Ancient Antarctic rivers challenge theory of a flat landscape, as mission for climate clues beneath Antarctic ice gets underway

Pre-glacial West Antarctica was a rugged, uneven landscape, not a flat plain, reshaping our understanding of how its ice sheet first formed and how it may behave in a warming climate, a new study led by Imperial College London has revealed.

This comes alongside the news – announced today – that an international team, also involving Imperial, has recently set up a remote camp on the ice in Antarctica to attempt to drill for mud and rocks that hold critical insights about the fate of the West Antarctic Ice Sheet due to climate change. 

Looking deep beneath the ice allows us to reconstruct Earth’s history during changing climates, and our latest study helps us understand today’s ice sheets by mapping the ancient landscape that existed before the ice ever formed. Dr James Marschalek Research Associate, Department of Earth Science and Engineering at Imperial

“Ancient Antarctica provides some of the most valuable clues about the future and consequences of a warming world,” said Dr James Marschalek, Research Associate in the Department of Earth Science and Engineering (ESE) at Imperial, who led the study. 

“Looking deep beneath the ice allows us to reconstruct Earth’s history during changing climates, and our latest study helps us understand today’s ice sheets by mapping the ancient landscape that existed before the ice ever formed. That bygone topography set the stage for the ice age and continues to guide how the ice flows as it warms and melts today.” 

Deep ice drilling 

Dr Marschalek is also part of the SWAIS2C (Sensitivity of the West Antarctic Ice Sheet to 2°C) project, which has recently embarked on its third expedition to the continent to attempt to drill for a 200-metre sediment core from the bedrock deep beneath 500 metres of ice at the Crary Ice Rise on the Ross Ice Shelf.  

This marks the third season of Imperial’s involvement to recover a geological record of the West Antarctic Ice Sheet (Antarctica’s biggest contributor to global sea-level rise), with Professor Tina van de Flierdt, Head of the Department of Earth Science and Engineering and Co-Chief Scientist for SWAIS2C, taking the helm for previous missions in 2023 and 2024.

This year, an ‘on-ice’ team of 29 scientists, drillers, engineers and Antarctic field specialists, including Dr Marschalek in the Geochemistry Science Team, is again hoping to obtain a crucial sediment core from the ice. Should they succeed, the core is expected to contain layers of sediment laid down within the past 23 million years – a period in Earth’s history when temperatures were warmer than they are today.  

The hope is that this will provide the insights needed to answer the critical question of what global temperature increase will trigger unsustainable melting of the Ross Ice Shelf, and the subsequent loss of the West Antarctic Ice Sheet. 

Antarctica’s pre-glacial past 

Casting an eye even further back to more than 34 million years ago, Antarctica was covered by forests instead of ice, with rivers flowing into the sea instead of glaciers.  

Uncovering what the land surface of Antarctica looked like at this time is key since it impacts how easy it was to form the earliest glaciers and how the continent has transitioned to the ice-covered world we know today. Dr James Marschalek Research Associate, Department of Earth Science and Engineering at Imperial

“Uncovering what the land surface of Antarctica looked like at this time is key since it impacts how easy it was to form the earliest glaciers and how the continent has transitioned to the ice-covered world we know today,” said Professor van de Flierdt, who was also an author of the study. 

This early history has also shaped the properties of the surface that the current West Antarctic Ice Sheet rests on, in turn influencing how the ice slides across it as Antarctica continues to warm due to climate change. 

However, the study, published in Science Advances, has reconstructed the West Antarctic land surface made by placing sediment eroded and deposited offshore back onto the continent and revealed a markedly different pattern, with areas of high and low ground and much shorter rivers. 

Sediments from the Amundsen Sea, off the coast of West Antarctica, dating to before it was covered with ice have recently been suggested to come from the Transantarctic Mountains, more than 1,500 kilometres away. This would mean that a long river flowed across West Antarctica, with a land surface that was relatively flat. 

Highs and lows 

The team, which also involved institutions including UCL, measured new sediment samples from the Amundsen Sea to find out more about the rocks currently beneath the ice and uncover whether the proposed long river system is likely to have existed. 

They found that the sediments are unlikely to have come from the Transantarctic Mountains and were instead delivered by a much shorter river network. That means the West Antarctic land surface before glaciation might have had areas of higher ground and parts below sea level, helping to reveal what the continent looked like before it was ice-covered. 

“This complex topography would translate to areas of erosion and deposition at this time, hinting towards a diverse mixture of bedrock areas and sediments of different ages beneath the modern ice sheet,” said Dr Marschalek.   

“Understanding how ice sheets respond to climate change is essential, and past warm intervals offer valuable analogues for potential future conditions,” said study author Dr Matthew Fox at UCL.   

“However, topography exerts a strong control on ice-sheet dynamics, complicating the interpretation of paleoclimate signals. Here we provide new constraints on Antarctic topography at the onset of glaciation.”