Abstract
AbstractThe Weddell Sea sector of the Antarctic Ice Sheet is hypothesized to have made a significant contribution to sea‐level rise since the Last Glacial Maximum. Using a numerical flowline model we investigate the controls on grounding line motion across the eastern Weddell Sea and compare our results with field data relating to past ice extent. Specifically, we investigate the influence of changes in ice temperature, accumulation, sea level, ice shelf basal melt, and ice shelf buttressing on the dynamics of the Foundation Ice Stream. We find that ice shelf basal melt plays an important role in controlling grounding line advance, while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat. There are two stable positions for the grounding line under glacial conditions: at the northern margin of Berkner Island and at the continental shelf break. Global mean sea‐level contributions associated with these two scenarios are ~50 mm and ~130 mm, respectively. Comparing model results with field evidence from the Pensacola Mountains and the Shackleton Range, we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle. However, we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re‐advanced. Better constraints on past ice sheet and ice shelf geometry, ocean temperature, and ocean circulation are needed to reconstruct more robustly past behavior of the Foundation Ice Stream.
Highlights
The extent to which grounded ice of the West Antarctic Ice Sheet expanded into the Weddell Sea during the last glacial cycle is one of the most poorly constrained aspects of recent Antarctic history [e.g., Bentley et al, 2014; Hillenbrand et al, 2014]
We seek to answer two key questions: (i) what controlling factors is the advance and retreat of the Foundation Ice Stream (FIS) sensitive to? and (ii) what advance/retreat evolution is compatible with the evidence for ice thickness change recorded in the Pensacola Mountains and the Shackleton Range, and the past ice extent change inferred from the marine record? We investigate both of these questions in the context of the changes that could have occurred during the last glacial cycle, we emphasize that our primary aim is to constrain the past configuration of the ice stream rather than reconstruct the precise timing of change
While we can rule out a scenario in which grounded ice extended to the continental shelf break for a prolonged period, it is not possible to determine the duration that the grounding line may have been located adjacent to Berkner Island for two reasons. (i) Our model suggests that it is possible for ice thickening in the Pensacola Mountains to keep pace with grounding line advance, and it is not necessary for the grounding line to stabilize for a given period of time before maximum thicknesses are transiently reached. (ii) ice thicknesses do not further increase once the grounding line stabilizes, and we cannot determine a maximum duration for this ice stream configuration
Summary
The extent to which grounded ice of the West Antarctic Ice Sheet expanded into the Weddell Sea during the last glacial cycle is one of the most poorly constrained aspects of recent Antarctic history [e.g., Bentley et al, 2014; Hillenbrand et al, 2014]. There remain unanswered questions regarding both the magnitude and timing of grounding line advance and retreat [Anderson et al, 2002], and the contribution of this sector to global sealevel rise since the Last Glacial Maximum (LGM) [Bentley, 1999] This latter factor depends on both the extent and the thickness of the LGM ice sheet. If the LGM grounding line in the Weddell Sea reached the continental shelf break this would have increased the area of grounded West Antarctic ice by ~45% compared with today If this expanded ice sheet were relatively thin and close to flotation, the net effect on global mean sea level would have been minimal. It is important to understand the past thickness and dynamics of this portion of the ice sheet
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