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An on-line flow injection mercury analyser (FIMA) for inorganic mercury (Hg) analysis in environmental waters is presented. The FIMA is a portable dual-channel and purge-and-trap system combining aqueous reduction with stannous chloride (SnCl2), two-stage gold (Au) amalgamation, thermal desorption of Hg0 and final detection with cold vapour atomic fluorescence spectrometry (CVAFS). Simultaneous on-line operations of sample loading and analysis make analytical throughput and accuracy improved and contamination eliminated. Results of system optimisation and reliability regarding the determination of inorganic Hg2+ are described. Analytical performances of both channels were the same in terms of data reliability. Low procedural blanks were obtained from laboratory and field trip (≤5 pg, n = 30). Excellent calibrations (r2 > 0.99) with a high precision and good stability (RSD −1 and −1, n = 30). The system was finally validated by measurements comparison of the two channels (r2 > 0.98), and analysis of a certified reference material (coastal seawater BCR-579, recoveries 101 ± 4%, n = 10). Overall, a sample throughput of ~10 samples per hour with two-channel detections of FIMA can be achieved. The onboard analysis of inorganic Hg species (e.g. elemental, reactive, and total Hg) in surface seawaters of the East China Sea (ECS) are also successfully achieved. The portable FIMA is fast, easy, and robust for reliable monitoring of Hg in natural seawaters.

Rates of seawater acidification and rise of partial pressure of CO

Significance Bluefin tuna (BFT) is an apex predatory, long-lived, migratory pelagic fish that is widely distributed throughout the world's oceans. These fish have very high concentrations of neurotoxic methylmercury (MeHg) in their tissues, which increase with age. Our study shows that Hg accumulation rates (MARs) in BFT as a global pollution index can reveal global patterns of Hg pollution and bioavailability in the oceans and further reflect both natural and anthropogenic emissions and regional environmental features. Overall, MARs provide a means to compare Hg bioavailability among geographically distinct populations of upper trophic level marine fish across ocean subbasins, to investigate trophic dynamics of Hg in marine food webs, and furthermore, to improve public health risk assessments of Hg exposure from seafood., Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here, we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation.

Seasonal and spatial distributions of total mercury (THg) in the Danshuei Estuary and adjacent coastal areas near the ocean outfall of Taipei, Taiwan, have been successfully investigated from May 2003 to January 2005. We found spatio-temporal variation in THg levels in the Danshuei coastal area was the result of sources and supplies of Hg. High THg concentrations in sediments and seawater were particularly found near the effluent outfall. Average THg levels (avg.: 9-22 ng L

The present study aims to understand the mechanisms controlling ecosystem metabolic states and atmospheric CO2 fluxes and explore their linkages through monthly investigations along the tropical Kaoping Submarine Canyon (KPSC) in southwestern Taiwan. The magnitudes of integrated gross production (IGP) and integrated dark community respiration (IDCR) were higher in summer than in winter, likely supported by greater inputs of freshwater in summer with high loads of nutrients and organic carbon. Strong positive correlations were observed between gross production (GP) (or dark community respiration (DCR)) and temperature, photosynthetically active radiation and nutrients, but negative correlations were observed between GP (or DCR) and salinity in discrete water samples; these results reveal the significant impacts of freshwater inputs on GP and DCR. GP was determined largely by DCR, and DCR was attributed largely (78%) to bacterial respiration in the KPSC. Approximately 60% of measurements were autotrophic conditions (IGP/IDCR >1) in most wet seasons except for certain offshore stations, which were apparently driven by higher temperature and nutrient availability, whereas 40% of measurements revealed heterotrophic conditions (IGP/IDCR

Distinct spatiotemporal distributions of sea surface dissolved elemental mercury (DEM) and its air-sea exchange flux were observed in the river-dominated and monsoon-influenced East China Sea (ECS). Spatially, DEM concentrations were higher in the nearshore Changjiang diluted water (90 ± 20 to 260 ± 40 fM) than in the offshore Kuroshio water (60 ± 10 to 160 ± 40 fM) and correlated with salinity and total Hg concentrations, suggesting that the total Hg discharged from the Changjiang river is a controlling factor. In summer, monsoon-driven coastal upwelling formed a transient nearshore water mass with very elevated DEM concentrations (290 ± 20 to 320 ± 70 fM). Seasonally, DEM concentrations in all water masses were the highest in summer (120 ± 30 to 320 ± 70 fM). Estimated rate coefficients for DEM production varied seasonally and strongly correlated with sea surface temperature (SST). Hg0 evasion fluxes also peaked in summer (670 ± 380 pmol m-2 day-1), while in winter, DEM was close to equilibrium with gaseous elemental mercury in the atmosphere. Based on the air-sea Hg fluxes for all four seasons from this study and regional atmospheric deposition fluxes from others, we conclude that the ECS is a net sink of Hg annually, but it is a source of Hg to the atmosphere in summer. Moreover, the contribution of the ECS to Hg evasion may increase as a result of flood-associated high Changjiang discharge and rising SST.

Temporal variations in hydrographic parameters and nutrients were observed in a 300 m deep submarine canyon (Hungtsai Trough) near the southern tip of Taiwan. A vigorous oscillation below the surface layer has been observed which relates closely to an internal tidal wave generated from the nearby Luzon Strait. The vertical movement can be measured by monitoring an 18 °C isothermal depth which shows an up-and-down oscillation between 90 and 240 m with an average displacement of 110 m within a tidal cycle, a scale significantly larger than has been reported elsewhere. The frequency of this oscillation coincides with the surface tide but in an almost opposite phase. All hydrographic and chemical parameters (oxygen, density, fluorescence, transmittance and nutrients including nitrate, phosphate and silicate) synchronize with the tidal movement, as judged by normalized plots against temperature. When the nutrient-rich deep water upwells and becomes an outcrop over the trough rim at 100 m deep, it is swept horizontally by the strong alongshore tidal current. Consequently, the trough acts as a source point to supply extra nutrients to the coastal ecosystem.

This study aims to understand the controlling mechanisms of ecosystem metabolic states and air-sea CO2 fluxes and their cross linkages in the northern South China Sea (NSCS). The integrated gross production (IGP), integrated dark community respiration (IDCR), and integrated bacterial respiration (IBR) were all higher in summer than in winter ranging from 851, 435, and 243 to 5032, 10707, and 7547 mg C m−2 d−1, respectively. The discrete estimates of gross production (GP) and dark community respiration (DCR) were modulated by temperature, salinity and nutrient availability through different mechanisms in summer and winter and in shallow (Zhujiang River plumes and shelves) and deep (slope and basin) sampling stations. GP was correlated with DCR (r = 0.74, p

Limited observations exist for a reliable assessment of annual CO2 uptake that takes into consideration the strong seasonal variation in the river-dominated East China Sea (ECS). Here we explore seasonally representative CO2 uptakes by the whole East China Sea derived from observations over a 14-year period. We firstly identified the biological sequestration of CO2 taking place in the highly productive, nutrient-enriched Changjiang River plume, dictated by the Changjiang River discharge in warm seasons. We have therefore established an empirical algorithm as a function of sea surface temperature (SST) and Changjiang River discharge (CRD) for predicting sea surface pCO2. Syntheses based on both observations and models show that the annually averaged CO2 uptake from atmosphere during the period 1998–2011 was constrained to about 1.8 ± 0.5 mol C m−2 yr−1. This assessment of annual CO2 uptake is more reliable and representative, compared to previous estimates, in terms of temporal and spatial coverage. Additionally, the CO2 time series, exhibiting distinct seasonal pattern, gives mean fluxes of −3.7 ± 0.5, −1.1 ± 1.3, −0.3 ± 0.8 and −2.5 ± 0.7 mol C m−2 yr−1 in spring, summer, fall and winter, respectively, and also reveals apparent interannual variations. The flux seasonality shows a strong sink in spring and a weak source in late summer–mid-fall. The weak sink status during warm periods in summer–fall is fairly sensitive to changes of pCO2 and may easily shift from a sink to a source altered by environmental changes under climate change and anthropogenic forcing.

