Reconstruction of the Morphology, Dynamics, and Thermal Characteristics of the Laurentide Ice Sheet at its Maximum

Abstract

On the assumption that the Laurentide ice sheet attained a steady-state maximum condition at some time during the Pleistocene, a reconstruction of its morphology, dynamics, and basal thermal regime was made largely by analogy with existing ice sheets. The maximum surface altitude was ca. 3400 m, maximum thickness ca. 4200 m, and total ice volume 37 × 10⁶ km³. Surface mean temperatures were below –40°C over a large central and northern part of the ice sheet, while accumulation decreased from 10 to 80 cm water equivalent near the periphery to 5 cm water equivalent near the center. Velocities increased from less than 10 m yr⁻¹ over much of the ice sheet center to 50 to 200 m yr⁻¹ near the periphery. Outlet glacier velocities were 300 to 800 m yr⁻¹. Basal shear stresses increased from <0.25 bars in the central areas to 1 bar near most peripheries. An exception was the high western plains area where surface gradients and basal shear stresses were low. Using a model developed by Budd et al. (1970), the basal temperatures of the ice sheet were calculated. From center to periphery there were basal zones of warm-melting, warm-freezing, cold-based ice, and finally warm-melting. Over the Queen Elizabeth Islands the ice was cold-based except over some straits. A sensitivity test suggests that the broad pattern was stable although the exact position of the zone boundaries is tentative. The basal temperature pattern has profound implications concerning processes of glacial erosion and deposition and the stability of the ice sheet.