Release of dissolved organic carbon (DOC) from sediments of the N.W. European Continental Margin (Goban Spur) and its significance for benthic carbon cycling

Pore water samples from N.W. European Continental Margin sediments (49°–48°N; 16°–10°W) were analyzed for dissolved organic carbon (DOC) using a high-temperature-combustion method. Two transects across the margin were investigated, a gentle undisturbed slope (Goban Spur: 670–4800 m) and the centre of a nearby precipitous canyon (Whittard Canyon: 180–3680 m). Concentrations of pore water DOC were typically an order of magnitude greater than those from the overlying water. Therefore, the sediments appear to act as a DOC source to the bottom water. Conservative estimates (ignoring possible bioirrigation) of the DOC-fluxes from the sediments gave daily fluxes of 0.09–0.15 mmol m−2 d−1 for the Goban Spur sediments and 0.05–0.16 mmol m−2 d−1 at the canyon transect. These relatively low variations in DOC concentrations and fluxes under widely differing environmental conditions suggest that production and consumption of labile DOC components proceed at similar rates irrespective of what the overall benthic activity is. To the total benthic degradation rate of organic carbon the DOC-fluxes contribute 2–32% (median 11%), a part that is missing when the carbon degradation rate is solely based on determinations of the oxygen consumption rate or on pore water modeling of the reaction. Thus, DOC-effluxes are a significant component of benthic carbon budgets in continental margin sediments.