Horizontal distributions of biogenic and lithogenic elements of suspended particulate matter in the Mediterranean Sea.

Price, N. B. and Brand, T. D. and Pates, Jackie M. and Mowbray, S. R and Civitarese, G. and Miserocchi, S. and Heussner, S. and Lindsay, F. S. (1999) Horizontal distributions of biogenic and lithogenic elements of suspended particulate matter in the Mediterranean Sea. Progress in Oceanography, 44 (1-3). pp. 191-218. ISSN 0079-6611

Abstract

A study has been made of the distribution of terrigenous (Al and Mnex, Feex) and biogenic (POC, PNtot, Porg, Sibio, Baex) elements of suspended particulate matter (SPM) on a series of transects in three marginal areas of the Mediterranean Sea; the NW Mediterranean, the western Adriatic to the Strait of Otranto and the southern (Cretan) and northern Aegean Sea, with the intention of assessing the influence that river discharges have on their concentrations. In the Adriatic, high Al concentrations (60–200 μgl−1) occur as a consequence of direct discharge from the River Po but importantly from sediment resuspension the amount of which, under steady state conditions, is also related to riverine discharge. In the Otranto Strait high Al concentrations overlie its western shelf and slope. On the NW Mediterranean only waters influenced by the River Rhone, as off Banyuls-sur-mer, show high Al. Particulate Mn is mostly river derived, but principally exists in marginal areas from redox cycling in surficial sediments, a consequence of high biological production induced by nutrient discharges from rivers. High particulate Mnex concentrations were measured in the northern Adriatic, off Banyuls-sur-mer and the northern Aegean, where there are strong river influences. In contrast, the more oligotrophic seawaters off Marseilles, the Balearics and the Cretan Sea show lower concentrations of Mnex, and depth profiles of Mnex especially in the latter area are similar to those found in ocean waters. Of the biogenic elements studied, the assumed presence of terrigenous organic carbon, especially on the Adriatic shelf, largely precludes POC concentrations from being an indicator of marine production. A better guide to productivity induced by river nutrient discharges is seen in the distribution of Porg and Sibio concentrations, which show a gradual southward reduction along the Adriatic shelf and higher concentrations off Banyuls-sur-mer than on other transects in the NW Mediterranean. In the Cretan Sea the close association between Baex and Sibio rather than Porg within cyclonic eddies, where upwelling occurs, implies degradation of organic matter associated with diatom production causes barite to precipitate in the seawater.