Anoxic mineralization of biogenic debris in near-shore marine sediments (Gulf of Trieste, northern Adriatic)

Abstract

Anoxic degradation of sedimentary biogenic debris using closed incubation experiments was studied at two sampling stations in the Gulf of Trieste (northern Adriatic). Production rates of dissolved inorganic carbon (DIC), NH 4 +, PO 4 3− and dissolved Si (dSi), and reduction rates of SO 4 2− were measured and anoxic mineralization rates were modeled using a first order G-model and multi-G approach. The depth profiles of these rates revealed an exponential decrease indicating that the largest fraction of mineralization of biogenic debris and SO 4 2− reduction occurs in the surficial sediment layer and on the sediment surface. Comparing the depth-integrated anoxic mineralization rates at both stations with benthic fluxes of DIC, NH 4 +, PO 4 3− and dSi measured at the in situ temperature in the dark, it appears that the DIC and PO 4 3− fluxes are higher because the mineralization mostly occurs at the sediment–water interface, and that besides SO 4 2− reduction, other electron acceptors are involved in the organic matter decomposition pathway in these surficial sediments. The NH 4 + production was higher than the benthic fluxes because of NH 4 + oxidation. The production of dSi was in good agreement with benthic fluxes implying that temperature is the main factor of dSi production and benthic fluxes in these sediments.