The toxic metal mercury is present only at trace levels in the ocean, but it accumulates in fish at concentrations high enough to pose a threat to human and environmental health. Human activity has dramatically altered the global mercury cycle, resulting in loadings to the ocean that have increased by at least a factor of three from pre-anthropogenic levels. Loadings are likely to continue to increase as a result of higher atmospheric emissions and other factors related to global environmental change. The impact that these loadings will have on the production of methylated mercury (the form that accumulates in fish) is unclear. In this article, we summarize the biogeochemistry of mercury in the ocean and use this information to examine past impacts that human activity has had on the cycling of this toxic metal. We also highlight ways in which the mercury cycle may continue to be affected and its potential impact on mercury in fish.

It is widely recognized that the variation of average surface chlorophyll a concentration (Chl) in the South China Sea (SCS) is closely related to wind forcing, especially during the intense winter monsoon. In this study we demonstrate that, after removal of the seasonal cycles, the variation of Chl showed strong asymmetric responses to wind speed under El Niño or La Niña conditions. The analysis was based on a time-series of Chl in the study area (115–117° E, 17–19° N) around the SEATS (South-East Asian Time-series Study) station located in the central northern SCS from September 1997 to the end of 2011, which was constructed by merging the SeaWiFS data (1997–2006) and MODIS data (2003–2011). The merged daily data were validated by shipboard observations at the SEATS station. The non-seasonal variations of monthly mean Chl, wind speed, sea surface height (SSH) and sea surface temperature (SST) were examined against the multivariate ENSO index (MEI). The analysis reveals strongly asymmetric correlations of Chl and SST with positive MEI (El Niño) or negative MEI (La Niña). Under El Niño conditions, both showed significant correlations with MEI or wind speed; under La Niña conditions, both showed weak or insignificant correlations. The contrast was more pronounced for Chl than for SST. The subdued responses of Chl to wind forcing under La Niña conditions were probably attributed to a deepened thermocline, for which wind driven nutrient pumping is less efficient. A deeper thermocline, which was observed during the 1999–2000 La Niña event and inferred by positive SSH anomalies during other La Niña events, was probably caused by reduced SCS throughflow under La Niña conditions. Intrusion of the nutrient-depleted Kuroshio water in the surface layer as observed during the 1999–2000 La Niña could be partially responsible for the suppressed Chl response.

National Science Council (Taiwan) [NSC 98-2611-M-001-003, NSC 98-2621-M-002005, NSC 99-2611-M-001-005, NSC 99-2628-M-001-006, NSC 100-2628-M-001-008-MY4]; thematic program Atmospheric Forcing on Ocean Biogeochemistry (AFOBi); Drunken Moon Lake Scientific Integrated Scientific Research Platform" of Academia Sinica

A super Asian dust (SAD) storm that originated from North China has affected East Asia since 20 March 2010. The tempo-spatial and size distributions of aerosol Al, a tracer of wind-blown dust, were measured on a regional aerosol network in March 2010. Two dust events were recorded: the SAD and a relatively moderate AD event. The SAD clouds raised Al concentrations to ~50 µg/m3 on 21 and 22 March over the East China Sea (ECS) and occupied there for ~5 days. The SAD plume also stretched toward the South China Sea (SCS) on 21 March however, it caused a maximum Al concentration of ~8.5 µg/m3 only, much lower than that observed in the ECS. In comparison, a weaker dust plume on 16 March caused Al maximum of ~4 µg/m3 over the ECS, and comparably, ~3 µg/m3 in the SCS. Dry dust deposition was measured during the peak phase of the SAD at 178 mg/m2/d, which corresponded to dry deposition velocities of 0.2–0.6 cm/s only, much lower than the commonly adopted one (1–2 cm/s). The corresponding increase in dust deposition by the SAD was up to a factor of ~12, which was, however, considerably disproportionate to the increase in dust concentration (i.e., the factor of over 100). In certain cases, synoptic atmospheric conditions appear to be more important in regulating dust contribution to the SCS than the strength of AD storms.

Model studies suggested that human-induced increase in nutrient load may have stimulated primary production and thus enhanced the CO2 uptake capacity in the coastal ocean. In this study, we investigated the seasonal variations of the surface water's partial pressure of CO2 (pCO2sw) in the highly human-impacted Changjiang–East China Sea system between 2008 and 2011. The seasonality of pCO2sw has large spatial variations, with the largest extreme of 170 ± 75 μatm on the inner shelf near the Changjiang Estuary (from 271 ± 55 μatm in summer to 441 ± 51 μatm in autumn) and the weakest extreme of 53 ± 20 μatm on the outer shelf (from 328 ± 9 μatm in winter to 381 ± 18 μatm in summer). During the summer period, stronger stratification and biological production driven by the eutrophic Changjiang plume results in a very low dissolved inorganic carbon (DIC) in surface waters and a very high DIC in bottom waters of the inner shelf, with the latter returning high DIC to the surface water during the mixed period. Interestingly, a comparison with historical data shows that the average pCO2sw on the inner shelf near the Changjiang Estuary has decreased notably during summer, but has increased during autumn and winter from the 1990s to the 2000s. We suggest that this decadal change is associated with recently increased eutrophication. This would increase both the photosynthetic removal of DIC in surface waters and the respiratory release of DIC in bottom waters during summertime, thereby returning more DIC to the surface during the subsequent mixing seasons and/or episodic extreme weather events (e.g., typhoons). Our finding demonstrates that increasing anthropogenic nutrient delivery from a large river may enhance the sequestration capacity of CO2 in summer but may reduce it in autumn and winter. Consequently, the coastal ocean may not necessarily take up more atmospheric CO2 in response to increasing eutrophication, and the net effect largely depends on the relative timescale of air–sea gas exchange and offshore transport of the shelf water. Finally, the case we report for the Changjiang system may have general ramifications for other eutrophic coastal oceans.

