Ice thickness and isostatic imbalances in the Ross Embayment, West Antarctica: model results

Abstract

Thermomechanical flowline simulations indicate that the Siple Coast ice streams of West Antarctica have experienced only small deglacial thickness changes, are thinning more rapidly than their beds are rising isostatically, and can continue to retreat. Thickness changes of O (100)m are modelled at the modern grounding line through the last glacial cycle. The accumulation-rate increase accompanying warming out of the last glacial maximum (LGM) leads to a maximum simulated thickness change at the modern grounding line approximately 8 ka. Idealized isostatic simulations support coupling the ice-sheet model to an underlying elastic-lithosphere and relaxed-asthenosphere bedrock model. Dynamic interactions between ice and bedrock over the last glacial cycle indicate that isostatic rebound is raising the ice sheet at the modern grounding line faster than the rising sea level is submerging it. While, in and of itself, this could potentially lead to a grounding-line re-advance, ice flow is modelled to respond to recent changes in temperature, accumulation rate, and basal processes more rapidly than it does to bedrock-elevation and/or sea-level fluctuations. Previous results based on thermal controls on ice-stream behavior [Parizek et al., 2002: Geophysical Research Letters 29 (2002); Parizek et al., 2003: Annals of Glaciology 36 (2003) 251] support the view that thinning of the ice streams at the retreating grounding line will likely continue. While results indicate an additional few tens of meters of rebound remaining, land- and air-based observations will help constrain this magnitude with potential implications for uncovering past ice-loading history and future ice-sheet stability.