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Estuaries play a crucial role in regional carbon cycling. Until now, accurate estimations of the impact of environmental variables on estuarine air⁻water CO2 fluxes have been mostly characterized by a low spatial-temporal sampling resolution. This study reports on the variations of CO2 partial pressure (pCO2) and related environmental parameters, at both tidal and seasonal temporal scales, in the surface seawater of a station located in the lower section of the Tagus estuary, Portugal. The study was carried out from February to December 2007. Air⁻water CO2 fluxes suggest that the lower estuary acted as a relatively weak source of CO2 to the atmosphere, with an average rate of 7.2 mol∙m−2∙year−1, with highest fluxes occurring in winter. Over a tidal cycle, pCO2 was mainly influenced by tidal-induced mixing. Results suggest an influence of upper and central estuary inputs with higher pCO2 values. pCO2 varied seasonally, with values decreasing from ~890 µatm in winter to ~400 µatm in summer and increasing again to ~990 µatm in autumn. The generalized linear model (GLM) applied to the data set explained 69.3% of the pCO2 variability, pointing to the thermodynamic effect of temperature and biological activity as the most relevant processes in CO2 dynamics. Tidal variation of pCO2 corresponded to ~35% of its seasonal variability, denoting the importance of tide conditions on the dynamics of inorganic carbon. Results showed distinct patterns in the dynamics of CO2 at the tidal scale. This outcome suggests that disregarding tidal variability in the use of seasonal data sets may lead to significant errors in annual carbon budget estimations.

An effort has been made for the first time in Asia's largest brackish water lagoon, Chilika, to investigate the spatio-temporal variability in primary productivity (PP), bacterial productivity (BP), bacterial abundance (BA), bacterial respiration (BR) and bacterial growth efficiency (BGE) in relation to partial pressure of CO2(pCO2) and CO2air–water flux and the resultant trophic switchover. Annually, PP ranged between 24 and 376 µg C L−1d−1with significantly low values throughout the monsoon (MN), caused by light limitation due to inputs of riverine suspended matter. On the contrary, BP and BR ranged from 11.5 to 186.3 µg C L−1d−1and from 14.1 to 389.4 µg C L−1d−1, respectively, with exceptionally higher values during MN. A wide spatial and temporal variation in the lagoon trophic status was apparent from BP/PP (0.05–6.4) and PP/BR (0.10–18.2) ratios. The seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter inputs via rivers, enhanced the bacterial metabolism during the MN, as evident from the highpCO2(10,134 µatm) and CO2air–water flux (714 mm m−2d−1). Large variability in BGE and BP/PP ratios especially during MN led to high bacteria-mediated carbon fluxes which was evident from significantly high bacterial carbon demand (BCD >100% of PP) during this season. This suggested that the net amount of organic carbon (either dissolved or particulate form) synthesized by primary producers in the lagoon was not sufficient to satisfy the bacterial carbon requirements. Lagoon sustained low to moderate autotrophic–heterotrophic coupling with annual mean BCD of 231% relative to the primary production, which depicted that bacterioplankton are the mainstay of the lagoon biogeochemical cycles and principal players that bring changes in trophic status. Study disclosed that the high CO2supersaturation and oxygen undersaturation during MN was attributed to the increased heterotrophic respiration (in excess of PP) fuelled by allochthonous organic matter. On a spatial scale, lagoon sectors such as south sector, central sector and outer channel recorded “net autotrophic,” while the northern sector showed “net heterotrophic” throughout the study period. [ABSTRACT FROM PUBLISHER]

We measured dissolved methane concentrations ([CH4]) in the coastal zone of the Southern California Bight-Mexican sector (SCBMex) during two cruises: S1 in the USA–Mexico Border Area (BA) during a short rainstorm and S2 in the entire SCBMex during a drier period a few days later. High spatial variability in surface mixed layer (ML) [CH4] was observed, ranging from 2.2 nmol L−1 to 17.8 nmol L−1. ML-[CH4] was supersaturated at all BA stations during both cruises. The highest [CH4] was 72.4 nmol L−1 (2819 % supersaturated) measured at 10 m depth during S2, about 3 km southwest of the discharge point of the South Bay Ocean Outfall (SBOO). Our results show an apparent connection between wastewater treatment discharges and [CH4]. Application of a sewer CH4 production model suggests that the SBOO may be a large source of CH4 to the BA and points to the need to consider point sources in developing coastal marine CH4 budgets for highly populated areas. Based on our data, the SCBMex appears to be a relatively strong source of CH4 to the atmosphere compared to other Pacific Basin areas. The average BA sea-to-air CH4 flux (F) during S1 was (15.5 ± 8.6) × 10−2 nmol m−2 s−1, about 1.5 times higher than F during S2, which had a flux of (9.5 ± 6.9) × 10−2 nmol m−2 s−1 mainly due to the higher wind speed during S1. [ABSTRACT FROM AUTHOR]

