Water Partial Pressure Of CO2 Research Articles

Seasonal dynamics and regional distribution patterns of CO2 and CH4 in the north-eastern Baltic Sea

Abstract. Significant research has been carried out in the last decade to describe the CO2 system dynamics in the Baltic Sea. However, there is a lack of knowledge in this field in the NE Baltic Sea, which is the main focus of the present study. We analysed the physical forcing and hydrographic background in the study year (2018) and tried to elucidate the observed patterns of surface water CO2 partial pressure (pCO2) and methane concentrations (cCH4). Surface water pCO2 and cCH4 were continuously measured during six monitoring cruises onboard R/V Salme, covering the Northern Baltic Proper (NBP), the Gulf of Finland (GoF), and the Gulf of Riga (GoR) and all seasons in 2018. The general seasonal pCO2 pattern showed oversaturation in autumn–winter (average relative CO2 saturation 1.2) and undersaturation in spring–summer (average relative CO2 saturation 0.5), but it locally reached the saturation level during the cruises in April, May, and August in the GoR and in August in the GoF. The cCH4 was oversaturated during the entire study period, and the seasonal course was not well exposed on the background of high variability. Surface water pCO2 and cCH4 distributions showed larger spatial variability in the GoR and GoF than in the NBP for all six cruises. We linked the observed local maxima to river bulges, coastal upwelling events, fronts, and occasions when vertical mixing reached the seabed in shallow areas. Seasonal averaging over the CO2 flux suggests a weak sink for atmospheric CO2 for all basins, but high variability and the long periods between cruises (temporal gaps in observation) preclude a clear statement.

Spatial and temporal variability of the sources and sinks of carbonate system in the southwest bay of Bengal from 2014 to 2020

This study presents a synthesis of surface water partial pressure of CO2 (pCO2) and nutrient measurement in the southwest Bay of Bengal (swBoB) from 2014 to 2020 and characterizes the spatial and temporal variability. pCO2 rates found to be high (1191 μatm) during the 2015 monsoon and low (176 μatm) in the summer season during the month of May 2015. The inter-annual CO2 fluxes varied from −4.79 to 9.97 mmol Cm−2d−1. The significant a negative CO2 flux (−4.79 mmol Cm−2d−1) was recorded during the summer season in the year 2019, whereas a positive significant CO2 flux (9.97 mmol Cm−2d−1) was observed during the monsoon in 2014. Major physical parameters are at their highest during summer owing to increased high solar radiation during cloud-free circumstances, reduced or inadequate riverine flux, and a lack of vertical mixing of the water column, which results in the lowest nutrients concentration, Dissolved Oxygen (DO), Dissolved Inorganic Nitrogen (DIN), Dissolved Organic Carbon (DOC), chlorophyll-a, Particulate Organic Carbon (POC), pCO2, that leads to negative CO2 flux to the atmosphere. In contrast during monsoon season colossal discharge of freshwater high DO, DIN, DOC, chlorophyll-a, POC, pCO2 as results source CO2 flux to the atmosphere. Statistical analysis the correlation coefficient depicts Total Alkalinity (TA), DIC, POC, DIN, and DO found a positive correlation with pCO2 and fCO2 during the monsoon season. In the swBoB, pCO2 had a negative relationship with sea surface temperature (SST), sea surface salinity (SSS), and pH because CO2 solubility changes with SST and increases in cold water rather than warm water. In this study, we examine the association between all carbonate variables and the SSS and SST to better understand seasonal fluctuations.

Chemical denudation dynamic based on hydrochemical measurements in the area of Drienovecká jaskyňa Cave basin (Slovak karst, Slovakia)

Denudation is a fundamental process for the development of karst relief. It has different intensity in different geological and climatic condition and beside this many other partial factors influence the intensity and dynamic of the process during the year. In karst systems, there is often a positive correlation between water partial pressure of CO2 and denudation. The Drienovecká jaskyňa Cave spring represents typical active fluviokarstic spring and its catchment area is represented by Wetterstein and Waxenec limestones, and Drienovec conglomerates. This catchment study area is located at the contact of the conti-nental and oceanic climate, in terms of altitude at the border between the lowland and moun-tain climate. During three hydrological years we measured main karst water parameters that helped us bring first results on chemical denudation in the catchment area. The water from the spring is of calcium-magnesium-bicarbonate type. Hydrogeochemical analyses in-dicate that it is mostly water from an open hydrogeological structure. Water of the cave spring is oversaturated with respect to calcite, which is documented by the saturation index of calcite, whose values are higher than the solubility product of calcite. During the studied period, the dynamic of the chemical denudation rate is clearly observable with peaks in spring months in year 2014 and 2016. The average value of denudation rate for the entire period is 21.06 mg Ca2+. Factors that influence chemical denudation include, for example, type of carbonate rock, CO2 partial pressure, water and air temperature, chemical compo-sition of the aqueous solution, activity of soil organisms, vegetation and others. Water from melted snow can also play a significant role in changes in water chemistry and thus chemical denudation. URL: https://www.gcass.science.upjs.sk/

