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Steep reverse bed slope at the grounding line of the Weddell Sea sector in West Antarctica


The bed of the West Antarctic Ice Sheet is, in places, more than 1.5 km below sea level1,2. It has been suggested that a positive ice-loss feedback may occur when an ice sheet’s grounding line retreats across a deepening bed1,2,3. Applied to the West Antarctic Ice Sheet, this process could potentially raise global sea level4 by more than 3 m. Hitherto, attention has focussed on changes at the Siple Coast5,6,7 and Amundsen Sea embayment8,9,10 sectors of West Antarctica. Here, we present radio-echo sounding information from the ice sheet’s third sector, the Weddell Sea embayment, that reveals a large subglacial basin immediately upstream of the grounding line. The reverse bed slope is steep, with about 400 m of decline over 40 km. The basin floor is smooth and flat, with little small-scale topography that would delay retreat, indicating that it has been covered with marine sediment5,11 and was previously deglaciated. Upstream of the basin, well-defined glacially carved fjords with bars at their mouths testify to the position of a former ice margin about 200 km inland from the present margin. Evidence so far suggests that the Weddell Sea sector of the West Antarctic Ice Sheet has been stable, but in the light of our data we propose that the region could be near a physical threshold of substantial change.

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Figure 1: Location, bed elevation, surface roughness and height above floatation of Institute and Möller ice streams.
Figure 2: Ice surface (black), bed elevations (red) and height above floatation (blue) over a distance of 100 km up ice flow of the grounding lines of six West Antarctic ice streams.


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Financial support was provided by the UK Natural Environment Research Council AFI grant NE/G013071/1. C. Robinson (airborne survey engineer), I. Potten and D. Cochrane (pilots) and M. Oostlander (air mechanic) are thanked for their invaluable assistance in the field. D.Y. and D.D.B. were supported by the National Science Foundation ANT-0636724 and the G. Unger Vetlesen Foundation. We thank K. Brunt and H. Fricker for discussions regarding ICESat data and for providing an in-press copy of their recent work.

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Authors and Affiliations



M.J.S. and N.R. wrote the paper. M.J.S., F.F., N.R., R.G.B., H.F.J.C., T.A.J., A.L.B. and D.M.R. planned the aerogeophysical survey. N.R. and T.A.J. collected the data. N.R., H.F.J.C. and T.A.J. processed the data. D.M.R. and R.G.B. led the basal roughness analysis of the Institute and Möller ice streams. D.Y. and D.D.B. produced bed roughness analyses for the Siple Coast and Thwaites Glacier. A.L.B. provided glaciological information on MISI. All authors commented on a draft of the paper. M.J.S. and N.R. provided the geomorphic interpretation. M.J.S. and F.F. led the project.

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Correspondence to Neil Ross or Martin J. Siegert.

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The authors declare no competing financial interests.

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Ross, N., Bingham, R., Corr, H. et al. Steep reverse bed slope at the grounding line of the Weddell Sea sector in West Antarctica. Nature Geosci 5, 393–396 (2012).

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