Abstract
Abstract. The Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Increases in the glacier velocity and dynamic thinning have been observed over the past two decades, especially after 2008 when only a small ice shelf remained at the Fleming Glacier front. It is important to know whether the substantial further speed-up and greater surface draw-down of the glacier since 2008 is a direct response to ocean forcing, or driven by feedbacks within the grounded marine-based glacier system, or both. Recent observational studies have suggested the 2008–2015 velocity change was due to the ungrounding of the Fleming Glacier front. To explore the mechanisms underlying the recent changes, we use a full-Stokes ice sheet model to simulate the basal shear stress distribution of the Fleming system in 2008 and 2015. This study is part of the first high resolution modelling campaign of this system. Comparison of inversions for basal shear stresses for 2008 and 2015 suggests the migration of the grounding line ∼9 km upstream by 2015 from the 2008 ice front/grounding line positions, which virtually coincided with the 1996 grounding line position. This migration is consistent with the change in floating area deduced from the calculated height above buoyancy in 2015. The retrograde submarine bed underneath the lowest part of the Fleming Glacier may have promoted retreat of the grounding line. Grounding line retreat may also be enhanced by a feedback mechanism upstream of the grounding line by which increased basal lubrication due to increasing frictional heating enhances sliding and thinning. Improved knowledge of bed topography near the grounding line and further transient simulations with oceanic forcing are required to accurately predict the future movement of the Fleming Glacier system grounding line and better understand its ice dynamics and future contribution to sea level.
Highlights
In the past few decades, glaciers in West Antarctica and the Antarctic Peninsula (AP) have experienced rapid regional atmospheric and oceanic warming, leading to significant retreat and disintegration of ice shelves and rapid acceleration of mass discharge and dynamic thinning of their feeding glaciers (Cook et al, 2016; Gardner et al, 2018; Wouters et al, 2015)
We obtain the spatial distributions for basal shear stress, τb (Fig. 3a and b), and basal velocity of the Wordie Ice Shelf (WIS)–Fleming Glacier (FG) system for 2008 and 2015 using an inverse method to determine the basal friction coefficient, C, with the geometry and velocity data described above
Low-resolution estimation of basal shear stress has been carried out for the whole Antarctic Ice Sheet (Fürst et al, 2015; Morlighem et al, 2013; Sergienko et al, 2014), this is the first application of inverse methods to estimate the basal friction pattern of the Fleming system at a high resolution and to use the full-Stokes equations
Summary
In the past few decades, glaciers in West Antarctica and the Antarctic Peninsula (AP) have experienced rapid regional atmospheric and oceanic warming, leading to significant retreat and disintegration of ice shelves and rapid acceleration of mass discharge and dynamic thinning of their feeding glaciers (Cook et al, 2016; Gardner et al, 2018; Wouters et al, 2015). Mercer, 1978; Thomas and Bentley, 1978; Weertman, 1974) This marine ice sheet instability has been invoked to explain the recent widespread and rapid grounding line retreat of glaciers in the Amundsen Sea sector, likely triggered by increased basal melting reducing the buttressing influence of ice shelves (Rignot et al, 2014). Rapid grounding line retreat and accelerated flow in these unstable systems leads to significant increases in ice discharge and increased contribution from these marine ice sheets to sea-level rise
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