Surface Water pCO2 Research Articles

High pore-water derived CO2 and CH4 emissions from a macro-tidal mangrove creek in the Amazon region

Abstract This paper presents the first aquatic CO2 and CH4 flux estimates from a macro-tidal mangrove creek located in the 0–5° latitude band, where ∼30% of the world’s mangroves occur. High resolution dissolved CO2, CH4 and 222Rn (a natural pore-water tracer) concentrations were measured over a spring-neap tidal cycle from a mangrove tidal creek located in North Brazil (∼0.8°S). Surface water pCO2, CH4 and 222Rn ranged from 592 to 15,361 μatm, 58 to 1469 nM, and 585 to 16,583 dpm m−3 with considerable temporal variability observed semi diurnally (i.e. hourly) and over the spring-neap cycle (i.e. weekly). Tidally-driven pore-water exchange (tidal pumping) drove surface water pCO2 and CH4, leading to high concentrations at low-tide (semi-diurnal variability). Higher pCO2 and CH4 were also observed after the inundation of the upper inter-tidal flat, with peak values coinciding with the “first flush” of aged pore-waters. We hypothesise that additional pore-water exchanges occur during forest inundation in macro-tidal mangrove systems, controlling mangrove creek water pCO2 and CH4 over spring-neap cycles. Estimated CO2 and CH4 water-atmosphere fluxes were 174 ± 129 mmol m−2 d−1 and 855 ± 406 μmol m−2 d−1, respectively. These emissions are amongst the highest reported for mangrove systems worldwide and suggests that the most recent global estimates based mostly on data from higher latitudes may have underestimated the role of mangroves in greenhouse gas emissions.

Distinguishing between physical and biological controls on the spatial variability of pCO2: A novel approach using OMP water mass analysis (St. Lawrence, Canada)

Present-day air-sea CO2 flux estimates in the coastal ocean are subject to large uncertainties due to its heterogeneous nature and concomitant lack of data. Factors controlling the dissolved inorganic carbon (DIC) and CO2 fluxes vary within and between coastal subsystems, hampering the development of robust upscaling and modeling techniques. By applying a multi-tracer, quantitative water mass analysis, physical and biogeochemical factors can be differentiated. This study adopts an expanded version of optimum multiparameter (OMP) water mass analysis, an inverse modeling technique, to estimate the mixing fractions of predefined source water masses as well as the contribution of biological activity (photosynthesis, respiration) at a given observation point in the surface mixed layer that exchanges CO2 gas with the atmosphere. We apply the method to hydrographic, nutrient, and inorganic carbon data collected in the Estuary and Gulf of St. Lawrence, the world's largest estuarine system and an excellent analogue of the more general coastal environment. Biological activity is identified as the dominant control on mixed-layer CO2 partial pressure (pCO2) dynamics along the St. Lawrence land—ocean continuum, explaining the upstream to downstream shift from pCO2 supersaturation (net heterotrophy) to pCO2 undersaturation (net autotrophy). Although mixing of freshwater and seawater along the Estuary is the major contributor to the DIC pool, it contributes little (or negligibly) to the spatial variability of surface-water pCO2.

Boron isotope-based seasonal paleo-pH reconstruction for the Southeast Atlantic – A multispecies approach using habitat preference of planktonic foraminifera

