Search

Environmental context: Dimethyl sulfide is an important biogenic gas, released from ocean to atmosphere, which contributes to aerosol formation and can therefore affect global climate. Studies on dimethyl sulfide in both seawater and atmosphere have linked the atmospheric chemistry of dimethyl sulfide with its circulation in the marine environment. This study showed that these biogenic emissions contribute to the sulfur cycle and particulate production, deepening our understanding of their role in the East China Sea. Dimethyl sulfide (DMS) is identified as an essential biogenic sulfur compound in the ocean. Its oxidation products are thought to be important contributors to cloud condensation nuclei, thereby influencing the earth's radiative balance and climate. The concentrations of DMS and its precursor, dimethylsulfoniopropionate (DMSP) were measured in seawater and sediment pore water in the East China Sea (ECS) during summer. In addition, dissolved DMSP (DMSPd) degradation rates, DMS production and consumption rates, and sea-to-air flux of DMS were determined, and the biogenic contribution to atmospheric non-sea-salt sulfate (nss-SO42-) was evaluated in PM2.5 and PM10 aerosols over the study area. The spatial distributions of DMS and DMSP were closely related to that of chlorophyll-a and decreased from the inshore to the offshore. The concentration of DMSPd in sediment pore water was significantly higher than that in bottom water, which indicated that sediment is a net source of DMSPd for bottom water. The biological incubation experiments showed that ~36.0 % of decomposed DMSPd was degraded into DMS, while 78.7 % of produced DMS was consumed by bacteria within the surface water. The sea-to-air flux of DMS varied from 1.30 to 31.84 μmol m-2 day-1, with an average of 7.45 ± 6.30 μmol m-2 day-1. Biogenic contributions of the ECS to total nss-SO42- were estimated to be 13.0 % ± 9.9 % in PM2.5 and 13.5 % ± 5.1 % in PM10 samples respectively, which indicated that marine DMS release cannot be neglected in the ECS during summer. [ABSTRACT FROM AUTHOR]

Abstract Spatiotemporal distributions of volatile halogenated organic compounds (VHOCs) were investigated in the marine boundary air and surface seawater of the Changjiang (Yangtze River) estuary and its adjacent East China Sea in two cruises from March 11, 2015 to March 21, 2015 and from July 9, 2015 to July 20, 2015. Results revealed that the concentrations of released chlorofluorocarbons (CFCs) such as CFC-12, CFC-11, and CFC-114 in China decreased, suggesting that limitations set by the Chinese government on CFCs production and consumption have taken effect. Atmospheric concentrations of CFCs were affected by local industrial sources of emission and transport of terrestrial pollutants from coastal areas to varying degrees. Seasonal variations in atmospheric VHOCs were probably due to seasonal differences in prevalent monsoon and biogenic production. In the study periods, the investigated area was an essential source of atmospheric CH 3 Br and CH 3 I but was a net sink of CFC-12, CFC-11, and CH 3 Cl. Highlights • Distributions and sources of VHOC over this estuary were studied for the first time. • VHOC mixing ratios exhibited significant spatiotemporal variations in the study area. • Coastal emissions contributed to the high atmospheric VHOC mixing ratios. • Elevated levels of VHOC in the Changjiang estuary were related to terrestrial input. • Changjiang estuary was a net source of atmospheric CH 3 Br and CH 3 I. [ABSTRACT FROM AUTHOR]

Environmental context: Volatile halocarbons play significant roles as halogen carriers in atmospheric chemistry where they contribute to global warming. We studied temporal and spatial variations of volatile halocarbons in the Northern Yellow Sea and Bohai Sea, and showed that their concentrations were governed by terrestrial input, hydrographic features and biological activity. The emission of volatile halocarbons from coastal regions could have important impacts on the budgets of atmospheric reactive halogen. Concentrations of five volatile halocarbons (VHCs), namely, chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), chlorodibromomethane (CHBr2Cl) and bromoform (CHBr3), in the Northern Yellow Sea and Bohai Sea were determined during the spring of 2013 and autumn of 2012. Strong seasonality in the concentrations of VHCs (except for CHCl3) were observed. Concentrations of CHCl3 were markedly higher (1.5 fold) to coincide with the higher concentration of chlorophyll a during the spring. The elevated concentrations of C2HCl3, C2Cl4, CHBr2Cl and CHBr3 were found to match with the higher inputs of land runoff during autumn. The VHCs distributions evidently decreased along the freshwater plume from the mouth of rivers, such as Yellow and Yalu Rivers, to the open sea. The elevated concentrations of the selected halocarbons arise from terrestrial input, complicated hydrographic features, such as the Yellow River effluent, Yalu River, Yellow Sea Coastal Current and Yellow Sea Cold Water, and biological release by phytoplankton. Correlation analyses were conducted among Chl- a , salinity and the concentrations of these gases to investigate possible controls for the concentrations of these gases. Significant correlation was only observed between the concentrations of CHBr2Cl and Chl- a in the surface layer during spring. We made the tentative conclusion that phytoplankton biomass might not be the main limiting factor of sources of VHCs in the surface water. The sea-to-air fluxes indicated that the Northern Yellow Sea and Bohai Sea act as sources of gas in the atmosphere during spring and autumn. Environmental context. Volatile halocarbons play significant roles as halogen carriers in atmospheric chemistry where they contribute to global warming. We studied temporal and spatial variations of volatile halocarbons in the Northern Yellow Sea and Bohai Sea, and showed that their concentrations were governed by terrestrial input, hydrographic features and biological activity. The emission of volatile halocarbons from coastal regions could have important impacts on the budgets of atmospheric reactive halogen. [ABSTRACT FROM AUTHOR]

The spatial distribution, chemical composition and ecological risk of 16 phthalate esters (PAEs) were investigated in the sea-surface microlayer (SML), seawater and sediment samples of the Bohai Sea (BS) and the Yellow Sea (YS). The concentration levels of the ΣPAEs spanned a range of 449–13441 ng L −1 in the SML, 453–5108 ng L −1 in seawater, and 1.24–15.8 mg kg −1 in the sediment samples, respectively, with diisobutyl phthalate (DiBP), di-n-butyl phthalate (DBP) and di-ethylhexyl phthalate (DEHP) as the dominant PAEs in both the water and sediment samples. The concentrations of ΣPAEs in the BS were higher than those in the YS. The vertical distribution of ΣPAEs in the water column showed that the concentrations were higher in the surface waters, but decreased slightly with depth, and started to increase at the bottom. Additionally, PAEs were significantly enriched in the SML, with an average enrichment factor of 1.46. The ecological risk of the PAEs was evaluated by the risk quotient (RQ) method, which indicated that DEHP posed a high risk to aquatic organisms in the whole water-phase, while the RQ values of DBP and DiBP reached a high risk levels in sedimentary environment. [ABSTRACT FROM AUTHOR]

