Study reveals where and when Antarctic ice sheet first formed

Combining unique geological samples with sophisticated modelling has led to insights into when and where today's Antarctic ice sheet formed.

Due to global warming, Antarctica’s ice is melting faster than previously assumed, particularly in West Antarctica more than East Antarctica.

An international team led by the Alfred Wegener Institute and involving Professor Tina van de Flierdt at Imperial College London, suggests that the reason for the faster melting rate may be linked to Antarctica’s ice sheet formation.

“By uncovering when and where the Antarctic ice sheet first formed – in East Antarctica – our findings help explain why West Antarctica is more vulnerable to melting today, offering important insights for predicting future climate change.” Professor Tina van de Flierdt

Using sediment samples from drill cores combined with complex climate and ice-sheet modelling, researchers found that permanent glaciation of Antarctica began around 34 million years ago – but it did not encompass the entire continent as previously assumed; rather it was confined to the East Antarctica.

It was not until at least 7 million years later that ice was able to advance towards West Antarctic coasts. The results of the new study show how substantially differently East and West Antarctica react to changes in the environment, as the researchers describe in the journal Science.

How, when and where did the Antarctic ice sheet form?

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, relatively warm and with no or very little accumulation of continental ice, to an ‘icehouse’ world, colder and with large permanently glaciated areas.

During this time, the Antarctic ice sheet was formed. How, when and, above all, where, was not yet known due to a lack of reliable data and samples from key regions, especially from West Antarctica, that document the changes in the past.

The international team of researchers has now been able to close this knowledge gap.

Based on a drill core that the researchers retrieved using the MARUM-MeBo70 seafloor drill rig in a location offshore the Pine Island Glacier on the Amundsen Sea coast of West Antarctica, they were able to better understand the history of the formation of the ice on the Antarctic continent for the first time.

Surprisingly, 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 large-scale, permanent first glaciation must have begun somewhere in East Antarctica,” said Dr Johann Klages, geologist at the Alfred Wegener Institute who led the research team.

“This is because West Antarctica remained ice-free during this first glacial maximum. At this time, it was still largely covered by dense broadleaf forests and a cool-temperate climate that prevented ice from forming in West Antarctica.”

East and West Antarctica react very differently to external conditions

In order to better understand where ice first formed in Antarctica, the palaeoclimate modelers in the team combined the newly available data together with existing data on air and water temperatures and the occurrence of ice.

According to the study, the basic climatic conditions for the formation of permanent ice only prevailed in the coastal regions of the East Antarctic Northern Victoria Land. Here, moist air reached the sharply rising Transantarctic Mountains – ideal conditions for permanent snow and subsequent formation of ice caps.

From there, the ice sheet spread rapidly into 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 for advance of an ice sheet to the West Antarctic coast,” explains Hanna Knahl, a palaeoclimate modeler at the AWI. “Our results clearly show how cold it had to get before the ice could advance to cover West Antarctica that, at that time, was already below sea level in many parts.”

What the research also shows is how different the two regions of the Antarctic ice sheet react to external influences and fundamental climatic changes. “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,” adds Dr Klages.

New insights to improve climate models

The team’s findings are essential for understanding how the Earth’s climate transitioned from the very warm greenhouse climate to our current cooler icehouse climate.

The study also provides new insights to improve climate models to simulate more accurately how permanently glaciated areas affect global climate dynamics – including the interactions between ice, ocean and atmosphere.

Study co-author, Professor Tina van de Flierdt, Head of the Department of Earth Science and Engineering, said:

“The deep sediment in the seabed off the West Antarctic Pine Island Glacier had been previously impossible to reach using conventional drilling methods.

“By uncovering when and where the Antarctic ice sheet first formed – in East Antarctica – our findings help explain why West Antarctica is more vulnerable to melting today, offering important insights for predicting future climate change.”

The research project, and the Polarstern expedition PS104 in particular, was funded by the AWI, MARUM, the British Antarctic Survey, and the NERC UK-IODP Programme.