AbstractThe benthic oxygen demand and inorganic nutrient release have been investigated in the coastal zone of the Mid‐Atlantic Bight of the United States usingin situand ship‐board incubations to estimate fluxes across the sediment‐water interface. Oxygen demand ranged from ca. 70 ml m−2hr−1nearshore in warm (25°C) muddy sediments to ca. 4 ml m−2hr−1in cold (6°C), coarse‐grained sediments offshore. Ammonium ion flux was out of the sediments in all but 4 of 29 incubations, while nitrate was often found to be utilized within or on the sediments, decreasing in 10 of 29 incubations. Those locations with fluxes of nitrate out of the sediment had concentrations in the pore water that were generally high, sometimes up to several mM l−1. Nitrate fluxes were always well below those of ammonia, even where high almost equivalent concentrations of both NH4and NO3were found at the same locale.On George's Bank only 13 % of total N demand by the phytoplankton was estimated to be supplied by the benthos, whereas in New York Bight the supply amounted to 42 % of the demand. This difference can be attributed to higher pelagic biological and advective (mixing and upwelling) inputs to George's Bank compared to the relatively well stratified New York Bight in lat