The boron isotopic composition of planktonic foraminiferal shell calcite (δ11BCc) provides valuable information on the pH of ambient water at the time of calcification. Hence, δ11BCc of fossil surface-dwelling planktonic foraminifera can be used to reconstruct ancient aqueous pCO2 if information on a second carbonate system parameter, temperature and salinity is available. However, pH and pCO2 of surface waters may vary seasonally, largely due to changes in temperature, DIC, and alkalinity. As also the shell fluxes of planktonic foraminifera show species-specific seasonal patterns that are linked to intra-annual changes in temperature, it is obvious that δ11BCc of a certain species reflects the pH and thus pCO2 biased towards a specific time period within a year. This is important to consider for the interpretation of fossil δ11BCc records that may mirror seasonal pH signals. Here we present new Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS) δ11BCc coretop data for the planktonic foraminifera species Globigerina bulloides, Globigerinoides ruber, Trilobatus sacculifer and Orbulina universa and compare them with δ11Bborate derived from seasonally resolved carbonate system parameters. We show that the inferred season-adjusted δ11BCc/δ11Bborate relationships are similar to existing calibrations and can be combined with published δ11BCc field and culture data to augment paleo-pH calibrations. To test the applicability of these calibrations, we used a core drilled on the Walvis Ridge in the Southeast Atlantic spanning the last 330,000 years to reconstruct changes in surface-water pCO2. The reconstruction based on G. bulloides, which reflects the austral spring season, was shown to yield values that closely resemble the Vostok ice-core data indicating that surface-water pCO2 was close to equilibrium with the atmosphere during the cooler spring season. In contrast, pCO2 estimated from δ11BCc of O. universa, T. sacculifer and G. ruber that predominantly lived during the warmer seasons, exhibits up to ∼50 ppmv higher values than the Vostok ice-core data. This is probably due to the higher austral summer and fall temperatures, as shown by Mg/Ca to be on average ∼4 °C higher than during the cooler spring season, accounting for an increase in pCO2 of ∼4% per 1 °C. Our results demonstrate that paleo-pH estimates based on δ11BCc contain a significant seasonal signal reflecting the habitat preference of the recording foraminifera species.

Variability of pCO2 in surface waters and development of prediction model

Inland waters are substantial sources of atmospheric carbon, but relevant data are rare in Asian monsoon regions including Korea. Emissions of CO2 to the atmosphere depend largely on the partial pressure of CO2 (pCO2) in water; however, measured pCO2 data are scarce and calculated pCO2 can show large uncertainty. This study had three objectives: 1) to examine the spatial variability of pCO2 in diverse surface water systems in Korea; 2) to compare pCO2 calculated using pH-total alkalinity (Alk) and pH-dissolved inorganic carbon (DIC) with pCO2 measured by an in situ submersible nondispersive infrared detector; and 3) to characterize the major environmental variables determining the variation of pCO2 based on physical, chemical, and biological data collected concomitantly. Of 30 samples, 80% were found supersaturated in CO2 with respect to the overlying atmosphere. Calculated pCO2 using pH-Alk and pH-DIC showed weak prediction capability and large variations with respect to measured pCO2. Error analysis indicated that calculated pCO2 is highly sensitive to the accuracy of pH measurements, particularly at low pH. Stepwise multiple linear regression (MLR) and random forest (RF) techniques were implemented to develop the most parsimonious model based on 10 potential predictor variables (pH, Alk, DIC, Uw, Cond, Turb, COD, DOC, TOC, Chla) by optimizing model performance. The RF model showed better performance than the MLR model, and the most parsimonious RF model (pH, Turb, Uw, Chla) improved pCO2 prediction capability considerably compared with the simple calculation approach, reducing the RMSE from 527–544 to 105μatm at the study sites.

Surface Water pCO2 Variations and Sea‐Air CO2 Fluxes During Summer in the Eastern Canadian Arctic

AbstractBased on a 2 year data set, the eastern Canadian Arctic Archipelago and Baffin Bay appear to be a modest summertime sink of atmospheric CO2. We measured surface water CO2 partial pressure (pCO2), salinity, and temperature throughout northern Baffin Bay, Nares Strait, and Lancaster Sound from the CCGS Amundsen during its 2013 and 2014 summer cruises. Surface water pCO2 displayed considerable variability (144–364 μatm) but never exceeded atmospheric concentrations, and average calculated CO2 fluxes in 2013 and 2014 were −12 and −3 mmol C m−2 d−1 (into the ocean), respectively. Ancillary measurements of chlorophyll a reveal low summertime productivity in surface waters. Based on total alkalinity and stable oxygen isotopes (δ18O) data, a strong riverine signal in northern Nares Strait coincided with relatively high surface pCO2, whereas areas of sea‐ice melt occur with low surface pCO2. Further assessments, extending the seasonal observation period, are needed to properly constrain both seasonal and annual CO2 fluxes in this region.

