Dimethylsulfide Flux Research Articles

The Central Great Barrier Reef as a Net Source of Climatically Relevant Biogenic Volatile Organic Compounds

AbstractBiogenic volatile organic compounds (BVOCs) such as dimethyl sulfide (DMS), methanethiol (MeSH), isoprene, and monoterpenes partly control the Earth's radiation budget. As such, measuring coral‐reef BVOC emissions are important for understanding the impact of future climate and shading interventions that are being developed as part of the Reef Restoration and Adaptation Program to protect the Australian Great Barrier Reef (GBR). Here we report high temporal resolution BVOC concentrations and fluxes from the central GBR in the austral summer of 2021–2022, including the first flux estimates of MeSH, isoprene, and monoterpenes from reef systems, using a proton‐transfer‐reaction quadrupole mass spectrometer. Median fluxes of DMS, MeSH, isoprene, and monoterpenes across the two voyages were 4.26 ± 2.53, 0.94 ± 0.64, 0.05 ± 0.03, and 0.03 ± 0.03 μmol m−2 d−1, respectively, indicating that the central GBR is a net source of climatically relevant BVOCs in summer. Dissolved concentrations of BVOCs were positively correlated with sea surface temperature and proximity to the coast, which was most likely due to a coastward gradient for chl‐a and nutrient concentrations. Predictably, wind speed and dissolved BVOC concentrations were the main drivers of BVOC fluxes. This study adds to our understanding of ocean‐atmosphere exchange processes in coral reef systems and will help improve model predictions of the local climate of the GBR under future climate change scenarios.

Nested cross-validation Gaussian process to model dimethylsulfide mesoscale variations in warm oligotrophic Mediterranean seawater

The study proposes an approach to elucidate spatiotemporal mesoscale variations of seawater Dimethylsulfide (DMS) concentrations, the largest natural source of atmospheric sulfur aerosol, based on the Gaussian Process Regression (GPR) machine learning model. Presently, the GPR was trained and evaluated by nested cross-validation across the warm-oligotrophic Mediterranean Sea, a climate hot spot region, leveraging the high-resolution satellite measurements and Mediterranean physical reanalysis together with in-situ DMS observations. The end product is daily gridded fields with a spatial resolution of 0.083° × 0.083° (~9 km) that spans 23 years (1998–2020). Extensive observations of atmospheric methanesulfonic acid (MSA), a typical biogenic secondary aerosol component from DMS oxidation, are consistent with the parameterized high-resolution estimates of sea-to-air DMS flux (FDMS). This represents substantial progress over existing coarse-resolution DMS global maps which do not accurately depict the seasonal patterns of MSA in the Mediterranean atmospheric boundary layer.

DMS behaviors in pen culture of Sinonovacula constricta in Longhai, China

Dimethyl sulfide (DMS) released by the ocean has received widespread attention due to its role in aerosol formation and impact on global climate change. Research on DMS mainly focuses on coastal and open ocean environments, with limited studies addressing the influence of aquaculture activities on the production and release of marine DMS. Thus, we investigated whether fertilization for algae cultivation and the feeding process in pen culture of Sinonovacula constricta significantly contribute to DMS release. We found notable diurnal variations in DMS concentrations during and after the culture period in the ponds. During the post-culture period, both the concentration and flux of DMS in the ponds were higher than those during the culture period. The average flux of DMS during the culture and post-culture period were only 0.1 ± 0.1 μmol/(m2·d) and 0.4 ± 0.3 μmol/(m2·d), respectively, indicating that aquaculture activities of Sinonovacula constricta may not produce or release substantial DMS when compared with those from the coastal aeras and open oceans.