The occurrence of 17 target PFAA analytes was determined in surface sediments ( n = 37) of the East China Sea and potential influencing factors were examined. ΣPFAAs ranged from 0.41 ng/g dw to 3.06 ng/g dw, with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) as the most abundant perfluorocarboxylic acid and perfluoroalkyl sulfonate, respectively. PFAAs in the sediments were strongly influenced by terrigenous input. Analysis of the relationship between dynamic influence factors and PFAA concentrations showed that the characteristics of PFAA distribution were rather complex. ΣPFAA concentrations and TOC were positively correlated ( p < 0.0001). Circumfluence also influenced the whole PFAA distribution and seasonal variation. In addition, correlation analysis suggested that log K oc values increased with increasing perfluoroalkyl chain length. Given the rapid economic development of eastern coastal cities of China, the environmental hazards of land source pollution cannot be ignored. [ABSTRACT FROM AUTHOR]

The spatiotemporal distribution patterns of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO) and chlorophyll a (Chl-a), as well as the oceanographic parameters influencing the concentrations of DMS, DMSP and DMSO, were measured in the Changjiang Estuary and its adjacent area during two cruises from 21 February to 10 March 2014 and from 10 to 22 July 2014. The concentrations of DMS and DMSP showed significant seasonal variation, i.e. higher values in summer than in winter. This result corresponded well with the seasonal change in Chl-a in the study area. The distribution of dissolved DMSO (DMSOd) decreased significantly with distance from shore, suggesting a primary source of terrestrial and riverine inputs. The seasonal variations of both DMSOd and particulate DMSO (DMSOp) were weaker than other sulfur compounds. Significant relationships were observed between DMS, particulate DMSP (DMSPp), DMSOp and Chl-a, suggesting that phytoplankton biomass plays an important role in controlling the distributions of DMS, DMSP and DMSO in the study area. The positive relationship between DMSPp and DMSOp suggested similar sources and cellular functions in algae, whereas the oxidation of DMS to DMSOd appeared to be a predominant source of DMSOd in winter in the area adjacent to the river mouth. The average sea-to-air fluxes of DMS in the Changjiang Estuary and its adjacent area were 0.37 and 1.70 µmol m-2 day-1 in winter and summer respectively; these values are much lower than those in other continental shelf seas. [ABSTRACT FROM AUTHOR]

The distribution and bioavailability of dissolved and particulate organic matter (DOM and POM) were determined throughout the water column in sampling transects across the South Yellow Sea (SYS), East China Sea (ECS), and its adjacent Kuroshio Current (KC) during March–April 2017. The carbon (C), nitrogen (N), and amino acids (AA) levels in DOM and POM, as well as other parameters including temperature, salinity, nutrients, chlorophyll- a , and biological parameters (heterotrophic bacteria, Synechococcus, and picoeukaryotes), were used in the multi-factor analysis to explore the underlying factors contributing to the distribution patterns and degrading status of DOM and POM. The AA contents in POM (PAA) were higher at shallower depths than the deep ones, whereas total dissolved amino acids (TDAA) levels showed minor variation with depth. Specifically, glycine and serine in the PAA were selectively preserved throughout the water column. High levels of heterotrophic bacteria were associated with high temperature and high levels of ammonium in shelf waters, indicating a spot for intensive remineralization of organic nitrogen. High concentrations of bulk organic parameters (POC and PON) were found more along the coast and correlated with arginine and alanine. The Kuroshio surface water was short of PAA, POC, and PON compared with the coastal and middle shelf water. The bioavailability of surface POM indicated by the percentages of AA in POC (PAA-C%) and PON (PAA-N%) was much higher in KC than in shelf and coastal waters. This study found the distinctive characterization of bioavailability and degradation status between KC and its adjacent seas. • The Kuroshio surface water was short of PAA, POC and PON compared with the coastal and middle shelf water. • The bioavailability of surface POM was much higher in the Kuroshio Current than in shelf and coastal waters. • The proportions of individual amino acids were more variable with increasing depth in the PAA pool than in the TDAA pool. [ABSTRACT FROM AUTHOR]

Concentrations of amino acids in dissolved and particulate pools in the East China Sea (ECS) were determined during two cruises (October–November 2013 and May–June 2014). The spatial distributions of total hydrolyzed amino acids (THAA), dissolved combined amino acids (DCAA), dissolved free amino acids (DFAA), and particulate amino acids (PAA) in the study area were considerably influenced by phytoplankton biomass and circulations. In addition, in situ phytoplankton production and terrestrial input are the major sources of amino acids in the ECS. The %C-PAA and %N-PAA positively correlated with chlorophyll a (Chl- a ), thus reflecting their phytoplankton sources. The concentrations of amino acids were higher in coastal waters than in open sea, revealing the effects of terrestrial input on amino acid concentrations. Moreover, the vertical distributions of THAA, DCAA, DFAA, and PAA exhibited similar patterns, i.e., decreasing trends from the surface water to the bottom water. Our study indicated that the deposition of phytoplankton biodetritus may affect the vertical distributions of amino acids. The major constituents of THAA were glycine, serine, and glutamic acid, whereas the major constituents of PAA are glycine, glutamic acid, and alanine. The diel variation of THAA presented a certain hysteresis, following the variation of Chl- a . Particle sorption had a contribution in describing the particulate pool and dissolved pool in the Changjiang River. [ABSTRACT FROM AUTHOR]

Temporal and spatial distribution patterns of volatile halogenated organic compounds (VHOCs), such as dichlorodifluoromethane (CFC-12), trichlorofluoromethane (CFC-11), trichlorotrifluoroethane (CFC-113), and methyl iodide (CH 3 I), in the Changjiang (Yangtze River) estuary and its adjacent marine area were measured during two cruises from 21 February to 10 March 2014 and from 10 to 21 July 2014. VHOC concentrations showed seasonal variation with higher values during winter. VHOC distributions evidently decreased along the freshwater plume from the river mouth to the open sea and from inshore to offshore regions. VHOC distributions were obviously influenced by the Changjiang runoff, anthropogenic inputs, and biological release of phytoplankton. The study area was a net sink for CFC-12 and CFC-11, but a net source for atmospheric CH 3 I during the study periods. [ABSTRACT FROM AUTHOR]

Six volatile halogenated organic compounds (VHOC), namely, chloroform, carbon tetrachloride, trichloroethylene, bromodichloromethane, dibromochloromethane, and bromoform, were studied in the Yellow Sea and East China Sea from April to May, 2009. The spatial variability of these VHOC was influenced by various factors, including anthropogenic inputs, biogenic production and complicated hydrographic features such as Changjiang Diluted Water, Yellow Sea Cold Water Mass, and Kuroshio Current. Diurnal study results showed that factors such as solar irradiation, biological activity, and tide affected the abundance of these VHOC. Correlation analyses revealed that bromodichloromethane was positively correlated with chlorophyll a in surface seawater. Principal component analysis suggested that chlorinated compounds like carbon tetrachloride originated from anthropogenic sources whereas brominated compounds such as bromodichloromethane originated from biogenic sources. Sources of other chlorinated and brominated compounds may not be governed by biological processes in the marine environment. [ABSTRACT FROM AUTHOR]