Abstract: Biogeochemical Carbon cycling was studied in Asia''s largest brackish lagoon, Chilika on the east coast of India. Systematic time-series observations were made at 35 hydrologically different stations over the entire lagoon. The first of these kinds of measurements reveal, inter and intra annual variability of partial pressure of CO2 (pCO2). A comparative analysis of pCO2, CO2 flux over four years (2005, 2009, 2010 and 2011) showed that the northern part of the lagoon maintained the highest levels of pCO2, with maximum CO2 efflux to the atmosphere associated with peak monsoon period. The high pCO2 corresponded to a significant decrease in pH (∼0.8) from the low to high flow periods. Higher bacterial abundance (1.55 ± 0.28 × 109 cells L−1) and bacterial respiration (185.31 ± 105.37 μg C L−1 d−1), suggested high levels of organic carbon decomposition during the high flow period. In contrast, the southern sector was least affected by river discharge, with low pCO2 values and CO2 flux as in the dry period. The central part and outer channel of the lagoon had intermediate characteristics. During high flow, the air–water CO2 flux from the entire lagoon was estimated to be 31.2 mol C m−2 y−1, which was comparatively very high with respect to the mean CO2 emission from the entire subtropical and tropical estuaries. Highest CO2 flux (65.98 mol C m−2 y−1) was observed in the northern sector, followed by the outer channel (17.61 mol C m−2 y−1), central sector (15.69 mol C m−2 y−1) and southern sector (14.44 mol C m−2 y−1). The northern part of Chilika lagoon being an important river-influenced region was responsible for the biological transformation of organic carbon to inorganic carbon and emitting CO2 to the atmosphere. Such a sectoral approach would reveal zonal influences of CO2 within a water body along with conditions leading to sink or a source. [Copyright &y& Elsevier]

Abstract: This paper describes the simulated temporal variation of surface seawater CO2 partial pressure (pCO2) in the northern South China Sea. We produced the simulations with a one-dimensional (1-D) coupled physical–biogeochemical model that had high-frequency, time-dependent atmospheric forcing and that were validated with field observations. We also examined the associated processes that modulate seawater pCO2 at different time scales, from diurnal to seasonal, using a series of process-oriented experiments. At seasonal time scales, we revealed that the sea–air CO2 exchange was a primary process that modulated surface pCO2 and exceeded the role of sea surface temperature (SST) even though the phase of the pCO2 variation generally followed the strong seasonal cycle of SST. This was because sea–air CO2 exchange is a slow process and has an accumulative effect on surface water pCO2 due to the buffering effect of the carbonate system once CO2 has dissolved in the seawater, which leads to a long equilibration time of CO2 between the atmosphere and seawater. The mixing effect on pCO2 induced by total alkalinity and dissolved inorganic carbon variations was, generally, positively correlated with the seasonal evolution of wind speed. Biological processes were the smallest contributors to pCO2 variations at the seasonal scale because of the oligotrophic characteristic of the region. At diurnal time scales, the dominant pCO2 controlling factor was mainly associated with the local physical and biological conditions. Temperature and wind-induced vertical mixing played major roles in pCO2 when the winter heat flux and upward transport of low temperature and high pCO2 in deep water were intensified. Phytoplankton blooms generally occur after a period of strong wind, as a result, biological metabolism becomes the most important pCO2 regulator when the surface chlorophyll-a reached its highest level. Unlike that in the seasonal scale, the effect of sea–air CO2 exchange was minor at diurnal time scales due to the long equilibration time of CO2 between the atmosphere and seawater. We also found that the frequency of the model driving force was important in reproducing the sea surface pCO2. The high frequency forcing was important in controlling the pCO2 variation through the feedback effect to the corresponding physical and biogeochemical responses. [Copyright &y& Elsevier]

