Thwaites and Pine Island Glaciers Rapid Melting Could Cause Four Foot Global Sea Level Rise

Caroline Weiss

Known as “Doomsday” and “West Antarctica's weak underbelly,” Thwaites Glacier is one of the most rapidly flowing and changing glaciers in Antarctica. The glacier is massive, covering an area larger than Pennsylvania; its 75-mile ice front faces the ocean without any mountains or rocks to prevent chunks of ice from entering the ocean (Figure 1). Another problematic feature of the glacier is its unstable structure. Thwaites becomes thicker and deeper closer to its core and its bed, which slopes inland, and is quickly retreating. Thwaites Glacier is one of the most significant origins of ice mass loss in the Antarctic. Its calving process, or formation of icebergs that are discharged into the ocean, is considered unpredictable. Over the past ten years, the western end of Thwaites has evolved to calve straight into the ocean within a few kilometers of its grounding zone, or the region where the ice sheet shifts into an independently floating ice shelf.

Figure 1: Thwaites Glacier’s location relative to the Amundsen Sea

Besides its structure, a widely accepted theory explains why Thwaites is losing so much ice: warmer ocean water beneath Antarctica’s colder surface layer has started to come in contact with the bottom of the glacier calving front. This encroachment of the warm and salty Circumpolar Deep Water (CDW) into Pine Island Bay through submarine glaciated valleys has catalyzed the ice shelf thinning by pulling warm water toward Thwaites (Figure 2). Since most of the glacier is below sea level, the glacier’s thickness increases further inland and more ice is exposed as the glacier recedes (Figure 3). Climate change is implicated in Thwaites’ instability crisis, as it is culpable for the changing wind patterns around Antarctica that are linked to altered atmospheric circulation and warming tropics. Shifting winds are drawing the warm offshore CDW ocean current toward the shore, where it can melt the ice. 

Figure 2: Thwaites Glacier’s melting process

Figure 3: Most of Thwaites Glacier is lower than sea level

A team of scientists from the UK and US, the International Thwaites Glacier Collaboration, is researching why the glacier is changing at such a fast pace. Their work is particularly significant because the glacier is very remote; its location is over 1,000 miles from the closest research station and only four people have been on the glacier’s front before this year (Figure 4). By drilling with hot water drills through approximately 2,000 feet of ice, the scientists measured water temperatures where the glacier initially meets the ocean; the water is zero degrees Celsius, which is over two degrees warmer than the region’s normal freezing point. They also discovered turbulent water in the region around Thwaites, which indicates the mixing of salt and freshwater as the ice melts. Researchers worry that the current melting may cause an eventual return to an open ocean environment. 

Figure 4: The International Thwaites Glacier Collaboration Camp on Thwaites Glacier

Recently, a huge hole (around six miles long and 1,000 feet deep) in the glacier was observed, implying that Thwaites is melting more rapidly than scientists had predicted. So far, an estimated 14 billion tons of ice has melted. If the enormous Thwaites Ridge melted entirely, sea levels would increase by over two feet, enough to flood and overwhelm coastal cities worldwide. Considering that the amount of ice melting off Thwaites and neighboring glaciers has almost doubled in the past three decades—accounting for four percent of sea-level rise globally—the recent discovery of this hole and warm water along the Thwaites grounding zone convey dire warnings regarding future sea-level rise.

Over the weekend of February 8-9, 2020, a significant calving event was observed by the European Space Agency’s Sentinel satellites on Thwaites’ neighbor Pine Island Glacier. A 120-mile ice chunk—approximately the size of three San Franciscos—broke off the glacier’s front and splintered into several smaller icebergs, one of which was huge enough to receive its own name, B-49. Pine Island Glacier’s unstable state is evidenced by the diminishing time between calving events; prior events this century happened in 2001, 2007, 2013, 2015, 2017, and 2018. Between Thwaites and Pine Island, the amount of ice lost from Antarctica’s ice shelves is rapid and indicates a serious future threat. Both are susceptible to the encroachment of warm sea level because the “grounding line,” where the glaciers meet bedrock, lies below sea level. These two glaciers form the gateway to a large supply of frozen water on land that if released into the sea would cause global sea levels to rise by an estimated four feet. Although Pine Island Glacier appears to have stabilized for now, the threat of an increasingly unstable ice shelf yielding larger and larger icebergs (marine cliff instability) may cause dangerously fast losses of ice in West Antarctica.

Posted: March 4, 2020

Works Cited

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Winberry, J. P., Huerta, A. D., Anandakrishnan, S., Aster, R. C., Nyblade, A. A., & Wiens, D. A. ( 2020). Glacial Earthquakes and Precursory Seismicity Associated with Thwaites Glacier Calving. Geophysical Research Letters, 47, e2019GL086178. https://doi.org/10.1029/2019GL086178