The oceanic production and release of volatile halocarbons (VHCs) to the atmosphere play a vital role in regulating the global climate. In this study, seasonal and spatial variations in VHCs, including trichlorofluoromethane (CFC-11), methyl iodide (CH 3 I), dibromomethane (CH 2 Br 2), and bromoform (CHBr 3), and environmental parameters affecting their concentrations were characterized in the atmosphere and seawater of the Yangtze River Estuary and its adjacent marine area during two cruises from October 17 to October 26, 2019 and from May 12 to May 25, 2020. Significant seasonal variations were observed in the atmosphere and seawater because of seasonal differences in the prevalent monsoon, water mass (Yangtze River Diluted Water), and biogenic production. VHCs concentrations were positively correlated with Chl- a concentrations in the surface water during autumn. The average sea-to-air fluxes of CH 3 I, CH 2 Br 2, and CHBr 3 in autumn were 19.7, 4.0, and 7.6 nmol m−2 d−1, respectively, while those in spring were 6.3, 6.4, and −3.6 nmol m−2 d−1. In the ship-based incubation experiments, ocean acidification and dust deposition had no significant effects on VHCs concentrations. The concentrations of CH 2 Br 2 and CHBr 3 were significantly positively correlated with phytoplankton biomass under lower pH condition (M3: pH 7.9). This result indicated that CH 2 Br 2 and CHBr 3 concentrations were mainly related to the biological release. [Display omitted] • The source of air masses influenced volatile halocarbons (VHCs) levels in the air. • Spatiotemporal variations of VHCs in seawater and atmosphere were investigated. • Seasonal variations in VHCs concentrations were dependent on complex factors. • Ocean acidification and dust addition had an impact on the production of VHCs. [ABSTRACT FROM AUTHOR]

Abstract: Temporal and spatial distributions of dissolved and particulate dimethylsulfoxide (DMSOd and DMSOp) were determined in the Bohai Sea (BS) and the Yellow Sea (YS) during November–December 2011 and May 2012. The average concentrations of DMSOd and DMSOp in the surface water in autumn were 14.6 (6.48−52.3) and 10.0 (4.94–31.1)nmolL−1, respectively, and those in spring were 19.7 (4.84–144) and 25.1 (5.09–108)nmolL−1. The distributions of DMSOd and DMSOp in the study area were obviously influenced by biological production of phytoplankton. A positive correlation was observed between DMSOp and chlorophyll a (Chl-a) concentrations in the surface water in autumn, suggesting that phytoplankton biomass might play an important role in controlling the distribution of DMSOp in the study area. The spring average ratio of DMSOp/Chl-a was approximately 1.3 times higher than the autumn value, corresponding with the temporal variation in phytoplankton species and biomass between spring and autumn. [Copyright &y& Elsevier]

Abstract: The concentrations of eight halocarbons, including methyl chloride (CH3Cl), methyl bromide (CH3Br), trichloroethene (C2HCl3), tetrachloroethene (C2Cl4), methyl chloroform (CH3CCl3), and three chlorofluorocarbons (CFCs) (CFC-11, CFC-113, and CFC-114), were measured using a canister sampling technique and an automated preconcentration gas chromatograph–mass spectrometer system in the marine atmosphere of the south Yellow Sea (SYS) in May 2012. The atmospheric concentrations of these halocarbons ranged from single digits to hundreds of pptv. Our results revealed elevated regional mixing ratios for most halocarbons (particularly C2HCl3 and C2Cl4) compared with the levels found in literature, thus suggesting substantial releases of C2HCl3 and C2Cl4 from anthropogenic sources in China. By contrast, the mean concentration of CFC-11 in the present study was lower than the global average value. The diffusion and transportation of terrestrial pollutants from coastal areas are important sources of halocarbons in the SYS, whilst terrestrial sources contribute to elevated concentrations of the selected halocarbons in coastal water. The sea-to-air fluxes of CH3Cl and CH3Br were estimated based on the simultaneous measurement of the atmospheric and seawater concentrations of these two gases. By simple extrapolation, the emissions of CH3Cl and CH3Br from the study area could account for 0.04% and 3% of the global oceanic emissions, respectively, thus indicating that the coastal area constituted important sources of atmospheric CH3Cl and CH3Br. [Copyright &y& Elsevier]

Halocarbons including chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), chlorodibromomethane (CHBr2Cl) and bromoform (CHBr3) were measured in the Yellow Sea (YS) and the East China Sea (ECS) during spring 2011. The influences of chlorophyll a, salinity and nutrients on the distributions of these gases were examined. Elevated levels of these gases in the coastal waters were attributed to anthropogenic inputs and biological release by phytoplankton. The vertical distributions of these gases in the water column were controlled by different source strengths and water masses. Using atmospheric concentrations measured in spring 2012 and seawater concentrations obtained from this study, the sea-to-air fluxes of these gases were estimated. Our results showed that the emissions of C2HCl3, C2Cl4, CHBr2Cl, and CHBr3 from the study area could account for 16.5%, 10.5%, 14.6%, and 3.5% of global oceanic emissions, respectively, indicating that the coastal shelf may contribute significantly to the global oceanic emissions of these gases. [Copyright &y& Elsevier]

Abstract: The concentrations of six volatile halogenated organic compounds (VHOC)–chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), carbon tetrachloride (CCl4), methylchloroform (CH3CCl3), and bromoform (CHBr3) in the East China Sea (ECS) in November and December 2010 were measured by a purge and trap system coupled to a gas chromatograph with an electron capture detection (ECD). Mean (range) concentrations of CHCl3, C2HCl3, C2Cl4, CH3CCl3, CCl4 and CHBr3 in the surface water were 16.90 (0.40–62.92), 16.27 (2.78–83.33), 2.40 (0.39–9.33), 32.29 (19.72–57.68), 1.70 (0.39–8.73) and 17.11 (4.33–34.46) pM, respectively. With the exception of C2HCl3, the concentrations of other five kinds of VHOC generally exhibited a decreasing trend with distance from the coast, with the low values found in the open sea. The anthropogenic sources contributed to the elevated levels of CCl4 and CH3CCl3, whereas a combination of the anthropogenic and biogenic sources might be responsible for the elevated levels of CHCl3, C2HCl3, C2Cl4 and CHBr3. In the depth profiles, vertical distributions of the six VHOC in the water column were complicated, with the maxima occurring at 0–100m depths. The mean sea-to-air fluxes of CHCl3, C2HCl3, C2Cl4 and CHBr3 were estimated to be 21.08, 29.94, 2.05 and 35.50nmolm−2 d−1, respectively, indicating that the ECS was a source for the four VHOC in the atmosphere. [Copyright &y& Elsevier]

