This is the first time that such a drainage phenomenon has been observed in East Antarctica, the researchers say — though it was previously spotted on the warmer Antarctic Peninsula and was likely part of what drove spectacular events there like the shattering of the Larsen B ice shelf in 2002.
When it comes to East Antarctica, however, “that’s the part of the continent where people have for quite a long time assumed that it’s relatively stable, there’s not a huge amount of change, it’s very, very cold, and so, it’s only very recently that the first supraglacial lakes, on top of the ice, were identified,” said Stewart Jamieson, a glaciologist at Durham University in the U.K. and one of the study’s authors.
The study was led by Emily Langley of Durham, who worked along with Jamieson and Chris Stokes from her university and Amber Leeson of Lancaster University. The work was recently published online by Geophysical Research Letters.
The research raises concern, for the following reason: Mounting evidence suggests one reason that Greenland has been melting so fast lately is precisely these kinds of lakes. In the summer as air temperatures warm, lakes form on top of the ice sheet, and on its finger-like glaciers that extend outwards into deep ocean fjords.
These lakes can then suddenly disappear all at once, or flow into rivers that drain into the ice below, lubricating the ice and helping to increase the lurch forward of glaciers. Sometimes, researchers have even been able to document fresh water flowing outward directly into the sea from the base of a glacier. That injection of cold fresh water into salty water can then create tornado-like underwater flow patterns at the submerged glacier front that cause further ice loss.
In the new study, Langley and her colleagues find large numbers of lakes forming atop Langhovde Glacier, both inland from, and outward from, the so-called “grounding line,” which is where the marine glacier touches the seafloor far below the ice surface. Past the grounding line, the glacier’s ice begins to float and forms an ice shelf, extending out across the surface of the ocean.
The occurrence of these lakes was strongly related to surface air temperatures — they formed when temperatures rose above zero Celsius, or, above freezing, and formed most frequently in the summer of 2012-2013, which saw 37 days with temperatures above the freezing point.
“What we find is that the appearance of these lakes, unsurprisingly, is correlated directly with the air temperature in the region, and so the maximum number of lakes, and the total area of the lakes, as well as the depth of the lakes, all of these things peak when the air temperatures peak,” said Jamieson.
The study found in particular that atop the Langhovde ice shelf, lakes not only formed but appeared to sometimes drain downward, as rapidly as in five days in one case (which is considerably slower than the fastest drainage events in Greenland).
This raises the concern that these events could possibly be weakening the ice shelf by widening or exploiting fractures within it. But Jamieson said the study could not prove that, in part because it is much harder to observe the consequences of lake draining events in Antarctica than it is in Greenland.
When glaciers lose large parts of their ice shelves, they become less stable and flow faster towards the ocean, contributing to an increased rate of global sea level rise.
“The size of the lakes … are probably not big enough to do much at present, but if climate warming continues in the future, we can only expect the size and number of these lakes to increase. So that’s what we’re looking at,” Jamieson said.
He added that the mid-sized Langhovde Glacier is not special when it comes to East Antarctic meltwater lakes — other parts of coastal Antarctica see them too. The reason the study focused on Langhovde is simply that there was a lot of satellite and temperature data available.
In Greenland, when meltwater from the ice sheet’s surface flows out from beneath glaciers and enters the sea, it often takes with it sediment from the glacier bedrock, washing it out as well. This leads to the appearance of what are called “meltwater plumes” in the ocean near glaciers, areas of water with significantly different coloration due to high levels of sediment concentration.
So far, such plumes have not been observed around East Antarctica, Jamieson said.
Still, the lakes, and especially the apparent drainage events, raise a distinct worry about the future of Antarctica, which contains vastly more ice than Greenland and which, thus far, has not been losing nearly as much. “The parallels between these mechanisms, and those observed on Greenland/the Antarctic Peninsula, suggest that lakes may similarly affect rates and patterns of ice melt, ice flow and ice shelf disintegration in East Antarctica,” the study concludes.
Richard Alley, a glaciologist at Penn State who was not involved in the study, noted in an email comment that seeing some Antarctic surface melt is not too surprising. “Across many sensors and studies, there is summertime melting on the surface of Antarctica around the edges, and sometimes in some places extending farther inland than you might think,” he said.
However, Alley continued, we should be very concerned about such melting increasing. Alley referred to a study from earlier this year, by Rob DeConto of the University of Massachusetts, Amherst, and David Pollard of Penn State, which found that surface melt is one factor that could greatly speed total Antarctic ice loss, by increasing the tendency for “hydrofracture” to occur, in which meltwater helps to break apart ice shelves.
“The lesson of DeConto and Pollard was that, based on current understanding, avoiding a major expansion of surface melting in Antarctica is taking out insurance against a very large and rapid sea-level rise,” Alley said. “This new work is part of the body of science needed to help us learn just how much warming may be too much if we wish to avoid large and rapid sea-level rise.”
For now, scientists plan to use the instruments available — mainly, at the moment, satellites — to further study the Antarctic lakes.
“It’s not hitting the glacier really hard at the moment, this process, but of course, as things warm up, we’d expect it to start doing more damage, like we see in Greenland,” said Jamieson.
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