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^-2d^-1 (4.8±2.5 μmol m^-2d^-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), δ¹⁵N^bulk-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.