A Low-Cost Carbon Dioxide Monitoring System for Coastal and Estuarine Sensor Networks

As the interest in marine or ocean-based carbon dioxide removal (mCDR) increases, so does the need for more spatially resolved measurement, reporting, and verification (MRV) of the CO2 sequestered (and for understanding the impacts of these environmental manipulation experiments). The mCDR/MRV community can borrow technology from the past decade’s exponential growth of interest in ocean acidification and monitoring. However, available sensors are insufficient to meet the growing demand for spatially resolved mCDR due to technological complexities, availability, and cost. For instance, in a recent review, there were few commercially available autonomous solutions for pH and pCO2 monitoring and none for total alkalinity or total dissolved inorganic carbon), and the majority of the pH and pCO2 sensors and analyzers cost well above $10,000. Proper MRV of mCDR requires high spatiotemporal resolution monitoring of the inorganic carbon system. Here we describe our efforts toward a low-cost CO2 flux or ∆pCO2 (the difference between air and water partial pressure of CO2) monitoring system intended for use in distributed sensor arrays in coastal, estuarine, and blue carbon research and in mCDR approaches.

Seasonal, Diurnal, and Tidal Variations of Dissolved Inorganic Carbon and pCO2 in Surface Waters of a Temperate Coastal Lagoon (Arcachon, SW France)

We report on diurnal, tidal, and seasonal variations of dissolved inorganic carbon (DIC), water partial pressure of CO2 (pCO2), and associated water–air CO2 fluxes in a tidal creek of a temperate coastal lagoon with 70% of intertidal flats, during eight tidal/diurnal cycles and two consecutive years covering all seasons. Surface waters of the lagoon were always slightly oversaturated in CO2 with respect to the atmosphere with an average pCO2 value of 496 ± 36 ppmv. Seasonally, subsurface water pCO2 values were controlled by both temperature and biological/tidal advection effects that compensated each other and resulted in weak annual variations. High-resolution temporal pCO2 records reveal that the highest fluctuations (192 ppmv) occurred at the tidal/diurnal scale as a result of biological activity, advection from the tidal flat, and porewater pumping that all contributed to water pCO2 and carbonate chemistry variations. Total alkalinity (TA) versus salinity plots suggest a net production of alkalinity in the lagoon attributed to benthic carbonate dissolution and/or anaerobic degradation of organic matter. We specifically highlighted that for the same salinity range, during flooding, daytime pCO2 were generally lower than nighttime pCO2 values because of photosynthesis, whereas during ebbing, daytime pCO2 were higher than nighttime pCO2 values because of heating. Waters in the lagoon were a relatively weak CO2 source to the atmosphere over the year compared to other estuarine and lagoon waters elsewhere, and to sediment-air fluxes measured simultaneously by atmospheric Eddy Covariance (EC) in the Arcachon lagoon. Because of low values and small variations of the air-sea pCO2 gradient, the variability of fluxes calculated using the piston velocity parameterization was greatly controlled by the wind speed at the diurnal and, to a lesser extent, seasonal time scales. During the emersion, the comparison of these pCO2 data in the tidal creek with EC fluxes measured 1.8 km away on the tidal flat suggests high heterogeneity in air-sea CO2 fluxes, both spatially and at short time scales according to the inundation cycle and the wind speed. In addition to tidal pumping when the flat becomes emerged, our data suggest that lateral water movement during the emersion of the flat generates strong spatial heterogeneity in water–air CO2 flux.