We have developed a technique that combines a high temperature quartz furnace with inductively coupled plasma-mass spectrometry for the determination of Hg stored in the annual CaCO 3 bands found in coral skeletons. Substantial matrix effects, presumably due to the discontinuous introduction of CO 2 to the gas stream, were corrected for by simultaneously supplying a stream of argon containing highly enriched elemental 202 Hg o and observing peaks in the 200 Hg/ 202 Hg signal as the sample was decomposed. Primary signal calibration for Hg was achieved using gas injections from a saturated vapor standard. The absolute instrument detection limit was low (about 0.2 fmol), with a practical limit of detection (3 σ of blanks) of 2 fmol. Reproducibility of samples was (RSD) 15–27%. We applied this method to the determination of Hg concentrations in two colonies of Diploria labyrinthiformis collected from Castle Harbour, Bermuda, at a site about to be buried under the municipal waste landfill. The temporal reconstructions of Castle Harbour seawater Hg concentrations implied by the coral record show a decline throughout the period of record (1949–2008). The coral archived no apparent signal associated with waste disposal practices in the Harbour (bulk waste land-filling or, since 1994, disposal of waste incinerator ash), and mercury concentrations in the coral did not correlate to growth rate as assessed by linear extension. There was, however, a large and nearly exponential decrease in apparent Hg concentration in the Harbour which circumstantially implicates the dredging and/or landfilling operations associated with the construction of the airport on St. David’s Island.

[1] A unique seasonal pattern in dissolved elemental mercury (DEM) was observed in the tropical monsoon-dominated South China Sea (SCS). The DEM concentration varied seasonally, with a high in summer of 160 ± 40 fM (net evasion 580 ± 120 pmol m−2 d−1, n = 4) and a low in winter of 60 ± 30 fM (net invasion −180 ± 110, n = 4) and showed a positive correlation with sea surface temperature (SST). The elevated DEM concentration in summer appears mainly abiologically driven. In winter, the SCS acts as a sink of atmosphere Hg0 as a result of low SST and high wind of the year, enhanced vertical mixing, and elevated atmospheric gaseous elemental mercury. Annually, the SCS serves as a source of Hg0 to the atmosphere of 300 ± 50 pmol m−2 d−1 (385 ± 64 kmol Hg yr−1, ~2.6% of global emission in ~1% of global ocean area), suggesting high regional Hg pollution impacts from the surrounding Mainland (mostly China).

The distribution of gaseous elemental mercury (GEM) was determined in the surface atmosphere of the northern South China Sea (SCS) during 12 SEATS cruises between May 2003 and December 2005. The sampling and analysis of GEM were performed on board ship by using an on-line mercury analyzer (GEMA). Distinct annual patterns were observed for the GEM with a winter maximum of 5.7 ± 0.2 ng m−3 (n = 3) and minimum in summer (2.8 ± 0.2; n = 3), with concentrations elevated 2–3 times global background values. Source tracking through backward air trajectory analysis demonstrated that during the northeast monsoon (winter), air masses came from Eurasia, bringing continental- and industrial-derived GEM to the SCS. In contrast, during summer southwest monsoon and inter-monsoon, air masses were from the Indochina Peninsula and Indian Ocean and west Pacific Ocean. This demonstrates the impact that long-range transport, as controlled by seasonal monsoons, has on the Hg atmospheric distribution and cycling in the SCS.

Measurements of dissolved inorganic carbon (DIC), pH, total alkalinity (TA), and partial pressure of CO 2 (pCO 2 ) were conducted at a total of 25 stations along four cross shelf transects in the East China Sea (ECS) in January 2008. Results showed that their distributions in the surface water corresponded well to the general circulation pattern in the ECS. Low DIC and pCO 2 and high pH were found in the warm and saline Kuroshio Current water flowing northeastward along the shelf break, whereas high DIC and pCO 2 and low pH were mainly observed in the cold and less saline China Coastal Current water flowing southward along the coast of Mainland China. Difference between surface water and atmospheric pCO 2 (ΔpCO 2 ), ranging from ~ 0 to − 111 μatm, indicated that the entire ECS shelf acted as a CO 2 sink during winter with an average flux of CO 2 of −13.7 ± 5.7 (mmol C m − 2 day − 1 ), and is consistent with previous studies. However, pCO 2 was negatively correlated with temperature for surface waters lower than 20 °C, in contrast to the positive correlation found in the 1990s. Moreover, the wintertime ΔpCO 2 in the inner shelf near the Changjiang River estuary has appreciably decreased since the early 1990s, suggesting a decline of CO 2 sequestration capacity in this region. However, the actual causes for the observed relationship between these decadal changes and the increased eutrophication over recent decades are worth further study.

A total of 47 marine aerosols collected from the East China Sea between the spring of 2005 and the spring of 2007 were analyzed for both the water-soluble and the total concentrations of 25 trace elements and phosphorus and the water-soluble major ions, organic carbon, as well as silicon. During the sampling periods, eight samples were significantly influenced by Asian dust events. The total concentrations of both the chemical species of dust origin and of anthropogenic origin were higher during the Asian dust period, suggesting that the Asian outflow of air pollutants often accompanies the Asian dust advection. Overall, the average solubilities were ≤ 20% for Al, Fe, Ti, Cr, Y, Sn, Ba, Ni, Ga, and Mo; 20–40% for Co, Cs, Rb, Sb, and Pb; 40–60% for Mn, V, Cu, Ge, and P; and ≥ 60% for Tl, Sr, As, Zn, Cd, and Se. The solubilities for many elements are lower in the high dust period than during the polluted northeasterly monsoon and the background summer period. A variety of controlling factors of the solubilities of the elements were discussed in this study. The relative importance could be concluded as follows: acid processing > chemical speciation ≈ aerosol source > dust loading. Finally, we estimated the dry depositional fluxes of soluble elements by assuming certain dry deposition velocities for each element. The fluxes were 39 ± 50 µg/m2/d for soluble Fe and 41 ±74 µg/m2/d for the combination of some bioavailable elements (e.g., Zn, Cu, Mn, Ba, Co, V, Ni, and Cd) during the northeasterly monsoon. Atmospheric deposition is an additional source of nutrient elements that may be important not only in the coastal/marginal sea, but also particularly in the remote open ocean because aerosol trace elements are associated mostly with fine mode particles that can be brought farther from the source regions.

It is demonstrated that weakened wind mixing and strengthened water column stratification resulted in the anomalously low sea surface chlorophyll in the northern South China Sea during the 1997–1998 El Nino event. Remotely sensed sea surface temperature, wind and chlorophyll, which were validated by shipboard observations at the SouthEast Asian Time-series Study (SEATS) station (18°N, 116°E) in the northern South China Sea (SCS) provided the basis for this study. During the 1997–1998 winter at the SEATS station, the sea surface temperature was elevated by about 2 °C above the climatological mean, while the wind speed of the northeast monsoon was reduced from a climatological mean of 9.4 to 6.8 m/s. The concentration of surface chlorophyll- a dropped from 0.2 to 0.1 mg/m 3 . The monthly area-averaged integrated primary production estimated for the northern SCS area (112–119°E, 15–21°N) was reduced by about 40% of the normal winter value. Under the anomalously high sea surface temperature and weak monsoon, the mixed-layer depth would have been reduced from an average of 65 to 45 m and the nutrients in the mixed layer would have been reduced by half, according to observations at the SEATS station in more recent years. During the 1997–1998 El Nino event, the onset of warming in the northern SCS lagged behind that in the eastern equatorial Pacific by about 5 months and lingered for 11 months. This course of change resembled that of the western Pacific warm pool region. However, contrary to the northern SCS, the sea surface chlorophyll was enhanced in the warm pool region during the event, probably mainly because of the uplifted nutricline. Unlike the eastern equatorial Pacific, the dramatic recovery of biological production did not happen in the SCS in the summer of 1998. These distinctive biogeochemical responses reflect fundamental differences between the SCS and the equatorial Pacific in terms of upper water column dynamics.

