When and where did the current Antarctic ice sheet form?

5 Jul. () –

The permanent glaciation of Antarctica began about 34 million years agobut it did not cover the entire continent as previously assumed, but was limited to the eastern region of the continent.

It was not until at least 7 million years later that the ice may have advanced toward the coasts of West Antarctica, according to sediment samples from drill cores combined with complex climate and ice sheet models.

With these results, an international research team led by the Alfred Wegener Institute presents in the journal Science how substantially different East and West Antarctica react to external forces, such as global warming.

About 34 million years ago, our planet underwent one of the most fundamental climate changes that still influence global climate conditions today: the transition from a greenhouse world, with little or no continental ice accumulation, to a greenhouse world, with large areas of permanent ice.

During this time, the Antarctic ice sheet accumulated. How, when and, most importantly, where, remained unknown due to a lack of reliable data and samples from key regions, especially West Antarctica, documenting past changes.

In this way, the research team has been able to close this knowledge gap. From a drill core that the researchers recovered with the MARUM-MeBo70 seafloor drilling rig at a site off the Pine Island and Thwaites glaciers on the coast of the Amundsen Sea in West Antarctica, They were able to establish for the first time the history of the dawn of the frozen Antarctic continentSurprisingly, no signs of the presence of ice can be found in this region during the first major phase of Antarctic glaciation.

“This means that a first large-scale permanent glaciation must have started somewhere in East Antarctica,” he says. it’s a statement Johann Klages, a 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 largely covered by dense broadleaf forests and a temperate-cold climate that prevented ice formation in West Antarctica.

To better understand where the first permanent ice formed in Antarctica, AWI palaeoclimate modellers 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,” explains Professor Gerrit Lohmann, palaeoclimate modeller at AWI. “This completely changes what we know about the first Antarctic ice age.”

According to the study, basic climatic conditions for permanent ice formation prevailed only in the coastal regions of Victoria Land north of East Antarctica. Here, moist air masses reached the Transantarctic Mountains in steep ascent – ​​ideal conditions for permanent snow and subsequent ice sheet formation. From there, the ice sheet rapidly spread into the interior of East Antarctica.

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 to the coast of West Antarctica,” explains Hanna Knahl, a paleoclimate modeller at AWI.

“Our results clearly show how cold it must have been before the ice could advance to cover West Antarctica, which at that time was already below sea level in many areas“The studies also show impressively how differently the two regions of the Antarctic ice sheet react to external influences and fundamental climate changes. “Even a slight warming is enough to cause the ice in West Antarctica to melt again, and that’s where we are now“, adds Johann Klages.

The results of the international research team are fundamental to understanding the extreme climate transition from the greenhouse climate to today’s greenhouse climate. Importantly, the study also provides new insights that enable climate models to more accurately simulate how permanently glaciated areas affect global climate dynamics, i.e. the interactions between ice, ocean and atmosphere. This is of crucial importance, as Johann Klages says: “Especially in light of the fact that we could be faced with extreme climate transitions again.” to such fundamental climate change in the near future.”