Sedimentary Carbon Oxidation and Denitrification on the Shelf Break of the Alaskan Beaufort and Chukchi Seas

Sediment-water fluxes were measured on transects across the northern Alaskan continental margin. Dissolved oxygen fluxes approximated total carbon dioxide fluxes when fluxes were low, but oxygen underestimated the higher total carbon dioxide fluxes. This follows a diagenetic model in which aerobic sediments occur below 86 μmol total carbon dioxide m -2 h -1 and anaerobic conditions intensify with increased organic matter loading. The relationship between the fluxes of nitrogen gas and total carbon dioxide agreed with the Redfield ratio, indicating that regenerated nitrogen predominantly returned to the overlying waters as nitrogen gas. On each transect, highest fluxes were found in a 20 km wide band located seaward of the 100 m continental shelf break. The magnitude of fluxes in these richer sediments exceeded that expected from the low productivity found on the outer continental shelf, suggesting upwelling-induced higher productivity at the shelf break.