The PRIME 1996 cruise: an overview

The UK PRIME cruise, June-July 1996 in the NE Atlantic, consisted of two le gs. During the first, detailed chemical and biological observations were ma de in time-series mode adjacent to the centre of a cold-core eddy in the vi cinity of 59 degreesN 20 degreesW using SF6 tracer techniques as the basis for the Lagrangian study. The eddy, which appeared to have been formed the previous winter, remained coherent over the 9 days of the survey and advect ed only slowly. The phytoplankton community in the eddy was dominated by th e coccolithophorid Coccolithus huxleyi. High microzooplankton grazing rates indicated minimal export losses from the surface layer. Significant shifts in many, but not all, of the chemical and biological properties measured w ere observed over the course of the experiment, especially after the passag e of a storm event, which resulted in considerable deepening of the mixed l ayer followed by a return to fully stratified conditions. The second leg co nsisted of a transect from 59 degreesN 20 degreesW to 37 degreesN 19 degree sW, with a further Lagrangian time-series study based on a drogue marker in itiated at the southern end of the transect. Maximal biological activity wa s generally encountered in the region between two fronts located at 52.5 de greesN and 48 degreesN, while to the south of 48 degreesN oligotrophic cond itions prevailed. At the southern Lagrangian site, a deep chlorophyll maxim um was present and high column new production was recorded as a result of t he euphotic zone extending below the depth of the nutricline. Microzooplank ton grazing rates were lower at this location than at the northern eddy sit e. The influx of a warm, saline water body into the upper layers during the southern survey led to a major shift in many of the biological and chemica l properties being measured. At both the northern and southern Lagrangian s ites, the biomass of the mesozooplankton exceeded that of the microzooplank ton. (C) 2001 Elsevier Science Ltd. All rights reserved.