One of the largest glaciers in Antarctica, the Thwaites Glacier, is apparently increasingly losing its grip. Using current satellite measurements, scientists have discovered a network of many kilometers long cracks in its ice shelf – the ice that lies like a cork in the Southern Ocean in front of the mouth of the glacier and slows its flow into the ocean. Within the next three to five years, recently announced glaciologists at the annual meeting of the American Geophysical Union (AGU) in New Orleans, this part of the Thwaites Glacier threatens to splinter. This could mean losing an important barrier against rising sea levels around the world.
The gigantic ice mass of the Antarctic does not lie everywhere on the mainland of the continent. Almost all glaciers push themselves tens to hundreds of kilometers beyond the coastline into the open ocean. On its way from the mainland to the ocean, the glacier ice initially has contact with the sea floor. Only when it gets into deeper water does it float up and become an ice shelf.
This ice sheet lying on the water, often hundreds of meters thick, could run aground again, explains Angelika Humbert, glaciologist at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, in Bremerhaven (AWI). Wherever the ice has to overcome shallows, submarine rock islands or rock ridges, it is slowed down. “This has an effect all the way back to the part of the glacier that lies on the continent,” says the scientist. Ice shelf plates thus hold back the flow of ice from the mainland into the sea. If this stabilizing effect breaks away, there is an acceleration of the runoff and thus a rise in the global sea level.
It is the same with the Thwaites Glacier. The ice colossus, which is part of the West Antarctic ice sheet, has a total area of 192,000 square kilometers. A third of it, around 65,000 square kilometers, is ice shelf – an area twice the size of Belgium.
The “Doomsday Glacier” could accelerate sea level rise considerably
The ice giant, which is far from any research station in Antarctica and is therefore difficult to reach, has been observed with the help of satellites, ships and airplanes for many years. It turned out that its meltwater has already contributed four percent to global sea level rise and that, should it collapse, this would lead to a considerable further rise. That earned him the nickname “Doomsday Glacier”, the end of the world glacier.
In order to get closer to the all-important glacier, the research project International Thwaites Glacier Collaboration (ITGC) was founded in 2018. During a field campaign, a team of scientists pierced the ice shelf in the beginning of 2020 in the south of summer – precisely above the boundary line or touchdown line at which the shelf ice plate separates from the sea floor and floats. There the Thwaites glacier is about 600 meters thick.
Through this borehole, the researchers lowered a diving robot that explored the area under the ice shelf, took photos and recorded various measurement data such as the water temperature. The result: warm deep water washes away the ice shelf of the Thwaites Glacier and melts it from below. As a result of this process, the baseline continues to recede, the ice shelf thins and becomes unstable.
The newly discovered, kilometer-long cracks that run diagonally and in a zigzag through the ice shelf are evidence of the increasing instability of the ice shelf. The thinning changes the tension – and “it is in the nature of the ice that it breaks when the tension becomes too great,” says Angelika Humbert, suddenly at a third of the speed of sound. 50 kilometers of cracks then appear within a minute.
The ice is like a cracked windshield: one blow and it can burst
Scientists are therefore comparing the state of the ice shelf on the Thwaites Glacier with that of a windshield that has broken in one place and is therefore unstable. At some point the final impact comes and the cracks spread like a network over the entire pane. Similarly, the glacier’s ice shelf could burst in the coming years. However, the many fragments of the ice shelf would not directly affect sea level. Because the ice shelf floats on the sea like a gigantic ice cube in a water glass, which takes up the same amount of space, regardless of whether it is liquid or frozen.
But the ice mass of the Thwaites Glacier, which lies on the mainland, loses its hold without a supporting ice shelf and slides faster into the sea. The scientists estimate that the flow speed of the eastern part of the glacier could triple. A complete collapse of the glacier would raise sea level by 65 centimeters. But that’s not all: Due to the stronger ice flow, this ice giant is also increasingly losing its role as a brake on the glacier structure of West Antarctica. Should it melt faster, it could further destabilize the entire West Antarctic ice sheet.