TRACE-METAL DISTRIBUTIONS IN SEAWATER AND ANOXIC BRINES IN THE EASTERN MEDITERRANEAN-SEA

The vertical distribution of dissolved and particulate trace metals (M n, Fe, Ni, Cu, Cd) is reported for seawater and the anoxic brines of T yro and Bannock Basins in the eastern Mediterranean. In normal Mediter ranean seawater, the distribution of dissolved trace metals is governe d by water mass circulation, as well as by local input sources. For Cd and possibly Cu, steady-state behaviour is not a viable assumption, p robably as a result of anthropogenic sources. In agreement with previo us reports, no correlation was observed between dissolved Ni, Cu, Cd, and the major nutrients. At the seawater-brine interface, all trace me tals show dramatic changes in concentration. In the brines, the concen trations of dissolved Fe and Mn are strongly elevated compared to over lying waters, yet probably limited by formation of solid sulfide and/o r carbonate phases. The distributions of dissolved Fe and sulfide show a remarkable mirror image of those found previously in the Orca brine (Gulf of Mexico), and the ionic concentration products are approximat ely the same in all three basins. The difference in absolute Fe and su lfide concentrations is thought to be caused by a high supply of Fe to Orca Basin. Concentrations of dissolved Ni, Cu, and Cd in the brines are at least one order of magnitude lower than in overlying waters, mo st likely due to formation of solid sulfide phases. We believe these d ata provide the first indication of substantial nickel-sulfide (co)pre cipitation within an anoxic basin. Particulate metal concentrations ar e elevated at the seawater-brine interface and are probably associated with the presence of solid sulfide phases. In addition, the extreme d ensity gradient at the interface will slow the sinking rate of particl es and lead to accumulation of particles at the interface due to accum ulation.