Seasonal and diel variability of CO2 emissions from a semiarid hard-water reservoir

Reservoirs represent a key component of the global carbon cycle. However, estimates of carbon dioxide (CO2) emissions from reservoirs remain poorly constrained due to the absence of spatially and temporally resolved measurements. We performed high-resolution monitoring of CO2 emissions (FCO2) in a semiarid hard-water reservoir to examine its seasonal and diel variability. Our results suggest that dissolved inorganic carbon input plays a central role in sustaining the surface water CO2 partial pressure (pCO2), which varies from 1076 to 4587 μatm. Although the reservoir is moderately to highly productive throughout the year, it is a net CO2 source with FCO2 values in the range of 308–1753 mg C m−2 d–1. This high CO2 efflux indicates that productive waters are not necessarily CO2 sinks. Both pCO2 and FCO2 exhibit clear seasonal and diel patterns. Surface water pCO2 is highest in March and presents a consistent diurnal/nocturnal pattern with the daytime pCO2 6–13% lower than the nighttime pCO2. High CO2 efflux is observed during the ice-thaw period, indicating the release of CO2 that was accumulated during the winter. CO2 effluxes are typically higher during the nighttime driven by aquatic metabolism, but episodic weather events (e.g., rainfall and strong winds) can significantly enhance CO2 emissions and even reverse the diel pattern. Our study also shows that using only daytime measurements to estimate daily CO2 emissions would underestimate it by 9–25%. Hence, future global assessments should incorporate CO2 emissions from hard-water reservoirs and account for their seasonal and diel variability.

Spatial and temporal variability of <i>p</i>CO<sub>2</sub> and CO<sub>2</sub> emissions from the Dong River in south China

Abstract. CO2 efflux at the water–air interface is an essential component of the riverine carbon cycle. However, the lack of spatially resolved CO2 emission measurements prohibits reliable estimation of the global riverine CO2 emissions. By deploying floating chambers, seasonal changes in river water CO2 partial pressure (pCO2) and CO2 emissions from the Dong River in south China were investigated. Spatial and temporal patterns of pCO2 were mainly affected by terrestrial carbon inputs (i.e., organic and inorganic carbon) and in-stream metabolism, both of which varied due to different land cover, catchment topography, and seasonality of precipitation and temperature. Temperature-normalized gas transfer velocity (k600) in small rivers was 8.29 ± 11.29 and 4.90 ± 3.82 m d−1 for the wet season and dry season, respectively, which was nearly 70 % higher than that of large rivers (3.90 ± 5.55 m d−1 during the wet season and 2.25 ± 1.61 m d−1 during the dry season). A significant correlation was observed between k600 and flow velocity but not wind speed regardless of river size. Most of the surveyed rivers were a net CO2 source while exhibiting substantial seasonal variations. The mean CO2 flux was 300.1 and 264.2 mmol m−2 d−1 during the wet season for large and small rivers, respectively, 2-fold larger than that during the dry season. However, no significant difference in CO2 flux was observed between small and large rivers. The absence of commonly observed higher CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant and consistent precipitation in this subtropical monsoon catchment.

Thermodynamic uptake of atmospheric CO2 in the oligotrophic and semiarid São Francisco estuary (NE Brazil)

