Sedimentary Nitrate Respiration Potentially Offsets the Climatic Benefits From CO2 Uptake by Marginal Seas

Abstract

Sediment nitrate respiration eliminates reactive nitrogen (Nr) and consumes organic carbon (OC) accompanying by CO2 and N2O 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 N2O 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 N2O-N, which may counter-balance 15.1 ± 8.1% of the air-sea CO2 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.