The supply of warm water to Antarctica's Thwaites Glacier, also known as the "doomsday glacier", is larger than previously thought, triggering concerns of faster melting and accelerating ice flow-a risk for global sea levels, say researchers. Thwaites is particularly sensitive to warm and salty ocean currents, due to its location and shape. For the first time researchers were able to take measurements beneath it, with the help of an uncrewed submarine called "Ran" that made its way under the glacier front.
Among other things, it measured the strength, temperature, salinity and oxygen content of the ocean currents under the glacier and found variations. This indicates that the area under the glacier is a previously unknown active area where different water masses meet and mix with each other.
Global sea level is affected 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, said lead author Anna Wahlin, Professor at the University of Gothenburg in Sweden.
Using the Ran results, the team mapped the ocean currents that flow below Thwaites's floating part. The observations, published in the journal Science Advances, show warm water approaching from all sides on pinning points, critical locations where the ice is connected to the seabed and give stability to the ice shelf.
Melting around these pinning points may lead to instability and retreat of the ice shelf and, subsequently, the upstream glacier flowing off the land, the researchers said. They also discovered a deep connection to the east through which deep water flows from Pine Island Bay -- a connection previously thought to be blocked by an underwater ridge.
Further, they measured the heat transport in one of the three channels that lead warm water towards Thwaites Glacier from the north.
"The channels for warm water to access and attack Thwaites weren't known to us before the research. 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," said Alastair Graham, from the University of Southern Florida.
Although the amount of ice that melts as a result of the hot water is not much compared to other global freshwater sources, the heat transport has a large effect locally and may indicate that the glacier is not stable over time.