Dimethyl sulfide (DMS) climatologies, fluxes, and trends – Part 2: Sea–air fluxes

Abstract. Dimethyl sulfide (DMS) contributes to cloud condensation nuclei (CCN) formation in the marine environment. DMS is ventilated from the ocean to the atmosphere, and, in most models, this flux is calculated using seawater DMS concentrations and a sea–air flux parameterization. Here, climatological seawater DMS concentrations from interpolation and parameterization techniques are passed through seven flux parameterizations to estimate the DMS flux. The seasonal means of calculated fluxes are compared to identify differences in absolute values and spatial distributions, which show large differences depending on the flux parameterization used. In situ flux observations were used to validate the estimated fluxes from all seven parameterizations. Even though we see a correlation between the estimated and observation values, all methods underestimate the fluxes in the higher range (>20 µmol m−2 d−1) and overestimate the fluxes in the lower range (<20 µmol m−2 d−1). The estimated uncertainty in DMS fluxes is driven by the uncertainty in seawater DMS concentrations in some regions but by the choice of flux parameterization in others. We show that the resultant flux is, hence, highly sensitive to both and suggest that there needs to be an improvement in the estimation methods of global seawater DMS concentration and sea–air fluxes for accurately modeling the effect of DMS on the atmosphere.

A 20-year (1998–2017) global sea surface dimethyl sulfide gridded dataset with daily resolution

Abstract. The oceanic emission of dimethyl sulfide (DMS) plays a vital role in the Earth's climate system and constitutes a substantial source of uncertainty when evaluating aerosol radiative forcing. Currently, the widely used monthly climatology of sea surface DMS concentration falls short of meeting the requirement for accurately simulating DMS-derived aerosols with chemical transport models. Hence, there is an urgent need for a high-resolution, multi-year global sea surface DMS dataset. Here we develop an artificial neural network ensemble model that uses nine environmental factors as input features and captures the variability of the DMS concentration across different oceanic regions well. Subsequently, a global sea surface DMS concentration and flux dataset (1° × 1°) with daily resolution spanning from 1998 to 2017 is established. According to this dataset, the global annual average concentration was ∼ 1.71 nM, and the annual total emissions were ∼ 17.2 Tg S yr−1, with ∼ 60 % originating from the Southern Hemisphere. While overall seasonal variations are consistent with previous DMS climatologies, notable differences exist in regional-scale spatial distributions. The new dataset enables further investigations into daily and decadal variations. Throughout the period 1998–2017, the global annual average concentration exhibited a slight decrease, while total emissions showed no significant trend. The DMS flux from our dataset showed a stronger correlation with the observed atmospheric methanesulfonic acid concentration compared to those from previous monthly climatologies. Therefore, it can serve as an improved emission inventory of oceanic DMS and has the potential to enhance the simulation of DMS-derived aerosols and associated radiative effects. The new DMS gridded products are available at https://doi.org/10.5281/zenodo.11879900 (Zhou et al., 2024).

Rapid cycling and emission of volatile sulfur compounds in the eastern Indian Ocean: Impact of runoff inputs and implications for balancing atmospheric carbonyl sulfide budget

Volatile sulfur compounds, such as dimethyl sulfide (DMS), carbonyl sulfide (OCS), and carbon disulfide (CS2), significantly influence atmospheric chemistry and climate change. Despite the oceans being an important source of these sulfides, the limited understanding of their biogeochemical cycles in seawater introduces considerable uncertainties in quantifying their oceanic emissions and assessing atmospheric OCS budgets. To address this issue, we conducted a comprehensive field survey in the tropical eastern Indian Ocean (EIO) to examine the spatial distributions, source-sink dynamics, and sea-air exchange fluxes of marine DMS, OCS, and CS2. Our study indicates that nutrients, organic matter, and freshwater input from terrestrial runoff significantly affect most of the source-sink processes of these sulfides in the Bay of Bengal and even the tropical EIO. The resulting sulfide accumulation in seawater combined with high wind speeds establishes the tropical EIO as a considerable direct and indirect atmospheric OCS source. These insights underscore the potentially critical role of marine environments influenced by runoff in contributing to the atmospheric OCS budget. However, by integrating these results with previous field surveys, we believe that actual OCS emissions from tropical oceans exceed some bottom-up box-model simulations, yet fall significantly below those predicted by top-down models, still insufficient to bridge the atmospheric OCS source gap. Our detailed examination of source-sink dynamics offers deeper insights into the marine sulfur cycle and has potential implications for refining future box-models, thus mitigating uncertainties in estimating marine sulfur emissions.

