Un-pinning of Antarctic ice shelves over the past 5 decades

Pinning points form when floating ice shelves locally reground on bathymetric highs. The anchoring of ice shelves onto these pinning points buttresses ice flow from the interior of the ice sheet, meaning they play a vital role in the mass balance of the ice sheet. However, we do not know how the hundreds of pinning points that fringe the Antarctic coastline have changed over recent decades. By utilizing the historic Landsat satellite image archive, we show that there has been an acceleration in pinning point loss over the past 5 decades, and in doing so help resolve the timeline of the onset of widespread ice shelf thinning in Antarctica. Between 1974 and 1990, only ice shelves in isolated regions were thinning and unanchoring from their pinning points, with 11% of all mapped pinning points reducing in size. Pinning point loss spreads from these isolated regions in the 1990s, with the proportion of pinning points reducing in size across the ice sheet more than doubles to 23%, before further increasing to 35% between 2000 and 2022. Pinning point loss is concentrated along the western Antarctic Peninsula, West Antarctic and Wilkes Land coastlines, but we do also observe the rapid growth and break-up of some large ice rises outside of these regions. Continued acceleration in pinning point loss will reduce the buttressing potential of ice shelves and ultimately result in enhanced discharge of ice into the Southern Ocean and contribute to sea level rise.