Particulate matter and downward flux in the Northern and Central Adriatic Sea

Abstract

During four oceanographic cruises carried out in June 1996, February and June 1997, and February 1998, particulate matter characteristics and short-term downward fluxes measured with drifting sediment traps were studied in two areas of the Adriatic Sea. The investigated areas were located one south of the Po River delta, and the other in the central Adriatic between Pesaro and Ancona. In each area, a frontal system was detected and two stations inside and outside the front, i.e . in coastal and offshore areas, were selected. The particulate and dissolved matter revealed a higher concentration in the coastal areas with the highest values in the central Adriatic coastal zone in both February surveys. Total mass fluxes ranged within two orders of magnitude from 11 to 3139 r mg m d in the northern area and similarly from 20 to 3864 r mg r m r d in the southern one, with higher values in the coastal stations. The organic carbon accounted for 3-30% of total flux in the northern coastal station with higher values in June, whereas at the offshore station it ranged from 6 to 39% in summer, decreasing to values lower than 10% in February. In the southern zone the organic carbon content was less than 2% in winter and from 3 to 33% in summer. The organic carbon fluxes (1-82 and 6-71 r mg C m d in the northern and southern area) were comparable with others measured with drifting sediment traps in the same area, though much lower with respect to those measured with long-term moored sediment traps. The export of organic carbon from the photic layer (expressed as the percentage of primary production) in the northern area was less than 10% at the coastal station, reaching a maximum of 12% in the offshore area. In the central Adriatic area it was greater, with values reaching up to 66% at the coastal station in June 1996. The organic carbon loss via sedimentation from the POC pool was low ( i.e. <1.5% per day) at both stations in the northern zone, while in the southern area the export was generally greater, exceeding 10% in the offshore area.