Record of Antarctic ice sheet response to climate cycles found in rock samples

Climate cycles and natural variability do exist then?! No need to re-visit those discussions. Quote: “One of the key findings is that the ice sheet was responding to temperature changes in the Southern Ocean”. The study says: ‘Our findings imply that oscillating Southern Ocean temperatures drive a dynamic response in the Antarctic ice sheet on millennial timescales, regardless of the background climate state.’
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By analyzing unusual rock samples collected years ago in Antarctica, scientists at the University of California, Santa Cruz, have discovered a remarkable record of how the East Antarctic Ice Sheet has responded to changes in climate over a period of 100,000 years during the Late Pleistocene, says Phys.org.

The East Antarctic Ice Sheet is the world’s largest ice mass. Understanding its sensitivity to climate change is crucial for efforts to project how much sea level will rise as global temperatures increase.

Recent studies suggest it may be more vulnerable to ice loss than previously thought.

The new study, published September 15 in Nature Communications, provides evidence of changes at the base of the ice sheet over a broad area in response to cyclic changes in climate during the Pleistocene. The changes are reflected in the types of minerals deposited at the base of the ice sheet.

“One of the key findings is that the ice sheet was responding to temperature changes in the Southern Ocean,” said coauthor Terrence Blackburn, associate professor of Earth and planetary sciences at UC Santa Cruz. “The warm water eats at the edges of the ice sheet and causes the ice to flow faster, and that response reaches deep into the heart of the ice sheet.”

The rock samples analyzed in the study consist of alternating layers of opal and calcite that formed as mineral deposits at the base of the ice sheet, recording cyclic changes in the composition of subglacial fluids.

“Each layer in these samples is a manifestation of a change at the base of the ice sheet driven by changes in the motion of the ice streams,” said first author Gavin Piccione, a Ph.D. candidate working with Blackburn at UCSC.

By dating the layers, the researchers found a striking correlation between the layers of mineral deposits and the record of polar sea surface temperatures derived from ice cores. The opal was deposited during cold periods, and the calcite during warm periods.

“These climate oscillations are causing changes in ice sheet behavior such that the chemistry and hydrology beneath the ice is changing,” said coauthor Slawek Tulaczyk, a professor of Earth and planetary sciences at UCSC who has been studying the behavior of ice sheets and glaciers for decades.

The climate cycles that match the mineral layers are relatively small fluctuations that occur every few thousand years within the more pronounced glacial-interglacial cycles that occurred every 100,000 years or so throughout the Pleistocene. The glacial-interglacial cycles are driven primarily by changes in Earth’s orbit around the sun.

The smaller millennial-scale climate cycles involve oscillations in polar temperatures driven by weakening and strengthening of a major ocean current (the Atlantic Meridional Overturning Circulation, or AMOC) which transports large amounts of heat northward through the Atlantic Ocean.

Tulaczyk said the new findings reveal the Antarctic Ice Sheet’s sensitivity to small, short-term climate fluctuations.

“As important as the Antarctic Ice Sheet is—it’s responsible for close to 17 meters of sea level rise since the last glacial maximum—we really know very little about how it has responded to climate variability,” he said. “We know the last 20,000 years pretty well, but beyond that we’ve been almost blind. That’s why these results are so mind-blowing. People have been banging their heads against the wall over this for decades.”

Full article here.
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Study: Subglacial precipitates record Antarctic ice sheet response to late Pleistocene millennial climate cycles (Sep. 2022)