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Biggest ice sheet on Earth more vulnerable to melting than thought
Shocking evidence suggests that the last time the East Antarctic ice sheet collapsed, it added over 10 feet to sea level rise, and that it’s likely to happen again.
Scientists had determined that this ice sheet last retreated about three million years ago. But a new paper in the journal Nature suggests—based on a study of crystals collected from the region—that a large part of it collapsed only 400,000 years ago. Most startling of all, the team’s calculations suggest that the dramatic change happened during an extended but relatively mild warm spell.
During that time period, the amount of carbon dioxide in the atmosphere never rose very high, peaking at only about 300 parts per million (ppm), says David Harwood, who studies Antarctic glacial history at the University of Nebraska in Lincoln.
“That’s the scary thing,” says Harwood. Modern carbon dioxide levels blew past 300 ppm way back in 1915—and they currently sit at 410 ppm. In the coming centuries, that extra carbon dioxide could raise temperatures, and sea level, well above what happened 400,000 years ago, he says. “This doesn’t bode well for the future.”
...
If these new findings bear out, then East Antarctica may contribute to sea level rise sooner than expected. The greenhouse gases that humans have produced to date may have already locked in 42 feet of eventual sea level rise from all of the glaciers predicted to melt in the coming centuries, including the ones in East Antarctica.
https://www.nationalgeographic.com/science/2020/07/east-antarctic-ice-sheet-more-vulnerable-to-melting-than-thought/
Scientists had determined that this ice sheet last retreated about three million years ago. But a new paper in the journal Nature suggests—based on a study of crystals collected from the region—that a large part of it collapsed only 400,000 years ago. Most startling of all, the team’s calculations suggest that the dramatic change happened during an extended but relatively mild warm spell.
During that time period, the amount of carbon dioxide in the atmosphere never rose very high, peaking at only about 300 parts per million (ppm), says David Harwood, who studies Antarctic glacial history at the University of Nebraska in Lincoln.
“That’s the scary thing,” says Harwood. Modern carbon dioxide levels blew past 300 ppm way back in 1915—and they currently sit at 410 ppm. In the coming centuries, that extra carbon dioxide could raise temperatures, and sea level, well above what happened 400,000 years ago, he says. “This doesn’t bode well for the future.”
...
If these new findings bear out, then East Antarctica may contribute to sea level rise sooner than expected. The greenhouse gases that humans have produced to date may have already locked in 42 feet of eventual sea level rise from all of the glaciers predicted to melt in the coming centuries, including the ones in East Antarctica.
https://www.nationalgeographic.com/science/2020/07/east-antarctic-ice-sheet-more-vulnerable-to-melting-than-thought/
Ice retreat in Wilkes Basin of East Antarctica during a warm interglacial
Abstract
Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth’s past interglacial warm periods1,2,3. About 400,000 years ago, during the interglacial period known as Marine Isotopic Stage 11 (MIS11), the global temperature was 1 to 2 degrees Celsius greater2 and sea level was 6 to 13 metres higher1,3. Sea level estimates in excess of about 10 metres, however, have been discounted because these require a contribution from the East Antarctic Ice Sheet3, which has been argued to have remained stable for millions of years before and includes MIS114,5. Here we show how the evolution of 234U enrichment within the subglacial waters of East Antarctica recorded the ice sheet’s response to MIS11 warming. Within the Wilkes Basin, subglacial chemical precipitates of opal and calcite record accumulation of 234U (the product of rock–water contact within an isolated subglacial reservoir) up to 20 times higher than that found in marine waters. The timescales of 234U enrichment place the inception of this reservoir at MIS11. Informed by the 234U cycling observed in the Laurentide Ice Sheet, where 234U accumulated during periods of ice stability6 and was flushed to global oceans in response to deglaciation7, we interpret our East Antarctic dataset to represent ice loss within the Wilkes Basin at MIS11. The 234U accumulation within the Wilkes Basin is also observed in the McMurdo Dry Valleys brines8,9,10, indicating11 that the brine originated beneath the adjacent East Antarctic Ice Sheet. The marine origin of brine salts10 and bacteria12 implies that MIS11 ice loss was coupled with marine flooding. Collectively, these data indicate that during one of the warmest Pleistocene interglacials, the ice sheet margin at the Wilkes Basin retreated to near the precipitate location, about 700 kilometres inland from the current position of the ice margin, which—assuming current ice volumes—would have contributed about 3 to 4 metres13 to global sea levels.
https://www.nature.com/articles/s41586-020-2484-5
Abstract
Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth’s past interglacial warm periods1,2,3. About 400,000 years ago, during the interglacial period known as Marine Isotopic Stage 11 (MIS11), the global temperature was 1 to 2 degrees Celsius greater2 and sea level was 6 to 13 metres higher1,3. Sea level estimates in excess of about 10 metres, however, have been discounted because these require a contribution from the East Antarctic Ice Sheet3, which has been argued to have remained stable for millions of years before and includes MIS114,5. Here we show how the evolution of 234U enrichment within the subglacial waters of East Antarctica recorded the ice sheet’s response to MIS11 warming. Within the Wilkes Basin, subglacial chemical precipitates of opal and calcite record accumulation of 234U (the product of rock–water contact within an isolated subglacial reservoir) up to 20 times higher than that found in marine waters. The timescales of 234U enrichment place the inception of this reservoir at MIS11. Informed by the 234U cycling observed in the Laurentide Ice Sheet, where 234U accumulated during periods of ice stability6 and was flushed to global oceans in response to deglaciation7, we interpret our East Antarctic dataset to represent ice loss within the Wilkes Basin at MIS11. The 234U accumulation within the Wilkes Basin is also observed in the McMurdo Dry Valleys brines8,9,10, indicating11 that the brine originated beneath the adjacent East Antarctic Ice Sheet. The marine origin of brine salts10 and bacteria12 implies that MIS11 ice loss was coupled with marine flooding. Collectively, these data indicate that during one of the warmest Pleistocene interglacials, the ice sheet margin at the Wilkes Basin retreated to near the precipitate location, about 700 kilometres inland from the current position of the ice margin, which—assuming current ice volumes—would have contributed about 3 to 4 metres13 to global sea levels.
https://www.nature.com/articles/s41586-020-2484-5
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