actually one of the largest uncertainties in global sea-level rise predictions. Whilst this is a small figure in actual terms, combined with the contribution from other melting glaciers around the world and expansion of the world's oceans, it will have an impact upon society through flooding of low-lying coastal regions.

Understanding what happened in the distant past provides another important part of the jigsaw. Computer model simulations have suggested that ice-sheet melting through warm water incursions could initiate a collapse of the WAIS within the next few centuries, raising global sea-level by up to 3·5 metres.

The team investigated sediment cores collected from Pine Island Bay in the Amundsen Sea from the German research vessel RV Polarstern on two expeditions in 2006 and 2010. The team analysed the chemical composition of tiny shells built by organisms (foraminifera) that had lived in the water column and at the sea bottom before their shells became embedded in the seafloor sediments. This chemical composition acts as a 'fingerprint' of the water that the shells were formed in. By comparing these shells with those of modern shells bathed in warm deep water today, the researchers were able to identify time intervals when warm deep water was either present or absent.

Co-author Dr James Smith, a marine geologist at BAS, says:

Our data also reveal a more recent history of the WAIS. A shift in the wind direction during the 1940s caused renewed upwelling of warm deep water on to the shelf. This has continued ever since and is responsible for the ice loss we are observing today and over the last few decades.

Co-author Dr Gerhard Kuhn, from the Alfred Wegener Institute in Germany, says:

Our results provide evidence that in the past WAIS retreat was also predominantly caused by melting through warm ocean water. This gives confidence in the predictions of the current generation of ice-sheet models which are used to forecast future ice loss from Antarctica and resulting sea-level rise.

Several of the team, including Dr Smith, Dr Hillenbrand and Dr Kuhn, are now are working on a new project to provide estimates of ocean temperatures during this time interval.

Pine Island Glacier is one of the most inhospitable areas in Antarctica to investigate and researchers have only been exploring this area since the 1990s. The study was a collaboration between BAS (NERC), the Alfred Wegener Institute, universities of Cambridge, Leicester and Exeter, the British Geological Survey (NERC), University College London and the universities of Copenhagen and Tromsø.

Further information

Issued by the British Antarctic Survey Press Office.

Athena Dinar
Senior Science Communications Manager
BAS
01223 221441
07909 008516
amdi@bas.ac.uk

Sarah Vincent
Senior Corporate Communications Manager
BAS
01223 221445
7850 541910
sarnce@bas.ac.uk

Sylvie Kruiniger
External Communications Officer
NERC
01793 442593
syluin@nerc.ac.uk

Notes

1. 'West Antarctic Ice Sheet retreat driven by Holocene warm water incursions' by Claus-Dieter Hillenbrand, James A Smith, David A Hodell, Mervyn Greaves, Christopher R Poole, Sev Kender, Mark Williams, Thorbjørn Joest Andersen, Patrycja E Jernas, Henry Elderfield, Johann P Klages, Stephen J Roberts, Karsten Gohl, Robert D Larter, Gerhard Kuhn is published in the journal Nature this week.

2. Pine Island Glacier and Thwaites Glacier are large ice streams located on the West Antarctic Ice Sheet (WAIS) in Antarctica. At around 2km thick, the glaciers drain an area of 346,000km², roughly 16 times the size of Wales, accounting for around 27% of ice drainage from the WAIS. The glaciers flow into Pine Island Bay at the south-east extremity of the Amundsen Sea.

3. Why are Pine Island and Thwaites glaciers important? Each of the two glaciers is responsible for a greater contribution of ice into the sea than any other glacier in Antarctica which, given the global concern about rising sea level, makes them very important. Significantly, this contribution appears to be increasing. Visit the BAS website - external link for more information.