Is breaking up hard to do? Clues from the sea bed

Karsten.Gohl [ at ]


Iceberg calving accounts for between one third and a half of the mass loss from Thwaites Glacier and Pine Island Glacier ice shelves. If increased calving results in ice-shelf retreat or break up, the loss of buttressing can be expected to lead to further flow acceleration and dynamic thinning of the glaciers. It has been suggested that if ice-shelf breakup exposes a floating terminus exceeding a critical thickness of ~1000 m, this will be structurally unstable and rapid retreat through Marine Ice Cliff Instability (MICI) could be initiated. Despite their importance, the factors controlling calving remain poorly understood. Two recent studies show how sea-bed topography can influence calving. Prior to 2015, despite rapid thinning for more than 20 years, the position from which large tabular icebergs calved from Pine Island Glacier had varied little since its ice shelf was first observed in 1947. In August 2015 calving occurred at a position ~15 km further upstream than on any previous occasion and the new calving front had a different orientation from previous ones. The area that the ice shelf retreated from at this time encompassed a former pinning point. Multibeam bathymetry data were collected over this area on RV Polarstern expedition PS104 in 2017. Consideration of a series of satellite images from 2002 to 2017 in the context of the detailed new bathymetry data suggests that calving events in 2007 and 2013 were triggered by interactions between the ice shelf and bathymetric highs (Arndt et al., 2018). Further offshore, an unusual episode of calving during the last deglaciation of the continental shelf is recorded by iceberg-keel plough marks in Pine Island Trough that are identified in multibeam bathymetry data collected on icebreaker Oden expedition OSO0910 in 2010. The relatively small size (width <450 m) and great depth (up to 848 m) of these plough marks, together with the fact that they formed during a short period of rapid retreat constrained by radiocarbon dates on foraminifera from sediment cores, were interpreted by Wise et al. (2017) as evidence of an episode of MICI during retreat of a merged Pine Island and Thwaites ice steam into Pine Island Bay.

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Conference (Talk)
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25th Annual WAIS Workshop, 16 Sep 2018 - 19 Sep 2018, Stony Point, NY, USA.
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Larter, R. D. , Arndt, J. E. , Wise, M. G. , Friedl, P. , Höppner, K. , Jakobsson, M. , Dowdeswell, J. A. and Gohl, K. (2018): Is breaking up hard to do? Clues from the sea bed , 25th Annual WAIS Workshop, Stony Point, NY, USA, 16 September 2018 - 19 September 2018 .

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