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Tuesday, 16 November, 1999, 16:55 GMT
Arctic sea ice gets thinner
All areas appear to be thinning
There has been a "striking" decline in the thickness of Arctic sea ice according to scientists who have studied data gathered by US Navy submarines.

The researchers say the average draught of the sea ice in the region has declined by 1.3 metres (4.3 ft) compared with the 1960s and 1970s. By draught they mean the difference between the surface of the ocean and the bottom of the ice pack - just like the draught of a boat.

This amounts to a 40% reduction, says Dr Andrew Rothrock of the University of Washington, Seattle, and colleagues, who report their findings in the journal Geophysical Research Letters.

"We were very surprised by the amount of thinning," Dr Rothrock told BBC News Online. "We did not expect to see such a big signal."

Polar bears

The study fits with other work that has shown how the Arctic climate is changing. Research has already shown how Arctic ice is retreating and the impact this is having on wildlife. Only on Monday, Canadian scientists reported that the situation was threatening polar bears with starvation by shortening their hunting season.

The bears' main food source, ringed seals, are becoming less accessible. The seals live on the ice of Hudson Bay but this ice is breaking up earlier and earlier.

Thickness data on Arctic ice have been collected since the late 1950s. Nuclear submarines went on regular cruises under the ice to make the necessary measurements. Information gathered until 1976 is publicly available.

So too are the data sets collected by the Scientific Ice Expeditions (SCICEX) program, which began regular submarine surveys in the 1990s. The newly published study compared the two periods.

Sign and magnitude

Measurements of the sea ice thickness using the most recent data showed a perennial ice cover of from one to three metres in mean draught, which was considerably thinner than previous estimates.

The changes are "striking in the uniformity of their sign and in their magnitudes," write Dr Rothrock and his colleagues in their journal paper.

The thinning was evident in all of the areas compared in the study, although the reductions were greater in some places than others. For example, in the Nansen Basin and the eastern Arctic, the reduction was 1.7 metres, whereas in the Beaufort Sea and Chukchi Cap, the thinning was just 1.0 metres.

At the North Pole and in the Canada Basin the decrease lies between these extremes.

Arctic Oscillation

The journal paper does not provide any reasons for the ice loss.

However, culprits will inevitably include human-induced global warming and the climate phenomenon known as the Arctic Oscillation, which can result in particular wind patterns that last several years.

"We just don't know," said Dr Rothrock. "It's going to be fascinating to watch in the next five of ten years and see what happens in the Arctic - whether the ice cover is headed in one direction or whether something will bring it back into a more normal historical pattern."

Dr Rothrock is currently trying to get the military to release further submarine data which it is hoped will give an even better picture of thickness trends.

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12 Aug 99 | Sci/Tech
Arctic wildlife feels the heat
07 Jan 99 | Sci/Tech
Bering Sea changes baffle scientists
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