Sea ice that slowed the flow of Antarctic glaciers abruptly shatters in three days

The Larsen Ice Shelf is situated along the northeast part of the Antarctic Peninsula, in the Weddell Sea. It is divided into four regions that occupy distinct embayments along the coastline, termed Larsen A, B, C and D running north to south, each of which has undergone its own changes in the last few decades. The great mass of the ice shelf holds back the flow of many glaciers from the steep mountains towards the sea, where they contribute to rise. Larsen-A was the first to disintegrate in 1995, followed by the abrupt partial collapse of Larsen-B in 2002. Larsen-C was the fourth largest Antarctic ice shelf as of July 2017, when a giant iceberg, named A68, calved from it, drawing worldwide attention to the region. Being furthest south, and hence least subject to warming, the only portion to be considered relatively stable is Larsen-D.

The loss of 3,250 square kilometers of ice from the Larsen B ice shelf in 2002 has been blamed on warmer ocean waters that melted it from below, and on the presence of meltwater on its surface, which also accelerated the loss of ice. With only a remnant portion left behind following the collapse, this section was much less stable and vulnerable to further disintegration. It grew thinner, which allowed glaciers on the landward side to flow faster. Sea ice formed in the newly opened area each winter, but it was not until 2011 that the sea ice remained year round, and did not melt the following spring. Between 2011 and 2022, the glaciers were somewhat stabilized because the remnant ice-shelf and sea ice that was permanent and attached, fast to the land, blocking their path into the ocean. But this large expanse shattered within three days in January, captured by NASA's Terra and Aqua satellites.

Remnants of the Larsen-B ice shelf, filled in with seasonal ice in January 2016. Until January 2022, sea ice helped to buttress the nearby glaciers, slowing their flow into the sea. Credit: O.V.E.R.V.I.E.W.

Satellite image of the Larsen-B ice shelf collapsing in 2002. Credit Oregon State University/Flickr

The path of the A68 iceberg between July 2017 and March 2021. As it drifted in the vicinity of the South Georgia islands, it is estimated to have dumped 152 billion tonnes of fresh water and nutrients into the surrounding ocean. (As seen in Figure 1). Credit: Laura Gerrish