Source, diagenesis, and fluxes of particulate organic carbon along the western adriatic Sea (mediterranean Sea)

In this study, we investigated the modern organic carbon (OC) cycling along the clinoform-shaped deposit that developed after the attainment of the modern sea-level in the Adriatic Sea (~5.5 kyr cal BP). Newly acquired data were combined with published results to characterize the (i) origin, (ii) diagenesis, and (iii) fluxes of OC along the Adriatic clinoform. 13C, Δ14C, and lignin phenols were used to constrain the composition of OC accumulating in surface sediments. Sediment cores collected at different water depths were used to describe the early diagenesis during burial in different regions. In addition, on the basis of an extensive number of accumulation rates and OC data, we assessed the flux of OC to the seabed and its burial. Our results showed that terrigenous OC is the dominant OC source in the Po prodelta mainly in the form of pre-aged soil-derived OC and vascular plant fragments. Along the clinoform, both Δ14C and the concentration of lignin-derived phenols decreased with increasing distance from the Po prodelta indicating the influence of an additional pool of aged OC that gradually becomes more important because of its selective preservation during the sediment transport. As a result, degradation rates (k) decreased along the clinoform as a function of the sediment oxidative history. The calculated half-life of reactive OC (t1/2) was ~14.6 yrs in the Po prodelta whereas topset/forest deposits south of this region exhibited higher values, ~100 yrs, indicating the presence of refractory material. In the distal bottomset region, the t1/2 was particularly high ranging from ~255 to ~912 yrs. Because of the significant southward component of the sediment transport, the OC deposition in the southern surface sediments exceeded the local OC input via rivers (ratio deposition/input 1.2). Conversely, the northern Adriatic was characterized by a marked imbalance (ratio deposition/input 0.3–0.5). According toour calculations, the OC flux to the seabed along the clinoform was ~309 Gg of C per year whereas the OC burial was ~180 Gg of C per year, corresponding to an overall burial efficiency of ~59%.