Significant geothermal heat under the ice stream

Ice losses from the Thwaites Glacier in West Antarctica are currently responsible for about 4 percent of global sea level rise. This figure could increase, as virtually no other ice flow in Antarctica changes. as radically as the huge Thwaites Glacier.

Until recently, experts attributed these changes to climate change and the fact that the glacier rests on the seabed in many places, and also comes into contact with bodies of warm water. But there is also a third influencing factor, so far difficult to narrow down. In a new study, researchers from Germany and the UK have shown that there is a remarkably large amount of heat from the Earth’s interior under the ice, which has likely affected the sliding behavior of ice masses for millions years.

This large geothermal heat flux, in turn, is due to the fact that the glacier sits in a tectonic trench, where the earth’s crust is significantly thinner than it is in neighboring East Antarctica. A new study describing this was published today in the Nature online journal Earth & Environment Communications.

Unlike East Antarctica, West Antarctica is a geologically young region. Moreover, it does not consist of a large contiguous landmass, where the earth’s crust is up to 40 kilometers thick, but rather of several small, relatively thin crustal blocks that are separated from each other by a so- saying trench system or fault system. In many trenches in this system, the earth’s crust is only 17 to 25 kilometers thick, and as a result much of the soil is one or two kilometers below sea level.

The existence of the trenches has long led researchers to speculate that comparatively large amounts of heat from the Earth’s interior are rising to the surface in this region. With their new map of this geothermal heat flux in the Amundsen Sea hinterland of West Antarctica, experts from the Alfred Wegener Institute, the Helmholtz Center for Polar and Marine Research (AWI) and of 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, a geothermal heat flux of up to 150 milliwatts per square meter can occur under the Thwaites Glacier. This corresponds to the values ​​recorded in the areas the Rhine Graben and the East African Rift Valley, ”explains AWI geophysicist and study lead author Dr Ricarda Dziadek.

Based on their data, geophysicists are unable to quantify how much rising geothermal heat is heating the glacier bottom. “The temperature under the glacier depends on a number of factors, for example whether the soil is made up of solid, compact rocks or meters of water-saturated sediment. Water conducts rising heat very efficiently. But it can also transport thermal energy before it reaches the bottom of the glacier, ”explains AWI co-author and geophysicist Dr Karsten Gohl.

Nonetheless, heat flow could be a crucial factor that needs to be taken into account when it comes to the future of the Thwaites Glacier. According to Gohl, “large amounts of geothermal heat can, for example, cause the bottom of the glacier bed to no longer freeze completely or a constant water film to form on its surface. Both would cause more sliding. large masses of ice. easily on the ground. If, in addition, the braking effect of the pack ice is lost, as can now be observed in West Antarctica, the flow of the glacier could accelerate considerably due to the increase in geothermal heat.

The new geothermal heat flux maps are based on various West Antarctic geomagnetic field data sets, which the researchers put together and analyzed using a complex procedure. “Deducing geothermal heat flux from magnetic field data is a proven method, mainly used in areas where little is known about the characteristics of the geological subsoil,” says Fausto Ferraccioli of the British Antarctic Survey and of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), one of the co-authors of the study.

Experts will soon find out how accurate their new assessment of heat flux under the Thwaites Glacier is for real-world application. An international team led by British and American polar experts, in which AWI also participates, is currently engaged in a major research project. In this context, core samples to the bottom of the glacier and corresponding heat flux measurements are planned. The results will provide the first opportunity to comprehensively verify the new West Antarctic heat flux maps.