The AMISOR mooring hunt

On 26 January 2002, when Aurora Australis set out from Hobart on the seventh voyage of the summer season, the major oceanic research objective around which the voyage schedule was planned — recovery of nine moorings with attached instruments — looked a lost cause. Sea-ice covered the region in front of the Amery Ice Shelf where the supply ship Polar Bird had been beset only weeks before.

The instrument moorings had been deployed a year earlier to complement 24 current, depth and conductivity casts. The invaluable data they had gathered was the main incentive to make an extra effort to retrieve them.

The use of satellite information was critical to the success of the voyage, allowing plans for the movement of the ship to be highly effective in combating the unseasonal conditions. Daily satellite images of weather and ice conditions provided the information needed to make the best of the changing conditions. Patience was rewarded when satellite images revealed a small area of open water at the eastern end of the Amery and the ship was able to enter, allowing the work to begin.

Over the following two weeks, Aurora Australis crisscrossed the face of the ice shelf several times to make the best of opportunities when the ice drifted away from mooring and instrument sites. This meant many hours of waiting, using the ship’s propellers to clear ice. It also meant returning to some sites several times to get the right conditions — releasing a mooring prematurely could mean losing the data and the equipment under the ice. One site was visited five times before its mooring was successfully retrieved.

Rob Easther (Voyage Leader), AAD