Oceanic production and occurrence of dimethyl sulfide (DMS) and its subsequent ventilation to the atmosphere significantly contribute to the global sulfur cycle and impact the climate regulation. Spatial distributions of DMS, dimethylsulfoniopropionate (DMSP, precursor of DMS), and dimethyl sulfoxide (DMSO, oxidation product of DMS), production and removal processes of DMS (including biological production, microbial consumption, photo-degradation, and sea-to-air exchange), and biogenic contributions to the atmospheric sulfate burden were simultaneously studied in the western Pacific Ocean during winter. Sea surface DMS, DMSP, and DMSO were strongly correlated and had similar distribution patterns. The DMS photo-degradation efficiency ratio (normalized using incident photon flux density) for ultraviolet B radiation (UVB): ultraviolet A radiation (UVA): photosynthetically active radiation (PAR) was 391: 36: 1. However, considering the solar spectral composition, the actual contributions of UVB, UVA, and PAR to DMS photo-degradation in surface waters were 40.6% AE 10.7%, 41.2% AE 15.6%, and 18.2% AE 7.2%, respectively. When integrated across the entire mixed layer, UVA and PAR became the dominant drivers, accounting for 45.2% AE 18.0% and 38.0% AE 17.3% of DMS photo-degradation, respectively, as UVB was significantly attenuated in seawater. The DMS budget of the entire mixed layer indicated that microbial consumption, photo-degradation, and ventilation accounted for about 74.3% AE 11.9%, 19.3% AE 9.3%, and 6.5% AE 4.0% of total DMS removal, respectively. Even if ventilation was a minor DMS removal pathway, DMS emissions still contributed approximately 45.2% AE 25.6% of the atmospheric non-sea-salt sulfate burden over the western Pacific Ocean.

Continuous input from the Changjiang River significantly reshuffled the ecosystems in the Changjiang Estuary and adjacent East China Sea, impacting the production, distribution, and emission of marine dimethyl sulfide (DMS). However, the effect of phytoplankton biomass and composition on DMS under different nutrient inputs remains poorly understood. Two comprehensive cruises to characterize their effects were conducted in spring and summer 2015. The areas with high concentrations of DMS, dimethylsulfoniopropionate (precursor of DMS), and dimethyl sulfoxide (photo‐oxidation product of DMS) were largely consistent with high phytoplankton abundances along the front of Changjiang Diluted Water in both seasons. Both the higher conversion ratio of dissolved dimethylsulfoniopropionate to DMS and the higher DMS biological production rate in summer contributed to the higher DMS levels. Once produced in seawater, more than half of the DMS was directly consumed by microbes, resulting in a turnover time of 1–2 days, which was shorter than that driven by ventilation. A ship‐based incubation experiment revealed that, with increasing N/Si and N/P ratios from the Changjiang River, phytoplankton biomass increased and the community shifted from diatom‐dominated to dinoflagellate‐dominated, which was conducive to DMS production. It was noteworthy that strong DMS photo‐degradation induced by high nitrate concentrations may have masked DMS production to some extent, while urea only had a promoting effect and therefore led to a maximum increase in DMS yield. Our findings indicated that the increase in phytoplankton biomass and succession of phytoplankton community induced by changes in nutrient inputs will promote DMS emissions from the Changjiang Estuary.

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Ocean-derived dimethyl sulfide (DMS) is widely concerning because of its hypothesized influence on global climate change. This study aims to explore the distribution characteristics and influencing factors of DMS and partial pressure of carbon dioxide (pCO2) in the Northwest Pacific Ocean, as well as the potential relationship between DMS and pCO2. A high-resolution, underway, shipboard measurement device was used to determine the DMS and pCO2 of the surface seawater and atmosphere in the Northwest Pacific and its marginal seas during November 2019. The result show that atmospheric and surface seawater DMS concentrations ranged from 3 to 125 pptv and 0.63 to 2.28 nmol L-1, respectively, with mean values of 46 ± 19 pptv and 1.08 ± 0.34 nmol L-1. The average sea surface pCO2 was 371 ± 16 μatm (range from 332 to 401 μatm). The trends in the surface seawater DMS in different current systems were primarily associated with phytoplankton abundance and composition. Biological activity and physical processes such as cooling jointly influenced the sea surface pCO2. A cold eddy along the transect in the Northwest Pacific Ocean increased DMS at the sea surface by 10% and CO2 uptake by 3%. We found a significant negative correlation between DMS and pCO2 in the Northwest Pacific Ocean at the 0.1° resolution [DMS]seawater = -0.0161[pCO2]seawater + 7.046 (R2 = 0.569, P < 0.01). The DMS and pCO2 sea-air fluxes were estimated to range from 0.04 to 25.3 μmol m-2·d-1 and from -27.0 to 4.22 mmol m-2·d-1 throughout the survey area. The Northwest Pacific Ocean, especially the Oyashio Current, is an important sink of CO2 and a source of DMS.