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

D Ottesen,E K Dowdeswell,F D W Christie,J A Dowdeswell,C L Batchelor,A Montelli,J Evans

doi:10.1126/science.aaz3059

D Ottesen, E K Dowdeswell + Show 5 more

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https://doi.org/10.1126/science.aaz3059

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Abstract

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.

Highlights

The ice shelves fringing about 75% of the Antarctic Ice Sheet represent a highly sensitive interface between ice and ocean, with potential for rapid grounding-line retreat and associated mass loss from the parent ice sheet [1, 2]
We investigate, using an autonomous underwater vehicle (AUV) [10], the morphology and shallow stratigraphy of an ~9 km2 area of five grounding-zone wedges (GZWs) within a 40 by 10 km grounding-zone complex preserved after ice retreat beneath about 500 m of water on the continental shelf offshore of Larsen Inlet, eastern Antarctic Peninsula (Figs. 1, 2) [11]
‘rungs’, are more laterally extensive, as we observe over several kilometers on the Larsen shelf, and where they overprint mega-scale glacial lineations (MSGLs) on the surface of GZWs (Fig. 2a), they likely form through regular vertical motion of an ice-sheet 110 grounding line that leads to the squeezing up of deforming soft sediment as small ridges on each falling tide [18]

Summary

10 Abstract

A suite of grounding-line landforms on the Antarctic seafloor, imaged at unprecedented sub-meter 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. 15 ridges, 10 km/yr) are inferred during regional deglaciation of the Larsen shelf after the Last Glacial Maximum. If repeated today, such rapid mass loss to the 20 ocean would have clear implications for increasing the rate of global sea-level rise. One Sentence Summary: Submarine landform patterns suggest past Antarctic ice-sheet retreat rates much faster than modern satellite observations

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Findings

Materials and Methods