Abstract: The concentrations of particulate and dissolved dimethylsulfoxide (DMSOp, DMSOd) in the surface water of the East China Sea (ECS) in December 2009 were measured for the first time. The concentrations of DMSOp and DMSOd ranged from 2.4 to 80.0nmolL−1 and from 3.2 to 357.0nmolL−1 with average values of 21.3nmolL−1 and 61.9nmolL−1, respectively. The distribution of DMSOd was obviously influenced by the Yangtze River, with high concentrations appearing around the mouth of it. DMSOd represented the main methylated sulfur compound and dominated over dimethylsulfide (DMS) and dissolved dimethylsulfoniopropionate (DMSPd) by 1–2 orders of magnitude. The distribution of DMSOp did not show the same pattern as that of DMSOd. The concentrations of DMSOp increased offshore in the northeast ECS due to the change of phytoplankton species coupled to the increasing temperature, while in the southwest ECS the concentrations of DMSOp decreased offshore due to the poor DMSO-producers in the open sea. A weak positive correlation was observed between DMSOd and DMS in the whole study area. In addition, a significant relationship between DMSOp/Chl-a and temperature in the northeast ECS as well as a negative significant relationship between DMSOp and particulate DMSP in the southwest ECS was found. However, no relationship was observed between DMSOp and the environmental factors such as chlorophyll a, temperature and salinity. The vertical profiles of DMSOd in the study area were characterized by a maximum at depth from 2 to 25m, while the DMSOp concentrations were characterized by a maximum at the bottom. Both DMSOd and DMSOp concentrations exhibited obvious diurnal variations with the maxima 7.4 and 2.4 times higher than the minima, respectively. [Copyright &y& Elsevier]

Abstract: Temporal and spatial distributions of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) were determined in the East China Sea and the Yellow Sea during June–July, 2006 and January–February, 2007. The concentrations of DMS and total DMSP in surface water in the study area were 5.64 (1.79–12.24) and 28.25 (13.98–44.93)nmolL−1 in summer, and were 1.79 (1.02–3.51) and 11.01 (6.90–17.98)nmolL−1 in winter, respectively. The distributions of DMS and DMSP in the study area were obviously influenced by the Yangtze River effluent and the Kuroshio water. Even under highly variable hydrographic conditions, a significant relationship was observed between DMS and chlorophyll a concentrations in summer as well as in winter, suggesting that phytoplankton biomass might play an important role in controlling DMS distribution in the study area. The summer ratios of DMS/chlorophyll a and DMSP/chlorophyll a were approximately twofold higher than winter values, corresponding with the temporal variation in phytoplankton community structure between summer and winter. The sea-to-air fluxes of DMS were estimated to be 5.32 and 11.92μmolm−2 d−1 using the equations of and , respectively. [Copyright &y& Elsevier]

Abstract: Carbon monoxide (CO) concentration distribution and microbial consumption rate constants, along with atmospheric CO mixing ratios, were measured in the Southern Yellow Sea (SYS) and the East China Sea (ECS) in November 2007. The surface water CO concentrations in the investigated area ranged from 0.13 to 2.30nmolL−1, with an average of 0.68nmolL−1. Vertical profiles showed that CO concentrations declined with depth, with the maximum values appearing in the surface water (0–1m). The diurnal variations of seawater CO concentrations were investigated at two anchor stations and the results showed that CO concentrations varied by a factor of 6–8 in the diurnal cycle, with maximum values appearing in the surface water (0–1m). Atmospheric CO mixing ratios varied from 165 to 671ppbv, with an average of 297ppbv; these ratios decreased from 380 to 253ppbv in the seaward direction and increased from 239 to 345ppbv from south to north in the studied areas. Undersaturation was observed at eight of the 55 stations measured (15%) and the saturation factors ranged from 0.58 to 15.42, with an average of 3.34±2.95. The sea-to-air fluxes of CO in the SYS and the ECS ranged from 0.50 to 4.20μmolm−2 d−1, with an average of 1.82±1.43μmolm−2 d−1. In the incubation experiments, the microbial CO consumption rate constants in the surface water (K co ) ranged from 0.15 to 2.14h−1. A negative correlation between K co and salinity was observed in the present study. [ABSTRACT FROM AUTHOR]

Abstract: We determined the distributions and fluxes of methyl chloride and methyl bromide in the East China Sea (ECS) and the Southern Yellow Sea (SYS) in November 2007. Methyl chloride and methyl bromide concentrations in the surface waters ranged from 47.1 to 163pmolL− 1 and from 0.70 to 9.82pmolL−1, with average values of 87.6 and 2.97pmolL−1, respectively. The distributions of the two methyl halides were clearly influenced by the Yangtze (Changjiang) River effluent and Kuroshio water, with high concentrations appearing in the coastal zone and low values occurring in the open waters. A positive linear correlation was observed between methyl chloride and methyl bromide concentration anomalies in the surface waters, suggesting that they may share some origins in this coastal area. However, no correlation was found between the two methyl halide concentration anomalies and chlorophyll a in the surface waters. The vertical profiles of the two methyl halides were characterized by the maxima in the upper mixed layer. Both gases were generally supersaturated in the surface seawater, with mean sea-to-air fluxes of methyl chloride and methyl bromide of 391 and 20.0nmolm− 2 d−1, respectively. [Copyright &y& Elsevier]

Abstract: Concentrations of 14 different dissolved free amino acids (DFAA), dissolved inorganic nitrogen (DIN), and chlorophyll a were determined in the surface microlayer and subsurface waters at 41 stations in the Yellow Sea, China in April 2006. The concentrations of DFAA in the subsurface water ranged from 0.13 to 1.62μM, with an average of 0.57±0.05μM, while those in the surface microlayer varied between 0.22 and 2.6μM, with an average of 0.94±0.08μM. Major constituents of DFAA present in the study area were glycine, alanine, glutamic acid, serine and histidine. One-way analysis of variance (ANOVA) showed no significant difference in average mol fractions of DFAA between microlayer and subsurface water (F=0.0440, P=0.8355). Hierarchical cluster analysis of the station similarity based on the DFAA composition in both the surface microlayer and subsurface water separated three clusters of stations at the 70% Bray–Curtis similarity level. The average concentrations of chlorophyll a and DIN were 1.18 (0.34–4.44)μgL−1 and 16.57 (3.98–49.59)μM in the subsurface water, and those in the surface microlayer were 1.30 (0.24–3.97)μgL−1 and 18.56 (5.77–48.93)μM, respectively. Our results showed that concentrations of chlorophyll a (r 2=0.7940, n=41, p<0.0001), DIN (r 2=0.6939, n=41, p<0.0001) and DFAA (r 2=0.2416, n=41, P=0.0011) in the microlayer were, respectively, correlated with their subsurface water concentrations, implying that there was a strong exchange effect between the microlayer and subsurface water. The enrichment factor of DFAA in the microlayer ranged from 0.47 to 2.24 with a mean of 1.88±0.16. [Copyright &y& Elsevier]

