An unmanned submarine called Ran made its way under the Thwaites glacier front, and the data generated from the submersible allowed researchers to make a number of new discoveries, according to researchers who published their findings in the journal, Science Advances April 9, 2021.
“This was Ran’s first venture to polar regions and her exploration of the waters under the ice shelf was much more successful than we had dared to hope. We plan to build on these exciting findings with further missions under the ice next year,” said Professor Karen Heywood of the University of East Anglia.
The submersible measured a number of important parameters, including the strength, temperature, salinity, and oxygen content of the underlying ocean currents. And even though the journey under the ice was successful, the results were not so promising, according to Science Alert.
Global sea levels are influenced by how much ice there is on land, and the biggest uncertainty in the forecasts is the future evolution of the West Antarctic Ice Sheet, says Anna Wåhlin, professor of oceanography at the University of Gothenburg and lead author of the study.
The ice sheet in Western Antarctica accounts for about ten percent of the current rate of sea-level rise, however, the potential for a greater rate of ice melt in this ice sheet is possible because the fastest changes worldwide are taking place in the Thwaites Glacier.
The Thwaites glacier is massive, and covers more than 74,000 square miles (192,000 square kilometers) and is more than 900 miles (1,500 km) from the nearest U.S. and British Antarctic research bases. And due to its size and location, Thwaites is particularly sensitive to warm and salty ocean currents that are finding their way underneath it.
Scientists already know, from a previous study of the flow of warm water taking place at the bottom of the glacier and inland movement of the so-called grounding zone, the area where the ice transitions from resting on the seabed to floating in the ocean, that melting is accelerating.
After deploying Icefin, the robotic submarine equipped with high-definition video cameras, sonar, and instruments for monitoring water flow, salinity, oxygen, and temperature, scientists were surprised to learn that waters at the glacier’s grounding line were more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, above the normal freezing point.
New data is very worrisome
It turns out that three inflows of warm water were identified by researchers, one of which they had been seriously underestimating. Deepwater underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay.
Deepwater flows from the east were thought to be blocked by an underwater ridge nearby, but the new data from Ran suggests these deep currents are still finding their way into the bay.
“The channels for warm water to access and attack Thwaites weren’t known to us before the research,” says geological oceanographer Alastair Graham from the University of Southern Florida.
“Using sonars on the ship, nested with very high-resolution ocean mapping from Ran, we were able to find that there are distinct paths that water takes in and out of the ice shelf cavity, influenced by the geometry of the ocean floor.”
This means that warm, salty waters are entering the cavity beneath the Thwaites Ice Shelf from both sides of its main pinning point in the north, possibly destabilizing the entire structure.
And while it is not clear how much of this heating will affect the stability of the glacier pinning points, the authors predict the energy transported by just one local current is sufficient to melt the above ice at a rate of more than 85 gigatonnes per year. That amounts to the equivalent of the total basal melt of the entire Thwaites Ice Shelf between 2010 and 2018,
“This pinning point is one of the last buttressing features restraining the flow of ice from upstream, and satellite observations indicate that its extent has decreased over the past decades,” the authors write.
