Satellite-derived concentrations of chlorophyll-like pigments in the Baltic Sea are clearly higher than in the Skagerrak and North Sea.
The highest summer concentrations were found in the Gulf of Finland, Gulf of Riga while lowest in the Bothnian Bay.
Results and assessment
Figure 1. Variation of mean summer (July-August) surface chlorophyll concentrations in various regions of the Baltic Sea area between 1998 and 2002 estimated from SeaWiFS. (JRC atmospheric correction) Click the regional trend images to enlarge.
Chlorophyll concentration is a proxy of phytoplankton biomass which is a primary link between nutrient reserves and the marine food web. Satellite remote-sensing images of ocean colour, calibrated as chlorophyll concentration provide a unique synoptic view of the marine ecosystem. A major value of satellite remote sensing of ocean colour lies in the spatial long-term monitoring of the marine environment.
Nutrient concentrations regulate primary productivity and amount of plankton algae in the marine food web. Thus chlorophyll a as a proxy for phytoplankton biomass helps to assess the response of marine ecosystem to eutrophication – one of the main problems in the Baltic Sea.
The annual mean summer (July-August) concentrations of chlorophyll-like pigments in various regions of the Baltic Sea in 1998-2002 are presented in Figure 1.
Summer concentrations in the Baltic Sea are clearly higher than in the Skagerrak and North Sea.
The highest summer surface concentrations were found in the Gulf of Finland and Gulf of Riga while lowest in the Bothnian Bay. The low concentration of chlorophyll in the Kattegat does not reflect the regional water column biomass as the subsurface peak is deep enough for not being detected by the sensor and shallow enough (light availability) to influence significantly the summer primary production (~60-70% compared to ~35% in the Central North Sea).
Subsurface chlorophyll maxima exist in the Baltic Sea, too but their importance to total production is low due to high absorption of light by coloured dissolved organic matter ("yellow substance") and to a lesser extent, by particles. This is especially the case in the Bothnian Bay.
The 5-year period is too short to show any general or regional trends in the concentrations.
For technical and quality information, see the report “ Chlorophyll a concentrations from satellite remote sensing of ocean colour”.
EU/JRC/IMW Marine Environ Unit
Last update 14 October 2003