Spatio-temporal mosaic of the phytoplankton spring bloom in the open Baltic Sea in 1986

Abstract

The spatio-temporal variability of the phytoplankton spring bloom in the open Baltic Sea during an international joint study (PEX'86) is described in relation to the physical and chemical environment. Simultaneous participation of 14 research vessels enabled highly synoptic sampling of the study area of 20 X 40 n mile. Onset of the bloom was controlled by mesoscale hydrodynamic features a pair of cyclonic and anticyclonic eddies; water masses with different salinities. The eddies supported an exceptionally high amount of chlorophyll (> 700 mg m-' in the cyclonic eddy). The temporal development of the bloom was different in each of the mesoscale features. Chlorophyll levels in the eddies started to decrease due to se&mentation before formation of the thermocline and the depletion of inorganic nutrients. Variability of the chlorophyll distribution was highest just before the peak in the spatially averaged concentrahon was attained.