Early diagenesis and benthic fluxes in Manfredonia Gulf (Southern Adriatic sea)

The Gulf of Manfredonia is situated in the western part of Southern Adriatic Sea. This shallow gulf is considered a complex area, presently not well studied (as opposed to the Northern Adriatic Sea), where anthropogenic pressure plays an important role for pollution phenomena and alteration of the marine ecosystem. The aim of this study was to investigate early diagenesis processes that produce benthic fluxes affecting the chemistry of water column. Two oceanographic cruises were carried out in late summer 2002 and in late winter 2003 to evaluate the seasonal variations of early diagenetic processes. Sediment cores were collected in two sites (inside and in the offshore boundary of the gulf) in which high sedimentation processes occur. Parameters on the solid fraction and pore waters profiles of TCO2, NH3, NO3, PO4 3-, SO4 2-, alkalinity, Fe, Mn, Ca and Mg were determined in each site. Benthic fluxes were measured using two benthic chambers in each site. The 234Th profiles show a more intense bioturbation in the firsts centimetre of sediment in the inner station and the sedimentation rate, calculated by 210Pbex and 137Cs profiles, ranging from 0.40 gcm-2 y-1 in the inner shelf to 0.49 gcm-2 y-1 in the outer gulf. In winter, pore water profiles suggest oxic and anoxic degradation of reactive organic matter less intense and occurring in a thinner layer close to the sediment-water interface in both site Reactive organic matter degradation products also show an intense irrigation in the firsts centimetres of sediments in both stations. During the summer, the pore water profiles reflect remineralization processes limited to a very thin layer close to the sediment water interface in both stations but higher in the shallowest site. Measured benthic fluxes will be compared with the fluxes obtained by pore water modelization to investigate sedimentwater interface processes.