“We might (and I stress might) have already reached and passed a point where there is really no turning back for Thwaites, no matter what we as humans do to our climate,” Alastair Graham, the University of South Florida and co-author of the study.

New data from under the ice stream at Thwaites glacier, commonly referred to as the doomsday glacier, in West Antarctica found the Florida-sized glacier is being assaulted by warm ocean water wherever it contacts the ice. Particularly alarming is that the phenomenon includes clear weakening of the glacier’s pinning points – where the ice meets the bedrock that provides stability for much of West Antarctica’s floating ice shelves. This is dire news for the world’s coastlines as ten feet of abrupt sea-level rise could happen sooner than anyone had dared to imagine.

The data research, published in Scientific Advances, was obtained by an uncrewed submarine. It identifies new pathways and modifications of warm ocean water under Thwaites.

Dharna Noor provides analysis in Earther:

What they found is pretty troubling. The authors explain that the supply of warm water to the glacier’s base is larger than scientists previously believed, which means it’s even more unstable than we thought. Given that it’s often called the “doomsday glacier,” that’s particularly ominous.

The new study is based on field observations from 2019 when a team of two dozen scientists sent an autonomous orange submarine named Ran down underneath Thwaites. For 13 hours, the underwater vehicle traveled around two deep troughs beneath the glacier that funnel warm water toward it. As it did, the vehicle captured data showing that warm water—warm for a glacier, at up to 33.89 degrees Fahrenheit (1.05 degrees Celsius)—is swirling around the glacier’s crucial “pinning points,” or the points of contact where the ice shelf meets the bedrock that holds it in place. This warm water is melting away these crucial holds, making room for cracks and troughs in ice that can make the shelf all the more unstable.

“The worry is that this water is coming into direct contact with the underside of the ice shelf at the point where the ice tongue and shallow seafloor meet,” Alastair Graham, associate professor of geological oceanography at the University of Southern Florida and study co-author, who was on the research expedition to the glacier, wrote in an email. “This is the last stronghold for Thwaites and once it unpins from the sea bed at its very front, there is nothing else for the ice shelf to hold onto. That warm water is also likely mixing in and around the grounding line, deep into the cavity, and that means the glacier is also being attacked at its feet where it is resting on solid rock.”

As the submarine moved around one of the troughs, it also captured data showing low-salinity water in the area 3,444 feet (1,050 meters) below the ice shelf. That salinity level it showed matches that of the neighboring Pine Island Bay. Scientists previously thought this part of the glacier was protected from the bay’s currents by a thick underwater ridge. But it seems they were wrong—the findings indicate it’s flowing into the trough freely. That closely links its fate to the bay more than climate models currently account for.

It’s not just Pine Island Bay’s encroaching warm waters we have to worry about, either. Using the submarine’s readings, the authors also mapped out the channels along which warm water is getting transported toward Thwaites Glacier. They found more warm water is also surging in from along the continental shelf.

Red arrows indicate main pathways of warm salty water, blue arrow indicates outflow of meltwater-laden fresher water, and red dashed arrow indicates possible warm salty inflow below the range of the ship-borne ADCP. Blue shading shows bathymetric troughs, and purple lines indicate grounding zones. The two arrows from Pine Island Trough indicate that it is not possible from the present dataset to identify which part of this region sources the deep water.
Red arrows indicate main pathways of warm salty water, blue arrow indicates an outflow of meltwater-laden fresher water, and red dashed arrow indicates possible warm salty inflow below the range of the ship-borne ADCP. Blue shading shows bathymetric troughs, and purple lines indicate grounding zones. The two arrows from Pine Island Trough indicate that it is not possible from the present dataset to identify which part of this region sources the deep water. MarloWordyBird

From the study:

Abstract

Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat.

Ran, the un-crewed submarine that the scientists used, heading down into the depths under the Thwaites Glacier
Ran, the un-crewed submarine.

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