The recovery of unique geological samples sheds light on the formation of today’s Antarctic ice sheet

In recent years, global warming has left its mark on the Antarctic ice sheets. The “eternal” ice in Antarctica is melting faster than previously thought, especially in West Antarctica more than East Antarctica. The root of this may lie in its formation, as an international research team led by the Alfred Wegener Institute has now discovered.

Sediment samples from drill cores combined with complex climate and ice sheet modeling show that Antarctica’s permafrost began around 34 million years ago – but did not cover the entire continent as previously assumed, but was instead limited to the eastern region of the continent. East Antarctica). It was not until at least 7 million years later that the ice was able to advance towards the west coast of Antarctica.

The results of the new study show how fundamentally East and West Antarctica respond to external forcing, as the researchers describe in the journal. science.

About 34 million years ago, our planet underwent one of the most fundamental climate changes that still affects global climate conditions today: the transition from a greenhouse world (with little or no accumulation of continental ice) to an ice world (with glaciers forever large. area). During this time, the Antarctic ice sheet rose. How, when, and above all, where was not yet known due to a lack of reliable data and samples from key regions, especially West Antarctica, that documented changes in the past.

Researchers from the Alfred Wegener Institute, the Helmholtz Center for Polar and Marine Research (AWI) have now been able to close this knowledge gap, together with colleagues from the British Antarctic Survey, the University of Heidelberg, Northumbria University (UK) and MARUM— Center. for Marine Environmental Sciences at the University of Bremen, in addition to collaborators from the Universities of Aachen, Leipzig, Hamburg, Bremen and Kiel, as well as the University of Tasmania (Australia), Imperial College London (UK), Université de Friborg (Switzerland), Universidad de Granada (Spain), University of Leicester (UK), Texas A&M University (USA), Senckenberg am Meer and the Federal Institute for Geosciences and Natural Resources in Hanover, Germany.

Based on a drill core that the researchers recovered using the MARUM-MeBo70 drilling rig at an offshore location on the Isle of Pines and Thwaites Glaciers in the Amundsen Sea coast of West Antarctica, they were able to determine the history of Antarctica’s dawn icy. continent for the first time. Surprisingly, no sign of the presence of ice can be found in this region during the first major glaciation phase of Antarctica.

“This means that the first large-scale permanent glaciation must have started somewhere in East Antarctica,” says Dr. Johann Klages, geologist at AWI who led the research team. This is because West Antarctica remained ice-free during this first glacial maximum. At the time, it was still mostly covered by dense broadleaf forests and a cold temperate climate that prevented the formation of ice in West Antarctica.

East and West Antarctica react very differently to external conditions

To better understand where the first permanent ice formed in Antarctica, AWI paleoclimate modelers combined newly available data with existing data on air and water temperatures and ice occurrence.

“The simulation has supported the results of the unique core of geologists,” says Prof Dr. Gerrit Lohmann, paleoclimate modeler at AWI. “This completely changes what we know about Antarctica’s first glaciation.”

According to the study, the basic climatic conditions for the formation of permafrost prevailed only in the coastal regions of Northern Victoria Land in the East Antarctic. Here, moist air masses reached the Transantarctic mountains in strong growth – ideal conditions for permanent snow and the subsequent formation of ice caps. From there, the ice sheet spread rapidly into the interior of East Antarctica. However, it took some time before it reached West Antarctica.

“It was only about seven million years later that conditions allowed the advance of an ice sheet on the west coast of Antarctica,” explains Hanna Knahl, a paleoclimate modeler at AWI. “Our results clearly show how cold it had to get before ice could advance to cover West Antarctica, which, at the time, was already below sea level in many parts.”

What the investigations also show impressively is how differently the two regions of the Antarctic ice sheet react to external influences and fundamental climate change.

“Even a slight warming is enough to cause the ice in West Antarctica to melt again – and that’s where we are right now,” adds Klages.

The international research team’s findings are critical to understanding the extreme climate transition from the greenhouse climate to our current ice climate. Importantly, the study also provides new insight that allows climate models to more accurately simulate how permafrost areas affect global climate dynamics, that is, the interactions between ice, ocean and atmosphere.

This is of crucial importance, as Klages says, “especially in light of the fact that we may again face such fundamental climate change in the near future.”

Using new technology to gain unique knowledge

The researchers were able to close this knowledge gap with the help of a unique drill core that they received during the PS104 expedition on the Polarstern research vessel in West Antarctica in 2017. The MARUM-MeBo70 drill rig developed at MARUM in Bremen was used for the first time seen in Antarctica.

The seabed off the West Antarctic Pine Island and Thwaites glaciers is so hard that it was previously impossible to reach deep sediments using conventional drilling methods. The MARUM-MeBo70 has a rotary cutting head, which made it possible to drill about 10 meters into the seabed and take samples.