Coevolution of continental ice cover and permafrost extent over the last glacial-interglacial cycle in North America

Abstract

The bed thermal characteristics of a glacial systems model that has been calibrated against a large set of relative sea level, geodetic, and strandline observations are examined for the previously glaciated sector of the North American continent. The model compares favorably against the present-day extent of permafrost and against the observed temperature profiles from three deep boreholes when appropriate bed thermal conductivities are employed. Estimates for the present-day depth field of the lower permafrost boundary are presented. We find a significant disequilibrium in the lower permafrost boundary for most of the Arctic region, with present-day depth as much as 250 in shallower than the equilibrium value for present-day climate forcing. This is largely due to the ongoing response to the loss of ice cover from the glacial period. The time evolution of the subglacial warm-based area fraction is also presented together with calibration-derived confidence intervals. A peak warm-based fraction of 50% ± 6% is obtained at Last Glacial Maximum. The timing of the three largest ice volume maxima that were produced in response to the obliquity component of orbital forcing during the last glacial cycle matches that of the maxima for the warm-based area fraction with no significant phase delay. Warm-based conditions are required to enable ice streaming (fast flow) in the model. It is therefore hypothesized that the expansion of the area covered by warm-based ice played a critical role in producing a highly dynamic ice sheet during both the most intense growth and recession phases. Copyright 2007 by the American Geophysical Union.