Phytoplankton production and biomass estimates in the northeast Atlantic Ocean, May–June 1990

Time series measurements of size-fractionated chlorophyll a concentrations and primary production were made over the course of the spring bloom in and adjacent to a mesoscale eddy in the N.E. Atlantic as part of the U.K. Biogeochemical Ocean Flux Study 1990 Lagrangian Bloom Experiment. Substantial production, dominated by the >5μm and >1–5,μm fractions, was recorded before the main growth phase of the bloom, although total chlorophyll a concentrations varied little over this period. The main growth phase of the bloom, which occurred over approximately one week, was dominated by the > 1–5 μm fraction; a principal constituent was the small diatom Nanoneis hasleae, which almost entirely displaced larger diatoms more typical of a spring bloom population. The >5 um phytoplankton fraction became dominant for approximately two weeks following the main bloom growth phase but was replaced at the end of the observation period by the > 1–5 μm and 0.2-1 μm fractions. Phytoplankton taxonomic data for the 1990 bloom period were very different to the more typical bloom conditions of 1989. An intercomparison of14C production measurements made by U.K. and Dutch participants during the period of the Experiment using common samples gave total column productivities differing by <4%.