Abstract
Abstract. The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45 mm yr−1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.
Highlights
Projecting the evolution of the Antarctic Ice Sheet (AIS) into the few centuries relies on simulating a complex and non-linear coupled Earth system
It is this ice-sheet/solidEarth (IS/SE) interaction that we explore in this paper for the AIS as a whole, using the vertical surface motions of bedrock glacial isostatic adjustment (GIA) (Ivins and James, 1999) and the 3-D thermomechanical ice flow (Pattyn, 2003) capability of the Ice Sheet System Model (ISSM) (Larour et al, 2012b)
This implicitly assumes that the differential ice height (DIH) before the Last Glacial Maximum (LGM) have a minimal impact on the current and future response of the solid Earth. (We demonstrate in Sect. 3.2 that this is a valid assumption.) Note that the ice loading on the ISSM/GIA model is assumed to vary in a piece-wise linear fashion between the adjacent time stamps
Summary
Projecting the evolution of the Antarctic Ice Sheet (AIS) into the few centuries relies on simulating a complex and non-linear coupled Earth system. If sea depth decreases (due to bed uplift and sea level drop associated with the thinning of inland ice) at the initially stable GL on a reverse bed slope, for example, the GL tends to advance further on a relatively flat bed. The GIA uplift can be important in providing basal resistance to ice flow and buttressing the ice sheet by raising bedrock pinning points (e.g., Favier et al, 2012; Siegert et al, 2013) Due to the lateral motion of this topographic bulge, local crustal motions (and slopes) may change sign during GIA (e.g., Fjeldskaar, 1994) These mechanisms are extremely difficult to isolate and quantify, and it is not obvious whether (and under what circumstances) each of these acts to accelerate or inhibit the ice flow. As long as the thermomechanical ice sheet model and other companion models (e.g., surface mass balance model and the hydrological model) are dynamically coupled to a comprehensive solid Earth model, most of these feedbacks are intrinsically taken into account
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