Phytoplankton biomass and production in the southern North Sea

Abstract

Surface chlorophyll concentrations in the southern North Sea have been contoured for a 15 mo period, from 4 August 1988 to 3 October 1989. Seasonal changes in chlorophyll concentration show low phytoplankton biomass in the western and central regions and highlight the high phytoplankton biomass which develops in the spring and early summer in the Southern and German Bights. I4C measurements made on each of the survey cruises have been used to estimate primary production for the whole of the southern North Sea. These data also highlight very high daily rates of primary production in phytoplankton blooms in the eastern North Sea. Regional estimates, based on the ICES subdivisions of the North Sea, are 79 g C m-'yr-' for Region 3 , 199 g C m 2 yr-' for Region 4 , 261 g C m-' yr-' for Region 5, and 119 g C m'* yr-' for Region 7 In winter and early spring, the euphotic depth in the region off the Belgian and Dutch coast is as great as the water column depth and light will reach the bottom sediments; this may be a factor in the early development of Phaeocystis blooms in these regions.