Sedimentary Nitrate Respiration Potentially Offsets the Climatic Benefits From CO ₂ Uptake by Marginal Seas

Abstract Sediment nitrate respiration eliminates reactive nitrogen (Nr) and consumes organic carbon (OC) accompanying by CO 2 and N 2 O production to partially neutralize the climate benefit of sedimentary carbon burial. The quantitative linkage between carbon and nitrogen stoichiometry and greenhouse potential of this syndepositional process, particularly at a marginal sea scale, remains unexplored. Here we show that temperature and organic matter co‐regulate the sediment nitrate respiration and associated N 2 O production in China's marginal seas. By establishing empirical equations, we access that 2.8 ± 0.4 Tg Nr (∼26.5% of riverine input) is annually respired via degrading 2.2 ± 0.2 Tg OC (∼12.5% of OC deposited) to produce 15.0 ± 3.5 Gg N 2 O‐N, which may counter‐balance 15.1 ± 8.1% of the air‐sea CO 2 influx. This link between anthropogenic Nr input and removal to carbon sequestration reveals that sedimentary nitrate respiration potentially reduces the climatic benefits of marginal seas.