1. Department of Oceanography, University of Southampton, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK,
2. Present address: Cambridge University Engineering Department, Trumpington Street, Cambridge CB4 1EE, UK.
3. Present address: Marine Science Program, Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA.
4. emu Environment Ltd, The Hayling Island Marine Laboratory, Ferry Road, Hayling Island, Hampshire, PO11 0DG, UK