The South China Sea (SCS) exhibits strong variations on seasonal to interannual time scale, and the changing Southeast Asian Monsoon has direct impacts on the nutrients and phytoplankton dynamics, as well as the carbon cycle. A Pacific basin-wide physical-biogeochemical model has been developed and used to investigate the physical variations, ecosystem responses, and carbon cycle consequences. The Pacific basin-wide circulation model, based on the Regional Ocean Model Systems (ROMS) with a 50-km spatial resolution, is driven with daily air-sea fluxes derived from the National Centers for Environmental Prediction (NCEP) reanalysis between 1990 and 2004. The biogeochemical processes are simulated with the Carbon, Si(OH)4, Nitrogen Ecosystem (CoSINE) model consisting of multiple nutrients and plankton functional groups and detailed carbon cycle dynamics. The ROMS-CoSINE model is capable of reproducing many observed features and their variability over the same period at the SouthEast Asian Time-series Study (SEATS) station in the SCS. The integrated air-sea CO2 flux over the entire SCS reveals a strong seasonal cycle, serving as a source of CO2 to the atmosphere in spring, summer and autumn, but acting as a sink of CO2 for the atmosphere in winter. The annual mean sea-to-air CO2 flux averaged over the entire SCS is +0.33 moles CO2 m−2year−1, which indicates that the SCS is a weak source of CO2 to the atmosphere. Temperature has a stronger influence on the seasonal variation of pCO2 than biological activity, and is thus the dominant factor controlling the oceanic pCO2 in the SCS. The water temperature, seasonal upwelling and Kuroshio intrusion determine the pCO2 differences at coast of Vietnam and the northwestern region of the Luzon Island. The inverse relationship between the interannual variability of Chl-a in summer near the coast of Vietnam and NINO3 SST (Sea Surface Temperature) index in January implies that the carbon cycle and primary productivity in the SCS is teleconnected to the Pacific-East Asian large-scale climatic variability.

The primary production in the South China Sea (SCS) has been assessed by a coupled physical–biogeochemical model with a simple NPZD ecosystem [Liu et al., 2002. Monsoon-forced chlorophyll distribution and primary production in the SCS: observations and a numerical study. Deep-Sea Research I 49(8), 1387–1412]. In recent years there have been an increasing number of observations in the SCS that may be used to check the validity of the previous approach. The coupled model of the SCS mentioned above employs a photo-adaptation scheme for the phytoplankton growth and uses the simplest bottom boundary condition of an inert benthic layer. These adopted schemes are checked against observations at the South-East Asian Time-series Study (SEATS) Station in the northern SCS and in the Gulf of Thailand. Numerical experiments with or without photo-adaptation or active benthic processes are carried out in this study. Additional experiments are performed with different parameters used for these processes. The observations at the SEATS Station provide direct evidence for the variable chlorophyll-to-nitrogen ratio in phytoplankton as required by photo-adaptation. It is concluded that a photo-adaptation scheme is critical to the phytoplankton growth, especially for the development of the subsurface chlorophyll maximum (SCM). Without photo-adaptation, the average value of the vertically integrated primary production (IPP) over the whole SCS domain would be 35% lower. It is noted that, the modeled SCM occurs at depths shallower than observations due to physical as well as biological processes employed by the model. Increasing the upper limit of the chlorophyll-to-nitrogen ratio, as suggested by observations, enhances chlorophyll level in the lower part of the euphotic zone and raises primary productivity in areas with rich nutrient supply. The observed values of the IPP in the Gulf of Thailand clearly demonstrate the importance of the benthic–pelagic coupling to the nutrient cycle. Without benthic nutrient regeneration the model grossly underestimates primary production due to failure to build up the nutrient reserve in the Gulf. On the other hand, a fully regenerated flux of particulate organic nitrogen at the sea floor without denitrification produces too strong a primary production. The improved model uses a higher upper limit for the chlorophyll-to-phytoplankton ratio of 3.5 g Chl/mol N and adopts benthic processes of a coupled nitrification–denitrification scheme with denitrification consuming 14% of the detritus flux at the bottom. The model predicts a mean annual IPP value of 406 mg C m −2 d −1 for the SCS, which is 44% higher than that predicted by the original model. The increase can be broken down to 39% attributed to the benthic nutrient regeneration and 5% to the enhanced photo-adaptation. The average IPP is 390 mg C m −2 d −1 for the basin region (>200 m) and 429 mg C m −2 d −1 for the shelf region ( −2 d −1 during denitrification for the shelf region.

As part of the time-series program in the Joint Global Ocean Flux Study (JGOFS), the major objective of the multidisciplinary and multi-institutional SouthEast Asian Time-series Study (SEATS) is to investigate through direct observations the processes that influence the carbon cycle and bioactive elements in the intra-annual to decadal time scale. The SEATS site is situated at 18.3°N and 115.5°E in the tropical oligotrophic northern South China Sea. Among the active time-series stations, it is located at the lowest latitude and it is the only one located in a marginal sea. The major defining environmental characteristics at this site include: oligotrophic water, outside the influence of major rivers, high surface temperature with little seasonality, strong and persistent stratification, thin mixed layer, shallow top of the nutricline depth, deep photic zone, distinct monsoonal seasons, frequent traverses of tropical cyclones, and a high depositional flux of aerosols. Given these environmental conditions, a site-specific hypothesis in SEATS is that the interactions between the upper waters and the atmosphere constitute a major controlling mechanism of the biogeochemistry in the northern South China Sea. The SEATS station has been occupied at approximately seasonal intervals since 1999. The results obtained primarily between 1999 and 2003 in the initial phase of this study are presented here. In contrast to the generally accepted notion that seasonal variations in the tropical waters are minimal, well defined, and regular seasonal patterns were observed in the carbon cycle, the nutrient dynamics and the biological community structure in the northern South China Sea. In the carbon cycle, superimposed on the large seasonal signals were the more subtle inter-annual variations of progressive increases in the mixed-layer CO2 fugacity (fCO2) and total dissolved CO2 (TCO2) that also were observed in other time-series stations. This suggests that the absorption of CO2 by the oceans in response to the increase in atmospheric CO2 in modern times may well be globally manifested. The nutrient dynamics indicate that N2 fixation could play a key role in keeping the nutrient cycle in balance in the northern South China Sea.

