MARINE GEOLOGY OF THE GULF OF TRIESTE (NORTHERN ADRIATIC) - GEOCHEMICAL ASPECTS

Geochemical analyses of surficial sediment in the Gulf of Trieste, in terms of organic carbon, total nitrogen and phosphorus C-13 composition of sedimentary organic matter, the trace metals Hg, Pb, Cr, Cu, Zn, Cd, Ni, Mn and Fe, and the radionuclides Cs-137 and Pb-210 were carried out. The higher values of organic carbon, total nitrogen and phosphorus are restricted to the clayey silty sediments of the small bays of Koper, Piran, Muggia and Panzano and around the River Isonzo outflow. On the basis of delta-C-13 values, the sedimentary organic matter is of entirely marine origin in the central part of the gulf, which is bordered by two areas of greater terrigenous influence. With the exception of Hg and Pb, the areal distribution of the trace metals is similar to that of carbon, nitrogen and phosphorus, with higher contents in the clayey silty and silty sediments. The mercury and Pb contents exhibit a gradual decrease from the mouth of the Isonzo River towards the southern part of the gulf. Riverine inputs also provide the most important sources of Cs-137 in the sediments of the gulf. High Cs-137 activities in the uppermost layer of the cores indicate the Chernobyl signal and, in contrast to Pb-210, the vertical profiles show its occurrence in deeper layers, which is attributed to diffusion of the Cs-137. Distribution studies of the biogenic elements carbon, nitrogen and phosphorus and the trace metals in the surficial and subsurficial layers of the 40 m deep borehole MK-6 in Koper Bay, shows practically no enrichment in the former, but an increase in the Hg and Pb contents. This would not indicate a rapid increase in eutrophication in the gulf or that the sediments are an important sink for biogenic elements.