Spatial variations in dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were surveyed in the surface microlayer and in the subsurface waters of the low productivity South China Sea in May 2005. Overall, average subsurface water concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) fractions were 1.74 (1.00–2.50), 3.92 (2.21–6.54) and 6.06 (3.40–8.68)nM, respectively. No enrichment in DMS and DMSPp was observed in the microlayer. In contrast, the microlayer showed a DMSPd enrichment, with an average enrichment factor (EF, defined as the ratio of the microlayer concentration to subsurface water concentration) of 1.40. In the study area, none of the sulfur components were correlated with chlorophyll a. An important finding in this study was that DMS, DMSP and chlorophyll a concentrations in the surface microlayer were respectively correlated with those in the subsurface water, suggesting a close linkage between these two water bodies. The ratios of DMS:Chl-a and DMSPp:Chl-a showed a gradually increasing trend from North to South. This might be due to changes in the proportion of DMSP producers in the phytoplankton community with the increased surface seawater temperature. A clear diurnal variation in the DMS and DMSP concentrations was observed at an anchor station with the highest concentrations appearing during the day and the lowest concentrations during the night. The higher DMS and DMSP concentrations during daytime might be attributed to the light-induced increase in both algal synthesis and exudation of DMSP and biological production of DMS. The mean flux of DMS from the investigated area to the atmosphere was estimated to be 2.06μmolm−2 d−1. This low DMS emission flux, together with the low DMS surface concentrations was attributed to the low productivity in this sea. [Copyright &y& Elsevier]

Abstract: The concentrations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the surface microlayer and subsurface water were measured at 21 grid stations and one anchor station in the Yellow Sea, China in March 2005. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were, respectively, 2.31 (1.20–4.54), 6.04 (2.13–9.48) and 7.98 (4.89–13.50) nM in the subsurface water, and those in the microlayer water were 2.26 (0.99–5.14), 9.10 (5.65–13.10) and 9.31 (4.08–15.64) nM. Among the sulfur components investigated, only DMSPd was found to be enriched in the microlayer with an average enrichment factor of 1.70. The concentrations of DMS, DMSPd and DMSPp in the microlayer were closely correlated with those in the corresponding subsurface water, implying that there was a strong exchange effect between the microlayer and subsurface water. The concentrations of DMS were positively correlated with the levels of chlorophyll a in the microlayer as well as in the subsurface water. The chlorophyll a-normalized DMS, DMSPd and DMSPp concentrations were 2.92 (1.47–5.72), 9.63 (2.07–27.88) and 13.10 (3.81–34.60) mmol g−1 in the subsurface water, and 2.91 (0.77–5.24), 15.86 (1.22–32.34) and 15.95 (2.75–40.10) mmol g−1 in the microlayer, respectively. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 3.14 μmol m−2 day−1. [Copyright &y& Elsevier]

Volatile brominated compounds are important trace gases for stratospheric ozone chemistry. In this study, the spatial variations of dibromomethane (CH 2 Br 2), bromodichloromethane (CHBrCl 2), dibromochloromethane (CHBr 2 Cl) and bromoform (CHBr 3) in the seawater and overlying atmosphere were measured in the Yellow Sea (YS) and the East China Sea (ECS) in winter. The air-sea fluxes of CH 2 Br 2 , CHBrCl 2 , CHBr 2 Cl and CHBr 3 ranged from −11.46 to 25.33, −4.68 to 7.91, −8.60 to 4.08 and −88.57 to 8.84 nmol m−2·d−1, respectively. In order to understand the mechanism of halocarbons production, we measured bromoperoxidase (BrPO) activity (39.18–186.74 μU·L−1) in the YS and ECS for the first time using an aminophenyl fluorescein (APF) method and performed in-situ incubation experiments in BrPO-treated seawater. The production rates of CH 2 Br 2 , CHBrCl 2 , CHBr 2 Cl and CHBr 3 ranged from 14.21 to 94.74, 0.00 to 19.74, 0.00 to 30.62 and 6.18–72.75 pmol L−1·h−1, respectively, in BrPO-treated seawater. There were significantly higher production rates in coastal waters compared with the open sea (P = 0.016) because of higher DOC levels near the coast. Moreover, the production rates of halocarbons increased with BrPO activity and H 2 O 2 concentration. The results showed that enzyme-mediated reaction was an important source for the production of halocarbons in seawater. The present research is of great significance for understanding the production mechanisms of halocarbons in seawater and global oceanic halocarbons emissions. [Display omitted] • Biological and environmental factors controlling concentration of halocarbons in the YS and the ECS were investigated. • Bromoperoxidase (BrPO) activities in the YS and ECS during winter were measured for the first time. • The production mechanism of halocarbons was identified through incubation experiments in BrPO-treated seawater. • The influences of specific factors on the production of halocarbons in the enzyme-mediated reaction. [ABSTRACT FROM AUTHOR]

The spatial distributions, fluxes, and environmental effects of non-methane hydrocarbons (NMHCs) were investigated in the Yellow Sea (YS) and the East China Sea (ECS) in spring. The average concentrations of ethane, propane, i-/n-butane, ethylene, propylene and isoprene in the seawater were 18.1 ± 6.4, 15.4 ± 4.7, 6.8 ± 2.9, 6.4 ± 3.2, 67.1 ± 26.7, 20.5 ± 8.7 and 17.1 ± 11.1 pmol L−1, respectively. The alkenes in the surface seawater were more abundant than their saturated homologs and NMHCs concentrations (with the exception of isoprene) decreased with carbon number. The spatial variations of isoprene were consistent with the distributions of chlorophyll a (Chl- a) and Chaetoceros , Skeletonema , Nitzschia mainly contributed to the production of isoprene, while the others' distributions might be related to their photochemical production. Observations in atmospheric NMHCs indicated alkanes in the marine atmosphere decreased from inshore to offshore due to influence of the continental emissions, while alkenes were largely derived from the oceanic source. In addition, no apparent diurnal discrepancy of atmospheric NMHCs (except for isoprene) were found between daytime and night. As the main sink of NMHCs in seawater, the average sea-to-air fluxes of ethane, propane, i-/n-butane, ethylene and propylene were 31.70, 29.75, 18.49, 15.89, 239.6, 67.94 and 52.41 nmol m−2 d−1, respectively. The average annual emissions of isoprene accounted for 0.1–1.3% of the global ocean emissions, which indicated that the coastal and shelf areas might be significant sources of isoprene. Furthermore, this study represents the first effort to estimate the environmental effects caused by NMHCs over the YS and the ECS and the results demonstrated contributions of alkanes to ozone and secondary organic aerosol (SOA) formation were lower than those of the alkenes and the largest contributor was isoprene. Image 1 • The emission and environmental effects of NMHCs were firstly estimated in the marginal seas of China. • Isoprene production was dependent on the phytoplankton species and biomass. • High concentrations of NMHCs (except for isoprene) were associated with abundant DOC. • The coastal and shelf sea represent an important source of atmospheric isoprene. • Alkenes contributed more to ozone and secondary organic aerosol formation than alkanes did. [ABSTRACT FROM AUTHOR]

Spatial distribution and sea-to-air flux of isoprene in the East China Sea and the South Yellow Sea in July 2013 were investigated. This study is the first to report the concentrations of isoprene in the China marginal seas. Isoprene concentrations in the surface seawater during summer ranged from 32.46 to 173.5 pM, with an average of 83.62 ± 29.22 pM. Distribution of isoprene in the study area was influenced by the diluted water from the Yangtze River, which stimulated higher in-situ phytoplankton production of isoprene rather than direct freshwater input. Variations in isoprene concentrations were found to be diurnal, with high values observed during daytime. A significant correlation was observed between isoprene and chlorophyll a in the study area. Relatively higher isoprene concentrations were recorded at stations where the phytoplankton biomass was dominated by Chaetoceros , Skeletonema , Pennate-nitzschia , and Thalassiosira . Positive correlation was observed between isoprene and methyl iodide. In addition, sea-to-air fluxes of isoprene approximately ranged from 22.17 nmol m −2 d −1 –537.2 nmol m −2 d −1 , with an average of 161.5 ± 133.3 nmol m −2 d −1 . These results indicate that the coastal and shelf areas may be important sources of atmospheric isoprene. [ABSTRACT FROM AUTHOR]

Carbohydrates are the largest identified fraction of dissolved organic carbon and play an important role in biogeochemical cycling in the ocean. Seawater samples were collected from the East China Sea (ECS) during June and October 2012 to study the spatiotemporal distributions of total dissolved carbohydrates (TCHOs) constituents, including dissolved monosaccharides (MCHOs) and polysaccharides (PCHOs). The concentrations of TCHOs, MCHOs and PCHOs showed significant differences between summer and autumn 2012, and exhibited an evident diurnal variation, with high values occurring in the daytime. Phytoplankton biomass was identified as the primary factor responsible for seasonal and diurnal variations of dissolved carbohydrates in the ECS. The TCHOs, MCHOs and PCHOs distributions in the study area displayed similar distribution patterns, with high concentrations appearing in the coastal water. The influences of chlorophyll- a , salinity and nutrients on the distributions of these carbohydrates were examined. A carbohydrate enrichment in the near-bottom water was found at some stations, implying that there might be an important source of carbohydrate in the deep water or bottom sediment. [ABSTRACT FROM AUTHOR]

Concentrations of 4 volatile halocarbons (VHCs) in seawater and atmosphere of the Northern South China Sea (NSCS) were measured during summer 2015. Mean surface seawater concentrations of CH 3 I, CH 3 Br, CHBr 3 , and C 2 Cl 4 were 2.0, 4.2, 15.7, and 12.5 pM, respectively; mean atmospheric concentrations were 0.4, 4.1, 8.0, and 7.2 ppt, respectively. The surface seawater concentrations of the 4 VHCs were significantly influenced by the coastal mixed water, South China Sea surface water, Kuroshio Current, and Qiongdong upwelling in summer, while atmospheric concentrations were affected by the prevailing southwest monsoon and terrigenous pollutants from the Southwest Asia region. Chl- a concentrations were positively correlated with CH 3 I and CHBr 3 , indicating that phytoplankton were an important source of these gases in the study area. The flux of the 4 VHCs showed that the NSCS was a net source to the atmospheric during the study period. • VHCs in atmosphere and seawater were determined in the northern South China Sea. • The enhanced VHCs in atmosphere originates from Southeast Asian regions. • Concentration maxima of most VHCs were associated with QiongDong upwelling. [ABSTRACT FROM AUTHOR]

The volatile halocarbons (VHCs) CH 3 I, C 2 HCl 3 , C 2 Cl 4 , and CH 2 Br 2 were measured in the Changjiang Estuary and adjacent waters during autumn 2018. Results revealed that their concentrations in coastal waters were influenced by anthropogenic activities, biological release, and complex hydrographic features. The vertical distributions of VHCs were determined mostly by the mixing of water masses. By investigating the impacts of temperature, salinity, chlorophyll a , nutrients, and pH on the distributions of these trace gases we revealed that C 2 HCl 3 and C 2 Cl 4 were positively correlated with salinity and nutrient availability. The sea-to-air fluxes of CH 3 I, C 2 HCl 3 , C 2 Cl 4 , and CH 2 Br 2 were estimated to be 27.62, 280.3, 221.73, and 142.41 nmol m−2 day−1, respectively, suggesting that the study area was a net source of these trace gases. The impact of elevated f CO 2 on the production of the four volatile halocarbons was studied using mesocosms in Wu Yuan Bay, Xiamen. The results showed that elevated f CO 2 had little impact on the VHCs. Positive relationships were observed between CH 2 Br 2 and phytoplankton biomass when f CO 2 was low, and between CH 3 I and phytoplankton biomass when f CO 2 was high, suggesting that algal release was a significant source of both compounds. Unlabelled Image • Distributions of VHCs were measured in the Changjiang Estuary and its adjacent area. • The environmental factors that influenced the distributions of VHCs were examined. • The Changjiang Estuary and its adjacent area were a source of the atmospheric VHCs. • Mesocosm experiments showed that elevated f CO 2 had little impact on the VHCs. [ABSTRACT FROM AUTHOR]

• Seawater, SPM, and sediment samples were analyzed for BTRs, BTHs, and BUVs. • Terrestrial runoff affects the spatial distribution of BTRs, BTHs, and BUVs. • Organic carbon plays an important role in the migration of BTRs, BTHs and BUVs. • BTRs, BTHs, and BUVs were significantly enriched in the surface microlayer. • BTRs, BTHs, and BUVs posed a risk at different levels in sediments. Benzotriazoles (BTRs), benzothiazoles (BTHs), and benzotriazole UV stabilizers (BUVs) have attracted increasing attention due to their ubiquity in the environment, toxicity, and potential ecological risks. However, information on their distributions in the ocean is scarce. In this study, BTRs, BTHs, and BUVs were firstly determined in the surface seawater, sea-surface microlayer (SML), suspended particulate matter (SPM), and sediments of the Yellow Sea (YS) and East China Sea (ECS). The spatial distributions of BTRs, BTHs, and BUVs in the YS and ECS showed offshore decreasing trend in their concentrations, indicating that terrestrial inputs from runoff and rivers had important influences on their distributions. The organic carbon normalized partition coefficients (log K oc) of target contaminants in surface seawater-SPM (3.06–4.16 L/g) and bottom seawater-sediment (2.55–4.82 L/kg) systems were determined. SPM showed greater sorption capacities for most target contaminants than the sediment. The burial capacities of BTHs, BTRs, and BUVs from SPM to surface sediments were evaluated using their respective log K ow values and their sedimentary fluxes in the YS and ECS were quantified. BTRs, BTHs, and BUVs were enriched in the SML, with the enrichment extents of the suspended particulate phase being obviously lower than those of the dissolved phase. The ecological risks of BTRs, BTHs, and BUVs were evaluated using the risk quotient (RQ) method, which showed no toxic risk to aquatic organisms throughout the water phases, but high risk in nearshore sediments. [Display omitted] [ABSTRACT FROM AUTHOR]