Estuarine carbonate chemistry predicts that thermodynamic equilibration during the mixing of freshwater with seawater will generate a carbon dioxide (CO2) sink in the case of warm and poorly buffered tropical rivers. The São Francisco River estuary has historically become oligotrophic after the construction of a series of hydroelectric dams in its watershed, where organic matter and nutrients are retained. During two cruises in late winter (Aug. 2014) and early summer (Nov. 2015), dissolved inorganic carbon (DIC) and total alkalinity (TA) were found to increase linearly with salinity in the main estuarine channel, where water mixing required half a day, and showed nearly conservative behaviour. In the main channel, the water partial pressure of CO2 (pCO2) recorded at a 1-min frequency followed an asymmetric bell-shaped trend versus salinity, similar to the curve predicted by the thermodynamic conservative mixing of freshwater DIC and TA with seawater DIC and TA. The low (0–3) salinity region was always a source of atmospheric CO2, where despite low chlorophyll concentrations, a pCO2 diurnal change of approximately 60 ppmv suggested the occurrence of photosynthesis in summer. At salinities above 3, undersaturated pCO2 values (down to 225 ppmv in winter and neap tides) and invasion of atmospheric CO2 of 0.38–1.70 mmol m−1 h−1 occurred because of the predominating thermodynamics during estuarine mixing. In winter and neap tides, the higher river discharge, intense estuarine mixing, lower temperatures and limited tidal pumping resulted in observed pCO2 differences from the theoretical conservative pCO2 by less than 3 ppmv at salinities >3. Conversely, in summer and spring tides, the recorded pCO2 values were on average + 43 ± 35 ppmv above the conservative mixing curve, when tidal pumping, CO2 invasion and surface heating were more significant in the mixing zone but not sufficient to offset the thermodynamic uptake of atmospheric CO2. By combining carbonate chemistry with estuarine mixing modelling and gas exchange calculations, we estimate that heating contributed to approximately 15% and gas exchange contributed to approximately 10% of the positive pCO2 deviation from conservative mixing during summer. The remaining 75% of the deviation reached its maximum at ebb tides and within salinity ranges consistent with the occurrence of tidal pumping from marches and mangrove soils. Indeed, in the mangrove channel, water was supersaturated, with pCO2 values of 976 ± 314 ppmv, while in the main channel, the highest positive pCO2 deviations from conservative mixing (up to +100 ppmv for several hours) occurred at ebb tides. An important finding was that in São Francisco, the thermodynamic and biological processes compete with each other for CO2 fluxes both at low salinities where evasion and autotrophy occur and at high salinities where invasion, heterotrophy and tidal pumping occur. Our study suggests that carbonate thermodynamics during mixing is a key process that has been overlooked in estuarine studies, although they can generate important air-water CO2 exchange and significantly contribute to the carbon budget of estuaries and river plumes.

Magnitude and drivers of CO2 and CH4 emissions from an arid/semiarid river catchment on the Chinese Loess Plateau

River systems are major sources of greenhouse gases (GHG). However, simultaneous CO2 and CH4 emissions from arid/semiarid rivers remain poorly studied. Here we investigated CO2 and CH4 emissions (diffusion + ebullition) and their potential sources and drivers in an arid/semiarid catchment on the Chinese Loess Plateau. The river water CO2 partial pressure (pCO2) averaged 885 ± 415 µatm and did not show a significant change along the stream network due to strong carbonate buffering. Groundwater inputs played a dominant role in controlling pCO2 which exhibited a pronounced seasonal variation. In-stream decomposition of organic matter mobilized by soil erosion was also an important contributor. The streams were consistently oversaturated in CH4, ranging between 0.06 and 0.77 µmol L−1. Both gas emissions exhibited significant seasonal variations, which were collectively controlled by gas concentration gradient across the water–air interface and flow dynamics. The mean CO2 and CH4 efflux were 55 mmol m−2 d–1 and 346 µmol m−2 d–1, respectively, with the highest efflux in August (high flow conditions) for both gases. River impoundment resulted in greatly reduced pCO2 due to enhanced primary production but elevated CH4 concentrations because of anaerobic degradation of organic-rich sediments. Reservoirs acted as a smaller CO2 source but a stronger CH4 source than flowing rivers. Ebullition was an important pathway of CH4 emissions in both lotic and lentic ecosystems, contributing 36 ± 23% and 55 ± 19% to the total CH4 emissions from rivers and reservoirs, respectively. Urban wastewater discharges modified riverine carbon cycling and created local hotspots of GHG production and emissions, which will be globally significant given the increasing human impacts worldwide. Our results reinforce the urgency to account for arid/semiarid rivers in future GHG emission estimates. Future work to better understand the impacts of groundwater inflows and aquatic ecosystem processes in controlling GHG dynamics is also needed.

Riverine export of water, sediment and carbon during flood events in the arid to semi‐arid Wuding River on the Chinese Loess Plateau

