Recovery of unique geological samples sheds light on the formation of the current Antarctic ice sheet

In recent years, global warming has left its mark on the Antarctic ice caps. The “eternal” ice in Antarctica is melting faster than previously assumed, especially in West Antarctica more than in East Antarctica. The cause of this could 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 models show that permanent glaciation of Antarctica began about 34 million years ago, but did not encompass the entire continent as previously thought, but was limited to the eastern region of the continent (East Antarctica). It was not until at least 7 million years later that ice could move to the West Antarctic coast.

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

About 34 million years ago, our planet underwent one of the most fundamental climate shifts that still influences global climate conditions: the transition from a greenhouse world (with no or very little accumulation of continental ice) to an ice world (with large permanently glaciated areas). During this time, the Antarctic ice sheet was built up. How, when and especially where were not yet known due to a lack of reliable data and samples from key regions, especially West Antarctica, that documented the changes in the past.

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

Using a drill core retrieved by the researchers using the MARUM-MeBo70 seafloor drilling rig at a site offshore of the Pine Island and Thwaites glaciers on the Amundsen Sea coast of West Antarctica, they were able to determine for the first time the dawn history of the icy Antarctic continent. Surprisingly, no signs of ice presence during the first major phase of the Antarctic glaciation can be found in this region.

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

East and West Antarctica respond very differently to external conditions

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

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

According to the study, the basic climatic conditions for the formation of permanent ice were only present in the coastal areas of the East Antarctic North Victoria Land. Here, moist air masses reached the strongly rising Transantarctic Mountains, ideal conditions for permanent snow and the subsequent formation of ice sheets. From there, the ice sheet quickly spread to the East Antarctic hinterland. However, it took some time before it reached West Antarctica.

“It wasn’t until about seven million years later that conditions allowed an ice sheet to advance toward the West Antarctic coast,” explains Hanna Knahl, a paleoclimatology modeler at AWI. “Our results clearly show how cold it had to get before the ice could cover West Antarctica, which was already below sea level in many places at that time.”

What the studies also impressively show is how differently the two parts of the Antarctic ice sheet respond to external influences and fundamental climate changes.

“Even a small amount of warming is enough to start melting the ice in West Antarctica again – which is exactly where we are now,” Klages adds.

The findings of the international research team are crucial for understanding the extreme climate transition from the greenhouse climate to our current icehouse climate. Importantly, the study also provides new insights that allow climate models to more accurately simulate how permanently glaciated areas influence global climate dynamics, that is, the interactions between ice, ocean and atmosphere.

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

Using new technology to gain unique insights

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

The seabed of 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 rotating cutter head, which made it possible to drill approximately 10 meters into the seabed and retrieve the samples.