Rapid early Holocene deglaciation of the Laurentide ice sheet

The demise of the Laurentide ice sheet during the early Holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the Northern Hemisphere, and thus allows an assessment of rates of ice-sheet decay as well as attendant contributions to sea level rise. Here, we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the Laurentide ice sheet, when melting ice contributed about 1.3 and 0.7 cm of sea level rise per year, respectively. Our simulations with a fully coupled ocean–atmosphere model suggest that increased ablation due to enhanced early Holocene boreal summer insolation was the predominant cause of Laurentide ice-sheet retreat. Although the surface radiative forcing in boreal summer during the early Holocene is twice as large as the greenhouse-gas forcing expected by the year 2100, the associated increase in summer surface air temperatures is very similar. We conclude that our geologic evidence for a rapid retreat of the Laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the Greenland ice sheet over the coming century. The demise of the Laurentide ice sheet during the early Holocene epoch allows rates of ice sheet decay under natural conditions to be assessed. Analysis of terrestrial and marine records of the deglaciation along with a climate model reveal two periods of rapid melting during the final retreat of this ice sheet, with rates of sea level rise of up to 1.3 cm per year.