Surveyor seals reveal secrets of Antarctic depths

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Original article at  New Scientist
05 November 2010 by Kate Ravilious

Ocean explorers (Image: D. Costa)

Seals are helping to map the ocean floor around Antarctica. And they are proving their worth: they have already revealed new features on the sea bed that could help researchers explain the rapid melting of ice in recent years.

Knowing the shape of the ocean floor is important because underwater mountains and valleys help to shape ocean circulation, which influences ice cover and production at the surface.

Normally such mapping is carried out by echo sounding, whereby the depth of the sea is calculated by timing how long it takes for sound waves to travel from a ship to the sea bed and back again. But the most of the sea and ocean beds around Antarctica remain unmapped because the thick ice that covers much of the region is impassable for ships.

So Daniel Costa, a marine biologist at the University of California, Santa Cruz, glued electronic depth sensors onto the heads of 57 elephant seals and tracked their movements in the Bellingshausen Sea off the Antarctic Peninsula between 2005 and 2009.

Ideal seals

“Seals are ideal because they go places where no one else has gone, and they don’t need a battery to drive them,” says Costa.

By tracking seals in previously well-mapped regions, Costa and his colleagues showed they dived all the way to the sea floor around 30 per cent of the time.

Next they analysed the maximum depths of seal dives in unmapped regions, to trace the contours of the sea bed to the west of the Antarctic Peninsula.

“We found that the troughs that cut across the continental shelf from the deep ocean to the coast are deeper and straighter than shown on existing maps,” says Laurie Padman, an oceanographer at Earth and Space Research, a non-profit research institute in Corvallis, Oregon.

In particular, the data revealed that troughs leading towards the Wilkins ice shelf were 600 to 200 metres deeper than previously thought. Such troughs act as conduits for warm water, so the greater depth may help to explain the dramatic collapse of the ice shelf in 2008.

The researchers are planning similar work in other areas around both Antarctica and the Arctic. “It is a cheap and very powerful technique,” saysPaul Holland, an ocean modeller from the British Antarctic Survey in Cambridge, UK, who was not involved in the study.

Journal reference: Geophysical Research Letters, DOI: 10.1029/2010gl044921

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