The distributions of nitrate+nitrite, or (N+N), and soluble reactive phosphate, or SRP, at the SouthEast Asian Timeseries Study (SEATS) station in the northern South China Sea (SCS) at 181N and 1161E were determined in 19 cruises between September 1999 and October 2003. In the deep water below 1500 m, the concentrations of (N+N) and SRP stayed constant with depth and time at 38.470.3 and 2.8470.03mM, respectively. The variability could be accounted for by the analytical uncertainties in the measurements alone. In contrast, variations in the upper water were significantly larger and far exceeded the analytical uncertainties. In the mixed layer, unlike what has been widely reported in other low-latitude waters, there was a distinct seasonal pattern. During most of the year, the concentrations were low and hovered around the detection limits. In the winter, readily detectable concentrations were found as a result of enhanced vertical mixing. In the deep water below 1500 m, the average (N+N)/SRP molar ratio, 13.670.2, was noticeably lower than the Redfield ratio of 16. The corresponding N-anomaly, N * , was � 4.070.6mM. In the upper nutricline, high (N+N)/SRP and N * , even exceeding 16 and 2mM, were found. These elevated values are suggestive of the remineralization of nitrogen-rich organic matter in the upper nutricline. Temporally, while there were considerable inter-annual variations, higher (N+N)/SRP and N * were found mostly between September and April during the period of higher depositional fluxes of atmospheric dust. In the Tropical Water, which was situated within the upper nutricline at 150 m, the average N * were 1.9 and � 0.3mM, and the average (N+N)/SRP were 15.0 and 12.6 in September–April and May–August, respectively. These seasonal patterns suggest that the nitrogen-rich organic matter could have originated from nitrogen fixation, which was enhanced by the availability of iron during seasons of high dust-depositions. A box model calculation indicates that, in the absence of nitrogen fixation, the deficit in combined nitrogen would lead to a rapid escalation in the concentration of SRP in the mixed layer in contradiction to the field observations. If nitrogen fixation is allowed, the deficit in combined nitrogen in the mixed layer could be satisfied and a steady state in (N+N) and SRP in the mixed layer maintained by supporting 3–13% of the net primary production by nitrogen fixation. r 2007 Elsevier Ltd. All rights reserved.

Flow cytometric analysis of picoplankton from the Southeast Asia Time-series Station (SEATS) in the South China Sea was performed for samples collected every 1–4 months during October 2001 to September 2002 (six cruises) and between November 2004 and December 2005 (four cruises). Prochlorococcus was the most abundant autotrophic picoplankton with the maximum abundance occurring in summer. Synechococcus and picoeukaryotes were 1 or 2 orders of magnitude less abundant during most of the year, but showed a much larger seasonal variation, with maximum abundance occurring in winter to early spring. The winter peak of Synechococcus and picoeukaryotes coincided with the deepening of the mixed-layer depth caused by surface cooling and the strong NE monsoon winds. Maximum bacterial biomass was observed in spring, and generally followed the winter peak of Synechococcus and picoeukaryotes with a time lag. Prochlorococcus contributed up to 80% of the total autotrophic biomass during summer, but Synechococcus and picoeukaryotes accounted for 60–80% of the total autotrophic biomass in winter. Bacterial biomass was less than the autotrophic biomass and the two were only weakly correlated. The interannual variability in the structure and composition of the picoplankton community may be related to the El Nino-Southern Oscillation (ENSO) cycle. During an El Nino year (2001–2002), with higher sea-surface temperature, chlorophyll a was lower and Prochlorococcus and bacterial biomass were higher. In contrast, the higher picoeukaryote biomass during winter was probably responsible for the higher chlorophyll a during the La Nina year of 2004–2005.

In this study, measurements of titration alkalinity (TA), total dissolved carbon dioxide (TCO2), and δ13C of TCO2 ( δ 13 C TCO 2 ) throughout the water column at the SouthEast Asian time-series study (SEATS) site were investigated in order to understand better the fundamental processes controlling their vertical distributions in the South China Sea (SCS). The linear correlations between TA and salinity in the shallow waters, as identified by the mixing line between the surface water and salinity maximum water suggested the predominant control of physical mixing on the variability of TA. In contrast, TCO2 and δ 13 C TCO 2 showed the non-conservative behavior in the respective TCO2 and δ 13 C TCO 2 vs. salinity plot due to the effect of biological production. A stoichiometric model further showed that the depth profile of NTA (=TA×salinity/35) largely reflects the increase of preformed NTA in the shallow waters, whereas carbonate dissolution was responsible for the continuous increase of NTA in the deep waters. A one-dimensional diffusion–advection model further revealed that the carbonate dissolution could account for 28% of NTCO2 (=TCO2×salinity/35) increase in deep waters, and the remaining 72% of NTCO2 was from organic decomposition. Calculation of excess TA further showed that it emerged well above the aragonite and calcite saturation depths at 600 and 2500 m, respectively, indicating that some biologically, chemically, and physically-mediated processes must be involved to provide excess TA into the shallow waters. The decrease in δ 13 C TCO 2 with depth primarily resulted from organic decomposition. The influence of anthropogenic CO2 throughout the water column was assessed with the carbon chemistry and the isotope-based approach in this study. Both methods obtained nearly the same results in which the signal of anthropogenic CO2 decreased exponentially with depth, and its penetration depth were found to be at ∼1000 m. The inventory of anthropogenic CO2 in the water column was estimated to be ∼16.6 mol C m−2, which was less than that reported in the northwest Pacific at the same latitude, presumably due to the enhanced upwelling in the SCS. Such an anthropogenic CO2 penetration had led to decreases of the saturation levels of aragonite and calcite by 17% and 14%, respectively, in the surface water, and an upward migration of aragonite saturation depth by ∼100 m since industrial revolution.

Two mercury-resistant strains of heterotrophic, aerobic, marine bacteria, designated AT1T and AS1T, were isolated from water samples collected from the Er-Jen River estuary, Tainan, Taiwan. Cells were Gram-negative rods that were motile by means of a single polar flagellum. Buds and prosthecae were produced. The two isolates required NaCl for growth and grew optimally at about 30 °C, 2–4 % NaCl and pH 7–8. They grew aerobically and were incapable of anaerobic growth by fermenting glucose or other carbohydrates. They grew and expressed Hg2+-reducing activity in liquid media containing HgCl2. Strain AS1T reduced nitrate to nitrite. The predominant isoprenoid quinone was Q8 (91.3–99.9 %). The polar lipids of strain AT1T consisted of phosphatidylethanolamine (46.6 %), phosphatidylglycerol (28.9 %) and sulfolipid (24.5 %), whereas those of AS1T comprised phosphatidylethanolamine (48.2 %) and phosphatidylglycerol (51.8 %). The two isolates contained C16 : 1 ω7c and/or iso-C15 : 0 2-OH (22.4–33.7 %), C16 : 0 (19.0–22.7 %) and C18 : 1 ω7c (11.3–11.7 %) as the major fatty acids. Strains AT1T and AS1T had DNA G+C contents of 43.1 and 45.3 mol%, respectively. Phylogeny based on 16S rRNA gene sequences, together with data from morphological, physiological and chemotaxonomic characterization, indicated that the two isolates could be classified as representatives of two novel species in the genus Alteromonas, for which the names Alteromonas tagae sp. nov. (type strain AT1T=BCRC 17571T=JCM 13895T) and Alteromonas simiduii sp. nov. (type strain AS1T=BCRC 17572T=JCM 13896T) are proposed.