The biogeochemical cycle of biogenic dimethylated sulfur compounds in oceans has received significant attention because of their critical role in the global climatic and atmospheric processes. The behavior of biogenic dimethylated sulfur compounds including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was measured in the waters of the Changjiang River Estuary and the coastal East China Sea during two cruises from 7 to 20 March 2016 and from 4 to 16 July 2016. The concentrations of DMS, particulate DMSP (DMSPp), dissolved DMSP (DMSPd), particulate DMSO (DMSOp) and dissolved DMSO (DMSOd) in the study area showed significant spatial and seasonal variation, with higher values in summer. DMS displayed significant relationships with DMSPp, DMSPd and DMSOp, and the dimethylated sulfur compound distributions showed similar patterns with that of chlorophyll a (Chl- a). The seasonal variation in DMSOd was inconspicuous compared to other sulfur compounds and its concentration inside the estuary was relatively high, suggesting an impact by anthropogenic activities and riverine inputs. Phytoplankton biomass and water mass mixing (upwelling and the Changjiang diluted water) played an important role in controlling the distributions of dimethylated sulfur compounds in the Changjiang River Estuary and the coastal East China Sea. The mean sea-to-air fluxes of DMS in this study area were 3.21 and 20.73 μmol m−2 d−1 in spring and summer, respectively. The study area was a net source for atmospheric DMS. Unlabelled Image • DMS distribution was influenced greatly by phytoplankton and water mass mixing. • Diatoms and dinoflagellates dominate phytoplankton communities in the study area. • DMSOd was influenced by anthropogenic activities and riverine inputs. • A significant correlation was observed between pH and DMS concentrations in summer. • DMS emission in the study area had a great contribution to the global DMS budget. [ABSTRACT FROM AUTHOR]

During an oceanographic campaign in the western Pacific Ocean from 12 August to 3 October 2014, the concentrations of five non-methane hydrocarbons (NMHCs) were measured in marine atmosphere and seawater. The average mixing ratios of ethane, ethylene, propane, propylene, and isoprene were 1.109 ± 0.359, 0.658 ± 0.137, 0.711 ± 0.377, 0.429 ± 0.139, and 0.255 ± 0.201 ppbv, respectively. In general, atmospheric concentrations of ethane and propane showed significant decrease from the inshore area to the open ocean, while ethylene and propylene exhibited decreasing trends from low latitudes to high latitudes. The results suggested that atmospheric ethane and propane with long lifetimes were more likely influenced by the air mass transported from continent, while ethylene, propylene and isoprene with short lifetimes were mainly derived from the surface seawater. The average concentrations of ethane, ethylene, propane, propylene, and isoprene in the surface seawater were 6.6 ± 5.8, 51.9 ± 23.5, 15.4 ± 4.3, 17.2 ± 3.8, and 23.5 ± 8.6 pmol L−1, respectively. A significant positive correlation was observed between ethane and propane (R 2 = 0.45, n = 39, p < 0.001), implying that their production and removal pathways in the surface seawater were similar. High concentrations of isoprene were observed in the waters with high Chl- a values, suggesting that the biological process was a controlling factor. The estimated sea-to-air fluxes of ethane, propane, ethylene, propylene, and isoprene were in the range of 0.1–24.9, 4.2–235, 1.0–43.8, 1.5–90.2, and 2.1–149 nmol m−2 d−1, respectively. This study is of great importance to the contribution to the atmospheric NMHCs from the western Pacific Ocean and provides data supporting for global NMHCs emission estimates. Unlabelled Image • Light C 2 -C 3 NMHCs and isoprene were measured in the seawater and atmosphere of the western Pacific Ocean. • High isoprene concentrations occurred in the highly productive waters. • The oceanic emissions in the surface seawater were main sources of atmospheric alkenes. [ABSTRACT FROM AUTHOR]

Abstract Concentrations and diurnal variations of inorganic nutrients (dissolved inorganic nitrogen (DIN), phosphate (PO 4 -P) and silicate (SiO 3 -Si)), as well as chlorophyll a (Chl-a) were determined in the subsurface water (SSW) and surface microlayer (SML) of the Bohai and Yellow Seas in summer 2015. The concentrations of DIN, SiO 3 -Si and Chl-a (except for PO 4 -P) in the SML were respectively correlated with their concentrations in the SSW, indicating that a major source of substances in the SML could be transported from the SSW. The enrichment factor (EF) was defined as the ratio of the concentration in the SML to that in the corresponding SSW. There was little difference in concentrations of PO 4 -P between the SML and the SSW samples by nonparametric difference test (P > 0.05). DIN, SiO 3 -Si and Chl-a (except for PO 4 -P) were found to be enriched in the SML relative to the SSW, with average EFs of 2.45, 1.18 and 2.37, respectively. No connection was identified between nutrients EFs and wind speed for our entire data. DIN, SiO 3 -Si, PO 4 -P and Chl-a concentrations in the SSW and the SML exhibited strong diurnal variations at an anchor station. Highlights • Nutrients and Chl-a concentrations in the surface microlayer were determined. • Nutrients and Chl-a in the surface microlayer showed more pronounced enrichment. • Nutrients and Chl-a revealed obvious diurnal variations in the surface microlayer. [ABSTRACT FROM AUTHOR]

Marine isoprene concentrations in the East China Sea were measured during two oceanographic cruises: one from October 10, 2013 to November 21, 2013 and another from May 16, 2014 to June 13, 2014. Mean (range) isoprene concentrations in the surface water in the study area were 32.85 (16.31–108.2) pmol L −1 in late spring and 26.83 (11.22–42.13) pmol L −1 in autumn. The isoprene concentrations showed seasonal variation and were higher in late spring, which could be attributable to terrigenous diluted water and seasonal variations of phytoplankton structure. Isoprene and chlorophyll a (Chl- a ) concentrations were significantly correlated in late spring and autumn even under complex hydrographic conditions. Isoprene and Chl- a concentrations also exhibited similar variations during a 25 h period and remained high during daytime. Analysis of depth profiles indicated that isoprene concentrations in the water column peaked at the surface layer and gradually decreased with increasing depth. The atmospheric concentration of isoprene (average: 53.4 ppt; range: 14.8–141 ppt) was high in the onshore area but low in the offshore area in late spring. The mean sea-to-air fluxes of isoprene in the East China Sea were 36.12 (late spring) and 48.34 (autumn) nmol m −2 d −1 . Results revealed the substantial isoprene emission from surface seawater, which was also a net source of atmospheric isoprene during the study period. [ABSTRACT FROM AUTHOR]

