Antarctic ice sheet is controlled by weather in the Northern Hemisphere

A new study from McGill University describes how changes in the Antarctic ice sheet are interconnected with melting ice sheets on the other side of the globe. The experts report that ice sheets located thousands of kilometers apart have influenced one another through sea level changes over the last 40,000 years.

The study reveals, for the first time, that  changes in the Antarctic ice sheet during the most recent glacial cycle were driven by melting ice sheets in the Northern Hemisphere.

Computer modeling showed that during the last Ice Age, water became locked up in land ice in the Northern Hemisphere. This led to a substantial decline in Antarctic sea levels. As the climate warmed, however, melting ice in the Northern Hemisphere led to rising water levels around Antarctica, which then caused the Antarctic ice sheet to retreat.

“Ice sheets can influence each other over great distances due to the water that flows between them,” said study senior author Natalya Gomez. “It’s as though they were talking to one another through sea level changes.”

“Polar ice sheets are not just large, static mounds of ice. They evolve on various different time scales and are in constant flux, with the ice growing and retreating depending on the climate and the surrounding water levels. They gain ice as snow piles up on top of them, then spread outwards under their own weight, and stream out into the surrounding ocean where their edges break off into icebergs.”

For the investigation, the researchers combined numerical modeling with a wide range of geological records, from Antarctic sediment cores to records of past shorelines. This data allowed the team to simultaneously simulate changes in the ice and sea levels across both hemispheres over the past 40,000 years, which is a time frame that covers the climate leading up to the peak of the last Ice Age all the way to the present. 

The records indicate that there were significant losses from the Antarctic ice sheet during this period, with sporadic points of acceleration. The only mechanism that could be responsible, according to the experts, were the sea level changes in Antarctica caused by changes to the ice sheets in the Northern Hemisphere.

“We found a very variable signal of ice-mass loss over the last 20,000 years, left behind by icebergs breaking off Antarctica and melting down in the surrounding oceans,” said study co-author Michael Weber. “This evidence could hardly be reconciled with existing models until we accounted for how the ice sheets in both hemispheres interact with one another across the globe.”

“The scale and complexity of ice sheets and the oceans, and the secrets of the Earth’s past climate that are locked up in the geological record are fascinating and inspiring,” said Gomez. “Our results highlight how interconnected the Earth system is, with changes in one part of the planet driving changes in another. In the modern era, we haven’t seen the kind of large ice sheet retreat that we might see in our future warming world. Looking to records and models of changes in Earth’s history can inform us about this.”

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer