Worsening rifts and fractures spotted at 2 important Antarctic glaciers

The evolution of damage to the Pine Island (boxes P1 and P2) and Thwaites (T1) glaciers from October 2014 to July 2020, as seen by the Copernicus Sentinel-1 mission. The ice sheets of both glaciers can be seen fracturing and tearing apart.

Satellite imagery has revealed fracturing and weakening of two of the fastest-changing glaciers on the Antarctic continent, the Pine Island and Thwaites glaciers.

According to a new study, published October 6, 2020 in the peer-reviewed Proceedings of the National Academy of Sciences, the two glaciers are disintegrating faster than ever, and are responsible for a substantial 5% of global sea level rise.

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Together, the two glaciers, in an area of Antarctica called the Amundsen Sea Embayment, form an area of flowing ice the size of Norway, and hold enough water to raise global sea levels by over a meter (more than three feet). In recent decades, both of the glaciers have distinctly changed in form along with changing atmospheric and oceanic conditions, with the warming oceans causing ice shelves to melt, thin, and retreat.

Map of section of Antarctica with glacier locations labeled.
Image via Wikipedia

Using imaging data from several different satellites for from 1997-2016, the researchers looked at how the glacier and ice shelf elevation had changed over this time, and changes in the speed of moving ice. They found structural damage at what’s called the ‘shear margins’ of the glaciers’ ice shelves, where the ice transitions from fast-moving to slow-moving: large crevasses, rifts and open fractures that indicate that the ice shelves are slowly tearing apart. Stef Lhermitte of Delft University of Technology in the Netherlands is lead author of the new study. He said in a statement:

Currently, the ice shelves are a little like a slow car in traffic: they force anything behind them to slow down. Once they’re removed, ice sitting further inland will be able to speed up, which in turn will cause sea levels to rise even faster.

Animation of a transverse crack appearing in a large ice sheet.
Rift evolution across the ice tongue – a long, narrow ice sheet extending seaward – of Antarctica’s Pine Island glacier (PIG) in September and October of 2018, as seen by the Copernicus Sentinel-1 mission. The video shows the emergence of an ice sheet rift in a region that was previously stable. Image via ESA.

The team modeled the potential impact of the damaged shear margins. Study co-author Thomas Nagler of ENVEO in Austria, said:

This fracturing appears to kick off a feedback process – it preconditions the ice shelves to disintegrate. As the glaciers fracture at their weak points this damage speeds up, spreads, and weakens more of the ice shelves, causing further deterioration – and making it more likely that the shelves will start crumbling apart even faster.

View of a glacier from the sea, with an icy mountain in the background.
Image via ESA.

As the ice shelves become increasingly damaged, the glaciers lose mass, and their ‘grounding lines’ – the region where ice sheets become buoyant enough to detach from the seafloor and float – retreat. Overall, the researchers said, damage feedback processes appear to be a key factor in the future stability of Antarctica’s ice shelves, and, in turn, in how fast the continent’s glaciers melt and cause global sea levels to rise. Mark Drinkwater is ESA’s Mission Scientist for CryoSat, and senior advisor on polar and cryosphere science. He said:

We know that a significant amount of glacial ice in West Antarctica is currently being affected by climate change. In fact, a recent study found 24% of this ice to be rapidly thinning and unstable. These new results underline just how quickly this damage is occurring, and reveal that Pine Island and Thwaites glaciers are more vulnerable than ever before.

Bottom line: A video shows the evolution of damage to Antarctica’s Pine Island and Thwaites glaciers from October 2014 to July 2020. The video, made using satellite images, shows the ice sheets of both glaciers fracturing and tearing apart.

Source: Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment


October 14, 2020

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