AbstractFloods have become increasingly important in fluvial export of water, sediment and carbon (C). Using high‐frequency sampling, the export of water, sediment and C was examined in the Wuding River catchment on the Chinese Loess Plateau. With groundwater as an important contributor to runoff all year round, floods were relatively less important in the export of water. However, large floods were disproportionately important in exporting sediment and inorganic C (DIC) and organic C (DOC and POC). The three largest floods in each year transported 53.6–97.3 and 41.4–77% of the annual sediment and C fluxes, respectively. An extreme flood in 2017 alone contributed 94.6 and 73.1% of the annual sediment and C fluxes, respectively, in just 7 days, which included 20.3, 92.1 and 35.7% of the annual DOC, POC and DIC fluxes, respectively. A stable carbon isotope (δ13C) analysis of POC indicated that modern soils and C3 plants were its primary source. Furthermore, floods greatly accelerated CO2 degassing due to elevated gas transfer velocity, although stream water CO2 partial pressure (pCO2) exhibited a decreasing trend with flow discharge. Although these results illustrated that increasing runoff diluted pCO2, the timing and magnitude of floods were found to be critical in determining the response of pCO2 to flow dynamics. Low‐magnitude floods in the early wet season increased pCO2 because of enhanced organic matter input, while subsequent large floods caused a lower pCO2 due to greatly reduced organic matter supply. Finally, continuous monitoring of a complete flood event showed that the CO2 efflux during the flood (2348 ± 664 mg C m–2 day–1) was three times that under low‐flow conditions (808 ± 98 mg C m–2 day–1). Our study suggests that infrequent, heavy storm events, which are predicted to increase under climate change, will greatly alter the transport regimes of sediment and C. © 2020 John Wiley & Sons, Ltd.

Spatio-temporal variability of surface water pCO2 and nutrients in the tropical Pacific from 1981 to 2015

This study presents a synthesis of surface water partial pressure of CO2 (pCO2) and nutrient observations in the tropical Pacific (20°S–20°N) from 1981 to 2015 and characterizes the spatio-temporal variability. We used data from the Surface Ocean CO2 Atlas version 5, which include about 2 million pCO2 measurements in the tropical Pacific. Unlike many previous studies that estimated pCO2 fields from relationships with other variables like sea surface temperature, we developed gridded products of monthly means using a technique to interpolate measured pCO2 values. Large seasonal variation of pCO2 appears in the cold tongue region (EQ–20°S, east of 120°W) corresponding to the seasonal variation of coastal upwelling, and in the off-equatorial region where the thermodynamic effect on pCO2 dominates. Consistent with previous findings, pCO2 along the equator declines during El Niño due to weakening of the easterly winds and therefore reduced upwelling of CO2 rich subsurface water. We also quantified the spatial distribution of the long-term pCO2 trend beyond the area-averaged trend presented previously. The long-term trend of pCO2 is positive in all regions with an area average of 1.8 ± 0.1 μatm yr−1. However, along the equator the trend is > 2 μatm yr−1 linked to the Pacific Decadal Oscillation forcing. Using the same methodology, we also analyzed about 20,000 surface nutrient measurements from the Global Ocean Data Analysis Project version 2, World Ocean Database 2013, and ship-of-opportunity sampling by the National Institute for Environmental Studies, Japan. We present the spatial patterns of reduced surface nutrient concentration in the central to eastern tropics along the equator during El Niño, but there are not enough data to characterize the trends of nutrients in the tropical Pacific.Decorrelation analyses are also applied using covariance between pCO2 anomalies separated by a lag increment for zonal, meridional, and temporal directions. The e-folding scale of pCO2 is estimated to be 6° in latitude, 13° in longitude, and 2 months with a signal-to-noise ratio of 4, which are used as input for the interpolation as well as an assessment of ideal observation density and frequency. Decorrelation analyses such as this are critical for evaluating existing observing system design and informing future sampling strategies.

Temporal Variability in Surface Water pCO2 in Adventfjorden (West Spitsbergen) With Emphasis on Physical and Biogeochemical Drivers

AbstractSeasonal and interannual variability in surface water partial pressure of CO2 (pCO2) and air‐sea CO2 fluxes from a West Spitsbergen fjord (IsA Station, Adventfjorden) are presented, and the associated driving forces are evaluated. Marine CO2 system data together with temperature, salinity, and nutrients, were collected at the IsA Station between March 2015 and June 2017. The surface waters were undersaturated in pCO2 with respect to atmospheric pCO2 all year round. The effects of biological activity (primary production/respiration) followed by thermal forcing on pCO2 were the most important drivers on a seasonal scale. The ocean was a sink for atmospheric CO2 with annual air‐sea CO2 fluxes of −36 ± 2 and −31 ± 2 g C·m−2·year−1 for 2015–2016 and 2016–2017, respectively, as estimated from the month of April. Waters of an Arctic origin dominated in 2015 and were replaced in 2016 by waters of a transformed Atlantic source. The CO2 uptake rates over the period of Arctic origin waters were significantly higher (2 mmol C·m−2·day−1) than the rates of the Atlantic origin waters of the following year.

