First Antarctic-Wide Map of Grounded Icebergs Reveals 'Picket Fence Effect'

For the first time, scientists have produced a high-resolution, Antarctic-wide map of grounded icebergs — large icebergs that run aground on the seafloor and stay stationary for days to decades. They trained an AI tool to recognize the icebergs in satellite radar images. Grounded icebergs anchor sea ice, which holds back land ice from slipping into the ocean and provides habitat and nutrients for marine life.

The mapping was led by Kaihong Jiao during his master's project with the Australian Antarctic Program Partnership at the University of Tasmania. "Traditionally, iceberg monitoring has relied heavily on manual analysis of satellite imagery," Jiao said. The study, by researchers from the Institute for Marine and Antarctic Studies, the Australian Antarctic Division and Geoscience Australia, was published in the journal Earth System Science Data.

Using Sentinel-1 satellite radar images — synthetic aperture radar, or SAR, which images through cloud and darkness — the team mapped nearly 40,000 stationary icebergs in 2025: 39,619 grounded icebergs covering 13,430 square kilometers along 57% of the Antarctic coastline. Just 14% of the coastline holds 80% of all grounded icebergs. The method reduced the minimum detectable size to 1.6 hectares, showing tiny icebergs under 1 square kilometer — often overlooked — make up 93% of all grounded icebergs and 54% of the grounded area.

These dense clusters of small grounded icebergs in shallow waters drive what researchers call the "picket fence effect": like fence posts, they catch and hold landfast ice — stationary sea ice attached to the coast — stopping it from breaking away and protecting Antarctic ice shelves from the rough Southern Ocean.

The findings may point to a unique sensitivity of Antarctica's coastal system to climate change: tiny icebergs are more prone to melting and "ungrounding" from ocean warming than larger ones, which could trigger abrupt shifts in landfast ice stability. "Our public dataset offers a crucial new baseline for modeling coastal ice stability," Jiao said.