Summer sea ice melting enhances phytoplankton and dimethyl sulfide production

AbstractThe relationships among sea ice melting, phytoplankton assemblages, and the production of climate‐relevant trace gases in the Southern Ocean are gaining increasing attention from the scientific community. This is particularly true for dimethyl sulfide (DMS), which plays an important role in atmospheric chemistry by influencing the formation of sulfated aerosols with radiative impacts and constituting cloud condensation nuclei. In the current study, chlorophyll a (Chl a), DMS and its precursors dimethylsulfoniopropionate (DMSP), were quantified in the Weddell–Scotia Confluence (WSC) during the 2018 record ice extent minimum period. Mixed layer changes were found to be generally associated with spatial variation in sea ice melt, with the depth being six times deeper in ice‐free, well‐mixed regions than in seasonal ice‐melting zones. The surface Chl a concentration increased from ice‐free to ice‐melting regions with elevated sea ice meltwater percentages and drawdown surface nutrient concentrations. The concentrations of surface and depth‐integrated Chl a in the upper 150 m reached maxima in the ice‐melting region with the highest fraction of sea ice meltwater, illustrating that sea ice melting promoted the occurrence of phytoplankton blooms. The DMS and DMSP concentrations in the vicinity of the ice‐melting zone were approximately three times higher than those in the ice‐free waters. The observations of this study show that the regions of ice melting in the WSC were a zone of particularly high sea–air fluxes of DMS, which could significantly contribute to the atmospheric budget of DMS in the polar regions.

Factors Controlling DMS Emission and Atmospheric Sulfate Aerosols in the Western Pacific Continental Sea

AbstractThe western Pacific continental sea significantly influences the regulation of climate‐active gases budget and the burden of sulfate aerosols. An underway shipboard measurement device was used to determine the dimethyl sulfide (DMS) in the surface seawater and overlying atmosphere in the East China Continental Sea. The average concentration of DMS in atmosphere and seawater was 122.8 ± 86.2pptv and 6.47 ± 3.58 nmol L−1, respectively. The variation trend of surface water DMS in the western Pacific continental sea was influenced by the abundance and composition of phytoplankton under different ocean current systems, with a significant impact from eddies on DMS production in the South China Sea. By eliminating the influence of terrestrial sources and limiting air mass transport within the marine boundary layer, strong correlations were established between atmospheric DMS and air mass exposure to chlorophyll (Echl), as well as between aerosol methanesulfonic acid (MSA) and Echl. During the aerosol sampling period, the atmospheric DMS levels (1,057 ± 371 ng/m3) were significantly higher than MSA levels (46.3 ± 59.8 ng/m3) in the East China Sea, where the conversion of DMS to MSA was not affected by changes in DMS concentration. The sea‐to‐air fluxes of DMS varied over a wide range, from 0.02 to 156.0 μmol m−2 d−1, with an average of 14.35 ± 18.58 μmol m−2 d−1. Marine DMS emissions play a critical role in the formation of sulfur aerosols on the western Pacific continental shelf, accounting for 24.6 ± 7.6% (14.8%–37.8%) of the total sulfate aerosols.

IPB-MSA&SO4: a daily 0.25° resolution dataset of in situ-produced biogenic methanesulfonic acid and sulfate over the North Atlantic during 1998–2022 based on machine learning