Aqueous production and water-air exchange of elemental mercury (Hg 0 ) are important features of the environmental cycling of Hg. We investigated Hg 0 cycling in ten Arctic Alaskan lakes that spanned a wide range in physicochemical characteristics. Dissolved gaseous Hg (DGM, dominated by Hg 0 ) varied from 40 to 430 fM and averaged 200 fM. All surface waters were supersaturated relative to the atmosphere. DGM averaged 3 ± 2% of dissolved (i.e., filter passing) dissolved total mercury (DTM) and 15 ± 6% of dissolved labile Hg (DLM). In-lake DGM profiles generally followed the vertical distribution of light, indicating photoreduction of Hg(II) complexes as a source of Hg 0 . Additionally, DGM correlated linearly with DLM (r 2 = 0.82, p a (light attenuation coefficient; r 2 = 0.73, p 2 = 0.60, p = 0.02) suggests that solar radiation and dissolved organic matter control DGM production and its cycling. An average rate of DGM formation (0.6 ± 0.2% of DTM d −1 ; range, 0.20.8) was estimated by assuming steady state with the evasional rate. In-lake DGM formation occurs at lower rates in waters with greater suspended particulate matter and dissolved organic carbon (DOC), pointing to the significant role of organic matter plays in controlling DGM formation in these aquatic systems. Estimated evasional fluxes of Hg 0 (average, 140 ± 50 pmol m −2 d −1 ; range, 60–200) were comparable to those of temperate lakes (e.g., Wisconsin, Michigan). In arctic lakes, the rate of evasion during ice-free periods (7 ± 3 nmol m −2 yr −1 ) is similar to the atmospheric input of Hg (wet + dry) to the lakes based on levels in summertime precipitation but not including additional sources, e.g., springtime depletion.

A new method for the determination of the concentration and conditional stability constant of dissolved organic matter that binds mercury (Hg) has been developed using an in vitro assay of reducible Hg. The technique is a wet chemical analogue to electrochemical approaches now in use for ligand studies of many other trace transition metals in natural waters. Ligand characteristics are obtained from additions of ionic Hg to buffered lake, river water, and seawater and determination of the wet chemically reducible fraction following equilibration of the spike. This approach is robust, as demonstrated by (i) analysis using three reducing agents of varying strengths, (ii) replicate analyses, (iii) comparison to well-characterized complexing species (chloride and EDTA) using a competitive ion-exchange resin, and (iv) kinetic studies. Results indicate that Hg-complexing equivalents are present in the dissolved phase (0.2 microm) ranging from1 to60 nN concentrations and with log conditional stability constants (log K') in the range of 21-24. Only one ligand class was found in the natural waters analyzed. There was indirect evidence for a class of organic ligands that formed reducible complexes with Hg in freshwater. Such ligand characteristics indicate that the vast majority of ionic inorganic Hg dissolved in freshwater and coastal saltwaters is associated with organic complexes. Concentrations, affinities, and kinetics implicate multidentate chelation sites as the principal complexing moieties for Hg and discourage the use of humic carboxylic acids as a proxy for the ligands/functional groups.

A novel semiautomatic dissolved elemental mercury analyzer (DEMA) was developed for investigating dissolved elemental Hg (DEM) in natural waters. This on-line setup couples the main analytical steps from sample introduction, gas-liquid separation, and Au amalgamation/separation to final detection/data acquisition using flow injection techniques. This approach provides ease of operation and high analytical performance and is suitable for shipboard use. The analyzer can be fully automated and also be modified to examine other Hg species (e.g., reactive and total Hg and monomethyl-Hg). Here, we present the results of laboratory performance tests and make a comparison with a traditional manual method. DEM measured by both manual and the DEMA show good agreement. Representative field DEM data from spring and summer 1999 in Long Island Sound, U.S.A. (LIS) are presented. Spatial and temporal DEM variations were evident. Rapid and accurate determinations of DEM are necessary to observe its distribution dynamics, evaluate emissions, and assess its role in the aquatic biogeochemical cycling of Hg.

cited By 16; International audience; The main tendencies in the adsorption of dissolved inorganic mercury (Hg2+) and methylmercury (MeHg+) on suspended kaolin particles have been investigated in synthetic aqueous solutions. The influence of NaCl, fulvic acid (FA) and suspended particulate matter (SPM) in the system has been studied at a constant pH of 7.2. The experiments were arranged according to a full factorial design with three factors (NaCl, FA SPM) at low (-) and high (+) levels. A central point (0) was repeated four times to estimate the reproducibility of the results. The low and high levels investigated were 0-35 g l-1, 0-10 mg l-1 and 0.5-5 g l-1 for the concentrations of NaCl, FA and kaolin respectively. In order to match the linear range of the analytical technique the total concentration of mercury (as Hg2+ or MeHg+) in the synthetic suspensions was 25 ng ml-1. After chemical stabilization of each suspension, the Hg2+ or MeHg+ content in the clear filtrate was determined by an automated hyphenated technique combining the following steps: derivatization by hydride generation, preconcentration by cryogenic trapping, separation by packed column gas chromatography and detection by quartz furnace atomic absorption spectrometry. The removal of Hg2+ and MeHg+ from the solution via adsorption on particles ranged, respectively, from 12.4 to 94.9% and from 1.7 to 45.6% of the total mercury compound concentration. High concentrations of NaCl led to lower adsorption rates of both mercury species. The adsorption of MeHg+ was enhanced in the presence of FA, whereas that of Hg2+ was clearly diminished. High levels of SPM promoted the adsorption of both Hg2+ and MeHg+ on kaolin particles. Several experiments were also conducted to check the adsorption rate of Hg2+ and MeHg+ on natural particles collected in the Gironde estuary. The results confirmed the general trends observed when using reference kaolin particles. The results presented here will be helpful for groups modelling the physico-chemical behaviour of mercury in estuary conditions. Copyright © 2001 John Wiley & Sons, Ltd.

cited By 43; International audience; A careful search for formation of methylmercury (MeHg+ as an artefact and for potential interferences has been carried out using an analytical procedure involving aqueous phase ethylation, cryogenic trapping, low temperature gas chromatography and quartz furnace atomic absorption spectrometry (Eth-CT-GC-QFAAS) for mercury speciation, after open-focused microwave extraction. The results show that spurious MeHg+ formation from Hg2+ can occur mainly in the chromatographic column during the determination step rather than during the extraction step. The silanizing agent, dimethyldisilazane, acting as a methyl donor, appears to be responsible for the EtMeHg formation when high concentrations of Hg2+ (> 1 ppm) are present in the solution during the analysis. On the other hand, the production of several unknown peaks, closely corresponding to Me2Hg, Et2Hg etc. in the chromatogram is the result of impurities in the derivatizing agent, NaBEt4. The magnitude of these interferences varies with different lots of reagent. The derivatization and determination steps must always be checked following standard QA/QC procedures. Once interference problems are taken into account, reliable understanding of Hg cycling and behaviour in aquatic environments will be achieved.

