Climate Crisis May Not Be the Main Threat to Thwaites Glacier Melt

A cavity in West Antarctica’s Thwaites Glacier caused in part by global heating. New research says it is soon to melt much faster, but this time the acceleration will be from something far different than most had imagined. Photo: NASA

The Thwaites Glacier, centered between 50 and 100 kilometers east of Mount Murphy in Antarctica, is about the size of Florida or all of Britain. As part of the West Antarctic Ice Sheet, it is considered one of the most worrisome parts of Antarctica because of the rapid melting and relatively instability of its vast marine ice sheets.

It is currently melting at such a rate that its freshwater dump rate contributes – all on its own -- to approximately 4 percent of sea level rise around the globe.

For most of the period in which climate scientists have looked to the two poles of Arctic and Antarctica, Greenland, and within the Himalaya Mountain Range as the most significant contributors to worldwide glacier melt, the Thwaites glacier’s rapid melting rate was thought to be mostly caused by global heating of the planet due to the climate crisis.

There was a secondary concern, that the glacier rests on the seafloor in several places and there is exposed to masses of warm water which might cause additional melting from underneath.

While those contributions were concerning enough, a new investigation by researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research suggests there is another far more serious threat to the Thwaites Glacier staying intact.

That threat is the large amount of heat present beneath this stretch of Antarctic ice emanating directly from the interior of the Earth. This heat flow, which the scientists call “substantial”, is coming from a tectonic trench which the Thwaites glacier sits within.

Within that trench the Earth’s crust is much thinner that are other glaciers located elsewhere but still nearby, such as in East Antarctica.

Unlike East Antarctica, West Antarctica is a geologically young region. In addition, it doesn’t consist of a large contiguous land mass, where the Earth’s crust is up to 40 kilometers thick, but instead is made up of several small and for the most part relatively thin crustal blocks that are separated from each other by a so-called trench system or rift system. In many of the trenches in this system, the Earth’s crust is only 17 to 25 kilometers thick, and as a result a large portion of the ground lies one to two kilometers below sea level. On the other hand, the existence of the trenches has long led researchers to assume that comparatively large amounts of heat from Earth’s interior rose to the surface in this region. With their new map of this geothermal heat flow in the hinterland of the West Antarctic Amundsen Sea, experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the British Antarctic Survey (BAS) have now provided confirmation.

“Our measurements show that where the Earth’s crust is only 17 to 25 kilometers thick, geothermal heat flow of up to 150 milliwatts per square meter can occur beneath Thwaites Glacier. This corresponds to values recorded in areas of the Rhine Graben and the East African Rift Valley,” says AWI geophysicist and first author of the study, Dr Ricarda Dziadek. 

Based on their data, the geophysicists are unable to put a figure on the extent to which the rising geothermal heat warms the bottom of the glacier: “The temperature on the underside of the glacier is dependent on a number of factors – for example whether the ground consists of compact, solid rock, or of metres of water-saturated sediment. Water conducts the rising heat very efficiently. But it can also transport heat energy away before it can reach the bottom of the glacier,” explains co-author and AWI geophysicist Dr Karsten Gohl.

Nevertheless, the heat flow could be a crucial factor that needs to be considered when it comes to the future of Thwaites Glacier. According to Gohl: “Large amounts of geothermal heat can, for example, lead to the bottom of the glacier bed no longer freezing completely or to a constant film of water forming on its surface. Both of which would result in the ice masses sliding more easily over the ground. If, in addition, the braking effect of the ice shelf is lost, as can currently be observed in West Antarctica, the glaciers’ flow could accelerate considerably due to the increased geothermal heat.”

The new geothermal heat flow maps are based on various geomagnetic field datasets from West Antarctica, which the researchers have collated and analysed using a complex procedure. “Inferring geothermal heat flow from magnetic field data is a tried and tested method, mainly used in regions where little is known about the characteristics of the geological underground,” explains Fausto Ferraccioli from the British Antarctic Survey and the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), one of the study’s co-authors.

The experts will soon find out how accurate their new assessment of the heat flow below Thwaites Glacier is. An international team led by British and American polar experts, which the AWI is also taking part in, is currently engaged in a major research project. In this context, collecting core samples down as far as the glacier bed and taking corresponding heat flow measurements are planned. The findings will provide the first opportunity to comprehensively verify the new heat flow maps from West Antarctica.

According to the researchers, while the current melt rate estimates for the Thwaites Glacier are accurate, the reality that the glacier is sitting on what amounts to a tectonic “hot plate” will likely accelerate its rate of melting. It will also bring far closer in the date at which the glacial ice sheet will splinter off, float northward, and eventually dump all its freshwater into the ocean.

Sea level rise would then see an immediate sudden jump on a global basis. If it were to melt in its entirely the sea would rise by 65 cm (26 inches) on average around the world.

The study results were published on August 18, 2021, in a paper entitled, “High geothermal heat flow beneath Thwaites Glacier in West Antarctica inferred from aeromagnetic data,” by Ricarda Dziadek, Fausto Ferraccioli, and Karsten Gohl. It was published in the peer-reviewed Nature online journal Communications Earth & Environment.

We encourage all readers to study the original research article to understand the full scope of the research involved and the implications of its conclusions.

The research was funded by Deutsche Forschungsgemeinschaft (DFG).