1. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.
2. Fisheries Research Services (FRS) Marine Laboratory Aberdeen, Post Office Box 101, Victoria Road, Aberdeen, AB11 9DB, UK.
3. The Open University, Department of Earth Sciences, Walton Hall, Milton Keynes, MK7 6AA, UK.
4. Southampton Oceanography Centre, Empress Dock, Southampton SO14 3ZH, UK.