Sedimentation of phytoplankton during a spring bloom in the Øresund

Rates of sedimentation of phytoplankton from a spring bloom in the Øresund, Denmark, were estimated from changes in the sediment content of phytoplankton pigments. From late March to early May about 20–26 g/m2 of phytoplankton carbon was deposited on the sediment surface. This deposition could explain 45–60% of the annual benthic metabolic activity. In the sedimentation period a fluid zone developed at the sediment-water interface, with high concentrations of organic matter and phytoplankton pigments. The existence of this zone is discussed in relation to feeding and growth of macrobenthos at this time. Observed microdistributions of sediment water, organic material and phytoplankton pigments were considered important for the distribution of benthos.