Author: ["Joerg M. Schaefer","Robert C. Finkel","Greg Balco","Richard B. Alley","Marc W. Caffee","Jason P. Briner","Nicolas E. Young","Anthony J. Gow","Roseanne Schwartz"]
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Abstract
Measurements of cosmic-ray-produced 10Be and 26Al in a bedrock core from beneath the summit of the Greenland Ice Sheet show that Greenland was nearly ice-free for extended periods under Pleistocene climate forcing. The Greenland Ice Sheet is a main contributor to modern sea-level rise, but its stability during past warm periods is uncertain, thus compromising our ability to robustly predict future rates and magnitudes of ice loss. Joerg Schaefer and colleagues present cosmogenic isotope evidence, from bedrock samples from beneath an ice core near the summit of the ice sheet, to show that the Greenland Ice Sheet was largely ice-free at some point during the Pleistocene. The data cannot constrain the time or duration of ice-free conditions, and seem incompatible with our current understanding of ice-sheet behaviour. Nevertheless, alternative explanations for the cosmogenic data are lacking, suggesting that our understanding of the response of the Greenland Ice Sheet to past warmth remains incomplete. The Greenland Ice Sheet (GIS) contains the equivalent of 7.4 metres of global sea-level rise1. Its stability in our warming climate is therefore a pressing concern. However, the sparse proxy evidence of the palaeo-stability of the GIS means that its history is controversial (compare refs 2 and 3 to ref. 4). Here we show that Greenland was deglaciated for extended periods during the Pleistocene epoch (from 2.6 million years ago to 11,700 years ago), based on new measurements of cosmic-ray-produced beryllium and aluminium isotopes (10Be and 26Al) in a bedrock core from beneath an ice core near the GIS summit. Models indicate that when this bedrock site is ice-free, any remaining ice is concentrated in the eastern Greenland highlands and the GIS is reduced to less than ten per cent of its current volume. Our results narrow the spectrum of possible GIS histories: the longest period of stability of the present ice sheet that is consistent with the measurements is 1.1 million years, assuming that this was preceded by more than 280,000 years of ice-free conditions. Other scenarios, in which Greenland was ice-free during any or all Pleistocene interglacials, may be more realistic. Our observations are incompatible with most existing model simulations that present a continuously existing Pleistocene GIS. Future simulations of the GIS should take into account that Greenland was nearly ice-free for extended periods under Pleistocene climate forcing.Cite this article
Schaefer, J., Finkel, R., Balco, G. et al. Greenland was nearly ice-free for extended periods during the Pleistocene. Nature 540, 252–255 (2016). https://doi.org/10.1038/nature20146 