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Changes to the Antarctic ice sheet in the lower southern hemisphere have been triggered by sea level changes in the northern hemisphere over the past 40,000 years, a new study has found.
Researchers at McGill University have found that ice sheets at opposite ends of the Earth can affect each other by changing the sea level in surrounding waters.
Scientists have struggled to explain how ice sheets changed during the last ice age – the Last Ice Period – which spanned 115,000 to 11,700 years ago.
New models found that as the climate cooled in the Northern Hemisphere and more water turned to ice, the sea level in Antarctica decreased, causing its ice sheet to grow.
Likewise, as temperatures rose again, ice sheets in the Northern Hemisphere retreated, causing levels to rise around Antarctica and its ice sheet retreat.
The polar ice caps evolve over different time scales and are in constant flux, with the ice growing and retreating depending on the surrounding climate and water levels
Professor Natalya Gomez, senior author at McGill University, said the ice sheets can affect each other for thousands of kilometers due to the water flowing between them.
“It is as if they are talking to each other through the sea level changes,” he said.
The team looked at existing models, geological records, core samples from the Southern Ocean bottom, and soil exposure records from the coasts.
Professor Gomez said the polar ice caps weren’t just large static ice mounds.
“They evolve on different time scales and are in constant flux, with the ice growing and shrinking depending on the surrounding climate and water level.
“They gain ice when snow accumulates above them, then spreads outward under their own weight and spills out into the surrounding ocean where their edges break into icebergs,” explained Gomez.
With this information, they were able to simulate simultaneous changes in sea level and ice dynamics on both hemispheres over the past 40,000 years.
This time frame provides a bigger picture of how climatic factors affect ice sheets, as it captures the retreat after the peak of the last ice age up to 26,000 years ago.
To investigate the mechanisms involved in driving changes in the Antarctic ice sheet, the researchers examined a wide range of geological records, from sediment cores from the ocean floor near Antarctica to records of land and coastal exposure in the past.
The Antarctic ice sheets lost a significant amount of ice during this period, with occasional periods of accelerated retreat, the logs show.
The only possible explanation, the scientists say, was changes in sea level caused by the growth or retreat of ice sheets in the Northern Hemisphere.
Co-author Michael Weber of the University of Bonn in Germany said: ‘We have found a highly variable signal of ice mass loss over the past 20,000 years left behind by icebergs that broke away from Antarctica and melted into the surrounding oceans. “.
“This evidence could hardly be reconciled with existing models until we had taken into account how the ice sheets in both hemispheres interact with each other.”
The Antarctic ice sheet spans nearly 5.4 million square miles, which is roughly the same size as the United States and Mexico combined.
Researchers were able, for the first time, to simultaneously simulate changes in sea levels and ice dynamics in both hemispheres over the past 40,000 years.
Professor Gomez added: ‘The scale and complexity of ice sheets and oceans, and the secrets of Earth’s past climate that are locked up in geological records are fascinating and inspiring.
“Our results highlight how interconnected the Earth system is, with changes in one part of the planet causing changes in another.
‘In the modern era, we haven’t seen the kind of ice sheet retreat that we might see in our future warming world.
“Searching for records and patterns of changes in Earth’s history can inform us of this.”
The findings were published in the journal Nature.
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