Geometry and dynamics of an East Antarctic Ice Sheet outlet glacier, under past and present climates

Abstract

The behavior of East Antarctic Ice Sheet (EAIS) outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics, and also with regard to epoch-scale ice sheet stability during Plio-Pleistocene climate transitions. Here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate Ferrar Glacier, first under present-day environmental conditions, and subsequently under both colder and warmer climate regimes representing the Last Glacial Maximum (LGM) and mid-Pliocene peak warmth respectively. Using airborne radar profiles, InSAR-derived surface velocities, ice core and geological data for empirical constraint, we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics. Our model suggests that the glacier is largely cold-based under present conditions, flows predominantly by way of internal deformation, and cascades over bedrock ridges due to the combined action of changes in cross-sectional valley geometry, local steepening of the glacier surface, and the non-local effects of longitudinal coupling. Time-dependent (evolutionary) simulation of a lower-profile glacier under a colder, drier, LGM climate, predicts flow velocities lower than present with minimal bedrock erosion or basal till flux. Conversely, the warmer-than-present mid-Pliocene climate produces a more dynamic glacier that is warm-based and sliding along much of its bed. We propose that EAIS outlet glaciers, such as the Ferrar, respond dynamically along their length in response to changing environmental forcings, with most significant changes taking place in their lower reaches. Adjustment to perturbations in upper catchments is more muted. © 2011 by the American Geophysical Union.