Seasonal and temporal CO2 dynamics in three tropical mangrove creeks – A revision of global mangrove CO2 emissions

Continuous high-resolution surface water pCO2 and δ13C-CO2 and 222Rn (dry season only) were measured over two tidal cycles in the wet and dry season in three tropical tidal mangrove creeks on the north-eastern coast of Queensland, Australia. Mangrove surface water pCO2 followed a clear tidal pattern (ranging from 387 to 13,031 µatm) with higher pCO2-values in the wet season than in the dry season. The δ13C-CO2 in the mangrove waters ranged from −21.7 to −8.8‰ and was rather indicative of a mixed source than a distinct mangrove signature. Surface water CO2 was likely driven by a combination of mangrove and external carbon sources, e.g. exchange with groundwater/pore water enriched in 13C, or terrestrial carbon inputs with a significant contribution of C4-vegetation (sugar cane) source. The kinetic and equilibrium fractionation during the gas exchange at the water-atmosphere interface may have further caused a 13C-enrichment of the CO2 pool in the mangrove surface waters. Average CO2 evasion rates (58.7–277.6 mmol m−2 d−1) were calculated using different empirical gas transfer velocity models. Using our high-resolution time series data and previously published data, the average CO2 flux rate in mangrove ecosystems was estimated to be 56.5 ± 8.9 mmol m−2 d−1, which corresponds to a revised global mangrove CO2 emission of 34.1 ± 5.4 Tg C per year.

Air‐Sea CO2 Exchange in the Ross Sea, Antarctica

AbstractAlthough the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO2 sink. We calculate instantaneous CO2 flux rates with in situ pCO2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO2 sink (–7.5 ± 0.5 Tg C yr−1, −1.3 ± 0.1 mol C m−2 yr−1) than previously reported (–13 Tg C yr−1, −1.7 to −4.2 mol C m−2 yr−1). One exception is Terra Nova Bay (TNB) in the western Ross Sea, with CO2 flux rates (–4.8 ± 0.3 mol C m−2, January–March) that are 3–4 times greater than the Ross Sea mean. The majority of the CO2 flux into TNB occurs during the late summer with instantaneous CO2 flux rates up to −246 mmol C m−2 d−1. These extraordinary CO2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pCO2 values. Although strong katabatic winds deepen the mixed layer and entrain CO2‐rich water from below, late season net community productivity maintains low surface water pCO2 levels. While TNB only covers ∼1% (3,600 km2) of the Ross Sea continental shelf, extraordinary air‐to‐sea CO2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km2 combined), including Antarctic Bottom Water formation regions.

CO2 Outgassing from an Urbanized River System Fueled by Wastewater Treatment Plant Effluents.

Continuous underway measurements were combined with a basin-scale survey to examine human impacts on CO2 outgassing in a highly urbanized river system in Korea. While the partial pressure of CO2 (pCO2) was measured at 15 sites using syringe equilibration, 3 cruises employing an equilibrator were done along a 30 km transect in the Seoul metropolitan area. The basin-scale survey revealed longitudinal increases in surface water pCO2 and dissolved organic carbon (DOC) in the downstream reach. Downstream increases in pCO2, DOC, fluorescence index, and inorganic N and P reflected disproportionately large contributions from wastewater treatment plant (WWTP) effluents carried by major urban tributaries. Cruise transects exhibited strong localized peaks of pCO2 up to 13 000 μatm and 13CO2 enrichment along the confluences of tributaries at an average flow, whereas CO2 pulses were dampened by increased flow during the monsoon period. Fluctuations in pCO2 along the eutrophic reach downstream of the confluences reflected environmental controls on the balance between photosynthesis, biodegradation, and outgassing. The results underscore WWTP effluents as an anthropogenic source of nutrients, DOC, and CO2 and their influences on algal blooms and associated C dynamics in eutrophic urbanized river systems, warranting further research on urbanization-induced perturbations to riverine metabolic processes and carbon fluxes.

