Nitrous oxide and Hydroxylamine in the East China Sea in 2015

The first analyses of N2O isotopocule signatures in the East China Sea (ECS) are presented, along with hydroxylamine (NH2OH) and N2O concentrations, to clarify the dominant N2O production processes in the coastal water. In the ECS in October 2015, N2O ranged from 6.3 to 33.1 nmol L-1, equivalent to 99% – 251% in saturation, leading to the air-sea fluxes of 1.6 – 10.5 μmol m-2 d-1 (4.8±2.5 μmol m-2 d-1) using the W2014 formula. The coexistence of high levels of NH4+, NH2OH, and NO2- indicated the potential for nitrification and/or hybrid N2O formation. In the shallow water (< 300 m), the concentration (~9.3 nmol L-1), δ15Nbulk-N2O (~6.8‰), δ18O-N2O (~45.1‰), and 15N site preference (SP, ~14.8‰) of N2O were close to those isotopic signatures in atmospheric N2O; whereas those values in the deep water increased downward, reaching their maxima of 33.1 nmol L-1, 8.6‰, 54.7‰, and 18.7‰, respectively.