Delicate seafloor landforms reveal past Antarctic grounding-line retreat of kilometers per year

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Science  29 May 2020:
Vol. 368, Issue 6494, pp. 1020-1024
DOI: 10.1126/science.aaz3059

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A rapid retreat

Are the rates at which we observe ice shelves shrinking today representative of how fast they shrank in the past? Dowdeswell et al. report observations of the Antarctic seafloor that reveal the presence of submarine grounding-zone wedges on the Larsen continental shelf (see the Perspective by Jakobsson). The authors interpret these ridges as being caused by the tidal rise and fall of the ice shelf at the grounding line, which squeezes the underlying sediments when it rests on the seafloor. From this, they calculated that ice shelf retreat at this location about 14,000 years ago was at times as much as 100 times as fast as the average over the past 10,000 years.

Science, this issue p. 1020; see also p. 939


A suite of grounding-line landforms on the Antarctic seafloor, imaged at submeter horizontal resolution from an autonomous underwater vehicle, enables calculation of ice sheet retreat rates from a complex of grounding-zone wedges on the Larsen continental shelf, western Weddell Sea. The landforms are delicate sets of up to 90 ridges, <1.5 meters high and spaced 20 to 25 meters apart. We interpret these ridges as the product of squeezing up of soft sediment during the rise and fall of the retreating ice sheet grounding line during successive tidal cycles. Grounding-line retreat rates of 40 to 50 meters per day (>10 kilometers per year) are inferred during regional deglaciation of the Larsen shelf. If repeated today, such rapid mass loss to the ocean would have clear implications for increasing the rate of global sea level rise.

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