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

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. The landforms are delicate sets of up to 90 ridges, <1.5 m high and spaced 20-25 m apart. We interpret these ridges as the product of squeezing up of soft sediment during the rise and fall of the ice-shelf grounding line during successive tidal cycles. Each ridge is preserved as the grounding line retreats. Grounding-line retreat rates of 40-50 m/day (>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 ocean would have clear implications for increasing the rate of global sea-level rise.