Fast-moving Antarctic ice loss redefines ‘glacial pace’

When we think of glacial motion, we probably imagine movement so slow as to seem perfectly still. But glaciers are constantly on the move, flowing like vast frozen rivers under the weight of immense amounts of ice. Glaciers normally move with seasons as well, seeming to advance during wintertime snow accumulation and to retreat when warmer summertime temperatures accelerate ablation, or loss of ice.

And ablation has been picking up speed at Thwaites Glacier in Antarctica. The amount of ice flowing from Thwaites has doubled in the last thirty years, while precipitation in its accumulation zone hasn’t been sufficient for the glacier to advance in the winter; its meltwater already contributes approximately 4% of the rising global sea level each year. While this Antarctic behemoth is still one of the fastest-flowing glaciers out there, glaciologists are concerned that the loss of ice we now see at Thwaites may become the new normal.

Thwaites Glacier is located in Marie Byrd Land, a region of Antarctica that lies within the Western Hemisphere. Roughly equivalent in square kilometers to the area of Florida or Great Britain, Thwaites Glacier starts deep within the West Antarctic Ice Sheet and flows into the Amundsen Sea, south of the Pacific Ocean. The satellite image below depicts the massive glacier in 2001; the area labelled “ice tongue” is a thick sheet of ice floating out over the Amundsen Sea. 

Landsat data from the US Geological Survey. December 2, 2001.

In 2002, not long after this satellite photo was taken, the rift bordering the ice tongue widened, and the glacier calved an iceberg designated B-22. By the end of 2019, a satellite photo of the same region showed substantial loss of ice: in place of the glacial tongue, a melange of icebergs (most too small to be named) and sea ice floats in the Amundsen Sea. 

Landsat data from the US Geological Survey. December 28, 2019. 

Why is this happening? It’s a two-sided dilemma. From above, warm air temperatures contribute to the fracturing ice tongue: as surface ice melts, the resulting pools of water can form crevasses as it drains through the ice. From below, currents of warm seawater flow under the floating tongue and accelerate its melting. The Thwaites Explorer, an interactive tool designed by the International Thwaites Glacier Collaboration, compiled data from the World Ocean Atlas to show ocean temperatures at a depth of 550 meters. The temperatures in the Amundsen Sea, near Thwaites Glacier (outlined in black for this image), are higher than anywhere else along the western Antarctic coast. 

Image data drawn from the World Ocean Atlas, 2018. 

The researchers and experts of the International Thwaites Glacier Collaboration, founded in 2019, hope to find out why Thwaites and its neighboring glaciers flow so fast–and to measure the interactions between ocean, ice, and bedrock in this rapidly changing region to better understand how this glacier and others may evolve.

Sources

Hansen, Kathryn. “Thwaites Glacier Transformed.” NASA Earth Observatory. February 6, 2020.

Laura Naranjo and Agnieszka Gautier. “The International Thwaites Glacier Collaboration.” NSIDC Highlights. The National Snow and Ice Data Center. January 28, 2019.

Thwaites Explorer online interactive tool. International Thwaites Glacier Collaboration. Image data drawn from the World Ocean Atlas, 2018. 

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