RRS Discovery Cruise 224 Leg 2, 30 Dec-17 Jan 1997. Biological and physical investigations in the region of the Almeira-Oran Front (western Mediterranean)

The purpose of Discovery Cruise 224, Leg 2, was to continue the physical and biological surveys previously undertaken during Leg 1 as part of the EEC MAST OMEGA Project; and to undertake comparisons of the western Mediterranean macrozooplankton and micronekton communities on either side of the Almeria-Oran Front. The sampling programme consisted of: 1) Fine scale SeaSoar surveys, at the beginning and end of the leg, to investigate the changes in the structure of the Almeria-Oran frontal system, and to establish the sites for biological sampling. 2) Investigations of the day and night depth distribution, throughout the water column, of the macroplankton and micronekton communities, by means of a vertically stratified series of RMT1+8M net deployments, at two sites on either side of the Almeria-Oran Front. This was largely successful, but bad weather prevented any near-bottom tows being carried out at one of the sites. 3) Investigations of the near-surface cross-frontal distribution of macrozooplankton and micronekton, again using the RMT1+8M net system. 4) Observations on the patterns of acoustic backscatter, using the shipborne ADCP and towed EK500 systems, throughout the cruise and to relate these with data from the biological sampling; with additional ‘sea-truthing’ from Longhurst-Hardy Plankton Recorder deployments. In addition studies were made on the bioluminescent characteristics of the interesting examples of the pelagic fauna