Abstract: We measured partial pressures of CH2Cl2 (dichloromethane) and CCl3F (CFC-11) in air and surface seawater of the Indian and Southern Oceans from November 2009 to January 2010. The excess CH2Cl2 saturation anomaly (ΔSACH2Cl2 >0) in surface seawater between 10°S and 40°S, which is the corrected value of saturation anomaly after subtracting the effects of summertime sea-surface temperature increase and of summertime decrease of atmospheric CH2Cl2 level, provides evidence for in-situ production of CH2Cl2. Depth profiles from the South Indian Ocean at 5°S, 20°S and 30°S showed concentration maxima of dihalomethanes (CH2I2, CH2ClI and CH2Cl2) and chlorophyll-a in the subsurface layer (20–150m). Our data suggest that phytoplankton production of dihalomethanes leads to concentration maxima in the subsurface layer and ΔSACH2Cl2 >0 in surface seawater between 10°S and 40°S. The average oceanic emission of CH2Cl2 derived from the region between 10°S and 40°S in the South Indian Ocean was calculated to be 0.29–0.43μg m−2 d−1. [Copyright &y& Elsevier]

Abstract: This work estimates new regionalized empirical parameterizations for preformed alkalinity (AT o) and the CO2 air–sea disequilibrium (∆Cdis). Both are key terms for the computation of anthropogenic CO2 in the back-calculation methods. Data from the subsurface layer (75–180m depth range) covering an area from North to South and from 19°E to 67.5°W (Pacific and Indian oceans) were taken from GLODAP (The Global Ocean Data Analysis Project) database. The subsurface layer is proved as a reliable reference for representing the main characteristics of the different water masses of the oceans. Besides, handing data from the two ocean basins altogether makes the new parameterizations of AT o and ∆Cdis to be more globally consistent. Nevertheless, each ocean basin, at least in some regions, has different oceanographic characteristics based on its proper dynamical processes and water masses formation. In order to maintain each ocean basin ‘identity’ the whole domain was divided in six different regions (two of them sharing waters from Pacific and Indian oceans) and parameterizations in each region for both terms were obtained. Previously, data were transformed into a grid of 4°lat.×5°lon. and the results obtained from the parameterizations were visualized and compare with pCO2 climatologies. From the comparisons with previous ∆Cdis estimations good results are obtained showing the reliability and robustness of the new regionalized empiric parameterizations. [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: Methane (CH4) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH4 concentration and stable isotopic signatures (δ 13CH4) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH4 were determined in sediment incubations. Surface water column CH4 (2 m depth) was in the range 3–180 nmol l−1 (110–8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH4 inputs from underlying porewaters in which CH4 concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l−1). Surface water CH4 concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH4 flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH4 and δ 13CH4 in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH4 oxidation, with an apparent isotopic fractionation factor (r c) of ∼1.004. Using turbulent diffusion models of air–sea exchange we estimate an annual emission of atmospheric CH4 from the Ría de Vigo of 18–44×106 g (1.1–2.7×106 mol). This estimate is approximately 1–2 orders of magnitude lower than a previous estimate based on a bubble transport model. [Copyright &y& Elsevier]

Abstract: One of the dominant sources of uncertainty in the calculation of air–sea flux of carbon dioxide on a global scale originates from the various parameterizations of the gas transfer velocity, k, that are in use. Whilst it is undisputed that most of these parameterizations have shortcomings and neglect processes which influence air–sea gas exchange and do not scale with wind speed alone, there is no general agreement about their relative accuracy. The most widely used parameterizations are based on non-linear functions of wind speed and, to a lesser extent, on sea surface temperature and salinity. Processes such as surface film damping and whitecapping are known to have an effect on air–sea exchange. More recently published parameterizations use friction velocity, sea surface roughness, and significant wave height. These new parameters can account to some extent for processes such as film damping and whitecapping and could potentially explain the spread of wind-speed based transfer velocities published in the literature. We combine some of the principles of two recently published k parameterizations [Glover, D.M., Frew, N.M., McCue, S.J. and Bock, E.J., 2002. A multiyear time series of global gas transfer velocity from the TOPEX dual frequency, normalized radar backscatter algorithm. In: Donelan, M.A., Drennan, W.M., Saltzman, E.S., and Wanninkhof, R. (Eds.), Gas Transfer at Water Surfaces, Geophys. Monograph 127. AGU,Washington, DC, 325–331; Woolf, D.K., 2005. Parameterization of gas transfer velocities and sea-state dependent wave breaking. Tellus, 57B: 87–94] to calculate k as the sum of a linear function of total mean square slope of the sea surface and a wave breaking parameter. This separates contributions from direct and bubble-mediated gas transfer as suggested by Woolf [Woolf, D.K., 2005. Parameterization of gas transfer velocities and sea-state dependent wave breaking. Tellus, 57B: 87–94] and allows us to quantify contributions from these two processes independently. We then apply our parameterization to a monthly TOPEX altimeter gridded 1.5°×1.5° data set and compare our results to transfer velocities calculated using the popular wind-based k parameterizations by Wanninkhof [Wanninkhof, R., 1992. Relationship between wind speed and gas exchange over the ocean. J. Geophys. Res., 97: 7373–7382.] and Wanninkhof and McGillis [Wanninkhof, R. and McGillis, W., 1999. A cubic relationship between air−sea CO2 exchange and wind speed. Geophys. Res. Lett., 26(13): 1889–1892]. We show that despite good agreement of the globally averaged transfer velocities, global and regional fluxes differ by up to 100%. These discrepancies are a result of different spatio-temporal distributions of the processes involved in the parameterizations of k, indicating the importance of wave field parameters and a need for further validation. [Copyright &y& Elsevier]