Modeled sensitivity of Lake Michigan productivity and zooplankton to changing nutrient concentrations and quagga mussels

AbstractThe recent decline in Lake Michigan productivity is often attributed to filter feeding by invasive quagga mussels, but some studies also implicate reductions in lakewide nutrient concentrations. We use a 3‐D coupled hydrodynamic‐biogeochemical model to evaluate the effect of changing nutrient concentrations and quagga mussel filtering on phytoplankton production and phytoplankton and zooplankton biomass. Sensitivity experiments are used to assess the net effect of each change separately and in unison. Quagga mussels are found to have the greatest impact during periods of isothermal mixing, while nutrients have the greatest impact during thermal stratification. Quagga mussels also act to enhance spatial heterogeneity, particularly between nearshore‐offshore regions. This effect produces a reversal in the gradient of nearshore‐offshore productivity: from relatively greater nearshore productivity in the prequagga lake to relatively lesser nearshore productivity after quaggas. The combined impact of both processes drives substantial reductions in phytoplankton and zooplankton biomass, as well as significant modifications to the seasonality of surface water pCO2, particularly in nearshore regions where mussel grazing continues year‐round. These results support growing concern that considerable losses of phytoplankton and zooplankton will yield concurrent losses at higher trophic levels. Comparisons to observed productivity suggest that both quagga mussel filtration and lower lakewide total phosphorus are necessary to accurately simulate recent changes in primary productivity in Lake Michigan.

Spatial variability in surface-water <i>p</i>CO<sub>2</sub> and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

Abstract. The incomplete spatial coverage of CO2 partial pressure (pCO2) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale estimates of estuarine CO2 emissions. Given the limited research on CO2 dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of pCO2 (carbonic acid dissociation constants, organic alkalinity), estimates of air–sea CO2 fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its surface-water pCO2 distribution. To fill this data gap, a comprehensive dataset was compiled from direct and indirect measurements of carbonate system parameters in the surface waters of the EGSL during the spring or summer of 2003–2016. The calculated surface-water pCO2 ranged from 435 to 765 µatm in the shallow partially mixed upper estuary, 139–578 µatm in the deep stratified lower estuary, and 207–478 µatm along the Laurentian Channel in the Gulf of St. Lawrence. Overall, at the time of sampling, the St. Lawrence Estuary served as a very weak source of CO2 to the atmosphere, with an area-averaged CO2 degassing flux of 0.98 to 2.02 mmol C m−2 d−1 (0.36 to 0.74 mol C m−2 yr−1). A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO2. Whereas we used the dissociation constants of Cai and Wang (1998) to calculate estuarine pCO2, formulations recommended for best practices in open ocean environments may underestimate pCO2 at low salinities, while those of Millero (2010) may result in overestimates.

Scales and drivers of seasonal pCO2 dynamics and net ecosystem exchange along the coastal waters of southeastern Arabian Sea

The impact of seasonal coastal upwelling on the dynamics of dissolved inorganic carbon (DIC) and sea-air fluxes of CO2 along the coastal waters of Kochi was investigated during 2015, as a part of Ecosystem Modelling Project. The surface water pCO2 varied from 396 to 630μatm during the study period. Significant inter-seasonal variations were found in the distribution of physico-chemical variables and surface pCO2. An increase of 102.1μatm of pCO2 was noticed over a two-decade period with a rate of 5.3μatmy−1. There was an agreement between the fluxes of CO2 and net ecosystem production (NEP) with respect to the trophic status while NEP was higher than CO2 fluxes by a factor of 3.9. The annual net ecosystem exchange (NEE) was estimated to be 15.02mmolCm−2d−1 indicating that the coastal waters of Kochi are highly heterotrophic in nature.

