Antarctica now has lakes — that could mean trouble
Atop the ice sheet covering the Arctic island of Greenland, you now see dramatic melting in the summer. It forms lakes, rivers and even dangerous “moulins” in the ice where rivers suddenly plunge into the thick ice sheet, carrying water deep below.
East Antarctica is supposed to be different. It is extremely remote and cold. It doesn’t see such warm temperatures in the summer — yet — and so its ice tends to remain more pristine.
“Many people refer to East Antarctica as being too cold for significant melt,” says Jan Lenaerts, a glaciologist with the Utrecht University in the Netherlands. “I mean there’s marginal melt in summer, but there’s not a lot.”
That’s the common wisdom, at least, but it is challenged in a new study in Nature Climate Change, by Lenaerts and his colleagues from universities in the Netherlands, Belgium and Germany. They do so based on research they conducted atop the very large Roi Baudouin ice shelf in East Antarctica, which floats atop the ocean, and where they found a very Greenland-like situation in early 2016.
The researchers had travelled to investigate what had been described as a nearly 3-kilometre-wide “crater” in the shelf, glimpsed by satellite, which some sources believed had been caused by a meteorite. To the contrary, they found that it was a large, 10 foot deep, icy lake bed. In its centre, meanwhile, were multiple rivers and three moulins that carried water deep down into the floating ice shelf.
And even this, perhaps, was not the most dramatic finding. The researchers also drilled through the ice and found what they called “englacial” lakes, sandwiched between the surface of the ice shelf and its base, which is in contact with the ocean beneath it. They found 55 lakes in total on or in the ice shelf, and a number of them were in this buried, englacial format.
This meant that the ice shelf is anything but solid — it had many large pockets of weakness throughout its structure, suggesting a greater potential vulnerability to collapse through a process called “hydrofracturing,” especially if lake formation continues or increases. That’s bad news because when ice shelves fall apart, the glacial ice behind them flows more rapidly to the ocean, raising sea levels. But why was all this happening, and here? The researchers postulate that a “microclimate” exists on the ice shelf that made it all possible — and that a similar mechanism is operating on other East Antarctic ice shelves.
In East Antarctica, so-called “katabatic” winds blow downhill from higher reaches of the ice sheet toward the sea. These powerful winds scour the surface and lift off all the snow, exposing blue ice beneath. At the same time, they mix with warmer air higher in the atmosphere and pull it downward. (In this part of Antarctica there is a temperature “inversion” with cooler winds near the surface and warmer air aloft.)
This has a double melting effect: The warmth raises temperatures atop the ice, even as the exposure of the blue ice reduces the “albedo,” or reflectivity, of the surface, meaning that more sunlight gets absorbed. The result is a pocket of melt in the form of a lake and in some cases the pouring of water into the ice shelf.
As for the submerged lakes, these appear to form from surface lakes that freeze over on top in winter, but stay liquid beneath, Lenaerts said. Then subsequent layers of snow may bury them, even as the steady flow of the glacier into the ice shelf carries them out farther over the ocean.
Indeed, it turns out that the farther out over the ocean you go, the deeper the lakes tended to occur, presumably due to this flow and burial process. The lake is four metres below the ice surface, but “we have found one 8 metres below the surface even further, and one 15 metres below the surface, even further,” Lenaerts said.
As for the plunging moulins, where that water ends up remains mysterious. But it does not appear to be feeding the buried lakes. “We don’t have the tools, the instrumentation, to detect this right now. This is a really big unknown,” Lenaerts said. The water could even be travelling all the way through the ice shelf and pouring into the ocean.
Importantly, the researchers went to satellite images to show that what’s happening on the Roi Baudouin ice shelf isn’t unique to East Antarctica. Rather, they say, they have seen similar features atop other nearby East Antarctic ice shelves, at least remotely.
“We see similar things going on on neighbouring ice shelves, and also for instance on the Amery ice shelf, which is also a notorious, very large ice shelf on East Antarctica,” Lenaerts said. “We see this link between strong winds and blue ice formation, enhanced absorption of solar radiation and the melt that is enhanced by this process.”
The researchers are not saying, to be sure, that these processes are caused by human-induced climate change — they note in particular that on the Roi Baudouin shelf, it appears that there has been some melting at the surface since the 1980s. However, Lenaerts said it is already clear that there is much more meltwater during warmer summers than in cooler ones. And global warming will gradually produce warmer Antarctic temperatures, which should increase the volume of meltwater atop of these ice shelves, pushing them still farther in the Greenland direction.
What this means is that the shelves could be subject to the risk of what researchers call “hydrofracturing”: when a great deal of meltwater forms atop the shelf and pushes inside of it, eventually leading to a crack-up.
That’s what’s believed to have happened in the classic case of the shattering of the Larsen B ice shelf in the Antarctic Peninsula in 2002. Now the fear is that it could happen in the East Antarctic too, where there is a massive amount of ice to potentially lose.
“If this region can get warmer in the future, the meltwater production will enhance a lot, and we can only expect these features, these processes to be more present than they are now,” said Lenaerts said. “With potential implications for hydrofracturing to happen and for ice shelf stability.”
“We don’t have the tools, the instrumentation, to detect this right now. This is a really big unknown.” JAN LENAERTS GLACIOLOGIST WITH THE UTRECHT UNIVERSITY IN THE NETHERLANDS ON WHERE THE WATER PLUNGING INTO THE ICE SHEETS GOES