Distributions and sea-to-air fluxes of volatile halocarbons in the southern Yellow Sea and the East China Sea

Distributions and sea-to-air fluxes of five kinds of volatile halocarbons（VHCs） were studied in the southern Yellow Sea（SYS） and the East China Sea（ECS） in November 2007. The results showed that the concentrations of 1,1,1-trichloroethane（C2H3Cl3）, 1,1-dichloroethene（C2H2Cl2）, 1,1,2-trichloroethene（C2HCl3）, trichloromethane（CHCl3） and tetrachloromethane（CCl4） in the surface water were 0.31–4.81, 2.75–21.3, 1.21–17.1, 5.02–233 and 0.045–4.47 pmol/L, respectively, with the average values of 1.89, 12.20, 6.93, 60.90 and 0.33 pmol/L. On the whole, the horizontal distributions of C2H3Cl3, C2H2Cl2 and CCl4 were affected mainly by anthropogenic activities, while C2HCl3 and CHCl3 were influenced by biological factors as well as anthropogenic activities. In the study area, the concentrations of VHCs（except C2HCl3） exhibited a decreasing trend from inshore to offshore sites, with the higher values occurring in the coastal waters. The sea-to-air fluxes of C2H3Cl3, C2HCl3, CHCl3 and CCl4 were calculated to be-56.00–（-5.68）,-7.31–123.42, 148.00–1 309.31 and-83.32–（-1.53） nmol/（m2·d）, respectively, with the average values of-6.77, 17.14, 183.38 and-21.27 nmol/（m2·d）. Our data showed that the SYS and ECS in autumn was a sink for C2H3Cl3 and CCl4, while it was a source for C2HCl3 and CHCl3 in the atmosphere.

夏季东海一氧化碳的浓度分布、海-气通量和微生物消耗研究

研究了夏季东海海水中和大气中一氧化碳（CO）的浓度分布、海-气通量和表层海水中CO的微生物消耗。夏季东海大气中C0的体积分数范围为63×10^-9～120×10^-9，平均值为87×10^-9（SD=18×10^-9，n=37），呈现出近岸高，远海低和北高南低的特点。夏季东海表层海水中CO的浓度范围为0．24～5．51nmol／L，平均值为1．48nmol／L（SD=1．46，n=37），CO的浓度受太阳辐射影响明显；CO在垂直分布上表现出浓度随深度增加迅速减小的特征，浓度最大值出现在表层。调查期间表层海水中CO相比大气处于过饱和状态，过饱和系数变化范围为3．65～113．55，平均值为23．63（SD=24．56，n=37），这表明调查海域是大气中C0的源。CO的海-气通量变化范围为0．25～78．50μmol／（m^2·d），平均值为9．97μmol／（m^2·d）（SD=14．92，n=37）。在CO的微生物消耗培养实验中，CO的浓度随时间增长呈指数降低，消耗过程表现出一级反应的特点，速率常数Kco范围为0．043～0．32／h，平均值为0．18／h（SD=0．088，n=9），Kco与盐度之间存在负相关关系。

Distributions of dimethylsulfide in the Bohai Sea and Yellow Sea of China

Dimethylsulfide(DMS) measurements in the surface seawater of China eastern coastline were conducted during March 9—10, 1993 in Bohai Sea along the cruise from Dalian to Tianjin and during September 24—25, 1994 in Yellow Sea along the cruise from Shanghai to Qingdao. On the cruise in Bohai Sea DMS concentrations varied from 0.11 to 2.63 nmol/L with an average of 1.31 nmol/L, while DMS flux was estimated to be 0.85 μmol/(m 2·d) with the range of 0.04—3.12 μmol/(m 2·d). On the cruise in Yellow Sea DMS concentrations varied from 0.95 to 7.48 nmol/L with an average of 2.89 nmol/L, and DMS flux was estimated to be 7.94 μmol/(m 2·d) with the range of 0.11—18.88 μmol/(m 2·d). Variations in DMS concentrations along the latitude in Yellow Sea were observed larger than those along the longitude in Bohai Sea. DMS concentrations and fluxes had a similar spatial trend both in Bohai Sea and Yellow Sea with the correlation coefficients of 0.75 and 0.64, respectively.

