Processes affecting the distribution of dissolved trace metals in the North Aegean Sea (Eastern Mediterranean)

Abstract

Dissolved Cd, Cu Ni and Mn were measured in the North Aegean Sea, during the MATER and INTERREG programmes, in order to evaluate the processes which control their distribution. The North Aegean receives the fresh waters from many of the rivers draining the Balkan Peninsula, as well as large amounts of brackish water from the Black Sea and the Sea of Marmara. Furthermore, the area consists of two shelf areas and discrete basins. Six sampling cruises were undertaken in the area, during three seasons (winter, spring, summer); a total of 402 samples were analysed. Trace metal levels in the area are comparable to those of other semi-closed Mediterranean regimes (Cd:0.018–0.278 nM; Cu:0.56–6.85 nM; Ni:2.22–18.6 nM; Mn:0.068–44.0 nM). The nutrient-like behaviour of Cd, Cu and Ni was not detectable. In contrast, surface enhancement of trace metals was apparent. The calculation of enrichment factors ( E f) showed that the two shelf areas were not enriched significantly in trace metals, relative to the deeper water parts of the system. Only Mn showed some degree of enrichment over the shelves. The transport of trace metals, towards the open waters, is controlled largely by the prevailing surface water circulation and mixing pattern of the two water masses—Black Sea Water and Levantine Intermediate Water. Occasionally, increases in Cu, Ni and Mn concentrations were observed at depth, near the slope or in the deep basins.