Net, actual, and potential sediment-water interface NH4+ fluxes in the northern Gulf of Mexico (NGOMEX): Evidence for NH4+ limitation of microbial dynamics

► Net NH4+ flux underestimated actual NH4+ regeneration rates at the sediment-water interface in the Northern Gulf of Mexico. ► Sediment ammonium demand (SAD), the difference between potential and actual NH4+ flux, indicated NH4+ limitation of microbial dynamics at the sediment-water interface in the northern Gulf of Mexico. ► Microbial N limitation status at the hypoxic site related to NH4+ was independent of oxygen status. ► Microbial N limitation status at the hypoxic site related to NH4+ was independent of oxygen status. ► Hurricane activity decreased N dynamics at the sediment-water interface in the northern Gulf of Mexico.