Antarctica: is a glacier collapse threatened? – Thwaites Glacier in West Antarctica shows signs of increasing instability –

Impending disintegration: One of the largest glaciers in West Antarctica is in acute danger and could lose an important “brake” in the next few years, according to researchers. Because the floating part of the Thwaites Glacier is criss-crossed by cracks and threatens to detach itself from its anchor in the form of an underwater mountain. When this happens, the ice can flow unchecked into the sea and much of the glacier collapses.

The Thwaites Glacier in West Antarctica is one of the largest ice streams in the region. Its glacier front is 120 meters wide and its area corresponds to that of the whole of Great Britain. Its ice volume is large enough to cause sea levels to rise 65 centimeters when it is completely defrosted. Because it also slows the flow of neighboring glaciers like a cork, its collapse could sweep away a large part of the West Antarctic ice.

The West Antarctic Thwaites Glacier flows into the Amundsen Sea. © Polargeo / public domain

For this reason, among other things, the Thwaites Glacier has been under intensive surveillance for a long time – and the observations so far have not bode well. Researchers had found that the glacier is increasingly being washed away by warmer seawater, which has melted huge caverns into the ice on its underside. In addition, the ice stream flows faster and faster towards the sea: “It has doubled its outflow speed in the last 30 years,” reports Ted Scambos from the University of Colorado.

Glacier loses its “brake”

Now there is more bad news, as scientists from the international Thwaites Glacier Collaboration (ITGC) report. According to this, there are several cracks in the eastern ice shelf of the ice flow – the floating part of the glacier tongue that was previously held by an underwater ridge. Now the ice shelf in the vicinity of this “anchor” threatens to break and could lose its last hold, warns the research team.

“You can think of it as a windshield that has a few cracks that are initially slow to spread,” explains glaciologist Erin Pettit of Oregon State University. “Then you drive the car over a hump and suddenly the whole thing breaks apart everywhere.” Should this happen to the Thwaites Glacier, its ice would flow into the sea three times faster than before – and could sweep away part of the surrounding glaciers.

The cracks in the eastern part of the ice stream increase in length by several kilometers each year and reach increasingly thinner, more fragile ice, the team reports. The tensions in the ice there have also increased measurably in recent years. This could lead to this part of the ice shelf collapsing within the next five years, Pettit reports.

Researchers from the Thwaites collaboration report on their findings.© AGU

Rugged baseline and warming tide pump

The situation at the baseline of the Thwaites Glacier looks similarly worrying – the area in the area in which the ice flow separates from the subsurface and begins to swim. A team led by Peter Washam from Cornell University has maneuvered a remote-controlled diving robot through an ice borehole into this zone of the glacier. The resulting images show that the underside of the glacier has already been severely attacked there: the ice has been severely fissured and melted by the warm seawater.

Further measurements revealed the reason for this: the seawater flowing to the underside of the glacier is unusually warm and salty by polar standards. This further accelerates the defrosting of the underside of the ice. This effect does not stop at the baseline of the glacier, as another team led by Lizzy Clyne from Lewis and Clark College has found. They had investigated the effect of the tides on the subglacial water currents.

The result: because the entire tongue of the glacier rises and falls slightly due to the ebb and flow of tides, this acts like a gigantic pump on the underside of the glacier. Each uplift of the ice stream detaches its underside from the baseline and creates a suction that transports warm water for kilometers upstream. As a result, the Thwaites Glacier is also melted from below in the part that is not yet floating.

View of the edge of the ice shelf belonging to the Thwaites Glacier. © NASA Icebridge

A higher ice front could trigger a chain reaction

And something else endangers the stability of the Thwaites Glacier: As with many ice flows in West Antarctica, the subsoil in the last part of its bed does not slope towards the sea, but rather sinks towards the interior. As a result, the ice thickness increases sharply inland from the baseline. As the glacier front retreats further and further, the break-off edge of the ice becomes higher and higher.

As a result, however, the edge of the ice and thus the glacier front is becoming more and more unstable, as Anna Crawford from the University of St Andrews in Scotland and her colleagues have determined with the help of models. These show that when the glacier loses the ice shelf in front of it and the glacier front becomes higher and higher, the forces of the ice flowing in more and more act on the ice cliff and cause it to break off more and more frequently. In extreme cases, this can lead to a chain reaction that causes the ice flow to collapse faster and faster, as Crawford reports.

“If that happens and the Thwaites Glacier collapses, it would take most of the West Antarctic ice with it,” says Scambos. That could raise the sea level by up to 2.40 meters. It is all the more important to continue to monitor and research the behavior of this glacier very closely. (American Geophysical Union (AGU) Fall Meeting 2021)

Those: CIRES / University of Colorado

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