Fine-sediment mass balance in the western Adriatic continental shelf over a century time scale

To obtain a quantitative estimate of the sediment accumulating on the muddy belt extending along the western Adriatic continental shelf, a budget was calculated based on the mass accumulation rates measured from more than one hundred activity–depth profiles of Pb-210. Cs-137 depth-distributions were used, when possible, to support Pb-210 results. Pb-210 profiles show quasi-monotonic declines in the foreset region of the central Adriatic clinoform. In the prodelta of the rivers Po and Isonzo, Pb-210 profiles are characterized by intervals of low and uniform activity, which are thought to be produced by flood deposition. Since the north Adriatic is shallow and occasionally affected by storms from Bora wind, sediments are not in steady-state and their accumulation is the net result of recurring deposition, resuspension and winnowing events. In the western Adriatic, mass accumulation rates range between 0.04 and 6.6 g cm-2 (cm to the minus 2) yr-1 (yr to the minus 1). Peak values were recorded in the Po and Isonzo prodeltas and along a narrow belt between Pescara and the Gargano promontory. Furthermore, the latter depocentre is located immediately seaward of the offlap break (40–50 m water depth) and parallels that of the most recent sigmoid of the HST. The integration of mass accumulation rates throughout the mud wedge of the north and central Adriatic gave a value of about 42.0 Tg yr-1 (yr to the minus 1) of sediment accumulating along the Italian coast. The balance between sediment accumulation and riverine sediment supply (about 46.6 Tg yr-1 (yr to the minus 1)) suggests an export of 4.6 Tg yr-1 (yr to the minus 1) to the south Adriatic basin and/or the Mediterranean Sea. The along-shore sediment transport is very effective and, in particular, 16.2 Tg yr-1 (yr to the minus 1) of sedimentary material (about 35% of the riverine supply) is transferred from north to central Adriatic, through the Ancona section.