Hurricane Arthur and its effect on the short-term variability of <i>p</i>CO<sub>2</sub> on the Scotian Shelf, NW Atlantic

Abstract. The understanding of the seasonal variability of carbon cycling on the Scotian Shelf in the NW Atlantic Ocean has improved in recent years; however, very little information is available regarding its short-term variability. In order to shed light on this aspect of carbon cycling on the Scotian Shelf we investigate the effects of Hurricane Arthur, which passed the region on 5 July 2014. The hurricane caused a substantial decline in the surface water partial pressure of CO2 (pCO2), even though the Scotian Shelf possesses CO2-rich deep waters. High-temporal-resolution data of moored autonomous instruments demonstrate that there is a distinct layer of relatively cold water with low dissolved inorganic carbon (DIC) slightly above the thermocline, presumably due to a sustained population of phytoplankton. Strong storm-related wind mixing caused this cold intermediate layer with high phytoplankton biomass to be entrained into the surface mixed layer. At the surface, phytoplankton begin to grow more rapidly due to increased light. The combination of growth and the mixing of low DIC water led to a short-term reduction in the partial pressure of CO2 until wind speeds relaxed and allowed for the restratification of the upper water column. These hurricane-related processes caused a (net) CO2 uptake by the Scotian Shelf region that is comparable to the spring bloom, thus exerting a major impact on the annual CO2 flux budget.

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.

The spatial and interannual dynamics of the surface water carbonate system and air–sea CO<sub>2</sub> fluxes in the outer shelf and slope of the Eurasian Arctic Ocean

Abstract. The Arctic is undergoing dramatic changes which cover the entire range of natural processes, from extreme increases in the temperatures of air, soil, and water, to changes in the cryosphere, the biodiversity of Arctic waters, and land vegetation. Small changes in the largest marine carbon pool, the dissolved inorganic carbon pool, can have a profound impact on the carbon dioxide (CO2) flux between the ocean and the atmosphere, and the feedback of this flux to climate. Knowledge of relevant processes in the Arctic seas improves the evaluation and projection of carbon cycle dynamics under current conditions of rapid climate change. Investigation of the CO2 system in the outer shelf and continental slope waters of the Eurasian Arctic seas (the Barents, Kara, Laptev, and East Siberian seas) during 2006, 2007, and 2009 revealed a general trend in the surface water partial pressure of CO2 (pCO2) distribution, which manifested as an increase in pCO2 values eastward. The existence of this trend was defined by different oceanographic and biogeochemical regimes in the western and eastern parts of the study area; the trend is likely increasing due to a combination of factors determined by contemporary change in the Arctic climate, each change in turn evoking a series of synergistic effects. A high-resolution in situ investigation of the carbonate system parameters of the four Arctic seas was carried out in the warm season of 2007; this year was characterized by the next-to-lowest historic sea-ice extent in the Arctic Ocean, on satellite record, to that date. The study showed the different responses of the seawater carbonate system to the environment changes in the western vs. the eastern Eurasian Arctic seas. The large, open, highly productive water area in the northern Barents Sea enhances atmospheric CO2 uptake. In contrast, the uptake of CO2 was strongly weakened in the outer shelf and slope waters of the East Siberian Arctic seas under the 2007 environmental conditions. The surface seawater appears in equilibrium or slightly supersaturated by CO2 relative to atmosphere because of the increasing influence of river runoff and its input of terrestrial organic matter that mineralizes, in combination with the high surface water temperature during sea-ice-free conditions. This investigation shows the importance of processes that vary on small scales, both in time and space, for estimating the air–sea exchange of CO2. It stresses the need for high-resolution coverage of ocean observations as well as time series. Furthermore, time series must include multi-year studies in the dynamic regions of the Arctic Ocean during these times of environmental change.

