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 a 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 capitalized on the unique capabilities of Autosub, a seven-meter 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 1,600 meters.

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 meters. 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 kilometers 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.

Autosub will spend the next 3 years exploring beneath ice shelves up to a kilometer thick, to investigate their role in the Earth`s climate. See this URL.

British Antarctic Survey (BAS) is responsible for most of the UK's research in Antarctica. It is a component of the Natural Environment Research Council.

More information about the work of the Survey can be found at this URL. The BAS Dynamics and Management of Ocean Ecosystems program measures how the food webs of the Southern Ocean respond to environmental change.

(Reference: Antarctic krill under sea ice: Elevated abundance in a narrow band just south of ice edge, SCIENCE, March 8th 2002.)


[Contact: Claire Grainger]

08-Mar-2002