Net retreat of Antarctic glacier grounding lines
Grounding lines are a key indicator of ice-sheet instability, because changes in their position reflect imbalance with the surround-ing ocean and affect the flow of inland ice. Although the grounding lines of several Antarctic glaciers have retreated rapidly due to ocean-driven melting, records are too scarce to assess the scale of the imbalance. Here, we combine satellite altimeter obser-vations of ice-elevation change and measurements of ice geometry to track grounding-line movement around the entire conti-nent, tripling the coverage of previous surveys. Between 2010 and 2016, 22%, 3% and 10% of surveyed grounding lines in West Antarctica, East Antarctica and at the Antarctic Peninsula retreated at rates faster than 25 m yr−1 (the typical pace since the Last Glacial Maximum) and the continent has lost 1,463 km2 ± 791 km2 of grounded-ice area. Although by far the fastest rates of retreat occurred in the Amundsen Sea sector, we show that the Pine Island Glacier grounding line has stabilized, probably as a conse-quence of abated ocean forcing. On average, Antarctica’s fast-flowing ice streams retreat by 110 metres per metre of ice thinning.