Spatial distribution of dimethylsulfide and dimethyl-sulfoniopropionate in the Yellow Sea and Bohai Sea during summer

The distributions of dimethylsulfide （DMS） and its precursor dimethylsulfoniopropionate （DMSP） in surface water of the Yellow Sea and the Bohai Sea were studied during June 2011. The mean concentrations and ranges of DMS, dissolved DMSP （DMSPd）, and particulate DMSP （DMSPp） in surface waters were 6.85 （1.60-12.36）, 7.25 （2.28-19.05） and 61.87 （6.28-224.01） nmol/L, respectively. There were strong correlations between DMSPp and chlorophyll a in the Bohai Sea and the North Yellow Sea, respectively, and concentrations of DMS and DMSP were high, with a relatively high proportion of dinoflagellates, in the region of the South Yellow Sea Cold Water Mass. Results show that phytoplankton biomass and species composition were important factors that controlled the distribution of DMS and DMSP. Complex environmental factors, including nutrients, transparency, and terrestrial runoff, might also influence the variability in DMS and DMSP. Biological production and consumption rates of DMS in the Bohai Sea were higher than those in the Yellow Sea. DMS production rates were closely correlated with DMSPd concentrations. DMS and DMSP exhibited obvious diel variations, with high concentrations occurring in the late afternoon （16：00-19：00） and low concentrations occurring during the night, implying that the intensity of solar radiation had a significant influence on these variations. Size distributions of chlorophyll a and DMSPp were also investigated and large nanoplankton （5-20 μm）, mainly diatoms, contributed significantly to chlorophyll a and DMSPp at most stations. The average sea-to-air flux of DMS in the study area was estimated to be 11.07 μmol/（m^2·d） during the summer.

Distribution and Cycling of Carbon Monoxide in the East China Sea and the Marine Atmosphere in Autumn

Carbon monoxide(CO) concentrations, sea-to-air fluxes and microbial consumption rate constants, along with atmospheric CO mixing ratios, were measured in the East China Sea(ECS) in autumn. Atmospheric CO mixing ratios varied from 96 to 256 ppbv, with an average of 146 ppbv(SD = 54 ppbv, n = 31). Overall, the atmospheric CO concentrations displayed a decreasing trend from inshore to offshore stations. The surface water CO concentrations in the investigated area ranged from 0.24 to 6.12 nmol L^(-1), with an average of 1.68 nmol L^(-1)(SD = 1.50 nmol L^(-1), n = 31). The surface water CO concentrations were affected significantly by sunlight. Vertical profiles showed that CO concentrations declined rapidly with depth, with the maximum appearing in the surface water. The surface CO concentrations were oversaturated, with the saturation factors ranging from 1.4 to 56.9, suggesting that the ECS was a net source of atmospheric CO. The sea-to-air fluxes of CO in the ECS ranged from 0.06 to 11.31 μmol m^(-2) d^(-1), with an average of 2.90 μmol m^(-2) d^(-1)(SD = 2.95μmol m^(-2) d^(-1), n = 31). In the incubation experiments, CO concentrations decreased exponentially with incubation time and the processes conformed to the first order reaction characteristics. The microbial CO consumption rate constants in the surface water(KCO) ranged from 0.063 to 0.22 h^(-1), with an average of 0.12 h^(-1)(SD = 0.062 h^(-1), n = 6). A negative correlation between KCO and salinity was observed in the present study.

Variations in Dissolved Methane in the Yellow Sea During the Spring Algal Blooms of 2009

Methane (CH4) is an important greenhouse gas and oceans are net sources of atmospheric CH4. The effects of environ- mental factors on the CH4 variation during different phases of the spring algal blooms were examined during two cruises conducted in the Yellow Sea (YS) from February to April of 2009. During the pre-bloom period from February to March, low CH4 saturation (< 134%) was observed in the surface water, except at two nearshore stations where the CH4 levels were above 140% in March due to mixing with the coastal water. During the bloom period, CH4 increased obviously at two bloom-tracking stations, especially at the surface with mean saturations of 140% and 170%. The increase in CH4 concentration/saturation is thought to be the result of in situ CH4 production. The particulate organic carbon (POC) and chlorophyll a contents were believed to be important factors that influ- enced the CH4 production. In addition, the presence of different dominant phytoplankton species and the grazing pressure may have stimulated the CH4 production by supplying potential methanogenic substrates (such as dimethylsulphoniopropionate (DMSP)). Both the incubation data and the in situ estimations further evidenced the significant influence of the spring blooms on the CH4 production. The calculated sea-to-air CH4 fluxes during the bloom period were not significantly higher than those during the pre-bloom period despite the bloom-increased CH4 saturation. This is due to the variation in physical forcing (such as wind speed), which is the main driver for determining the CH4 flux. Finally, we estimated the annual CH4 flux in the YS as 9.0 μmol m 2 d 1;the findings suggest that the YS is a natural source of atmospheric CH4.