Abstract. Accurate long-term marine-derived biogenic sulfur aerosol concentrations at high spatial and temporal resolutions are critical for a wide range of studies, including climatology, trend analysis, and model evaluation; this information is also imperative for the accurate investigation of the contribution of marine-derived biogenic sulfur aerosol concentrations to the aerosol burden, for the elucidation of their radiative impacts, and to provide boundary conditions for regional models. By applying machine learning algorithms, we constructed the first publicly available daily gridded dataset of in situ-produced biogenic methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4=) concentrations covering the North Atlantic. The dataset is of high spatial resolution (0.25° × 0.25°) and spans 25 years (1998–2022), far exceeding what observations alone could achieve both spatially and temporally. The machine learning models were generated by combining in situ observations of sulfur aerosol data from Mace Head Atmospheric Research Station, located on the west coast of Ireland, and from the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) cruises in the northwestern Atlantic with the constructed sea-to-air dimethylsulfide flux (FDMS) and ECMWF ERA5 reanalysis datasets. To determine the optimal method for regression, we employed five machine learning model types: support vector machines, decision tree, regression ensemble, Gaussian process regression, and artificial neural networks. A comparison of the mean absolute error (MAE), root-mean-square error (RMSE), and coefficient of determination (R2) revealed that Gaussian process regression (GPR) was the most effective algorithm, outperforming the other models with respect to simulating the biogenic MSA and nss-SO4= concentrations. For predicting daily MSA (nss-SO4=), GPR displayed the highest R2 value of 0.86 (0.72) and the lowest MAE of 0.014 (0.10) µg m−3. GPR partial dependence analysis suggests that the relationships between predictors and MSA and nss-SO4= concentrations are complex rather than linear. Using the GPR algorithm, we produced a high-resolution daily dataset of in situ-produced biogenic MSA and nss-SO4= sea-level concentrations over the North Atlantic, which we named “In-situ Produced Biogenic Methanesulfonic Acid and Sulfate over the North Atlantic” (IPB-MSA&SO4). The obtained IPB-MSA&SO4 data allowed us to analyze the spatiotemporal patterns of MSA and nss-SO4= as well as the ratio between them (MSA:nss-SO4=). A comparison with the existing Copernicus Atmosphere Monitoring Service ECMWF Atmospheric Composition Reanalysis 4 (CAMS-EAC4) reanalysis suggested that our high-resolution dataset reproduces the spatial and temporal patterns of the biogenic sulfur aerosol concentration with high accuracy and has high consistency with independent measurements in the Atlantic Ocean. IPB-MSA&SO4 is publicly available at https://doi.org/10.17632/j8bzd5dvpx.1 (Mansour et al., 2023b).

Spatial distribution and environmental/biological co-regulation mechanism of dimethyl sulfur compounds in the eastern Indian Ocean

Dimethyl sulfur compounds including dimethylsulfoniopropionate (DMSP), dimethyl sulfide (DMS), and dimethyl sulfoxide (DMSO), play a crucial part in global sulfur cycling. The eastern Indian Ocean (EIO), characterized by its remarkable diversity of biomes and climate dynamics, is integral to global climate regulation. However, the regulation mechanism of DMS (P, O) in the EIO remains to be elucidated in detail. This paper presented a field survey aimed at investigating the spatial distribution of DMS (P, O) and their relationships with environmental and biological factors in the EIO. The surface concentrations of DMS, DMSPt, and DMSOt varied from 0.07 to 7.37 nmol/L, 0.14 to 9.17 nmol/L, and 0.15 to 3.32 nmol/L, respectively, and their distributions are attributed to high Chl-a concentration near Sri Lanka and the influence of ocean currents (Wyrtki jets, Bay of Bengal runoff). Higher concentrations of DMS (P) and DMSOt were predominantly observed in water columns shallower than 75m and deeper than 75m deep, respectively. The monthly DMS fluxes in the study area peaked in August. Temperature and Dissolved Silica Index (DSI) were the key environmental determinants for DMS distribution, while nitrate (NO3-) was the primary factor for both DMSPt and DMSOt. In terms of biological factors, Prochlorococcus and Synechococcus were significant contributors to DMS (P, O) dynamics. Synechococcus was the dominant influence on the DMS source and DMSPt sink, whereas Prochlorococcus primarily consumed DMSOt. Furthermore, the structural equation modeling (SEM) revealed the relationship between DMS, DMSPt, DMSOt, and the key environmental/biological factors, as well as among them, and together they formed a co-regulatory network in the EIO. This contributes significantly to the advancement of global ecosystem models for DMS (P, O).

Improving Estimates of Dynamic Global Marine DMS and Implications for Aerosol Radiative Effect

AbstractDimethyl sulfide (DMS) is the predominant natural sulfur source and plays a pivotal role in regulating global climate. However, the current method for estimating seawater DMS concentrations has limitations, and the existing DMS‐induced radiative effect heavily relies on bottom‐up DMS climatologies. This study aims to improve the method for estimating seawater DMS concentrations as well as to evaluate its induced aerosol direct radiative effect (DRE) and indirect radiative effect (IRE) using a state‐of‐the‐art aerosol microphysics scheme integrated with a chemical transport model. The predicted seawater DMS concentrations based on data‐driven methods were verified with multi‐year in situ measurements, revealing a marked reduction in mean bias by over 80%. Results show that our estimates generally indicate lower seawater DMS concentrations (1.48–1.88 μmol/m3) compared to previous seawater DMS climatologies, with differences ranging from −37% to 11%, and that interannual variability in DMS concentrations is varies significantly, particularly in polar regions. The DRE and cloud‐albedo IRE induced by DMS were −0.06 and −0.19 W/m2, respectively, representing a cooling effect on radiative effect that was weaker by 31.4% and 27.0% of those derived from the commonly used bottom‐up DMS climatology. The comprehensive evaluation of the model's performance of atmospheric DMS prediction based on global‐scale observations shows a significant improvement after using our estimates. Thus, we conclude that the global DMS fluxes provided in the past are overestimated, including its resulting DMS radiative effect, which highlights the need for refining the estimation of global aerosol radiative effect to enhance the accuracy of assessing aerosol‐induced climate impacts.

Occurrence and emissions of biogenic dimethylated sulfur compounds and their responses to mesoscale eddies and typhoon Yutu in the western tropical Pacific Ocean

The western tropical Pacific Ocean (WTPO) plays a vital role in the global sulfur biogeochemical cycle. Here, an investigation was conducted to explore the spatial variations in biogenic dimethylated sulfur compounds (BDSCs) and their controlling factors in the WTPO in 2018. Dimethylsulfide (DMS) sea-to-air fluxes and the contribution of DMS emissions to the atmospheric sulfate burden were estimated. The concentrations of BDSCs in the surface seawater were low compared to the marginal seas of the western Pacific Ocean, attributed to a limited supply of nutrients and low primary production. Besides, higher values of the BDSCs were observed in surface and subsurface water. The nanophytoplankton was the main dimethylsulfoniopropionate (DMSP) producer, and the abundance of low DMSP and dimethylsulfoxide (DMSO) producers determined the DMSP/O concentrations in the oligotrophic WTPO. Moreover, mixed layer depth might be the crucial factor affecting DMS values. DMS fluxes were low in the WTPO, but they still contributed substantially to global DMS emissions, given the vast areas of the Pacific Ocean. The contribution of biogenic non-sea-salt sulfate (nss-SO42-) to total SO42- reached 25.87%, which showed the oxidation products of DMS were the crucial sources of SO42- in aerosols. Responses of BDSCs to mesoscale eddies and a typhoon were investigated for the first time. The warm eddy increased the concentrations of chlorophyll a (Chl-a) and BDSCs. Nevertheless, no effect of a mesoscale cold eddy on Chl-a or BDSCs was evident. The values of Chl-a, DMS, DMSP, biogenic nss-SO42-, and the DMS fluxes increased after Typhoon Yutu passed, indicating that typhoons play a prominent role in DMS emissions and the global sulfur cycles.

Effects of coastal shellfish farming on dimethylsulfide production

Dimethylsulfide (DMS) plays an important role in the sulfur biogeochemical cycle and cloud formation on Earth. In the past few decades, coastal shellfish breeding facilities have developed rapidly in shallow coastal regions. However, the effects of coastal shellfish farming on DMS production remain controversial at present. The Yantai offshore is an important shellfish farming region in northern China and the effect of shellfish farming on DMS production was explored combining field investigation and laboratory cultivation in this study. The results showed that coastal shellfish farming can promote the conversion of DMSP to DMS, especially in the shellfish rapid growth period and harvest period. However, different from the zooplankton “sloppy feeding”, the shellfish “filter-feeding” first repackages the phytoplanktonic DMSP into fecal DMSP, and then degrades DMSPp into DMS by attracting attached bacteria. Throughout the entire shellfish farming period, average DMS flux in shellfish region was 1.37 μmol m−2 d−1 higher than that in non-shellfish region. Based on the investigation results Yantai coastal shellfish farming region, it can be estimated that the increment of DMS caused by Chinese coastal shellfish farming can reach 2.96 × 106 mol per year.