K.-K. Liu1, L.-W. Wang1, M. Dai2, C.-M. Tseng3, Y. Yang4, C.-H. Sui5, L. Oey1, K.-Y. Tseng1, and S.-M. Huang1 1Institute of Hydrological and Oceanic Sciences, National Central University, Chungli, Taiwan 2State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China 3Institute of Oceanography, National Taiwan University, Taipei, Taiwan 4Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, Taiwan 5Department of Atmospheric Science, National Taiwan University, Taipei, Taiwan

A simple and rapid method has been developed to determine methylmercury in sediments. The procedure is based on the quantitative microwave-assisted leaching of methylmercury from sediments with an acidic extractant. Sample preparation is achieved in an open focused microwave field by heating about 1 g of dry sediment suspended into 10 ml of 2 mol l -1 HNO 3 during 3–4 min at a power of 40–60 W. The extracted mercury compounds are ethylated, cryogenically trapped in a chromatographic phase, successively eluted and detected in an electrothermally heated quartz furnace by CV AAS. The method has been validated by the analysis of the certified IAEA-356 and CRM 580 reference materials and one sediment sample, BCR S19, from an intercomparison study within the framework of a certification exercise sponsored by the Community Bureau of Reference (BCR) of the European Commission. The detection limit of the procedure is 0.5 ng of methylmercury per gram of dry sediment. After analysis of the sediments mentioned above (methylmercury ranging from 5 to 80 ng g -1 ), a mean methylmercury recovery of 97% and an RSD of 7% were obtained. Under optimum conditions, sample throughput is restricted by the instrumental analysis time (about 20 min per sample), rather than by the sample preparation step. In addition, the methylmercury extraction efficiency of four different acids, nitric, hydrochloric, sulfuric and acetic acid, has been investigated for comparison. Results on the behaviour and stability of methylmercury in a microwave field are also provided.

A rapid and simple microwave-assisted digestion method with alkaline solution (tetramethylammonium hydroxide or methanolic KOH solution) for speciation analysis of inorganic mercury and methylmercury (MeHg + ) in biological tissues was developed. Extracts with quantitative recoveries of mercury species after microwave-assisted alkaline dissolution of the sample were directly analysed by an automated on-line hyphenated system incorporating aqueous hydride generation, cryogenic trapping, gas chromatography and detection by atomic absorption spectrometry. Optimum conditions allow sample throughput to be controlled by the instrumental analysis time (≈10 min per sample) and not by the sample preparation step. At a power of 40–60 W, sample preparation time is only 2–4 min, which is much faster than previous literature methods. The proposed method was validated by the analysis of three biological certified reference materials, CRM 463, DORM-1 and TORT-1, and one BCR sample from an interlaboratory study, Tuna Fish 2. The detection limit of the overall procedure was found to be 3 ng per gram of pulverised dried biological tissue, for both labile Hg 2+ and MeHg + . After alkaline extraction, a mean recovery of 102% with a relative standard deviation of 7% was obtained for methylmercury concentrations ranging from 0.128 to 3.464 µg g -1 as Hg in the four reference fish tissues mentioned above. Total mercury, calculated as the sum of determined inorganic mercury and methylmercury, was also in agreement with the certified values. The methylmercury extraction efficiency of five extractants, viz. , nitric, hydrochloric and acetic acid, and tetramethylammonium hydroxide and methanolic KOH solution, the temperature profile of these extractants under microwave irradiation and the behaviour and stability of methylmercury in a focused microwave field were also investigated.

[1] Limited knowledge exists concerning the unusually large CO2 uptake capacity in the East China Sea (ECS), which is the eminent continental shelf pump for efficient transfer of atmospheric CO2 to the deep ocean. Here we show evidence of strong control of river runoff on the CO2uptake capacity of the ECS. From 8-years of observations in the productive ECS shelf, we present the first dataset to show the complete seasonal cycle of CO2 flux, which gives an annual flux of 2.3 ± 0.4 mol C m−2 y−1 as a net sink of atmospheric CO2. Further, we found biological sequestration of CO2 taking place in the highly productive Changjiang river plume in warm seasons due to the riverine nutrient enrichment. Consequently, changes in the plume area due to changes in the Changjiang River Discharge (referred to as the Discharge hereafter) strongly affect the CO2 uptake capacity. As the Discharge may decrease due to the Three Gorges Dam operation, the Changjiang plume will probably also decrease, resulting in reduction in CO2 uptake capacity and even a shift from a CO2 sink to a source.

[1] The occurrence of extreme weather conditions appears on the rise under current climate change conditions, resulting in more frequent and severe floods. The devastating floods in southern China in 2010 and eastern Australia 2010–2011, serve as a solemn testimony to that notion. Accompanying the excess runoffs, elevated amount of terrigenous materials, including nutrients for microalgae, are discharged to the coastal ocean. However, how these floods and the materials they carry affect the coastal ocean ecosystem is still poorly understood. Yangtze River (aka Changjiang), which is the largest river in the Eurasian continent, flows eastward and empties into the East China Sea. Since the early twentieth century, serious overflows of the Changjiang have occurred four times. During the two most recent ones in July 1998 and 2010, we found total primary production in the East China Sea reaching 147 × 103 tons carbon per day, which may support fisheries catch as high as 410 × 103 tons per month, about triple the amount during non-flooding periods based on direct field oceanographic observations. As the frequencies of floods increase world wide as a result of climate change, the flood-induced biological production could be a silver lining to the hydrological hazards and human and property losses inflicted by excessive precipitations.

The volatilization behaviors of Cd, Cu, Ni and Pb in different extracting media have been studied using graphite furnace atomic absorption spectrometry (GFAAS) to determine metal concentrations in natural sediments. Considerable interference was found for Cd, Ni, and Pb in the extracts of high matrix concentrations, and could be largely reduced by carefully selecting the ashing and atomization temperatures of GFAAS. Optimal heating programs are proposed to suit a variety of extracts containing different matrices.

The sea surface chlorophyll concentrations in low latitude marginal seas, such as the South China Sea or Gulf of Mexico, are higher than those in the adjacent open oceans by >60%, the biomass higher by >28% and primary productivity higher by >100%. It is demonstrated by a coupled physical-biogeochemical model of the South China Sea that the enhanced phytoplankton growth in the SCS is probably mainly caused by rich supply of nutrients from localized upwelling along margins of the basin, whereas the river-borne nutrients may contribute to the enhancement to a relatively small degree. Although the upwelling process is wind-driven, it is the confinement of the marginal seas by the surrounding land masses that gives rise to the occurrences of upwelling under certain favorable conditions.

