Higher melt rates found under vital glacier

Hidden under kilometres of thick ice, very little is known about subsurface meltwater, yet it plays an important role in how quickly the ice sheet moves towards the sea, as it creates less friction between the ice and the bedrock.

When the outflow exits from under the ice and comes into contact with warm ocean waters, it also has the potential to increase ice melting and affect global sea levels, according to scientists.

The new study found that the rate of melting at the base of the ice sheet has been underestimated by 150 per cent.

Glacial drainage
Experts analysed a decade’s worth of data from the European Space Agency’s (ESA’s) CyroSat satellite, and were surprised to discover that the lakes below Thwaites Glacier – a vast frozen expanse the size of Britain – drained and recharged again in quick succession – in 2013 and in 2017.

The study, led by Edinburgh researchers, estimates that the drainage speed peaked at around 500 cubic metres a second – around eight times faster than the speed of the River Thames as it flows into the North Sea.

We used CryoSat to show a period of lake activity only four years after the previous drainage event in 2013. But what is interesting about this second drainage event is how different it is from the first, with a faster transfer of water and increased water discharge. Our observations highlight that there were potentially significant modifications to the subglacial system between these two events.

George Malczyk
Lead author, School of GeoSciences, University of Edinburgh
Melting rates
The relatively short time it took to recharge the lakes between the two drainage events, gives scientists an unprecedented estimate of the rate of melting at the base of the ice sheet.

By comparing the rates to modelled estimates, the team found that previous models underestimated basal melting by nearly 150 per cent.

The finding will help glaciologists reassess models and improve predictions of how the ice sheet might behave in the future.

What takes place under the ice sheet is critical to how it responds to changes in the atmosphere and ocean around Antarctica, and yet it is hidden from view by kilometres of ice which makes it very difficult to observe. This movement of water give us a glimpse of where the water is and how much and how fast it moves across the system. Together this is key information about the nature of the subglacial environment and the processes of the hydrological network under the ice sheet. These findings provide key information that can help us project how the ice sheet adds to sea level as it responds to climate change.

Dr Noel Gourmelen
Reader, School of GeoSciences, University of Edinburgh
Dr Gourmelen added that it was important to continue monitoring such remote regions from space over long periods of time. The planned CRISTAL mission, which is part of Europe’s Copernicus expansion programme, will be crucial in ensuring continuity and expansion of the current capabilities to study the entire ice sheet from space, he said.

Thwaites Glacier
At around 120 km wide, Thwaites is the largest glacier on Earth and one of the most fragile in Antarctica.

The International Thwaites Glacier Collaboration and ESA’s 4D Antarctica programmes were set up to continuously monitor the entire Antarctic ice sheet using simulation of the ice sheet and observations from space.

The project draws together several years of research from different teams to form a new comprehensive assessment of Antarctic ice-sheet hydrological processes – from the lithosphere and subglacial environment to surface-melting process. This will certainly contribute to establishing a robust scientific based to develop a Digital Twin of Antarctica in the future.

Diego Fernandez
ESA’s head of Earth Observation Science Section- overseeing the 4D Antarctica project
The paper, published in Geophysical Research Letters was funded by the European Space Agency’s project 4DAntarctica, and from the PROPHET project, a component of the International Thwaites Glacier Collaboration (ITGC) supported by the US National Science Foundation and the UK Natural Environment Research Council.