Marine Dimethyl Sulfide Fluxes in the Yellow and East China Seas: Scenario Variation During the 1980s–2090s and Its Drivers

AbstractShedding light on the response of oceanic dimethyl sulfide flux (FDMS) on the sea shelf to multi‐pressures (intensified terrigenous nutrient inputs and climate change) is of great importance for regional aerosol budget. Here, we designed 4‐group experiments in scenario (the 1980s, 2010s, 2050s, and 2090s) for the Yellow and East China seas (YECS) based on climate change signals gained from CMIP6 and a 3‐dimension biophysical and geochemical model. Results show that the climatological annual mean of YECS's FDMS will rise from ∼6 μmol m−2 day−1 in the 1980s to >9 μmol m−2 day−1 in the 2090s under Shared Socioeconomic Pathway (SSP) 2−4.5/5−8.5 scenario, and with multi‐pressures, the FDMS peak in the 2050s is one season earlier when compared to that in the 1980s. The elevated terrigenous inputs affect the phytoplankton biomass and/or community on the inner shelf, leading to the rise and phenology change in the YECS's FDMS between the1980s and 2010s, while climate change has little impact. The influence of climate change on the FDMS is projected to increase in the 2050s; climate change will change seasonal pattern of the FDMS on the central part (middle and outer shelves) of East China Sea (CECS) under every SSP scenario. Thereinto, wind change exerts a crucial role, it will enhance summertime offshore transport and, accordingly, stimulate phytoplankton growth in summer changing the phenology of FDMS on the CECS.

Distribution and physical–biological controls of dimethylsulfide in the western tropical Indian Ocean during winter monsoon

New field observation on distribution, turnover, and sea–air flux of three dimethylated sulfur compounds (dimethylsulfide (DMS), dimethylsulfoniopropionate, and dimethylsulfoxide) in the western tropical Indian Ocean (WTIO; 4°N–10°S, 61°–65°E) were conducted under the major Global Change and Air–Sea Interaction Program during the 2021/2022 Northeast Monsoon (December 21, 2021 to January 11, 2022). Significantly high surface concentrations of DMS were identified in the region of the Seychelles–Chagos Thermocline Ridge (SCTR; 5°–10°S). This occurred because the shallow thermocline/nitracline and associated upwelling fueled biological production of DMS in the subsurface, which was brought to the surface through vertical mixing. The calculated sea–air DMS flux was also significantly strong in the SCTR region during the Northeast Monsoon owing to combination of high wind speed and high surface concentration of DMS. This finding is similar to results obtained previously during the Southwest Monsoon, suggesting that the SCTR region is an area of active DMS emission during both the Northeast Monsoon and the Southwest Monsoon. Microbial consumption was the dominant pathway of DMS removal, accounting for 74.4% of the total, whereas the processes of photolysis (17.7%) and ventilation (7.9%) were less important. Future work should be undertaken in the WTIO to establish how DMS emission is linked to aerosol properties and climate change.

The effect of temperature and salinity on DMSP production in Gephyrocapsa oceanica (Isochrysidales, Coccolithophyceae)

ABSTRACT A subtropical clone of Gephyrocapsa oceanica was grown over the temperature and salinity range 10–30°C and 20‰–45‰ respectively. Cellular DMSP increased with increasing salinity, compatible with the hypothesis that DMSP is a compatible osmolyte. Cellular DMSP content was highest at colder temperatures and decreased as temperature increased. Net DMSP production rate also depended on cell size and growth rate was greatest about 2°C below the optimum growth temperature of 20°C for this clone. This resulted in a unimodal response of net DMSP production to increasing temperature: net DMSP production increased with increasing temperature when the cells were growing at temperatures below optimum for growth. At and above optimum growth temperature, further warming decreased net DMSP production. For the effect of temperature alone, in the subtropical oceans, where G. oceanica is growing at or above its optimum, further warming due to climate change will result in decreased net DMSP production and so a probable decrease in the flux of DMS to the atmosphere and sulphate aerosol production. Inasmuch as these aerosols modulate cloud albedo and longevity then these too will both decrease, resulting in a positive feedback response for temperature. The reverse effect may occur in higher latitude oceans where growth temperature is below optimum. The exact response in both regions is complicated because warming will also enhance water column stratification and may reduce mixed layer depths, affecting both nutrient and light regimes, as well as possible species succession effects. Further work is required to investigate these other indirect temperature effects.