Abstract: A previously developed renewal model included parameterizations for the thermal skin effect and interfacial gas transfer velocity. The more readily available cool skin data were used for an adjustment of the gas transfer parameterization. In this work, the renewal concept is extended to include the velocity difference across the viscous sublayer and to account for the stage of surface wave development. As a result, the empirical coefficients that enter the renewal model have been specified more accurately using laboratory data on the surface wind drift current. In addition, the coefficient linking the cool skin and gas transfer parameterization formulas has been determined from the probability distribution function for renewal events. A comparison of the upgraded renewal model with the thermal skin data collected during the COARE and more recent field programs and with gas transfer data collected during GasEx-01 experiment suggests that the renewal model can be a useful tool for producing a physically based parameterization for the interfacial CO2 transfer velocity. Model uncertainties associated with the effect of surface films are discussed. [Copyright &y& Elsevier]

Abstract: Recent research work provided the basis for a much improved understanding of the open ocean sources of dimethylsulphide (DMS), carbonyl sulphide (COS), and carbon disulphide (CS2) to the atmosphere. Coastal ocean emissions remained less well constrained, arguably because of the inherently high variability of coastal and estuarine systems. This article presents a review of the spatial and seasonal distributions of DMS, COS and CS2 together with a preliminary assessment of their respective emissions from European coastal waters. Our data compilation considers winter/summer scenarios and explicitly distinguishes shelf waters and estuarine systems. For DMS, our findings indicate similar emission rates for shelf waters and estuarine systems and an annual DMS source of approximately 16Gmola−1. Our annual emission estimates for COS and CS2 are 0.26Gmola−1 and 0.16Gmola−1, respectively, and suggest significant contributions from estuarine systems to total shelf emissions in both cases (COS: 27%; CS2: 19%). On this basis we recommend that estuarine COS and CS2 emissions should be considered in future global emission estimates. Comparisons of our emission estimates to previous estimates of global marine sulphur gas emissions indicate disproportionally high contributions from European coastal waters. Given that emission rates from European shelves may be similar to those of other coastal shelf areas, our findings suggest that the coastal marine sources of DMS, COS and CS2 may have been underestimated in previous work. [Copyright &y& Elsevier]

Estuaries play a crucial role in regional carbon cycling. Until now, accurate estimations of the impact of environmental variables on estuarine air–water CO2 fluxes have been mostly characterized by a low spatial-temporal sampling resolution. This study reports on the variations of CO2 partial pressure (pCO2) and related environmental parameters, at both tidal and seasonal temporal scales, in the surface seawater of a station located in the lower section of the Tagus estuary, Portugal. The study was carried out from February to December 2007. Air–water CO2 fluxes suggest that the lower estuary acted as a relatively weak source of CO2 to the atmosphere, with an average rate of 7.2 mol∙m−2∙year−1, with highest fluxes occurring in winter. Over a tidal cycle, pCO2 was mainly influenced by tidal-induced mixing. Results suggest an influence of upper and central estuary inputs with higher pCO2 values. pCO2 varied seasonally, with values decreasing from ~890 µatm in winter to ~400 µatm in summer and increasing again to ~990 µatm in autumn. The generalized linear model (GLM) applied to the data set explained 69.3% of the pCO2 variability, pointing to the thermodynamic effect of temperature and biological activity as the most relevant processes in CO2 dynamics. Tidal variation of pCO2 corresponded to ~35% of its seasonal variability, denoting the importance of tide conditions on the dynamics of inorganic carbon. Results showed distinct patterns in the dynamics of CO2 at the tidal scale. This outcome suggests that disregarding tidal variability in the use of seasonal data sets may lead to significant errors in annual carbon budget estimations. [ABSTRACT FROM AUTHOR]