Rapid, buoyancy-driven ice-sheet retreat of hundreds of metres per day.

Rates of ice-sheet grounding-line retreat can be quantified from the spacing of corrugation ridges on deglaciated regions of the seafloor 1,2 , providing a long-term context for the approximately 50-year satellite record of ice-sheet change 3-5 . However, the few existing examples of these landforms are restricted to small areas of the seafloor, limiting our understanding of future rates of grounding-line retreat and, hence, sea-level rise. Here we use bathymetric data to map more than 7,600 corrugation ridges across 30,000 km 2 of the mid-Norwegian shelf. The spacing of the ridges shows that pulses of rapid grounding-line retreat, at rates ranging from 55 to 610 m day -1 , occurred across low-gradient (±1°) ice-sheet beds during the last deglaciation. These values far exceed all previously reported rates of grounding-line retreat across the satellite 3,4,6,7 and marine-geological 1,2 records. The highest retreat rates were measured across the flattest areas of the former bed, suggesting that near-instantaneous ice-sheet ungrounding and retreat can occur where the grounding line approaches full buoyancy. Hydrostatic principles show that pulses of similarly rapid grounding-line retreat could occur across low-gradient Antarctic ice-sheet beds even under present-day climatic forcing. Ultimately, our results highlight the often-overlooked vulnerability of flat-bedded areas of ice sheets to pulses of extremely rapid, buoyancy-driven retreat.