April 25, 2014
Ice thaw could spell bad news for polar bears
A thaw of sea ice floating on the Arctic Ocean last year sent extra plant food to exotic creatures on the deep sea floor in a shift that might leave polar bears hungry at the surface, scientists said.
The study, using robot submarines down to 4,400 metres (14,400 ft) deep, could be a glimpse of radical changes for life in the sunless depths of the Arctic Ocean after ice thinned and shrank to cover a record low area in September 2012.
Scientists found large amounts of algae growing on the underside of the ice last year, apparently because more light was getting through as it thinned in a trend blamed on global warming, according to the study in the journal Science.
Much of the algae, of a type that forms strands up to a metre (3 ft) long, then sank to the seabed where they were food for brittle stars, which are related to starfish, and tube-like sea cucumbers that grow up to about 5 cms (2 inches) long.
"For surface life it could be bad news, for the deep sea floor it could be a feast," Antje Boetius, of the Alfred Wegener Institute for Polar and Marine Research in Germany and lead author of the study made on the research vessel Polarstern.
If the algae keep taking scarce nutrients from surface waters to the sea floor in coming years, then "the food for fish and eventually for the polar bear will be totally diminished," Boetius said.
In the Arctic food chain, fish eat algae, seals eat fish and polar bears eat seals.
"We were totally surprised that there were all these clumps of sea ice algae on the sea floor," she said. Scientists saw no fish there but many sea cucumbers were bloated with algae food.
On average, the scientists found that the amount of algae on the seabed worked out at 9.0 grammes of carbon per square metre(0.03 oz per sq foot), nine times the amount measured in the 1990s in a sign of changes as the ice receded.
Boetius said algae were making a small contribution to getting rid of carbon dioxide, the main greenhouse gas in the atmosphere emitted by burning fossil fuels, by burying it on the seabed.
"But it's too small to make a large difference," she said of the findings in Science, which is run by the American Association for the Advancement of Science.
"Arctic climate models predict a further decline in the sea ice cover, toward a largely ice-free Arctic in coming decades", according to the scientists, from German, Dutch and Russian research institutes.
Ice has thinned to about a metre (3 ft) thick on much of the Arctic Ocean from perhaps five in recent decades, letting through more light in the May to August summer growing season.
Boetius said most studies of the Arctic relied on satellite measurements rather than observations under the ice.
"This study gives us some evidence that a system can change from the surface to the deep sea," she said. Some fish stocks are moving polewards because of climate change but their advance may be stopped by a lack of nutrients.
The Arctic is warming twice as fast as the global average. White sea ice reflects sunlight and as it recedes it exposes water that is a darker colour and soaks up more of the sun's heat, accelerating the thaw.