Retrieving scientific instruments moored deep in the seas off Antarctica's coast was never going to be easy. But two weeks of hide-and-seek in the polar pack by the crew of Australian research ship Aurora Australis, using technical know-how, satellite technology and good old-fashioned ingenuity, ended in success.
The collection of oceanographic and glaciological equipment to be collected was moored near the Amery Ice Shelf a year ago, in depths of between 500 and 1200 metres. This area was close to where the Australian supply ship Polar Bird was trapped by ice for more than a month in December last year.
The instruments being retrieved included seven oceanographic moorings attached to large blocks of concrete as well as several glaciological tools called CTDs, used to measure current, temperature and salinity. Deployed to collect valuable data as water moved across the face of the shelf, the instruments were expected to give scientists a better idea of how the seas around the white continent behave and how they might affect global climate.
The instruments, worth around $2 million in total, were designed so they could be released remotely and float to the surface as the ship approaches, where they could then be scooped up onto the ship in a net for their data to be downloaded by scientists. This would be achieved through acoustic signals transmitted by the ship, which would tell the anchored moorings to release and float to the surface. In practice however, the retrieval wasn't so straightforward.
According to CSIRO's John Church, onboard leader of the oceanographic program that deployed the moorings, retrieving the instruments was always going to be difficult. Although it wasn't the first time such equipment had been used in the Antarctica, this latest experiment was the largest to look under an ice shelf.
"We knew the data would be invaluable, so it was important for us to get them if we could," he said.
Church admitted that at first he was sceptical the expedition would be able to recover all of the moorings. Unseasonal weather conditions prior to the team's departure in late January meant ice conditions were far worse than those experienced in previous expeditions, he said.
When the team arrived in the region, Church's doubts became reality.
"The first three moorings were easy (to retrieve)," he said. "The rest were covered by ice."
At one point, Church said, "an upward-looking sonar (ULS) that looks at the underside of the floating sea ice became embedded in an iceberg and was moved several kilometres".
In his situation report, voyage leader Rob Easther said the usual southerly winds that would normally push the ice northwards, and thus make the expedition possible, had not eventuated.
"Before the task of retrieving the instruments was over, we would use helicopters, satellite technology, the icebreaking capacity of the ship, as well as advice from experienced people both on the ship and back in Australia to achieve the successful result," he said.
At one point, the Aurora spent ten hours pushing ice out of the way to reach the moorings.
"On several occasions we came frustratingly close to retrieving the instrument," Easther said.
"We were concerned new ice was forming and we wouldn't see a breakout of ice this season at all.
"But on our fifth attempt we finally bagged the last instrument - we were pretty happy."
Despite the hampering ice conditions, all of the moorings were retrieved.
CSIRO's Church says technology was absolutely essential to the success of the expedition.
In particular, satellite technology, which was used throughout the expedition to monitor ice conditions.
"The technology worked very well. We used satellite images throughout the expedition, which told us how ice conditions were changing and whether there were opportunities to retrieve the moorings," he said.
Easther agreed the satellite technology proved absolutely critical in the expedition's success, particularly in terms of maneuvering around the shelf.
"Quite often we swapped from one end of the shelf to the other, based on satellite imagery. Without that satellite imagery, we'd be in all sorts of strife," he said.
A helicopter was also used for reconnaissance flights, reporting back to Aurora the current state of the ice.
"What you see on the ship is limited. If you can get up in the air and have a look, with a helicopter and Global Positioning System (GPS) and plot out the break in conditions, and then plan a route for the ship, the technology proves invaluable," Easther said.