“Important and unexpected discovery” – the formation of the ice sheet of West Antarctica was very different from what was previously thought

The German icebreaker research vessel Polarstern (operated by the Center for Polar and Marine Research of the Alfred Wegener Institute). Author: Alfred-Wegener-Institut / Thomas Ronge

AWI experts confirm the slow spread of the ice shield 35 million years ago.

About 35 million years ago the Earth quickly cooled. Around the same time, the Drake Strait formed between South America and Antarctica, paving the way for the Antarctic Circumpolar Current. Due to these two factors, Antarctica was soon completely covered with ice. According to a study by the Alfred Wegener Institute, this mass glaciation has been delayed in at least one region. This new puzzle piece, which relates to the early history of the West Antarctic ice sheet, can help predict its volatile future. The study has just been published in the journal Nature Communications Earth and Environment.

For climate researchers, West Antarctica has been the focus for years. Here, the ice sheet of West Antarctica, which lies on top of the continent, stretches to the adjacent Amundsen Sea. Near the coast the ice is still in direct contact with the soil; further to the open sea, he sails. As climate change gradually heats seawater, the latter is increasingly eroding the shelf glacier below. The ground line – the last point where the ice still lies on the ground – is moving farther and farther inland. Due to meltwater and calving icebergs, the Twaits Glacier, which flows into the Amundsen Sea, is now losing twice as much ice as it did 30 years ago. If the ice sheet of West Antarctica had completely collapsed, the world sea level would have risen more than three meters.

“The stability of the ice sheet of West Antarctica is crucial for the future development of world-class sea level,” said study first author Gabriele Wenzelman-Neben of the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI). “Accordingly, researchers around the world are working to predict the future behavior of ice in a warmer world through numerical simulations. The more we know about the history of the West Antarctic ice sheet, the more accurate we can make these models. Its recent history is well documented, but we still know very little about its earlier years – especially about the formation stage. Our research provides an important piece of the puzzle. ”

During two research cruises aboard the Polarstern, a geophysicist and her team explored sediments near the Pine Island Basin, a canal-like furrow on the seabed of a shallow part of the Amundsen Sea that stretches from north to south and leads directly to the Antarctic west coast. To collect the data, the AWI team relied on a proven method of seismological mapping: Polarstern towed a 3,000-meter-long measuring cable – or extension. The streamer is equipped with hydrophones that use a total of 240 measuring channels. During sightseeing cruises an air pistol is used to generate seismic pulses from behind the ship. These impulses penetrate the seabed and are reflected back to geological boundaries – such as between sediments and hard rocks – which are recorded by streamer hydrophones. On the basis of different time of movement of waves and the corresponding position of separate channels it is possible to put on a card internal structure of a seabed.

Measurement data revealed a large body of sediment, drift precipitation, on the eastern flank of the Pine Island Trough, unparalleled on its western side. “Because of the Cariolis effect caused by the Earth’s rotation, this asymmetric precipitation drift deposition on the east side of the valley, but not on the west, can only be caused by a deep-water current that sailed to the coast from north to south,” Wentzelman-Neben says. “For this to happen, the circulation of the ocean at the time of the deposition had to be similar to today’s conditions, i.e. the predominant western and Antarctic circumpolar currents had to be located far to the south. And like today, the deep water that rose through the gutter had to be relatively warm. ”

Additional study of pollen from sediment nuclei collected near the basin shows that the basis of sediment drift was formed about 34 to 36 million years ago. At the same time – on the border of the Eocene and Oligocene – the temperature dropped sharply around the globe, and the Antarctic continent was covered with ice. “Our study offers compelling evidence that during the Great Glaciation, warmer deep water rose near the Amundsen Sea shelf and delayed the expansion of the West Antarctic ice sheet to the sea,” explains AWI geophysicist. “This important and unexpected finding underscores the enormous importance that ocean currents had even at the stage of the formation of the West Antarctic Ice Shield and continue to have today. Armed with this additional knowledge about the earliest phase of the ice sheet, it is now possible to improve predictions about its future stability and ice retreat. ”

Reference: “Deep water inflow has slowed the expansion of the western Antarctic ice sheet at the Eocene-Oligocene transition” Gabriele Wenzelman-Neben, Carsten Gaul, Katharina Hochmut, Ulrich Salzmann, Robert D. Larter, Klaus-Clappen-Dieter Heaven PS104, February 21, 2022, Communications Earth and Environment.
DOI: 10.1038 / s43247-022-00369-x “Important and unexpected discovery” – the formation of the ice sheet of West Antarctica was very different from what was previously thought

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