The Response of Oceanic Dimethylsulfide Fluxes Off the Chinese Coastal Waters to Altered Changjiang (Yangtze) Nutrient Inputs

The Response of Oceanic Dimethylsulfide Fluxes Off the Chinese Coastal Waters to Altered Changjiang (Yangtze) Nutrient Inputs

High-resolution distribution and emission of dimethyl sulfide and its relationship with pCO2 in the Northwest Pacific Ocean

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.

Oceanographic controls on Southern Ocean dimethyl sulfide distributions revealed by machine learning algorithms

AbstractWe developed two machine learning models to map the Southern Ocean distribution of the climate‐active gas dimethyl sulfide (DMS) at 20 km resolution. Results obtained from ensembles of random forest regressions and artificial neural networks reproduce observed DMS distributions with significantly higher accuracy than traditional statistical techniques, and are less prone to biases and spatial distortions than existing interpolation‐based climatologies. Both models predict persistently low offshore DMS concentrations associated with the Antarctic circumpolar current, suggesting that wind‐driven overturning mixing is the dominant regional control on DMS distributions. In addition, 60% of the variance in DMS seasonality is explained by changes in mixed layer depth and sea surface temperature, with a significant correlation between DMS concentrations and sea‐ice cover in coastal waters. We further identify the tracer Si* (defined as ) as a potentially important predictor for regional DMS distributions in Southern Ocean waters. At finer scales, our models capture various oceanographic features, including eddies, hydrographic fronts and jets that appear to play a role in driving DMS variability. Our results yield an estimated Southern Ocean sea‐air DMS flux of 8.7 ± 2.1 Tg S integrated across the phytoplankton growing season (October to April), representing 30.8% of total global oceanic S emissions, and highlighting the region's importance to the marine sulfur cycle. Our work provides new insights into the drivers of spatial variability in Southern Ocean DMS concentrations and sea‐air fluxes, and their potential responses to future climate‐dependent changes.

Winter season Southern Ocean distributions of climate-relevant trace gases

Abstract. Climate-relevant trace gas air–sea exchange exerts an important control on air quality and climate, especially in remote regions of the planet such as the Southern Ocean. It is clear that polar regions exhibit seasonal trends in productivity and biogeochemical cycling, but almost all of the measurements there are skewed to summer months. If we want to understand how the Southern Ocean affects the balance of climate through trace gas air–sea exchange, it is essential to expand our measurement database over greater temporal and spatial scales, including all seasons. Therefore, in this study, we report measured concentrations of dimethylsulfide (DMS, as well as related sulfur compounds) and isoprene in the Atlantic sector of the Southern Ocean during the winter to understand the spatial and temporal distribution in comparison to current knowledge and climatological calculations for the Southern Ocean. The observations of isoprene are the first in the winter season in the Southern Ocean. We found that the concentrations of DMS from the surface seawater and air in the investigated area were 1.03 ± 0.98 nmol−1 and 28.80 ± 12.49 pptv, respectively. The concentrations of isoprene in surface seawater were 14.46 ± 12.23 pmol−1. DMS and isoprene fluxes were 4.04 ± 4.12 µmol m−2 d−1 and 80.55 ± 78.57 nmol m−2 d−1, respectively. These results are generally lower than the values presented or calculated in currently used climatologies and models. More data are urgently needed to better interpolate climatological values and validate process-oriented models, as well as to explore how finer measurement resolution, both spatially and temporally, can influence air–sea flux calculations.