Concealed floods drive flow of Antarctic iceA hidden network of glacial lakes far below the Antarctic surface regulates the motion of the continent's ice rivers, a study has found. When the subglacial lakes overflow, the ice above accelerates towards the ocean.
"It's like putting in a squirt of oil," says Andy Smith of the British Antarctic Survey, who was not involved in this latest study. "The water lubricates the base of the glacier."
What causes the lakes to flood is not known, but researchers watching the movement of ice in satellite images have noticed that the ice appeared to "breathe" in some places, apparently linked to the ebb and flow of water underneath. Now, for the first time, evidence has emerged sub-surface floods can indeed act like a "turbo lubricant" for glaciers.
By tracking both the ocean-bound movement of East Antarctica's Byrd glacier and the events in two lakes that lie beneath it, Leigh Stearns of the University of Maine and colleagues showed that the glacier sped up between late 2005 and mid 2007 – precisely when ice-penetrating radar imagery from satellites showed that both lakes were overflowing.
Conversely, the movement of the glacier slowed when the flood ceased and the lakes began to refill.
Slow melt
Smith says that similar events have been seen in Greenland, but since the lakes there lie at the surface of the ice, the mechanism must be different. Temperatures in Greenland vary more than they do in Antarctica, where the summers are not warm enough to generate significant melt ponds at the surfaceMovie Camera.
"In Antarctica, it appears that the ice at the very bottom of the glacier melts slowly and accumulates in hollows in the rock," says Smith. He says the temperature at the bottom of the ice sheet stays very close to melting point: geothermal energy and friction warm it slightly and the kilometres of ice insulate the area keeping it at a relatively stable temperature.
When the hollows overflow, a flood of water spreads beneath Byrd Glacier, says Stearns. "The extra water overwhelms the subglacial drainage system. It can't escape fast enough, so spreads out beneath the glacier bed and reduces the friction between the ice and the rock, allowing the glacier to slide faster."
Smith emphasises that there is no reason to believe the Antarctic floods are in any way linked to climate change. "It is hard to see how anthropogenic global warming would affect the base of the ice sheet," he says.
A lot of people don't know it but there is actually a hell of a lot of water under the Antarctic ice cap, including at least one humungous lake called
Lake Vostok. There was speculation a few years ago that movement of water would affect the ice sheets above it but this seems to be the first time a direct correlation has been demonstrated.
Topic: Lakes in Antarctica. Big ones.