Undersea anchors of ice that help prevent Antarctica’s land ice from slipping into the ocean are shrinking at more than twice the rate compared with 50 years ago, research shows.

More than a third of these frozen moorings, known as pinning points, have decreased in size since the turn of the century, experts say.

Further deterioration of pinning points, which hold in place the floating ice sheets that fortify Antarctica’s land ice, would accelerate the continent’s contribution to rising sea levels, scientists warn.

Floating ice sheets fringe 75 percent of Antarctica’s coastline and cover an area equivalent to the size of Greenland.

The findings are part of the first ever study of changes in the thickness of Antarctic ice shelves—extensions of land ice that float on the ocean—stretching back to 1973. Previous observations only date from 1992.

Researchers from the University of Edinburgh used satellite imagery from the NASA/United States Geographical Survey (USGS) Landsat program’s fifty-year-old archive to track variations in the appearances pinning points on the ice’s surface.

Pinning points form when part of a floating ice sheet anchors itself to an elevation on the ocean floor, creating a visible bump on the otherwise smooth ice shelf surface.

Using changes in pinning points as a reliable proxy for variations in the thickness of ice shelves, the team measured changes in these features during three periods: from 1973 to 1989, 1990 to 2000 and from 2000 to 2022.

The scientists found that only 15 percent of pinning points reduced in size from 1973 to 1989, leading to small, localized pockets of thinning ice shelves.

However, a widespread acceleration and un-anchoring of ice shelves from pinning points began in the 1990s in the western Antarctic Peninsula and the Amundsen Sea.

The number of pinning points that shrank increased to 25 percent from 1990 to 2000 and 37 percent from 2000 to 2022.

The paper, published in Nature, was funded by the Leverhulme Trust.