Distributions of N2O concentration and sea-to-air flux in the western Tropical North Pacific: Influences of eddies and typhoons

Abstract

Marine systems are active regions for producing and emitting nitrous oxide (N2O), a potent greenhouse gas. In October 2018, samples were collected in the western tropical North Pacific (WTNP) to study the distributions, emissions, and influencing factors of N2O. The N2O concentrations in surface seawater showed little variation, ranging from 6.2 to 7.9 nmol L−1 (corresponding to N2O saturation range of 104–125%), with an average of 6.7 ± 0.6 nmol L−1. The vertical N2O distribution is a mirror image of dissolved oxygen (DO), increasing with depth from the surface to a maximum in the vicinity of the DO minimum. The sea-to-air fluxes of N2O ranged from 0.1 to 7.5 μmol m−2 d−1, with an average of 1.7 ± 2.2 μmol m−2 d−1, indicating that the WTNP was a net source of N2O to the atmosphere. Nitrification is the main process for N2O production. The presence of the Mindanao Eddy noticeably changes the vertical profiles of N2O in the water column, allowing the N2O-rich deep water to reach the subsurface layers, but has little effect on the surface N2O concentration. After Typhoon “Yutu” passed through, N2O concentrations in surface and subsurface water increased dramatically. The surface concentration increased by about 20%, and the sea-to-air flux of N2O increased by about 56%. Despite the short duration of the typhoon, its effect on N2O distribution and sea-to-air flux was more pronounced than that of eddies.