Variations of CO2 Exchange Fluxes Across Water-air Interface and Environmental Meaning in a Surface Stream in Subtropical Karst Area, SW China

CO2 cycle process or sources/sinks are not only the basis of understanding and responding to global climate change, but also the core of the current global climate change research. Gas exchange across water-air interface in terrestrial surface water is an important way of nutrient elements (carbon, nitrogen) exchange between aquatic ecosystems and ambient air. Escaping CO2 gas from surface water is also actively involved in the modern carbon cycle. In the material cycle in karst regions, CO2 plays a key role in karst processes, driving the formation of karst features. Karst groundwater with high water CO2 partial pressure (pCO2) often shows highly positive CO2 concentration gradient to atmosphere after it is discharged to surface, so the evaluation of CO2 exchange fluxes across karst water-air interface is important for karst carbon cycle research. This paper researched CO2 exchange fluxes across water-air interface in the karst surface stream in detail which was fed by Guancun subterranean stream in Liuzhou city, Guangxi province. Closed static chamber method and portable hand-holding CO2 sensor (GM70) were both employed in CO2 exchange fluxes monitoring. The results showed that CO2 degassing was the mainly form of CO2 exchange across the steam water-air interface. CO2 degassing flux in subterranean stream outlet (G1 site) ranged from 139.48 to 890.84 mg·(m2·h)-1 with an average of 445.72 mg·(m2·h)-1. CO2 degassing flux in stream downstream site (G2 site) ranged from 16.54 to 844.18 mg·(m2·h)-1 with an average of 159.81 mg·(m2·h)-1. The CO2 degassing flux in G1site was higher than that in G2 site. CO2 degassing fluxes in rainy season in both G1 and G2 site were higher than those in dry season. Stable carbon analysis of CO2 gas (δ13C-CO2) found that CO2 degassing from karst stream might influence air CO2 carbon isotope near water surface, which resulted in the more negative δ13C-CO2 value with the increase of CO2 degassing flux. Significant spatio-temporal variations of δ13C-CO2 were found, and the δ13C-CO2 in the rainy season was more negative than that in dry season and δ13C-CO2 in G1 site was more negative than that in G2 site. As a result of stream CO2 degassing, the hydrochemical characteristics of steam varied along stream running, which resulted in decrease of HCO3-, EC and pCO2 and increase of pH, SIc and δ13C-DIC in the stream.

Physical and biological forcing of mesoscale variability in the carbonate system of the Ross Sea (Antarctica) during summer 2014

Water samples (0–200m) were collected in a coastal area of the Ross Sea in January 2014 to evaluate the physical and biological forcing on the carbonate system at the mesoscale (distance between stations of 5–10km). Remote sensing supported the determination of the sampling strategy and helped positioning each sampling station. Total alkalinity, pH, dissolved oxygen, phytoplankton pigments and composition were investigated in combination with measurements of temperature, salinity and current speed. Total inorganic carbon, sea water CO2 partial pressure and the saturation state (Ω) for calcite and aragonite were calculated from the measured total alkalinity and pH. In addition, continuous measurements of atmospheric CO2 concentration were completed. LADCP measurements revealed the presence of a significant change in current speed and direction that corresponded to a clearly defined front characterized by gradients in both temperature and salinity. Phytoplankton biomass was relatively high at all stations and the highest values of chlorophyll-a were found between 20 to 50m, with the dominant taxonomic group being haptophyceae. The carbonate system properties in surface waters exhibited mesoscale variability with a horizontal length scale of about 10km. Sea-ice melt, through the input of low salinity water, results in a dilution of the total alkalinity and inorganic carbon, but our observations suggest that phytoplankton activity was the major forcing of the distribution of the carbonate system variables. Higher CO3−, Ω and pH in the surface layer were found where the highest values of chlorophyll-a were observed. The calculated ΔpCO2 pattern follows both MODIS data and in situ chlorophyll-a measurements, and the estimated CO2 fluxes ranged from –0.5±0.4 to –31.0±6.4mmolm−2d−1. The large range observed in the fluxes is due to both the spatial variability of sea water pCO2 and to the episodic winds experienced.

Ocean acidification has different effects on the production of dimethylsulfide and dimethylsulfoniopropionate measured in cultures of Emiliania huxleyi and a mesocosm study: a comparison of laboratory monocultures and community interactions

Environmental context Approximately 25% of CO2 released to the atmosphere by human activities has been absorbed by the oceans, resulting in ocean acidification. We investigate the acidification effects on marine phytoplankton and subsequent production of the trace gas dimethylsulfide, a major route for sulfur transfer from the oceans to the atmosphere. Increasing surface water CO2 partial pressure (pCO2) affects the growth of phytoplankton groups to different degrees, resulting in varying responses in community production of dimethylsulfide. Abstract The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing CO2 partial pressure (pCO2) on concentrations of volatile biogenic dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulfur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulfate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900μatm pCO2, but DMSP production normalised to cell volume was 12% lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60 and 32% respectively at pCO2 up to 3000μatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.

