Wind-driven incursions of warm, deep water forced the retreat of West Antarctic glaciers from the end of the last ice age until 7,500 years ago and since the 1940s.
These findings were published in a new article in Nature. An international team of researchers investigated several marine sediment cores recovered directly in front of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea. They analysed the chemical composition of tiny calcareous 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. The chemical composition of the shells acted as a ‘fingerprint’ of the waters, in which the shells were formed. By analysing the shells in the cores and comparing their composition to that of modern shells bathed by warm deep water today, the team was able to identify time intervals when warm deep water was either present or absent.
The reconstructions showed that warm deep water incursions flooded Pine Island Bay at the end of the last ice age and forced West Antarctic Ice Sheet retreat from the shelf during that time. The incursions decreased at about 7,500 years ago, when the belt of westerly winds driving the deep water onto the shelf shifted northwards. The data also revealed that a southward shift in the position of the westerly winds during the 1940s caused renewed upwelling of warm deep water onto the shelf, which has continued ever since and is responsible for the ice loss observed in the Amundsen Sea sector over the last few decades. The new findings do not only expand the understanding of ice sheet-ocean interactions to the times before direct observations were carried out and satellite data became available but also give confidence in the predictive capability of the current generation of ice-sheet models that are used to forecast future ice loss from Antarctica and resulting sea-level rise.
West Antarctic Ice Sheet retreat driven by Holocene warm water incursions
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