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As a contribution to the EC-OMEX-II program, sediment carbon and nitrogen budgets are presented for the Iberian Margin (northeastern Atlantic). The budgets for degradable organic carbon and associated nitrogen were calculated from sediment and pore water properties, using a steady-state version of a numerical coupled diagenetic model, OMEXDIA. Data were collected throughout the major upwelling period along five transects, four of which were located on the open margin and one positioned in a major submarine canyon, the Nazaré Canyon. A comparison of in situ oxygen profiles measured with monocathodic microelectrodes and with Clark type microelectrodes showed that monocathodic electrodes overestimate the oxygen concentration gradient near the sediment-water interface. This artifact probably results from the loss in sensitivity of the monocathodic microelectrode during profiling. Shipboard time course measurements with Clark type electrodes demonstrated transient conditions upon sediment retrieval on deck and indicated enhanced The sediments from the canyon and from a depositional area on the shelf were enriched in organic carbon (3-4.5 wt%) relative to the open margin stations (0.5-2 wt%) and showed C/N ratios exceeding Redfield stoichiometry for marine organic matter, indicating there was deposition of organic carbon of terrestrial origin in these areas. The oxidation of organic carbon on the open margin declined from ~11 gCm2y1 on the shelf to 2 gCm2y1 at 5000 m water depth, and was dominated by aerobic oxidation. T Anaerobic oxidation, denitrification and, therefore, total oxidation of organic carbon was enhanced within the canyon relative to the open margin. Total organic carbon oxidation decreased with water depth from 22 gCm2y1 at the head of the canyon to 3 gCm2y1 over its fan. The reactivity of the organic carbon deposited in the canyon was lower than those of the shelf stations, suggesting that the canyon is being enriched in older, laterally advected organic matter. The burial of refractory organic The burial of refractory organic carbon and the deposition of degradable organic carbon were both positively correlated with the sedimentation rates for the Iberian Margin, and indicated burial efficiencies were 0.6 to 48%. A single trend for burial efficiency versus sedimentation rate for both the canyon and the open margin indicates that the sedimentation rate was the master variable for the geographical distribution of organic carbon oxidation and carbon preservation on the NW Iberian Margin.
Original languageEnglish
Pages (from-to)399-431
JournalProgress in Oceanography
Issue number2-4
StatePublished - 2002

ID: 99968