Dissolved trace metals in the western Mediterranean Sea: total concentration and fraction isolated by C18 Sep-Pak technique

An investigation of trace metal distributions in the Western Mediterranean Sea was carried out during the RRS Discovery cruise (July 1993) in which a transect from the Strait of Gibraltar to the Strait of Sicily was conducted . Organically complexed dissolved trace metals and their total concentratio ns were measured to investigate the end-members and to predict the environm ental capacity of the Mediterranean for potential toxic metals. The distrib ution of trace metals can be accounted for by the mixing of several end-mem bers and by some atmospheric inputs to the surface water. For Pb and Fe, th e effects of the atmospheric inputs are more pronounced than for the other metals. Due to the rapid exchange of water masses, the Western Mediterranea n may have the ability to assimilate the increased external inputs for some trace metals such as Cu, Cd, Ni and Zn. But the external inputs for Pb and Fe exceed the removal capacity of the Western Mediterranean and these elem ents may accumulate in the water column of the western basin. The C18 Sep-P ak technique and direct determination by DPASV were used to determine the a mount of trace metal-organic complexes. The Cls Sep-Pak column isolates onl y a small fraction of trace metals except for Cu. The maximum hydrophobic f ractions for the studied trace metals, except for Cd and Pb, which are not detectable, were found in the subsurface layer at all stations. This maximu m may well be Linked to picoplankton activity and the picoplankton, prochlo rophytes may have an important role in the speciation of dissolved Cu as we ll as Synechococcus. These organic ligands for Cu were produced at the maxi mum of biological activity in the Western Mediterranean basin and seem to b e accumulated at halocline level by Mediterranean hydrodynamic characterist ics. However, direct determination by DPASV showed that the major part of C u, Cd and Pb, complexed by organic materials, was not isolated by Cls Sep-P ak technique. (C) 1999 Elsevier Science B.V. All rights reserved.