Dissolved Nitrous Oxide and Methane in the Taiwan Strait: Distribution, Seasonal Variation, and Emission

Abstract The global ocean plays an important role in the overall budgets of nitrous oxide (N 2 O) and methane (CH 4 ), especially in continental estuaries and shelf areas. Four cruises were conducted between 2021 and 2022, covering the spring, summer, and fall seasons, to study the spatial and seasonal characteristics of N 2 O and CH 4 distributions and emissions in the Taiwan Strait (TWS). The surface N 2 O and CH 4 concentrations gradually decreased from the coast to the open sea, with maximum values (14.3 and 15.6 nmol L −1 ) occurring near the Jiulong and Minjiang estuaries, respectively. The mean surface N 2 O concentration (8.2 nmol L −1 ) was highest in the spring and approximately the same in the summer as in the fall. The mean surface concentrations of CH 4 (8.8 nmol L −1 ) were greater in summer than in spring and fall, probably because of the high freshwater input in summer. Except for several stations in fall, surface waters were oversaturated with N 2 O and CH 4 relative to the atmosphere in other seasons, and the TWS was a net source of atmospheric N 2 O and CH 4 in the spring, summer, and fall. In situ production is the main source of N 2 O and CH 4 in the TWS, with nitrification being the dominant mechanism of N 2 O production in the TWS. In contrast, physical influences (riverine inputs and water mass mixing) reshape the distributions of N 2 O and CH 4 . The annual emissions of N 2 O and CH 4 from the TWS were estimated to be 0.9 × 10 −3 ± 2.9 × 10 −3 Tg yr −1 and 1.6 × 10 −3 ± 3.0 × 10 −3 Tg yr −1 , respectively. Taken together, the TWS accounts for 0.025% of the surface area of the world's oceans and 0.022% ± 0.07% and 0.017% ± 0.033% of global oceanic N 2 O and CH 4 emissions, respectively.