Featured Science Paper
Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance
Understanding the way the Earth’s ice sheets have waxed and waned in the past is an important part of our ability to predict their future behaviour and resulting impacts on the Earth System. Many ‘reconstructions’ of the shape of the West Antarctic Ice Sheet in the past assume a progressive retreat since the end of the last Ice Age, continuing up to its present day position, but in the Weddell Sea area this gives two problems. Firstly, the large glaciers draining the ice sheet seem to be more stable than would be expected, and secondly, the expected isostatic rebound from removing the weight of the ice does not agree with the actual measured values. This is a discrepancy that needs to be understood before realistic predictions of the ice sheet’s coming behaviour can be made and treated with confidence.
In a recent paper published in Earth and Planetary Science Letters, Bradley and co-authors use new modelling that initially has the ice retreating further back than the current position, followed by re-advancing ice continuing right up to the present day. A re-advance in the Weddell Sea region can help to explain the two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice streams grounded on beds that deepen inland; and (ii) the inability of models of glacial isostatic adjustment to match present-day uplift rates.
By combining a suite of ice loading histories that include a re-advance, with a model of glacial isostatic adjustment, the authors report substantial improvements to predictions of present-day uplift rates, including reconciling one problematic observation where the land is sinking. They suggest that retreat behind present grounding lines occurred when the bed was lower, and isostatic recovery has since led to shallowing, ice sheet re-grounding and re-advance. The paradoxical existence of grounding lines in apparently unstable configurations on reverse bed slopes can thus be resolved by a process of ‘unstable advance’, in accordance with their ice load modelling.
Link to the full paper in the NERC Open Research Archive
Authors
Sarah Bradley, Richard Hindmarsh, Pippa Whitehouse, Michael Bentley and Matt King
Publication
Earth and Planetary Science Letters, vol. 413 (2015) 79-89