A total of 133 seawater samples and 17 sediment samples were collected from 81 sampling sites in the Changjiang River Estuary and its adjacent area and were analyzed for 16 phthalate esters (PAEs). The Σ 16 PAE concentrations in the seawater and sediment samples ranged from 180.3 ng·L − 1 to 3421 ng·L − 1 and from 0.48 μg·g − 1 to 29.94 μg·g − 1 dry weight (dw), respectively, with mean values of 943.6 ng·L − 1 and 12.88 μg·g − 1 . The distribution of ∑ 16 PAE concentrations in the water column showed that PAE concentrations in the bottom samples were higher than those in the surface samples (except the transect C located inside the Changjiang River Estuary), with the maxima appearing in the bottom layer at the offshore stations. Among the 16 PAEs, di (2-ethylhexyl) phthalate (DEHP), diisobutyl phthalate (DiBP), and dibutyl phthalate (DnBP) dominated the PAEs, with 25.1%, 21.1%, and 18.9% of the Σ 16 PAEs in seawater, respectively. The comparison of ∑ 16 PAEs and salinities in transects C and A6 suggested that the Changjiang River runoff was an important driving factor influencing the distribution of PAEs. DEHP concentrations in water samples and DEHP and DnBP concentrations in sediment samples exceeded the environmental risk levels (ERL), indicating their potential hazard to the ocean environment. [ABSTRACT FROM AUTHOR]

Dimethylsulfide (DMS) is an important and dominant sulfur compound that is transferred from the ocean to the atmosphere. In this study, the spatiotemporal variations in DMS concentrations and its two closely related compounds, namely, dimethylsulfoniopropionate (DMSP) and acrylic acid (AA), were investigated in the Yangtze (Changjiang) River Estuary and its adjacent waters, where the salinity changed dramatically in June 2014. The concentration ranges (average values) of DMS, DMSP, and AA were 1.10–27.5 (8.53), 5.93–195 (40.1), and 4.2–122.6 (17.9) nmol L −1 in the surface waters, respectively. The DMS and DMSP concentrations were higher in the study area than in its neighboring regions because of the high levels of nutrients originating in the Yangtze and Qiantang Rivers. However, the AA concentration was lower in the study area. Although no significant correlations were found between DMS, DMSP, or AA and salinity, high concentrations of DMS, AA, and DMSP were recorded between the salinity levels of 26‰ and 31‰. DMS and AA concentrations were positively correlated with chlorophyll a . The average AA/(DMSP+AA) and DMS/(DMSP+AA) ratios were 36.9% and 17.1%, respectively. The vertical profiles of DMSP and DMS presented similar variation patterns, and high concentrations of both compounds were mostly detected in the surface waters. By contrast, AA showed a different variation pattern compared with those of DMSP and DMS because AA could have other potential sources. The low average sea-to-air flux of DMS (that is, 6.55 μmol m −2 d −1 ) was mainly attributed to the low wind speed in early summer. [ABSTRACT FROM AUTHOR]

Concentrations of volatile halocarbons (VHCs), such as CHBr 2 Cl, CHBr 3 , C 2 HCl 3 , and C 2 Cl 4 , in the Bohai Sea (BS) and North Yellow Sea (NYS) were measured during the spring of 2014. The VHC concentrations varied widely and decreased with distance from the coast in the investigated area, with low values observed in the open sea. Depth profiles of the VHCs were characterized by the highest concentration generally found in the upper water column. The distributions of the VHCs in the BS and NYS were clearly influenced by the combined effects of biological production, anthropogenic activities, and riverine input. The sea-to-air fluxes of CHBr 2 Cl, CHBr 3 , C 2 HCl 3 , and C 2 Cl 4 in the study area were estimated to be 47.17, 56.63, 162.56, and 104.37 nmol m − 2 d − 1 , respectively, indicating that the investigated area may be a source of atmospheric CHBr 2 Cl, CHBr 3 , C 2 HCl 3 , and C 2 Cl 4 in spring. [ABSTRACT FROM AUTHOR]

As the largest marginal seas, the Southern Yellow Sea (SYS) and the East China Sea (ECS) are important areas to study the biogeochemical cycles of organic matter from different sources. Seawater samples were collected from the SYS and ECS to determine the composition of organic carbon and major biochemicals (amino acids and carbohydrates) making up the dissolved (DOM) and particulate organic matter (POM). Concentrations of dissolved organic carbon (DOC) in the surface waters exhibited a latitudinal gradient, with high values appearing in the Yellow Sea Coastal Current Water (YSCCW). As the labile fraction of DOM, the concentrations of total hydrolysable amino acids (THAA) and total dissolved carbohydrates (TDCHO) were variable and tended to decrease from inshore to offshore sites. The DOC, THAA, and TDCHO concentrations were negatively correlated with salinity, suggesting that physical mixing and lateral transport played an important role in the distribution of DOM. In contrast, phytoplankton production directly affected the particulate amino acid (PAA) concentrations. High concentrations of PAA in the bottom water along a transect were probably due to resuspension by strong currents. DOC-normalized yields of THAA and TDCHO (THAA-C% and TDCHO-C%) were used to characterize the bioavailability of DOM in different water masses. Elevated THAA-C% values occurred in regions with high phytoplankton biomass, while high TDCHO-C% values were widespread in the Yellow Sea Warm Current Water (YSWCW) and the YSCCW. THAA-C% and TDCHO-C% had similar depth distributions, higher in the surface and middle layers than in the bottom layer, suggesting that organic matter undergoes diagenetic alterations as it sinks. The degradation index (DI) of DOM was lower than that of POM, which could be explained by their different sources and degradation states. The sporadic occurrence of hot spots likely represented important sites of biological activity. • Concentration, chemical composition, and bioavailability of OM were studied. • Physical mixing and lateral transport affect the distribution of DOM. • Amino acid and carbohydrate yields decreased with water depth. • Hot spots of bioavailable DOM occur sporadically in the surface water. [ABSTRACT FROM AUTHOR]

Marine-derived reactive gases constitute a substantial fraction of volatile organic compounds and directly impact atmospheric chemistry and the global climate. Light alkene emissions from marginal seas are limited, and their contribution to atmospheric concentrations is likely underestimated. We surveyed oceanic emissions of ethylene, propylene, and isoprene, as well as their potential controlling factors in the marginal seas of China during the cruises in 2014–2015. Significant temporal-spatial variations in ethylene, propylene, and isoprene concentrations were observed, with the highest occurring in summer near the coastal regions. Isoprene concentrations were primarily controlled by phytoplankton biomass (i.e., Chl-a) in coastal regions, while the elevated concentrations of ethylene and propylene were attributed to photochemical reactions with the high levels of dissolved organic matter (DOM). Additionally, the vertical distributions of ethylene and propylene mirrored light penetration, with exponential decrease in concentrations with depth. However, there were high values of ethylene and propylene observed at deep chlorophyll maximum, suggesting the existence of non-photochemical production pathways, most likely biological origin. Emissions of ethylene, propylene, and isoprene from the marginal seas of China were estimated to be 0.022, 0.024, and 0.011 Tg C yr−1, respectively, indicating they are important contributors to global non-methane hydrocarbons. Due to the scarcity of alkene emission data for marginal seas, current global emissions have been underestimated to some extent. It is essential to incorporate the contributions from marginal seas to accurately estimate alkene budgets on global scales. Unlabelled Image • The distributions of light alkenes in seawater and atmosphere were simultaneously investigated in the marginal seas of China. • Marginal seas represented an important source of atmospheric alkenes. • Global oceanic alkene emissions will be underestimated if the contributions of marginal seas are neglected. [ABSTRACT FROM AUTHOR]