CO2 emissions from a temperate drowned river valley estuary adjacent to an emerging megacity (Sydney Harbour)

The Sydney Harbour Estuary is a large drowned river valley adjacent to Sydney, a large urban metropolis on track to become a megacity; estimated to reach a population of 10 million by 2100. Monthly underway surveys of surface water pCO2 were undertaken along the main channel and tributaries, from January to December 2013. pCO2 showed substantial spatio-temporal variability in the narrow high residence time upper and mid sections of the estuary, with values reaching a maximum of 5650 μatm in the upper reaches and as low as 173 μatm in the mid estuary section, dominated by respiration and photosynthesis respectively. The large lower estuary displayed less variability in pCO2 with values ranging from 343 to 544 μatm controlled mainly by tidal pumping and temperature. Air-water CO2 emissions reached a maximum of 181 mmol C m−2 d−1 during spring in the eutrophic upper estuary. After a summer high rainfall event nutrient-stimulated biological pumping promoted a large uptake of CO2 transitioning the Sydney Harbour Estuary into a CO2 sink with a maximum uptake of rate of −10.6 mmol C m−2 d−1 in the mid-section of the estuary. Annually the Sydney Harbour Estuary was heterotrophic and a weak source of CO2 with an air-water emission rate of 1.2–5 mmol C m−2 d−1 (0.4–1.8 mol C m−2 y−1) resulting in a total carbon emission of around 930 tonnes per annum. CO2 emissions (weighted m3 s−1 of discharge per km2 of estuary surface area) from Sydney Harbour were an order of magnitude lower than other temperate large tectonic deltas, lagoons and engineered systems of China, India, Taiwan and Europe but were similar to other natural drowned river valley systems in the USA. Discharge per unit area appears to be a good predictor of CO2 emissions from estuaries of a similar climate and geomorphic class.

SIPCO2: A simple, inexpensive surface water pCO2 sensor

AbstractEfforts to estimate air‐water carbon dioxide (CO2) exchange on regional or global scales are constrained by a lack of direct, continuous surface water CO2 observations. Sensor technology for the in situ measurement of the partial pressure of carbon dioxide (pCO2) has progressed, but still poses limitations including expense and biofouling concerns. We describe a simple, inexpensive, in situ pCO2 method (SIPCO2) in which a non‐dispersive infrared (NDIR) detector is paired with an air pump in an enclosed housing to produce air‐sea equilibration. We first evaluated this approach in a laboratory setting, then in an estuarine‐coastal ocean laboratory for several months to continuously monitor aquatic pCO2. An accepted, accurate NDIR‐based CO2 measurement technique was employed alongside SIPCO2 to provide an assessment of sensor performance. SIPCO2 allows for low‐cost, relatively accurate measurements of pCO2 (mean difference of −5 ± 5 μatm from validation system after laboratory calibration) without reagents or membranes, and can be assembled and operated with a minimal amount of technical skill. While not suitable for some exacting applications, this SIPCO2 approach could rapidly and effectively increase the number of quality CO2 observations in a range of aquatic environments. We also provide detailed instructions for the assembly of SIPCO2 from commercially available components.

Enhanced greenhouse gas emission from exposed sediments along a hydroelectric reservoir during an extreme drought event

An active debate has been underway on the magnitude and duration of carbon (C) emissions from hydroelectric reservoirs, yet little attention has been paid to stochastic C emissions from reservoir sediments during extreme climatic events. A rare opportunity for field measurements of CO2 efflux from a hydroelectric reservoir in Korea during an extreme drought event was used to examine how prolonged droughts can affect microbial organic matter processing and the release of CO2, CH4 and N2O from exposed sediments. Chamber measurements of CO2 efflux along an exposed sediment transect, combined with high-frequency continuous sensor measurements of the partial pressure of CO2 (pCO2) in the reservoir surface water, exhibited extraordinary pulses of CO2 from exposed sediments and the turbulent inflowing water in contrast to a small CO2 sink in the main water body of the reservoir and a low efflux of CO2 from the flooded sediment. Significant increases in the production of CO2, CH4 and N2O observed in a laboratory incubation of sediments, together with enhanced activities of phenol oxidase and three hydrolases, indicate a temporary activation of microbial organic matter processing in the drying sediment. The results suggest that drought-triggered pulses of greenhouse gas emission from exposed sediments can offset the C accumulation in reservoir sediments over time scales of years to decades, reversing the trend of declining C emissions from aging reservoirs.

