環境：かつて急速な氷床後退があったことを示す証拠

The Eurasian Ice Sheet may have retreated by up to about 600 m per day across the Norwegian continental shelf during the last deglaciation, a Nature paper reports. The findings suggest that ice-sheet retreat rates in this region may have far exceeded previous estimates and highlight the vulnerability of flat-bedded areas of ice sheets to pulses of rapid retreat.

Many coastal regions of the Greenland and Antarctic ice sheets have retreated over recent decades, contributing to about 0.7 mm annually to global sea-level rise since the 1990s. Using ship-born imagery, rates of ice sheet grounding-line (the point at which glaciers and ice shelves start to float) retreat can be quantified from the spacing of regular ridge formations, known as corrugation ridges, on deglaciated regions of the seafloor. However, the few existing examples of mapped corrugation ridges are restricted to small areas of the seafloor, which has limited our understanding of future rates of grounding-line retreat and sea-level rise.

To quantify rates of ice-sheet grounding-line retreat during the last deglaciation, Christine Batchelor and colleagues measured the spacing of over 7,600 corrugation ridges across about 30,000 km2 of deglaciated regions of the seafloor of the mid-Norwegian shelf. They found evidence of rapid grounding-line retreat, at rates ranging from 55 to 610 m per day across nearly flat ice-sheet beds during the last deglaciation. These values are up to an order of magnitude higher than previously reported rates of grounding-line retreat derived from satellite measurements or inferred from marine-geological records. The highest retreat rates were measured across the flattest areas of the former seabed, suggesting that near-instantaneous ice-sheet ungrounding and retreat can occur where the grounding line approaches full buoyancy.