The BIOTRANS-site (47°N, 20°W), is presently the main working area of the JGOFS "Long-term study on the variability of particle flux in the North Atlantic". This site is frequently influenced by stream-arms of the North Atlantic Current, introducing mesoscale hydrographical variability into the upper ocean. One goal of M 27/2 was to study mesoscale variability of wintertime mixed layer depths in relation to the hydrographical structure in the investigation area. Lateral variability in the mixed layer and their forcing functions (solar insulation, air temperature and wind stress) were monitored by CTD-profiles and shipborne sensors. The hydrographic measurements were carried out to estimate the relevant depths for biological and chemical probing and for characterization of the wintertime physical properties (depth of the mixed layer, distribution of temperature, salinity). Special emphasis was taken on the upper 500 m of the water column for characterization of the distribution of relevant physical, chemical and biological properties within the epipelagic zone.
During Meteor 27/2 from La Coruña to Lisbon (20 January 1994 to 8 February 1994) hydrographic measurements were carried out in the vicinity of the BIOTRANS-station (47°N, 20°W) and during cruising from La Coruña to 47°N, 15°W. During leg M 27/2 ten XBTs were dropped, mainly during the transit from 47°N, 15°W back to La Coruña. The distance between the XBT drops was about 30 miles. The water column was probed by a Neil Brown CTD with a fluorometer and a 12 bottle water sampler with 12 L Niskin bottles. From the Niskin bottles water samples were taken for calibration of fluorescence and salinity measurements and for determination of nutrients, oxygen, alkalinity, total dissolved inorganic carbon, dissolved organic carbon and nitrogen, and various biological stock parameters from distinct water depths. Due to heavy weather conditions electronic and mercury reversing thermometers for in-situ calibration of the temperature sensor of the CTD were not used.