Calculation of sea-to-air flux of substances

DIMETHYL sulfide （DMS） is a principal volatile organic sulphur compound in seawater. Once released to the atmosphere, DMS is rapidly oxidized to non-sea-salt sulfate (NSS-SO42-) and thus participates in the climate change and the acid rain formation. Therefore, widespread attention has been paid to DMS. So far, there are few reported studies regarding the

Temporal variations of dimethylsulfide and dimethylsulfoniopropionate in the southern Yellow Sea in spring and autumn

Temporal distributions of dimethylsulfide（DMS） and dimethylsulfoniopropionate（DMSP） were studied in the southern Yellow Sea（SYS） during April and September 2010. The mean concentrations（range） of DMS, dissolved and particulate DMSP（DMSPd and DMSPp） in the surface waters in spring are 1.69（0.48–4.92）, 3.18（0.68–6.75）and 15.81（2.82–52.33） nmol/L, respectively, and those in autumn are 2.80（1.33–5.10）, 5.45（2.19–11.30） and 30.63（6.24–137.87） nmol/L. On the whole, the distributions of DMS and DMSP in spring are completely different from those in autumn. In the central part of the SYS, the concentrations of DMS and DMSP in spring are obviously higher than those in autumn, but the opposite situation is found on the south of 34°N, which can be attributed to the differences in nutrients and phytoplankton biomass and composition between spring and autumn. Besides,the seasonal variations of water column stability and the Changjiang diluted water also have significant impact on the distributions of DMS and DMSP in spring and autumn on the south of 34°N. DMS and DMSPp concentrations coincide well with chlorophyll a（Chl a） levels in the spring cruise, suggesting that phytoplankton biomass may play an important role in controlling the distributions of DMS and DMSPp in the study area. Annual DMS emission rates range from 0.015 to 0.033 Tg/a（calculated by S）, respectively, using the equations of Liss and Merlivat（1986） and Wanninkhof（1992）. This result implies a significant relative contribution of the SYS to the global oceanic DMS fluxes.

Recent Trends in Satellite-Derived Chlorophyll and Aerosol Optical Depth Together with Simulated Dimethylsulfide in the Eastern China Marginal Seas

The biogenic compound dimethylsulfide(DMS)produced by a range of marine biota is the major natural source of re-duced sulfur to the atmosphere and plays a major role in the formation and evolution of aerosols,potentially affecting climate.The spatio-temporal distribution of satellite-derived chlorophyll_a(CHL)and aerosol optical depth(AOD)for the recent years(2011-2019)in the Eastern China Marginal Seas(ECMS)(25°-40°N,120°-130°E)are studied.The seasonal CHL peaks occurred during late April and the CHL distribution displays a clear zonal gradient.Elevated CHL was also observed along the northern and western coastlines during summer and winter seasons.Trend analysis shows that mean CHL decreases by about 10%over the 9-year study period,while AOD was higher in south and lower in north during summertime.A genetic algorithm technique is used to calibrate the key model parameters and simulations are carried out for 2015,a year when field data was available.Our simulation results show that DMS seawater concentration ranges from 1.56 to 5.88 nmol L^(−1) with a mean value of 2.76 nmol L^(−1).DMS sea-air flux ranges from 2.66 to 5.00mmol m^(−2) d^(−1) with mean of 3.80mmol m^(−2) d^(−1).Positive correlations of about 0.5 between CHL and AOD were found in the study region,with higher correlations along the coasts of Jiangsu and Zhejiang Provinces.The elevated CHL concentration along the west coast is correlated with increased sea-water concentrations of DMS in the region.Our results suggest a possible influ-ence of DMS-derived aerosol in the local ECMS atmosphere,especially along the western coastline of ECMS.