Source, diagenesis, and fluxes of particulate organic carbon along the western Adriatic Sea (Mediterranean Sea) T. Tesi a, b, ⁎, L. Langone a , M. Giani c , M. Ravaioli a , S. Miserocchi a a ISMAR-CNR UOS di Bologna Istituto di Scienze Marine P. Gobetti 101 40129 Bologna Italy b ITM Department of Applied Environmental Science Stockholm University via Svante Arrhenius väg 8 SE-11418 Stockholm Sweden c OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale Dipartimento di Oceanografia Biologica via Auguste Piccard 54 34151 Trieste Italy abstract article info Article history: Received 21 April 2012 Received in revised form 24 February 2013 Accepted 2 March 2013 Available online 15 March 2013 Communicated by G.J. de Lange Keywords: Adriatic Sea carbon cycling organic carbon flux and burial diagenesis fossil terrigenous and marine carbon 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. δ 13 C, Δ 14 C, 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 (t 1/2 ) 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 t 1/2 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 to our 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%. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Clinoform-shaped deposits are ubiquitous sedimentological bodies of modern continental margins, including both carbonate and silicoclastic platforms. They formed after the attainment of the modern sea level high-stand (mid-late Holocene) when river outlets and shoreline migrated landward. Their shape and thickness are affected by a series of factors including relative sea level, sediment supply, depositional regime, and sediment type (Pirmez et al., 1998). Typical clinoforms developing along continental margins consist of a prograding body capped by aggrading topsets that become thinner upwards. Clinoforms formed over the last few thousands of years were described along the inner shelf of diverse settings: tectonically passive margins, such as the Amazon prodelta (Nittrouer et al., 1986), active margins, such as the Ganges–Brahmaputra setting (Goodbred et al., 2003) and several epicontinental-shelves (Alexander et al., 1991). As clinoform-shape deposits are essential building blocks of the infill of sedimentary basins (Mitchum et al., 1977; Vail et al., 1977), they are sites of intense organic carbon (OC) deposition and account for a significant fraction of the OC burial in the ocean during intergla- cial periods. In addition to the high deposition rates, the OC burial in these deposits is promoted by the relatively low reactivity of the land-derived material being diagenetically pre-altered and matrix- protected against degradation (Mayer, 1994; Mead and Goñi, 2008). Furthermore, hypopycnal coastal plumes experience intense new primary productivity constituting another pool of organic biomass accumulating along the clinoform body (Lohrenz et al., 1990; Campanelli et al., 2011). However, in high energy environments, some clinoforms can act as efficient incinerators where OC burial is limited by the prolongated residence of particles in refluxing suboxic mobile mud (e.g. Fly river delta, Gulf of Papua; (Aller and Blair, 2004). In this biogeochemical study, we focused on sigmoidal clinoforms that are generally associated with low-energy environments (Pirmez Marine Geology 337 (2013) 156–170 ⁎ Corresponding author at: ITM, Department of Applied Environmental Science, Stockholm University, Svante Arrhenius väg 8, SE-11418 Stockholm, Sweden. Tel.: +46 8 674 7245. E-mail addresses: tommaso.tesi@bo.ismar.cnr.it, tommaso.tesi@itm.su.se (T. Tesi). 0025-3227/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.margeo.2013.03.001 Contents lists available at SciVerse ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo