5 August 2024

Around 34 million years ago, our planet underwent one of the most fundamental climate shifts that still influences global climate conditions today: the transition from a greenhouse world, with no or very little accumulation of ice, to an icehouse world, with large permanently glaciated areas. That was when the Antarctic ice sheet formed. How, when and, above all, where, it formed was not yet known due to a lack of samples from West Antarctica, among other things. Using a drill core from the Amundsen Sea along West Antarctica, the international research team led by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) has now been able to close this knowledge gap. The core was retrieved in 2017 during an expedition of the Polarstern research vessel off the Pine Island and Thwaites Glaciers. The expedition recovered the first sediment samples from the West Antarctic margin that document this key climate transition 34 million years ago.

The samples were expected to offer initial insight into the birth of the ice sheet in West Antarctica. Surprisingly, no signs of the presence of ice could be found in this region during the first major phase of Antarctic glaciation. In order to better understand where the first permanent ice formed in Antarctica, the geological data from the drill core was combined in computer simulations with the newly available and existing data on air and water temperatures and the occurrence of ice. Micropalaeontologist and paleoclimatologist Steve Bohaty, who directs the “Paleontology and Paleoclimate” research group at the Institute of Earth Sciences at Heidelberg University, played a significant role in dating the drill cores. “Dating the core based on microfossils proved difficult, but, by combining different stratigraphic methods, we were ultimately successful in constraining the age of the core to a very short interval of time,” states the researcher.

The scientists report that the data from the drill core, combined with the computer simulations, indicate that the first large-scale, permanent glaciation must have begun in the East Antarctic region. Moist air masses in the coastal region of Northern Victoria Land collided with the strongly rising Transantarctic Mountains, creating ideal conditions for permanent snow and the subsequent formation of ice caps. From there, the ice sheet spread rapidly into the East Antarctic hinterland. Meanwhile, the West Antarctic remained ice-free; at that time the region was covered largely by dense deciduous forests, as shown by the pollen obtained from the sediment samples. It wasn’t until at least seven million years later that ice was able to form there.

The investigations also show how differently the two regions of the Antarctic ice sheet react to external influences and fundamental climatic changes. This could be due to the difference in ice formation in the two regions and explain why ice in West Antarctica is disappearing more quickly than the East Antarctic. “Even a slight warming is enough to cause the ice in West Antarctica to melt again – and that’s exactly where we are right now,” explains Dr Johann Klages, the AWI geologist leading the research team. 

The research results were published in the journal “Science”. Researchers from Australia, Germany, Spain, Switzerland, the United Kingdom and the USA participated in the study. The research project, in particular Expedition PS104 of the Polarstern research vessel led by Prof. Dr Karsten Gohl (AWI), was funded by the Alfred Wegener Institute, MARUM – Center for Marine Environmental Sciences of the University of Bremen, the British Antarctic Survey, and the British International Ocean Discovery Program (UK-IODP).