If it decides it's not happy it will have to turn round and run away from the ice

Nick Millard

The vehicle, called Autosub, is to be used to study the abundance and distribution of krill, the crustaceans at the centre of the Antarctic food web.

There is some concern that warming in the Antarctic may damage populations of these shrimp-like creatures, with potential knock-on effects for the whales that feed on them.

An echosounder on the sub will emit pulses of sound and the strength of the reflections will indicate the type and quantity of the crustaceans detected.

The biggest challenge on this expedition is an engineering one. Most underwater research vehicles are either manned or controlled remotely by scientists on a mother ship, sometimes attached to it by a cable.

Ice diving

Autosub, however, is entirely autonomous.

Navigation is usually assisted by regular resurfacing to take readings from the Global Positioning Satellite (GPS) system. But under Antarctic sea ice, this will not be possible.

Krill: Vital food for some whales

"From a scientific point of view, this is very exciting, but from an engineering point of view, it's a worry," said Nick Millard, of the Southampton Oceanography Centre, UK. Millard is part of a 10-member team which left for the Southern Ocean this week.

"If Autosub gets into trouble, it usually just jettisons an abort weight and surfaces. This time, if it decides it's not happy, it will have to turn round and run away from the ice as quickly as possible."

Around 10 short missions will be carried out in the Weddell Sea. The submersible will be tested under relatively thin sea ice, just two to three metres thick, and under icebergs.

The ultimate aim is to explore the waters beneath the polar ice shelves, which can be several hundred metres thick. Exactly what lies beneath these features remains a mystery.