Plankton Distributions and Processes across a Front in the Open Baltic Sea

Kahru, M, Elken J, Kotta I, Simm M, Vilbaste K.  1984.  Plankton Distributions and Processes across a Front in the Open Baltic Sea. Marine Ecology-Progress Series. 20:101-111.


Sections of the temperature-salinity structure in the southeastern Gotland Basin, central Baltic Sea, revealed the existence of a pronounced salinity front. A water mass with anomalously low salinity extended vertically across the horizontally uniform thermocline. Plankton distribution and primary productivity showed consistent features with the frontal structure: the near-surface primary productivity increased ?-fold adjacent to the front and levelled down farther away from it; the column chlorophyll had a broader and less distinct maximum on the high-salinity side of the front; the zooplankton community was similar in composition but its biomass more than doubled in the higher- salinity water. It is suggested that upwelling of nutrient-rich water in the frontal zone had triggered the productivity peak, whereas the subsequent advection and diffusion were instrumental for the broader chlorophyll maximum. Owing to the lower phytoplankton/zooplankton ratio, the nutrient cycling had to be faster in the higher-salinity water mass.