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

Anoxic degradation of sedimentary biogenic debris using closed incubation e xperiments was studied at two sampling stations in the Gulf of Trieste(nort hern Adriatic). Production rates of dissolved inorganic carbon (DIC), NH4+, PO43- and dissolved Si (dSi), and reduction of SO42- were measured and ano xic mineralization rates were modeled using a first order G-model and multi -G approach. The depth profiles of these rates revealed an exponential decr ease indicating that the largest fraction mineralisation of biogenic debris and SO42- reduction occurs in the surficial sediment layer and on the sedi ment surface. Comparing the depth-integrated anoxic mineralization rates at both stations with benthic fluxes of DIC, NH4+, PO43- and dSi measured at the in situ temperature in the dark, it appears that the DIC and PO43- flux es are higher because the mineralization mostly occurs at the sediment-wate r interface, and that besides SO42- reduction, other electron accepters are involved in the organic matter decomposition pathway in these surficial se diments. The NH4+ production was higher than the benthic fluxes because of NH4+ oxidation. The production of dSi was in good agreement with benthic fl uxes implying that temperature is the main factor of dSi production and ben thic fluxes in these sediments. (C) 2001 Elsevier Science B.V. All rights r eserved.