Robot submarine reveals secret stash of key Antarctic food source under sea ice

A robot submarine expedition under the Antarctic sea ice has discovered a major food reserve in the Southern Ocean. The findings, reported this week in SCIENCE, show a dense band of the shrimp-like krill under the ice, five times more concentrated than in open water. The importance of sea ice as a nursery for krill – key food for penguins, whales and fish – has long been suspected, but these are the first large scale measurements.

Scientists from the British Antarctic Survey, the Open University and the Marine Laboratory, Aberdeen, took the revolutionary £5 million Autosub, one of the most advanced underwater probes ever made, on its first mission under sea ice. Krill, which graze the underside of sea ice, were detected by a special echosounder. The concentrated band of krill was located 1-13km inside the ice edge.

Project leader Dr. Andrew Brierley, now based at the University of St. Andrews, said, “Discovery of this band is major new insight because it shows that it is the ice edge, rather than sea ice generally, that is important for krill. Large reductions in ice area, perhaps following melting due to regional climatic warming, might not be so harmful to krill populations because, in summer at least, krill are not widely distributed under ice.”

The expedition capitalised on the unique capabilities of Autosub, a seven-metre long torpedo-shaped submarine, designed, built and operated by Southampton Oceanography Centre with Natural Environment Research Council (NERC) funding. Running on torch batteries, the unmanned submarine can conduct pre-programmed missions of up to 40 hours long and can dive to depths of 1600 metres.

Dr Brierley added, “Prior to the advent of Autosub, it was impossible to investigate the environment under sea ice over ranges of more than a few metres. SCUBA divers have looked under ice but they can only spend limited periods of time underwater and can only see short distances. Ice breaking ships can penetrate the pack ice to make biological measurements but, while breaking the ice, they can disturb any natural krill/ice associations. Autosub enabled us to make continuous measurements up to 27 kilometres inside the ice covered ocean.”

In addition to looking at krill, the team made the first ever continuous measurements of Antarctic sea ice thickness. Changes in sea ice thickness over time provide insight into environmental responses to climate change. Detailed studies of ice thickness have been made from military submarines in the Arctic, but data are not available for the Southern Ocean. Autosub has thus made a major contribution to our understanding of physical and biological ocean processes in a previously inaccessible environment.

Issued jointly by University of St Andrews and British Antarctic Survey.

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