Science

“Glacier of the Apocalypse” (Thwaites) hangs in the balance and threatens 40% of the world’s population

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The melting of the Thwaites Glacier could have catastrophic consequences for the entire planet. After a recent expedition, researchers have discovered that this glacier must have melted much faster in the past than previously thought, suggesting that its next ice loss may be inevitable and even more dramatic, while its survival today won’t last any longer. . away. Appropriately dubbed the “glacier of the apocalypse”, it could cause sea levels to rise up to three meters in the near future, resulting in the loss of surrounding glaciers. An unprecedented threat that could affect 40% of the world’s population living less than 100 kilometers from the coast.

Thwaites Glacier, one of the most massive glaciers in Antarctica, is at least 120 km wide and 600 km long (equivalent to one third of France). Height will be more than 3 km. Given its size, it is a key element in maintaining the planet’s geoclimatic balance. It really has a strategic position, in particular in the west of Antarctica at the entrance to several valleys located below sea level, as a result of which it plays the role of a kind of wedge, preventing other glaciers from giving way and drifting.

However, tracing its history, glaciologists have noticed that due to the warming episodes that our planet has gone through, Thwaites will be especially prone to change compared to other glaciers. Due to its melting, it will now be responsible for 4% of sea level rise each year, a figure that could rise to 25% given the acceleration of global warming. According to scientists, it is now in a phase of “rapid” collapse.

A new study published in the journal Nature Geoscience outlines the results of an expedition in which researchers have obtained high-resolution cartographic images of the underside of a glacier for the first time. This zone represents the fundamental frontal area to maintain its structure. If the researchers were able to obtain underwater images of this quality, it is, in part, due to the fact that this summer the pack ice was especially thin and dispersed.

The images were originally collected to estimate the rate at which the glacier has melted in the past in order to more accurately estimate future loss of ice volume.

A 3D view of the seafloor, first seen from the crest of the seafloor just in front of the ice shelf. © Alastair Graham/University of South Florida

The research team then found more than 160 parallel bathymetric ridges, such as footprints, marking the movements of the glacier (when it advanced or retreated with daily tides). The space between the ridges shows the amount of retreat over the last 200 years. Seizures recorded by the satellite between 2011 and 2019 are minimal compared to what has happened in the past, according to researchers from the University of South Florida who participated in the expedition.

Thus, at the pace of global warming, the worst is yet to come. “Today, Thwaites is really holding on to the wire, and we should expect big changes on small time scales in the future — even year after year — as the glacier retreats behind the shallow ridge in its bed,” warns Robert Larter. Marine geophysicist with the British Antarctic Survey and co-author of the study.

The real domino effect

At some point in the last 200 years, the edges of the glacier must have broken off one of the seafloor’s rocky ridges and drifted at a rate of 2.1 kilometers per year, in less than six months, according to the researchers’ analysis of the new study. “Our results indicate that very rapid retreat pulses have occurred at Thwaites Glacier over the past two centuries and possibly as recently as the mid-20th century,” says Alastair Graham, a marine geophysicist at the University of South Florida and lead author of the study. study.

The glacier is noticeably restrained by the rock on which it rests. However, water from warm currents seeped into depressions in this rock, melting the ice. According to previous studies, the temperature of this water under the glacier will be one to two degrees above freezing, which will accelerate the melt. Thus, the glacier loses volume both from above and from below (the submerged part resting on the rock).

The consequences of the loss of the Thwaites Glacier would be catastrophic on a planetary scale, because it serves as a support for other glaciers behind, namely the Thwaites Glacier, which flows directly into the sea. therefore, neighboring glaciers would also be swept away by its fall, resulting in the loss of a significant portion of Antarctica’s glaciers. If that happens, scientists estimate there will be a significant rise in sea levels, but it will also affect global temperature, ocean salinity and other key aspects of the climate system.

Nature Geoscience

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