The Antarctic ice sheet has been even more volatile in the past than previously thought, and could sometimes approach collapse, new research shows.
The findings raise concerns that in warmer climates, exposure to the ground under the ice sheet during the retreat will increase precipitation in Antarctica, and this could trigger processes that accelerate further ice losses.
The study is based on climate modeling and comparison of data for the Middle Miocene (1
The study was conducted by the Met Office, the universities of Exeter, Bristol, Cardiff and Stockholm, NORCE and the Climate Research Center in Bjerknes.
“When the ice sheet melts, the newly discovered ground below is less reflective and local temperatures become warmer,” said lead author Dr. Catherine Bradshaw of the Met Office and the Global System Institute at the University of Exeter.
“This could drastically change the weather patterns.
“With a large ice sheet on the continent, as we have today, Antarctic winds usually blow from the continent to the sea.
“However, if the continent warms up, it could be reversed, with winds blowing from the cooler sea to warmer land – just as we see with monsoons around the world.
“This would bring additional rainfall to the Antarctic continent, which would lead to more fresh water leaking into the sea.
“Freshwater is less dense than salt water and can therefore sit on the sea surface instead of sinking and circulating like salt water.
“This effectively breaks the connection between the deep ocean and the surface ocean, leading to the accumulation of warmer water at depth.”
The study suggests that processes caused by increased rainfall would reduce the climate system’s ability to maintain a large Antarctic ice sheet.
“Essentially, if more land is exposed in Antarctica, it becomes more difficult to reform for a large ice sheet, and without favorable orbital positions in the Middle Miocene, a role played, perhaps the ice sheet would collapse at that time.” Mr. Bradshaw said.
During the warm period of the Middle Miocene, unusually large swings back and forth at deep-water temperatures were recorded.
The study shows that fluctuations in the area covered by the ice sheet were a major factor in causing deep sea temperatures to change so drastically. Fluctuations in ice volume have been found to be much less significant.
Variations in the positioning of the Earth relative to the Sun caused the ice sheet to move and recede, and this changed meteorological patterns – triggering processes that could accelerate the loss or gain of ice.
Rain falling on the ice sheet can cause cracking, melting of the surface and leakage of additional fresh water from the continent, which in turn can lead to rising sea temperatures – potentially affecting the Antarctic ice below.
The findings of the new study suggest that the Antarctic ice sheet retreated significantly during the Middle Miocene and then stabilized when the warm season ended.
Co-author Associate Professor Agatha De Boer of the University of Stockholm said: “As the climate in the Middle Miocene cooled, the link we found between the ice sheet area and deep sea temperatures through the hydrological cycle came to an end.
“Once Antarctica was completely covered by the ice sheet, winds would always move from land to sea, and as a result, rainfall would be reduced to low levels falling like snow over the continent we see today.”
Dr Petra Langbrook, a senior researcher at NORCE and the Center for Climate Research in Björknes, another co-author, added: land. “
Professor Carrie Lear of Cardiff University, who first developed the project, concluded: “This study suggests that during a warm period about 15 million years ago, the Antarctic ice sheet in the Miocene was able to occur significantly and retreat across the continent. .
“This is worrying, but further research is needed to determine what exactly this means for the long-term future of the modern Antarctic ice sheet.”
Dr Bradshaw emphasized that current conditions are not identical to those in the Middle Miocene and the model used in the study does not include the impact of carbon cycle feedback or the ice sheet itself.
The report published in the journal Nature Geoscience, is entitled: “Hydrological impact of the Middle Miocene Antarctic regions without ice, combined with deep ocean temperatures.”
Modeling ancient Antarctic ice sheets helps us see the future of global warming
Hydrological impact of the Middle Miocene Antarctic regions without ice, combined with deep ocean temperatures, Nature Geoscience (2021). DOI: 10.1038 / s41561-021-00745-w
Provided by the University of Exeter
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