VERY deep, beautiful lakes like the one above may be the product of something rather ugly. They are a regular feature of ice sheets, but it is only in the last few years that scientists have linked them to the fact that ice flow within those sheets appears to be accelerating in response to climate change. British photographer Nick Cobbing captured this image from a helicopter during a summer research trip to the Greenland ice cap, sponsored by the environmental campaign group Greenpeace International.
Greenland鈥檚 ice cap is the largest in the northern hemisphere and the second largest in the world, after the Antarctic ice cap. Researchers at NASA have found that increases in the ice velocity during the summer correlate with the timing and intensity of ice sheet surface melting. Based on GPS measurements, they found that the meltwater accumulating in these lakes drains through the 1.2-kilometre-thick ice sheet to the bedrock, lubricating the ice sheet and making it slide faster.
We鈥檝e known for decades that this phenomenon contributes to the movement of small mountain glaciers, but it was only in 2002 that it was discovered in large, polar ice sheets. The meltwater carries heat with it as it drains through moulins 鈥� crevasses and large tunnels up to 10 metres in diameter. Over time, this process means that the ice thins and spreads out towards lower elevations. The result is that the Greenland ice sheet seems to be moving faster and faster towards the coast.
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Another member of the Greenpeace expedition, climatologist Jason Box of the Byrd Polar Research Center at Ohio State University, Columbus, is trying to correlate the intensity of the blue colour of the lakes with accurate depth soundings. He hopes to develop an algorithm that will enable him to gauge the depth of the lake from satellite images, simply by measuring the intensity of its colour.
