Processes influencing the fate of trace metals in the North Sea

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Abstract
Measurements were made in the southern North Sea of trace metals (dissolved and particulate Mn, Fe, Ni, Co, Cu, Zn, Cd, Pb) with contrasting biogeochemical behaviours. The extent to which distributions of dissolved metals over the survey area were determined by the mixing of river waters with seawater varied among the metals, and also seasonally; even for nickel and copper, which behaved most conservatively, other processes were significant. Specific instances of the effects of scavenging by particles and of inputs from benthic recycling are evident from the data and these processes lead generally to modifications of fluxes of dissolved metals in estuarine plumes. While the effect of atmospheric inputs on dissolved concentrations of metals is, on the basis of other evidence, a factor contributing to spatial and temporal variability, specific features arising from them were not identified; they probably account, however, for increased concentrations of dissolved lead observed at high salinities in the Humber plume. Seasonal variations in concentrations of dissolved metals, paralleling those of micronutrients, were not identified but manganese showed a pronounced seasonal variability related to its reduction—oxidation chemistry. Wide differences occurred in the partition between dissolved and particulate fractions, although for copper and zinc the partition could be described by a narrow range of distribution coefficients under certain conditions.