Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
Bundesamtes für Seeschifffahrt und Hydrographie, Hamburg, Rostock
(Federal Maritime and Hydrographic Agency of Germany, Hamburg, Rostock)
In general the 2003 results of heavy metal concentrations in the Baltic Sea revealed no pronounced changes compared to previous years. Regional and temporal limited variations of trace metal concentrations, which have been observed periodically in the western Baltic, have been attributed to the changing enrichment of suspended matter in the watercolumn.
A new awareness has been observed in connection with the saltwater inflow event in January 2003. Not only the rivers and the atmosphere are potential input sources for trace metals into the Baltic Sea. Also the higher Cadmium and Copper concentration of the inflowing North Sea water contributes to an increase of the concentrations in the deepwater. It was calculated, that with the inflow of 200 km³ of North Sea water, which happened in January 2003, an additional input of 3000 kg (3 t) of Cadmium and 60000 kg (60 t) of Copper entered the Baltic Sea.
In a further step, the question has been discussed, if long-term trace metal trends in surface and deep waters of the Gotland Basin (Central Baltic) are a result of enhanced/reduced input to the Baltic Sea or if they are related to a "feedback mechanism” including the stabilisation of the anoxic deep water regime and the irreversible trace metal export by diffusive exchange across the oxic-anoxic interface. A first example was calculated for Cadmium. Estimations of the internal export Cd-fluxes show, that diffusive Cddiss fluxes (0.764 nmol/m² * d) across the oxic–anoxic interface and particulate Cd-fluxes (0.8 nmol/m² * d; Pohl et al.2003) are in the same range. External atmospheric (1.6 nmol/m² * d; HELCOM 1998) and riverine input fluxes (1.4 nmol/m² * d; HELCOM 1998) are also in the same range, but by a factor of 2 higher, than the internal export fluxes. About 50 % of the Cd which has been supplied by rivers and by the atmosphere is eliminated by diffusive and particulate export across the oxic-anoxic interface, and accumulated in the sediments.
This result demonstrates, that the decrease of cadmium concentrations in surface and deep waters is not only a result of decreasing anthropogen input, but also a result of internal geochemical cycling associated with a change of metal speciation, which has been induced by long-term stagnation and the change to anoxic conditions in deep waters.
The complete report is available in German on the internet at:
http://www.bsh.de/de/Meeresdaten/Beobachtungen/MURSYS-Umweltreportsystem/PDF/osretro032004.pdf (8,63 MB)