Annual cycle of particle size fractions and phytoplankton biomass in the northern Baltic proper

Abstract

A large data set of particle concentrations in the range 1-1000 μm, chlorophyll a, and associated measurements from the surface waters of the N Baltic during 1985-1989 was analyzed to construct spatially and temporally averaged annual time curves of particle size fractions and phytoplankton biomass. Chlorophyll a concentration was well correlated with the 28-73 μm size fraction and had seasonal peaks in April-May, corresponding to the diatom spring bloom, and in August, corresponding to the late-summer bloom of blue-green algae. The 2 maxima were separated by the early summer minimum when the 1-10 μm particle fractions corresponding to a mixed assemblage of small phytoplankton and microheterotrophs reached their maxima. The largest particles (163-1000 μm), corresponding to smaller mesozooplankton, reached their maximum in July-August before the blue-green maximum. -from Authors