Abstract
The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene. Determining the proper surface geometry and elevation of the LIS is of central importance to estimate global changes in sea-level and atmospheric circulation patterns during the late Pleistocene and Holocene. Despite largely disappearing from the landscape during the late Holocene, LIS remnants are found in the Penny and Barnes ice caps on Baffin Island (Canada) and ongoing permafrost degradation has been exposing relics of the LIS buried along its northern margin since the late Pleistocene. Here, we use the δ18O records of six LIS remnants and the late Pleistocene δ18O-elevation relation to establish ice elevation in their source area during the last glacial maximum (LGM). Contrary to some modeled reconstructions, our findings indicate an asymmetric LIS topography with higher ice on Keewatin Dome (~3200 m) and thinner ice in the prairies along the Plains divide (1700–2100 m) during LGM. The resiliency of icy permafrost to past warm intervals preserved relics of the LIS; these ice-marginal landscapes, now poised for thaw, should uncover more valuable clues about the conditions of the last major ice sheet on Earth.
Highlights
The maximum and recessional limits of the Laurentide Ice Sheet (LIS) have been defined using empirical data[1]; whereas its surface geometry and elevation have been assessed from glaciological and geophysical models using a range of boundary conditions, such as past positions of its margins, ice rheology, presence of deformable beds and glacio-isostatic adjustments[2,3,4,5,6]
By analogy to the ice found along the margin of Greenland Ice Sheet[25,26], the buried LIS ice near its maximum northern extent must have originated from their local accumulation centers and their δ18O records likely preserve details about paleo-ice elevation that can be extracted using the δ18O-elevation relation
On Barnes Ice Cap, late Pleistocene-age LIS ice is exposed along the western margin in a distinctive bubble-rich white band that spreads over 200 m22
Summary
The maximum and recessional limits of the LIS have been defined using empirical data[1]; whereas its surface geometry and elevation have been assessed from glaciological and geophysical models using a range of boundary conditions, such as past positions of its margins, ice rheology, presence of deformable beds and glacio-isostatic adjustments[2,3,4,5,6]. This approach was used to reconstruct Holocene changes in ice surface elevation for the Greenland Ice Sheet and Agassiz Ice Cap[16,17], with the findings used to infer an increased contribution from Greenland Ice Sheet to sea level change[17] For the former North American late Wisconsinan ice sheets, this approach is challenged by the fact that the ice had largely disappeared from the landscape by 3–4 ka BP; remnants of late Wisconsinan LIS ice are still found in Penny and Barnes ice[18,19] (Baffin Island, Canada; Fig. 1). Our findings are compared to the various modeled LIS configurations during the late Wisconsinan, including Fisher-1985, Tarasov-2012, ICE5G, ICE6G, NAICE and an alternative version of the Fisher-1985 LIS elevation model[2]
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