ATMOSPHERIC DRY DEPOSITION FLUX OF METALLIC SPECIES TO THE NORTH-SEA

Air sampling on a series of 10 research cruises on the North Sea (sout h of 56-degrees-N) has yielded detailed spatial distributions of atmos pheric metal concentrations, Al, Ca, Cd, Cu, Fe, Mg, Na, Pb and Zn whi ch closely parallel the results of earlier published models. Air mass back trajectory analysis demonstrates the strong influence which sourc e region may have upon the elemental composition of the North Sea atmo sphere. A cascade impactor designed to collect efficiently large as we ll as small aerosol has produced detailed size distributions from whic h mass weighted deposition velocity estimates have been produced (Al, 0.33; Cd, 0.24, Cu, 0.44; Fe, 0.30; Pb, 0. 1 3; Zn, 0.30 cm s-1) enabl ing estimates for the dry deposition flux to the study area to be made . Extrapolation of these data to the whole of the North Sea yields dry deposition flux estimates (Cd, 33; Cu, 350, Pb, 370; Zn, 2640 tonnes yr-1) which are in some instances substantially lower than those previ ously reported, but nevertheless represent a significant pathway for m etallic species to enter this marine environment. The size distributio ns show the clear dominance that large aerosol has upon the overall dr y deposition flux. Flux estimates are thus highly sensitive to the sam pling of this large aerosol component, and to assumptions made regardi ng the sea surface as a source of giant trace metal-enriched particles which act only as a means of recycling marine metals.