In Antarctica, the giant Thwaites glacier “holds only by the tips of the nails”

In Antarctica, the giant Thwaites glacier “holds only by the tips of the nails”

In Antarctica, the giant Thwaites glacier “holds only by the tips of the nails”

Seven times the size of Brittany, the Thwaites Glacier flows into Ile du Pin Bay in West Antarctica. It juts out into the sea like a giant floating ice shelf. VSupon which the frozen titan rests
feet of clay for decades, the fault of natural climatic variations and climatic changes due to human activities, the scientists point out.

It is followed like burning milk by teams from all over the world. “Its floating ice shelf is like a cork on a bottle, it preserves the upstream part of the glacier. However, it is increasingly in the process of fracturing ”, observes glaciologist Olivier Gagliardini, of the Institute of Environmental Geosciences in Grenoble.

A possible rise in sea level of 3.3 m

The ice lost by Thwaites contributes 4% of global sea level rise today, the International Thwaites Glacier Collaboration reminds us, but its impact could be much greater in the future, due to the acceleration of its decline. says it has doubled in the past 30 years. According to some simulations, the complete collapse of the Thwaites glacier would raise the global sea level by 65 cm. Worse still, its disappearance could cause a chain reaction on nearby glaciers, which could lead to the total loss of the West Antarctic ice sheet, Science magazine teases. Consequence, therefore, for the global sea level: a cataclysm, a 3.3 m rise … How much is the media nickname of “apocalypse glacier” worth to the Thwaites glacier.

The question is when such an event could occur. “Over a very long period of several centuries”, estimates Olivier Gagliardini. “But hasToday’s models of the future of the polar ice caps are limited by the fact that there is a lack of data on the maximum retreat speed of the glacier stranding line, which marks the boundary between the ice resting on the rock and the one floating in the ocean (see infographic). When this line recedes, the part of the glacier that rests on the continent will decrease in quantity and all that is lost will contribute to the rise in the level of the oceans ”, observes the glaciologist from Grenoble.

A decline of over 2.1 km per year

A new study published Monday, September 5 in the journal Nature Geoscience brings new, not very reassuring elements. It shows that the speed of movement of the ground line it could rise to more than double what recently experienced. The team led by Alastair Graham, a marine geologist at the University of South Florida, has mapped the seabed in front of the Thwaites Glacier, which it once covered. Using an autonomous submarine, scientists discovered hundreds of parallel ribs on the ocean shelf, ancient stranding lines. These ribs formed daily to the rhythm of the movements initiated by the tides. The scientists measured the distance between them and were able to conclude that the glacier had experienced a very rapid retreat episode in the relatively recent past, before the emergence of satellite technology that allows it to follow, with supporting images, the ‘evolution of the ice floes: “Over a period of 5.5 months, the stranding line of Thwaites retreated at a speed exceeding 2.1 km per year, double that observed by the satellite in the part of the stranding area that is shrinking more rapidly between 2011 and 2019 “. They cannot say exactly when it happened, probably between 50 and 200 years ago; perhaps in the 1940s. The authors suggest that these episodes of accelerated glacier retreat alternate with slower episodes similar to those of today, during which the glacier’s floating platform gets “stuck” on a rocky ridge, which keeps it in place and it also reduces the destructive passage of the warm ocean waters beneath it …

Too late to act?

Worryingly, these new findings cause Robert Larter, co-author of the study, to tell the Washington Post that “Thwaites is at the end of his nails today. We should expect to see big changes on small time scales in the future, even from year to year, once the glacier retreats beyond a shallow ridge in its bed. ”

What can be done to try to stem the process? “We must, of course, continue to reduce our greenhouse gas emissions. But for the Thwaites glacier the possibilities for human intervention are now limited, since the time of inertia is large – several decades without a doubt – between our actions and the effects they could have on it ”, concludes Olivier Gagliardini.

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