Effects of offshore drilling activities on the geochemical and sedimentological processes in the Northern Adriatic Coastal area

The aim of the research was to study the geochemical and sedimentological effects on the sea bottom of discharging water-based drilling mud in the sea, and the presence of the drilling platform. Six sampling survey were repeated during seven years on the Antares platform area situated in the Northern Adriatic Sea. The samples were analysed to determine grain size, mineralogical composition, total Fe, Mn, Ba, Cr, Pb, Zn, Cu, Cd, Co, Ni and V content (the last four only in the final survey), organic-C, bond type and mineralogical association with the solid matrix of Cr, rb, Zn and Cu. The discharge of cuttings and drilling fluids and the presence of the platform caused an increase in grain size and Ba, Cr, Pb and Zn concentrations. Their areal distribution dependent on the marine hydrodynamic conditions, with accumulations under the platform during the summer and greater dispersion during the winter. In the latter case the presence of the platform increased marine hydrodynamics and consequently sea bottom erosion. After seven years, the chemical and grain size anomalies in the surface sediments had attenuated, although there were still anomalous concentration of some elements. Ba and Cr proved to be effective tracers of, respectively, the coarser and finer particles discharged during drilling. Pb and Zn were associated with the presence of the exploitation platform. Elements introduced with the drilling mud, such as Cr, were subject to a bond ageing process which reduced their bioavailability. Elements introduced into the environment after discharges had ceased, such as Zn, are more bioavailable.