Modeling Allochthonous Dissolved Organic Carbon Mineralization Under Variable Hydrologic Regimes in Boreal Lakes

Here, we explore the interaction between hydrology and the reactivity of allochthonous dissolved organic carbon (DOCalloch) in determining the potential of DOCalloch to generate CO2 through biological and photo-chemical mineralization in boreal lakes. We developed a mechanistic model that integrates the reactivity continuum (RC) concept to reconstruct in-lake mineralization of DOCalloch under variable hydrologic conditions using empirical measurements of DOCalloch concentrations and reactivity as model inputs. The model predicts lake DOCalloch concentration (L-DOCalloch) and its average overall reactivity $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ , which integrates the distribution of DOCalloch ages within the lake as a function of the DOC loading (DOCin), the initial reactivity of this DOCin (k 0), and the lake water residence time (WRT). The modeled DOCalloch mineralization rates and concentrations were in agreement with expectations based on observed and published values of ambient lake DOC concentrations and reactivity. Results from this modeling exercise reveal that the interaction between WRT and k 0 is a key determinant of the ambient concentration and reactivity of lake DOCalloch, which represents the bulk of DOC in most of these lakes. The steady-state $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ also represents the proportion of CO2 that can be extracted from DOCalloch during its transit through lakes, and partly explains the patterns in surface water pCO2 oversaturation that have been observed across gradients of lake size and volume. We estimate that in-lake DOCalloch mineralization could potentially contribute on average 30–40% of the observed surface carbon dioxide partial pressure (pCO2) across northern lakes. Applying the RC framework to in-lake DOCalloch dynamics improves our understanding of DOCalloch transformation and fate along the aquatic network, and results in a predictable mosaic of DOC reactivity and potential CO2 emissions across lakes within a landscape.

Remote estimation of surface pCO2 on the West Florida Shelf

Surface pCO2 data from the West Florida Shelf (WFS) have been collected during 25 cruise surveys between 2003 and 2012. The data were scaled up using remote sensing measurements of surface water properties in order to provide a more nearly synoptic map of pCO2 spatial distributions and describe their temporal variations. This investigation involved extensive tests of various model forms through parsimony and Principal Component Analysis, which led to the development of a multi-variable empirical surface pCO2 model based on concurrent MODIS (Moderate Resolution Imaging Spectroradiometer) estimates of surface chlorophyll a concentrations (CHL, mg m−3), diffuse light attenuation at 490nm (Kd_Lee, m−1), and sea surface temperature (SST, °C). Validation using an independent dataset showed a pCO2 Root Mean Square Error (RMSE) of <12µatm and a 0.88 coefficient of determination (R2) for measured and model-predicted pCO2 ranging from 300 to 550µatm. The model was more sensitive to SST than to CHL and Kd_Lee, with a 1°C change in SST leading to a ~16µatm change in the predicted pCO2. Application of the model to the entire WFS MODIS time series between 2002 and 2014 showed clear seasonality, with maxima (~450µatm) in summer and minima (~350µatm) in winter. The seasonality was positively correlated to SST (high in summer and low in winter) and negatively correlated to CHL and Kd_Lee (high in winter and low in summer). Inter-annual variations of pCO2 were consistent with inter-annual variations of SST, CHL, and Kd_Lee. These results suggest that surface water pCO2 of the WFS can be estimated, with known uncertainties, from remote sensing. However, while the general approach of empirical regression may work for waters from other areas of the Gulf of Mexico, model coefficients need to be empirically determined in a similar fashion.

Partial Pressure of Carbon Dioxide and Methane from Autumn to Winter in Xiangxi Bay of the Three Gorges Reservoir

The Concentrations of dissolved CH4 and CO2 in Xiangxi Bay of the Three Gorges Reservoir from autumn to winter in 2014 were determined with headspace gas chromatography technology. Then their partial pressures of CH4 and CO2 were calculated according to the Henry's law. Their temporal variation and the effects of environmental parameters were also discussed. The results indicated that the CH4 partial pressure in the surface water ranged 0.64-4.43Pa, with an average of (1.69±0.94)Pa. The CO2 partial pressure varied from 49.90 to 868.91Pa, with the average of (328.48±251.63)Pa. The pCO2 and pCH4 had a strong negative correlation (r=-0.618,P<0.01). During the period of monitoring, the pCO2 and pCH4 in surface water were significantly correlated with pH, DO, chlorophyll a, TP, surface water temperature and water level. Compared with pCH4, pCO2 was more closely correlated with various environmental factors.

