Organic carbon oxidation and benthic nitrogen and silica dynamics in San Clemente Basin, a continental borderland site

Organic carbon oxidation rates in San Clemente Basin were determined by benthic chamber experiments using the Bottom Lander, along with studies of pore water chemistry. Non-steady-state diagenetic models are developed for interpreting concentration-time data from the benthic chamber experiments. O 2, NO 3 −, and SO 4 2− are all important oxidants for organic carbon at our study site. Regenerated fixed nitrogen was consumed by NO 3 − reduction. There is a flux of NO 3 − into the sediments, and the benthic flux of NH 4 + is undetectable. The total rate at which fixed nitrogen is removed from the oceans at this site is about twice the flux of PON to the sea floor. SiO 2 fluxes calculated from interfacial pore water gradients are in satisfactory agreement with those determined using the Lander. Most silica dissolution must therefore occur within the sediments, although interstitial profiles show that little dissolution occurs below 1 cm depth.