Ice melt barriers disappearing by the double

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.

Pine Island Glacier 1973
1973 satellite image of Antarctica's Pine Island Glacier ice shelf showing several visible bumps on the ice surface.

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.

First study

Floating ice sheets fringe 75 per cent 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.

2001 image
Pine Island Glacier's ice shelf in 2001. Pinning points are mostly smooth indicating that the floating ice has lost contact with high points on the seafloor.

NASA imagery

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.

Ice shelves

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 per cent of pinning points reduced in size from 1973 to 1989, leading to small localised pockets of thinning ice shelves.

Pine Island Glacier’s ice shelf in 2024. The thinning shelf has lost ice along its front and northern margin and fractured ice is visible along the southern edge.

Widespread unanchoring

However, a widespread acceleration and unanchoring 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 per cent from 1990 to 2000 and 37 per cent from 2000 to 2022.

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

The switch over the past 50 years from relatively limited and regionally concentrated ice shelf melt, to much more widespread unanchoring, is striking. The ongoing concern is how many more of these vitally important pinning points will begin to melt away in the coming 50 years.

Dr Bertie MilesLead author, Leverhulme Early Career Fellow, School of GeoSciences, University of Edinburgh.

What we are seeing around Antarctica is a sustained attack by climate warming to the buttresses, that slow the conversion of ice melting, into global sea-level rise. This reinforces the need for us to take action where we can to reduce global carbon emissions.

Professor Robert BinghamCo-lead author,  Professor of Glaciology and Geophysics, School of GeoSciences, University of Edinburgh.

Related links

School of GeoSciences   

NASA Earth Observatory     

Journal paper    

Image credit: NASA Earth Observatory images by Wanmei Liang, using using Landsat data from the United States Geological Survey and pinning point data from Miles, B. and Bingham, R. (2024).