Large amounts of meltwater on the East Antarctic ice shelf
The East Antarctic ice shelves may be more vulnerable to climate change than previously assumed. A research team in cooperation with the Alfred Wegener Institute has detected large amounts of meltwater on the Roi Baudouin shelf ice. This is due to strong winds that blow away the snow. This is the result of a study which has now been published in the online edition of the journal Nature Climate Change.
Two years ago, international researchers by chance discovered an unusual ring-shaped fracture area on the Roi Baudouin shelf ice in East Antarctica. Soon speculations arose about whether this may be the impact crater of a meteorite weighing hundreds of tons. Upon closer investigation by ice experts, this turned out not to be the case.
In January 2016, the Belgian scientist and lead author of the study, Jan Lenaerts of Utrecht University, and his team visited the crater. Using a combination of climate models and satellite images they discovered the cause of this ring structure. They now published their results in the online edition of the journal Nature Climate Change.
The structure is indeed not due to a meteorite impact. However, the speculation led to surprising findings. With the participation of the AWI glaciologist Prof. Olaf Eisen and Dr Veit Helm, the researchers were able to demonstrate that there is a significantly larger amount of meltwater in East Antarctica than previously assumed. They discovered numerous glacial lakes on and in the ice. And the fracture area that was discovered two years ago is a glacial lake that used to be filled with water. What's more, there are many previously unknown meltwater rivers in the shelf ice.
Shelf ice is the part of a glacier that floats on the surface of the sea. It is important for the stability of the ice sheet, because it slows down the speed of flow of the ice coming from inland. “The whole system, however, is on a brink,” says Olaf Eisen. “With more frequent warmer summers, the melting area will expand. This could make the shelf ice less stable and eventually cause it to break apart. It's not yet a nightmare scenario, but it should be taken seriously as an observation.”
The researchers believe that it is caused by strong, so-called katabatic winds. These winds blow from the high plateau of the Antarctic inland ice down towards the coast. There is what can be described as a kink in the transition between the slope of the mainland ice and the shelf ice that horizontally rests on the water. The winds constantly blow air into this region (like the foehn in the Alps), which creates stronger swirls of wind around the kink. At this point, the winds constantly blow away the surface snow.
“The solid ice that is partially exposed as a result is darker than the white snow and consequently absorbs more solar energy, which in turn more heating of the surface,” says Olaf Eisen. “Usually, the cold mean annual temperatures are enough to cause the water to quickly freeze again. But if it gets too warm, then there will be so much meltwater that it tries to find its way into the sea through the shelf. In the long run, this can weaken the shelf ice and make it less stable.”
The ring structure itself is what's called an ice doline. “An ice doline develops when meltwater accumulates inside a glacier or close to its surface, freezes again at the top, and then water underneath drains downwards. This creates a cavity in the glacier whose ceiling will eventually collapse. In Greenland and on shelf ice in the Antarctic peninsula, this has been observed since the 1930s,” says Olaf Eisen. However, such findings are new for East Antarctica – but the crater itself is certainly not new: satellite images show that the ring structure has existed since 1989. Olaf Eisen: “The meltwater has been there for some time, and overall the system appears to have been stable over the past decades. However, it should be much more sensitive than previously known. This could mean that even a minor disruption to the system could have major impacts.”
J. T. M. Lenaerts, S. Lhermitte, R. Drews, S. R. M. Ligtenberg, S. Berger, V. Helm, C. J. P. P. Smeets, M. R. van den Broeke, W. J. van de Berg, E. Van Meijgaard, M. Eijkelboom, O. Eisen, F. Pattyn: Meltwater produced by wind-albedo interaction stored in an East Antarctic ice shelf, Nature Climate Change, DOI: 10.1038/nclimate3180
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The Alfred Wegener Institute pursues research in the polar regions and the oceans of mid and high latitudes. As one of the 19 centres of the Helmholtz Association it coordinates polar research in Germany and provides ships like the research icebreaker Polarstern and stations for the international scientific community.