2024-04-18 23:46:25
Mighty peaks, deep lakes and flat terrain: a research expedition has for the first time mapped the underground beneath Antarctica’s Thwaites Glacier – the widest glacier on earth. The mapping reveals that under the 800 to 1,200 meter thick ice lies a varied landscape with both braking and smooth sections. Lakes 100 oceans deep can also be found under the huge ice flow. Knowledge of this subglacial landscape now helps to more accurately assess the future of Thwaites Glacier.
The Thwaites Glacier in West Antarctica is one of the largest ice streams in this region and the widest glacier on Earth: the front, which flows into the Amundsen Sea, is 120 kilometers wide. The impact of the giant ice flow is correspondingly large: the loss of ice from just this one glacier is already responsible for around four percent of global sea level rise. The tongue of Thwaites Glacier also has warm deep water undermined and riddled with cracks.
If the Thwaites Glacier were to thaw completely, levels worldwide would rise by 65 centimeters. It is therefore important to be able to assess the further development of this ice giant as accurately as possible.
View of the tongue of Thwaites Glacier from an airplane. © NASA
With vibrating plates and radar
Therefore, a research team from the “International Thwaites Glacier Collaboration” (ITGC) has intensively investigated the Thwaites Glacier on site over the past two years. The main focus was to map the glacier floor – the landscape that lies beneath the ice flow. The shape and properties of the bedrock of the Antarctic Thwaites Glacier affect how quickly the glacier will retreat and contribute to sea level rise.
During two field expeditions, snowcats and airplanes took scientists from the British and American polar stations Rothera and McMurdo, more than 1,600 kilometers away, to the Thwaites Glacier. On site, the team used special vibrating plates to seismically investigate the underground. 480 geophones recorded the waves reflected from the ice and the underlying ice. In addition, the researchers mapped the subglacial subsurface using high-resolution radar measurements.
Powerful rocks and smooth expanses
The result is the first accurate map of the landscape beneath Thwaites Glacier. For the first time, it provides insight into what the subsurface of this ice flow is like. “Knowing the properties of the bed over which Thwaites Glacier flows was the most important piece of information missing to improve predictions of how quickly it will lose ice in the future,” explains Robert Larter of the British Antarctic Survey. “The new results begin to close this gap.”
Specifically, the mapping revealed a varied subglacial landscape: there are relatively flat areas a few kilometers long that are characterized by smooth, soft sediments. Such subglacial plains facilitate the sliding of the glacier on the subsoil and therefore form “slides” for the ice flow. In between, however, there are always sections of rugged terrain characterized by hard bedrock, where hills and cliffs rise to hundreds of meters high. These act as brakes on the ice flow.
Also surprising: beneath some parts of the Thwaites Glacier, the team discovered subglacial lakes up to 100 meters deep.
Evidence of glacial dynamics
– This is the first time we have obtained such a clear picture of such a large part of the underground, says Olaf Eisen from the Alfred Wegener Institute. “This has major implications for modeling ice flow dynamics and understanding how much Thwaites Glacier may contribute to sea level rise, which will affect coastal communities around the world, particularly in the Northern Hemisphere.”
The new measurements show that the glacier bed in the area still covered by ice is similar to the area in front of the ice tongue that has already thawed. – New seismic data collected offshore confirms the strong similarities, says Larter. This can also make it possible to draw conclusions about the future mobility and vulnerability of the glacier.
Sometimes soft, sometimes hard
The seismic images also revealed striking structures inside the glacier. These so-called englacial reflections are primarily found in the areas of the Thwaites ice stream where the subsoil is rougher. This suggests that the ice above these rough parts of the rock is deformed more and that the ice crystals there are in line with the prevailing stresses. This means that the knitting is softer in one direction than the other. Future ice flow models must also take this into account. (European Geosciences Union (EGU) meeting 2024)
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), British Antarctic Survey (BAS)
19 April 2024 – Nadja Podbregar
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