The response of inorganic carbon distributions and dynamics to upwelling-favorable winds on the northern Gulf of Mexico during summer

Upwelling-favorable winds and an offshore-distributed Mississippi and Atchafalaya River plume trajectory were observed in summer 2009 in contrast to the mean conditions from 2002 to 2010 (upwelling-unfavorable winds and an alongshore river plume trajectory), a set of conditions which was also observed in summer 2007. The responses of dissolved inorganic carbon (DIC) distributions and dynamics to upwelling-favorable winds are studied by comparing the contrasting conditions between summer 2009 and summer 2007 on the northern Gulf of Mexico. Patterns of surface water partial pressure of CO2 (pCO2), DIC, δ13C in DIC, and total alkalinity (TA) determined in July 2009 and August 2007 were strongly related to river plume trajectories, and differed between the two summers.The slope of the relationship between dissolved oxygen (DO) and DIC in summer 2007 was comparable to the Redfield O/C ratio of 1.3, which was attributed to respiration of organic matter in the bottom water. The slope of the DO and DIC relationship and δ13CDIC values in bottom waters during July 2009 were clearly affected by mixing since their salinities were <35. A three end-member mixing model was used to remove mixing effects in (1) δ13CDIC, to estimate the organic source of respiration, and (2) in DIC concentrations, to calculate DIC removal and release. δ13CDIC results in both summers were consistent with an apparent release of DIC in hypoxic waters (DO less than 2mgL−1) associated with respiration of surface organic matter. The area-weighted surface DIC removal (i.e., biological production) was lower in 2009 than in 2007 on the shelf, as the plume was distributed offshore. The release of DIC in bottom waters was higher over the shelf in 2009 and was surmised to be related to stronger mixing, which was favorable for the DO supply for respiration. Overall, surface waters on the continental shelf in the region of study in July 2009 acted as a weak CO2 source to the atmosphere, but a weak CO2 sink in August 2007. We contend that the inorganic carbon distribution and concentrations on the shelf were related to regional wind forcing, through its influence on the distribution of coastal currents and plume trajectories and their subsequent impact on biogeochemical processes.

Sensitivity of the air–sea CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchange in the Baltic Sea and Danish inner waters to atmospheric short-term variability

Abstract. Minimising the uncertainties in estimates of air–sea CO2 exchange is an important step toward increasing the confidence in assessments of the CO2 cycle. Using an atmospheric transport model makes it possible to investigate the direct impact of atmospheric parameters on the air–sea CO2 flux along with its sensitivity to, for example, short-term temporal variability in wind speed, atmospheric mixing height and atmospheric CO2 concentration. With this study, the importance of high spatiotemporal resolution of atmospheric parameters for the air–sea CO2 flux is assessed for six sub-basins within the Baltic Sea and Danish inner waters. A new climatology of surface water partial pressure of CO2 (pCO2w) has been developed for this coastal area based on available data from monitoring stations and on-board pCO2w measuring systems. Parameterisations depending on wind speed were applied for the transfer velocity to calculate the air–sea CO2 flux. Two model simulations were conducted – one including short-term variability in atmospheric CO2 (VAT), and one where it was not included (CAT). A seasonal cycle in the air–sea CO2 flux was found for both simulations for all sub-basins with uptake of CO2 in summer and release of CO2 to the atmosphere in winter. During the simulated period 2005–2010, the average annual net uptake of atmospheric CO2 for the Baltic Sea, Danish straits and Kattegat was 287 and 471 Gg C yr−1 for the VAT and CAT simulations, respectively. The obtained difference of 184 Gg C yr−1 was found to be significant, and thus ignoring short-term variability in atmospheric CO2 does have a sizeable effect on the air–sea CO2 exchange. The combination of the atmospheric model and the new pCO2w fields has also made it possible to make an estimate of the marine part of the Danish CO2 budget for the first time. A net annual uptake of 2613 Gg C yr−1 was found for the Danish waters. A large uncertainty is connected to the air–sea CO2 flux in particular caused by the transfer velocity parameterisation and the applied pCO2w climatology. However, as a significant difference of 184 Gg C yr−1 is obtained between the VAT and CAT simulations, the present study underlines the importance of including short-term variability in atmospheric CO2 concentration in future model studies of the air–sea exchange in order to minimise the uncertainty.