New research from the University of Massachusetts Amherst definitively resolves a long-standing discrepancy in the geological record that pitted studies of marine ice sheet behavior against those that reconstructed past conditions on land. The research, recently published in the journal Geology, and funded by the National Science Foundation and the National Environment Research Council, lends added weight to evidence that the Antarctic ice sheet is sensitive to small changes in CO2 levels and that in the past large parts of the ice cap could have disappeared under the effect of CO2 levels similar to those of today.
There has been a decades-long debate among scientists studying Antarctic ice sheet history, and it revolves around the discrepancy between marine data from the Ross Sea and data collected in the valleys. from McMurdo, an adjacent ice-free mountainous coastal region to the Ross Sea. In one corner are marine records from the seafloor which showed that the Antarctic ice sheet has repeatedly shrunk to a size smaller than modern size over the past 10 million years and that the ice-covered Ross Sea was periodically an open ocean. This suggests that the Antarctic ice sheet is sensitive to relatively low CO2 and temperature fluctuations and have receded during past warm periods.
In the other corner are terrestrial studies of ancient and well-preserved landforms in the McMurdo Dry Valleys which reveal that cold desert conditions on earth were maintained over the same ten million year period, leading some researchers to conclude that a stable Antarctic ice sheet has persisted through several past warm periods and may therefore be less sensitive to global warming than marine data suggest.
Is the West Antarctic ice sheet sensitive or not to global warming? Resolving this debate is of planetary importance, because the same parts of the Antarctic ice sheet that collapsed in the past could raise sea levels by 10 feet or more if they were to collapse in our time. .
Using a series of high-resolution climate models and ice sheets, Anna Ruth Halberstadt, who carried out this research as part of her PhD. in geosciences at UMass Amherst, and his colleagues were able to show that it is entirely possible for sub-freezing temperatures to exist in the McMurdo Dry Valleys, even when the nearby Ross Sea is completely ice-free. . “We can now say, ‘ok, now we understand why these two sets of data seemed to be at odds,'” says Halberstadt, the paper’s lead author.
Halberstadt and his team conducted a series of experiments using state-of-the-art climate and sea ice models to show that McMurdo’s Dry Valleys could certainly have remained frozen, even during periods of ice sheet collapse. Halberstadt says “this work finally brings all the geological information online and suggests that large parts of the Antarctic ice sheet may have collapsed under climatic situations similar to today.”
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