Hide-and-seek in Antarctic seas

It spent a year beneath the ice

By Dr David Whitehouse BBC News Online science editor

After weeks of playing hide-and-seek in polar pack ice, the Australian research ship Aurora Australis has successfully retrieved scientific instruments that have been lying in deep water off Antarctica's coast for more than a year.

The instruments were moored near the Amery Ice Shelf, between 500 and 1,200 metres (1,600 - 4,000 feet) below the ocean surface.

They were placed there to collect valuable data as water moved across the face of the shelf.

This will give scientists a better idea of how the seas around the White Continent behave and how they might affect global climate.

Remote release

"The instruments are very expensive and retrieving them was always going to be difficult," said Australian scientist Dr John Church, onboard leader of the oceanographic program that deployed the moorings.

Chasing down the instruments among the pack ice

"We knew the data would be invaluable, so it was important for us to get them if we could."

One of the instruments, an upward-looking sonar that monitors the underside of floating sea ice, became embedded in an iceberg and was moved several kilometres from its original position.

The other instruments measuring the current, salinity, conductivity, temperature and depth of the ocean provided crucial information on the ocean's conditions.

The instruments were designed so that they could be released remotely from their sub-surface moorings, to float to the surface as the retrieval ship approached.

Unseasonal weather

They could then be scooped up into a net for their data to be downloaded by scientists. In practice however, their retrieval was not so straightforward.

Unseasonal weather with a lack of the usual southerly winds had prevented ice surrounding the moorings from being blown out to sea.

At one stage, Aurora spent about 10 hours pushing ice out of the way to reach the moorings.

"As fast as we could clear a patch of water, it would fill in with floes again," said Rob Easther, voyage leader. "On several occasions, we came frustratingly close to retrieving the instruments.

"But on our fifth attempt we finally bagged the last instrument. We were pretty happy," he said.