Variability of dissolved and particulate trace metals in the kiel and mecklenburg bights of the Baltic Sea, 1990-1992

Water samples from surface and bottom waters of two bights of the Baltic Sea were analysed for dissolved and/or particulate concentrations of Al, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb and Zn, in addition to the main oceanographic variables, at 27 stations during six cruises between February 1990 and July 1992. The metal values show distinct regional differences, with maximum concentrations at the near-shore stations, The levels of total Hg exhibit a significant negative relationship with salinity. In surface layers, seasonal differences due to biogenic uptake of elements could not be detected for any of the dissolved metals. In bottom waters, however, summer-time concentrations of a number of metals are in clear excess of winter levels either due to diffusion of metals (Go, Fe, Mn) from the sediments under low-oxygen or anaerobic conditions, or due to mineralization processes (Cd, Zn) of recently sedimented biogenic particulates. With the exception of Fe and Pb, the particulate fractions are of minor importance, with slight variabilities between the seasons only. The K-D values (ratio between metal concentrations in the particulate and dissolved fractions) decrease by more than two orders of magnitude in the order Fe-Pb-Mn-Co-Zn-Cd-Cu-Ni. Finally, the results are discussed with regard to a trace metal monitoring programme in the area.