Trace metals at two sites in the southern North Sea: Results from a sediment resuspension study

Abstract

Particulate and dissolved trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) have been determined following intensive sampling in January and May 1989 at two sites in the southern North Sea. Site A (52° 39.5′N, 003° 40.0′E) had sandy sediments, a permanently well-mixed water column and salinities >34.5, associated with waters from the English Channel. Particulate trace metal concentrations were higher in January than in May. The concentrations in the dissolved phase were unchanged between the two periods, except for dissolved Mn which had low concentrations in January, as a result of uptake onto particles. Atmospheric inputs to surface waters were evident in January, mainly for particulate Pb. Tidally induced resuspension processes produced temporary changes in the particulate and dissolved trace metal concentrations of the bottom waters for Mn, Pb and Zn. The variation in particulate trace metal concentrations, in May, fitted a two-component particle mixing model. It is argued that a significant source of dissolved metals was from the remineralisation of particulate material held within biological fluff at the sea bed. Site B (54° 35.0′ N, 004° 50.0′ E) had sediments of muddy sand, a seasonally stratified water column and it was influenced mainly by Central North Sea Water, with salinities >34.5. Particulate and dissolved trace metal concentrations did not vary between the cruises, only particulate Pb had higher concentrations in January. The tidal resuspension of particulate metals was negligible and, in May, only the concentrations of dissolved Pb and Zn increased at higher current velocities. The results identify pathways and particle–water interactions that affect trace metal transport in the North Sea.