Tallinn - Helsinki transect in the Gulf of Finland

Dissolved inorganic nitrogen concentration in the water column; Phytoplankton growth; Raw in-situ nutrient analyser output

CTD; autoanalysers

The Gulf of Finland is one of the most eutrophic parts of the Baltic Sea and although the external nutrient loads to the Gulf have declined during the last decade, the water dissolved inorganic phosphorus (DIP) concentrations have increased during the same period. The variability of phytoplankton biomass and species composition is very high both in time and space and depends largely from hydrodynamic processes accompanied by water movement and mixing, and transport of nutrients. The cyclonic general circulation scheme and estuary like inclination of density isopycn have been considered as one reason for higher productivity in the northern coastal sea of the Gulf of Finland. In shorter time scale the wind-induced vertical mixing and upwelling events (both coastal an offshore) are more important processes which bring nutrient rich water from lower layers to the upper layers and which form the patchy pattern in phytoplankton distribution. The sediments in the Gulf of Finland are significant sources of bioavailable phosphorus and in the present state the ecosystem of the Gulf of Finland is very sensitive to increased sediment effluxes of nutrients. Therefore it is necessary to investigate more closely the general hydrographical regime and related possible nutrient fluxes to the upper layers to be able to differentiate and demonstrate the importance of internal loading to the Gulfs ecosystem. The main goals of the project are: 1) to describe the hydrographical regime in a sea area between Tallinn and Helsinki during two different seasons in spring and summer; 2) to describe the concentrations of dissolved inorganic nutrients and their variability in depth, space and time in the sea area under investigation in spring and summer; 3) to describe the variability of phytoplankton biomass and species composition in the sea area under investigation in spring and summer; 4) to demonstrate the link between the variability of nutrient concentration and prevailing hydrographical conditions in the area under investigations; 5) to demonstrate in which scale the measured variability in phytoplankton biomass and species composition can be connected with the internal and external nutrient loads made available by the prevailing hydrographical features.

Department of Marine Systems at Tallinn University of Technology
MSI, Akadeemia tee 15a
Tallinn

12618
Estonia