Autumn CO2 chemistry in the Japan Sea and the impact of discharges from the Changjiang River

AbstractWe made comprehensive surface water CO2 chemistry observations in the Japan Sea during each autumn from 2010 to 2014. The partial pressure of CO2 (pCO2) in surface water, 312–329 μatm, was 10–30 μatm lower in the Japan Sea than in the same latitude range of the western North Pacific adjacent to Japan. According to the sensitivity analysis of pCO2, the lower pCO2 in the Japan Sea was primarily attributable to a large seasonal decrease of pCO2 associated with strong cooling in autumn, particularly in the northern Japan Sea. In contrast, the lower pCO2 in relatively warm, freshwater in the southern Japan Sea was attributable to not only the thermodynamic effect of the temperature changes but also high total alkalinity. This alkalinity had its origin in Changjiang River and was transported by Changjiang diluted water (CDW) which seasonally runs into the Japan Sea from the East China Sea. The input of total alkalinity through CDW also elevated the saturation state of calcium carbonate minerals and mitigated the effects of anthropogenic ocean acidification, at least during autumn. These biogeochemical impacts of CDW in the Japan Sea last until November, although the inflow from the East China Sea to the Japan Sea almost ceases by the end of September. The long duration of the high saturation state of calcium carbonate benefits calcareous marine organisms.

Using satellite data to estimate partial pressure of CO2 in the Baltic Sea

AbstractIn this study we focused on estimating the pressure partial of CO2 (pCO2) in the entire Baltic Sea which can be considered a coastal area in its entirety. We used the self‐organizing multiple linear output (SOMLO) method to estimate the ocean surface pCO2 in the Baltic Sea from the remotely sensed sea surface temperature, chlorophyll a, colored dissolved organic matter, net primary production, and mixed‐layer depth. Uncertainties in the estimates include sparsity of in situ data used to train the algorithms, in particular, for some sectors and seasons. For this application we divided the Baltic Sea in four basins. When comparing the results obtained with this division to those obtained in previous studies, we notice a decrease in the root‐mean‐square error (&lt;40 μatm) between the reconstruction of the pCO2 and their corresponding in situ measurements, as well as an increase of the correlation coefficient (&gt; 0.96) between them. The outputs of this research have a horizontal resolution of 4 km and cover the 1998–2011 period. For the first time, a climatological mean distribution of surface water pCO2 over the Baltic Sea was calculated based on the SOMLO method with a mean pCO2 of 368.3 ± 100 μatm, and a range of 234–514 μatm. The seasonal variability is similar throughout the Baltic Sea, being high in winter and low in summer.

Ocean salinity from satellite-derived temperature in the Antarctic Ocean

AbstractThe aim of the MINERVE project (Mesures à l’INterface Eau-aiR de la Variabilité des Échanges de CO2) is to observe and understand the seasonal and interannual variability of the partial pressure of CO2(pCO2) in surface waters using hydrological and biogeochemical data in the Southern Ocean south of Australia. Logistics routes of the RVAstrolabeprovide access to scarcely studied areas, thus allowing us to understand the different processes acting in this area of the Antarctic Ocean. The surface area covered by these cruises, however, is tiny compared with the total surface area of the Antarctic Ocean. Correlations betweenin situsurface temperature and salinity data were applied to satellite images of sea surface temperature to map ocean surface salinity over a much wider area than under the cruise tracks. Comparisons with salinity data from satellites which provide ~100 km resolution and 0.1 accuracy indicate that we are able to map salinity at 4 km resolution and almost the same accuracy of ± 0.1.