Through analyses of water and sediments, we investigate tungsten and 14 other heavy metals in a stream receiving treated effluents from a semiconductor manufacturer-clustered science park in Taiwan. Treated effluents account for ∼ 50% of total annual river discharge and1% of total sediment discharge. Dissolved tungsten concentrations in the effluents abnormally reach 400 μg/L, as compared to the world river average concentration of0.1 μg/L. Particulate tungsten concentrations are up to 300 μg/g in suspended and deposited sediments, and the corresponding enrichment factors are three orders of magnitude higher than average crust composition. Surprisingly, the estimated amount of tungsten exported to the adjacent ocean is 23.5 t/yr, which can approximate the amount from the Yangtze River should it be unpolluted. This study highlights the urgency of investigating the biological effect of such contamination.

[1] Anomalous biogeochemical conditions were observed at the SouthEast Asian Time-series Study (SEATS) station in the northern South China Sea (SCS) during the 1997–98 and 2002–03 El Nino events. The time-series records showed decreases of monthly mean sea surface chlorophyll-a (S-chl) (and integrated primary production, IPP) by 42% (and 42%) and 13% (and 10%), respectively, below the climatological mean in the winter months (DJF) of the two events. The negative anomalies in S-chl and IPP corresponded to elevated sea surface temperature by 1.2°C and 0.4°C, respectively, above the climatological mean, while the mean wind speed was reduced by about 20% and 11%, respectively. Statistical analysis demonstrated the reduction in S-chl and IPP during El Nino events was caused by the diminished vertical mixing and strengthened stratification. Regional anomalies in hydrographic and biological conditions in the northern SCS (15–21°N and 112–119°E) were consistent with those found at the SEATS site.

[1] Dichotomous (PM2.5–10 and PM2.5 modes) and size-resolved marine aerosols collected during the northeastern monsoon on two wintertime cruises in the subtropical South China Sea (SCS) were analyzed for water-soluble ions. During the sampling periods the study region was under the influence of strong pollution originating primarily from the Asian continent. Elevated levels of non-sea-salt sulfate and ammonium ions of up to 4.5 and 1.2 μg/m3, respectively, were observed, indicating that the SCS is now substantially contaminated by massive amounts of air pollutants most likely from China and South/Southeast Asia. The non-sea-salt sulfate to nitrate mass ratios reaching 3.8 ± 1.9 are much larger than those (approximately 2) in and around East Asia and the western Pacific Ocean, suggesting that the Asian outflow aerosols measured in the SCS experienced different traveling history from those in the vicinity of source regions. High chloride depletion (Cl-depletion) measured in the SCS marine aerosols was, on average, 30% for coarse-mode particles and nearly 90% for fine-mode particles. Cl-depletion is size-dependent, and maximizes in submicrometer particles (i.e., Cl has almost been completely lost). Acid displacement is responsible for the observed high Cl-depletion: nitrate substitution accounts for the coarse-mode depletion, whereas sulfate substitution accounts for the fine-mode depletion. The acid displacement of sea salt aerosols may be related to a variety of factors, especially the substantial air pollution, which is discussed in detail in this paper. On cloudy/rainy days, fine-mode aerosol samples have moderate Cl-depletion (i.e., ∼40–50%), in contrast to nearly complete Cl loss on sunny days, presumably indicating that photochemical reactions would play a key role in the Cl-deficit; however, it merits further investigation as the available samples were limited.

[1] The continuous summertime drawdown of normalized dissolved inorganic carbon has been observed repeatedly in the mixed-layer at the South East Asia Time-series Study (SEATS) site, northern South China Sea (SCS) between March 2002 and November 2004. Mass balance calculation reveals that a net community production (NCP) of −4.47 mmolC m−2 day−1 is responsible for this drawdown. Nonetheless, bioavailable nitrogen (Nbio) from atmospheric deposition, vertical diffusion, and N2-fixation by Trichodesmium and Richelia together could only account for ∼55% of Nbio required for the calculated NCP. Unicellular cyanobacteria, which are identified unambiguously by the presence of nitrogenase genes (nifH) in 1–10 μm fraction of planktons collected at SEATS, may account for the Nbio deficit. Our results, thus, support the potential importance of unicellular cyanobacteria in providing an additional Nbio source in oligotrophic waters such as the SCS.

[1] The East China Sea (ECS) is one of the largest continental shelves in the world; however, the role that biota plays in the carbon fluxes of this shelf ecosystem is still obscure. To evaluate the organic carbon balance and the roles played by planktonic communities in organic carbon consumption, two cruises with stations covering almost the entire shelf were conducted during the high productivity and high river flow season of the ECS in June (the early summer) and August (the middle summer) 2003. Results showed that biological activity was significantly higher in the early summer. To flourish in the early summer, plankton need a significant fluvial input of dissolved inorganic nutrients and organic matter from the Chinese coast, especially from the Changjiang (aka Yangtze River), might be one of the main driving forces. Further analysis showed that most planktonic community respiration (PCR) could be attributed to phytoplankton and bacterioplankton, which accounted for over 96% of the total planktonic biomass (in carbon units) in summer. This might partially explain why mean PCR was higher in June (∼114 mg C m−3 d−1), with higher phytoplankton biomass, than in August (∼40 mg m−3 d−1). The ratio of integrated primary production to PCR (i.e., the P/R ratio) was, however, less than 1, with a mean ± SD value of 0.35 ± 0.41 for all the pooled data. This indicates a significant amount of organic carbon has been regenerated through planktonic activity in the water column. The sea-air difference in fCO2, however, changed from a mean value of −64.5 ± 61.3 ppm in June to 10.0 ± 37.5 ppm in August. To explain the contradictory results between PCR and fCO2, we suggest that the dissolved inorganic carbon regenerated through planktonic respiration could be stored in the subsurface layer and may affect the fCO2 in the surface water, which is what controls the shelf sea either as an atmospheric CO2 sink or as a source, depending on the prevailing physical forces. These results also suggest that the controversy between atmospheric CO2 sink or source in the ECS shelf needs further exploration.

We reconstruct from lake-sediment archives atmospheric Hg deposition to Arctic Alaska over the last several centuries and constrain a contemporary lake/watershed mass-balance with real-time measurement of Hg fluxes in rainfall, runoff, and evasion. Results indicate that (a) anthropogenic Hg impact in the Arctic is of similar magnitude to that at temperate latitudes; (b) whole-lake Hg sedimentation determined from 55 210Pb-dated cores from the five small lakes demonstrates a 3-fold increase in atmospheric Hg deposition since the advent of the Industrial Revolution; (c) because of high soil Hg concentrations and relatively low atmospheric deposition fluxes, erosional inputs to these lakes are more significant than in similar temperate systems; (d) volatilization accounts for about 20% of the Hg losses (evasion and sedimentation); and (e) another source term is needed to balance the evasional and sedimentation sinks. This additional flux (1.21+/-0.74 microg m(-2) yr(-1)) is comparable to direct atmospheric Hg deposition and may be due to some combination of springtime Arctic depletion and more generalized deposition of reactive gaseous Hg species.