A potential source of organic pollutants into the Northeastern Atlantic: The outflow of the Mediterranean deep lying waters through the Gibraltar Strait

Small and large-size particles were collected in the water column (50-3000 m) of a Northeastern Atlantic area where deep Mediterranean waters, outflow ing through the Strait of Gibraltar, are incorporated at mid-depth. Particl es collected by water filtration (0.7 mum pore size) and by vertical hauls of a neuston net (50 mum mesh size) were analyzed for organic pollutants, n amely aliphatic and aromatic hydrocarbons, and organochlorine compounds. Sm all-size particles represented the largest bulk of particulate organic carb on as well as of hydrophobic organic pollutants. Surface concentrations of n-alkanes (C-14-C-35), aromatic hydrocarbons (12 parent compounds), PCBs (7 congeners), and DDTs (DDT+DDE) were, respectively, in the range of 50-63 n g/L, 23-68 pg/L, 8-13 pg/L, and 0.05-1.7 pg/L. These concentrations showed a general decrease with depth, particularly significant in the upper 200 m, consistently with the POC contents. Compositional changes with depth were also evident in small-size particles and included the depletion of low mole cular weight n-alkanes and low chlorinated PCB congeners as well as a decre ase of the fossil to pyrolytic PAHs ratio. Unusual increases of concentrati ons were observed at mid-depths (900-1100 m), indicating additional particl e inputs, either by in-situ formation or by advective transport from the Me diterranean. The latter was recognized because small-size particles within these water veins exhibited distribution patterns out of the vertical seque nce and similar to those of deep Mediterranean waters. An input of 8 and 0. 5 tons per year of the above PAH and PCB compounds, respectively, has tenta tively been calculated as the contribution of these Mediterranean waters to the Northeastern Atlantic.