Dissolved Carbon Species Research Articles

Minimize Energy Consumption of CO2 Release in a Flow Electrolyzer By Optimizing Direct Air Capture Solvents

Under the 2015 Paris Agreement, almost 200 nations have committed to the global goal of limiting the rise in average temperatures to 2.0 °C above preindustrial levels, with an even more ambitious aim of striving for 1.5 °C. Achieving the 1.5 °C objective requires a 45% reduction in global greenhouse gas emissions by 2030, ultimately reaching net-zero emissions by 2050. Numerous industries are increasingly making commitments to combat climate change by minimizing their CO2 emissions. However, certain sectors face challenges due to the current high costs associated with emissions reduction through available technologies, though these costs are expected to decrease over time. Moreover, in specific industries like cement production, there are emissions sources that cannot be entirely eliminated, such as those arising from the inherent calcination process. Given these constraints, realizing the emissions reduction pathway to the 1.5 °C target requires the adoption of negative emissions processes, including technologies like direct air capture (DAC), to actively remove CO2 from the atmosphere.The operational concept of the DAC process explored in this study is based on the utilization of both the solvent-based method and alkaline water electrolysis. This involves regenerating the solvent through pH fluctuations generated by a carbonate electrolyzer. As depicted in Figure 1, the consumption of OH- ions during O2 evolution leads to a decrease in pH at the anolyte loop, while the production of OH- ions through water splitting causes an increase in pH at the catholyte loop. Consequently, the lowered pH environment facilitates the release of CO2 gas from dissolved carbon species such as CO32-, while the heightened pH environment promotes the formation of alkaline hydroxides for carbon capture in an air absorber.In this work, we will aim to analyze the energy consumption per mole of CO2 released from the anolyte loop of a flow electrolyzer. Utilizing a combination of theoretical predictions and experimental validations, significant insights were obtained for optimizing the DAC solvent. This optimization involves minimizing energy consumption by adjusting alkalinity levels and incorporating supporting electrolytes. Figure 1

Illuminating the “Invisible”: Substantial Deep Respiration and Lateral Export of Dissolved Carbon From Beneath Soil

AbstractDissolved organic and inorganic carbon (DOC and DIC) influence water quality, ecosystem health, and carbon cycling. Dissolved carbon species are produced by biogeochemical reactions and laterally exported to streams via distinct shallow and deep subsurface flow paths. These processes are arduous to measure and challenge the quantification of global carbon cycles. Here we ask: when, where, and how much is dissolved carbon produced in and laterally exported from the subsurface to streams? We used a catchment‐scale reactive transport model, BioRT‐HBV, with hydrometeorology and stream carbon data to illuminate the “invisible” subsurface processes at Sleepers River, a carbonate‐based catchment in Vermont, United States. Results depict a conceptual model where DOC is produced mostly in shallow soils (3.7 ± 0.6 g/m2/yr) and in summer at peak root and microbial respiration. DOC is flushed from soils to the stream (1.0 ± 0.2 g/m2/yr) especially during snowmelt and storms. A large fraction of DOC (2.5 ± 0.2 g/m2/yr) percolates to the deeper subsurface, fueling deep respiration to generate DIC. DIC is exported predominantly from the deeper subsurface (7.1 ± 0.4 g/m2/yr, compared to 1.3 ± 0.3 g/m2/yr from shallow soils). Deep respiration reduces DOC and increases DIC concentrations at depth, leading to commonly observed DOC flushing (increasing concentrations with discharge) and DIC dilution patterns (decreasing concentrations with discharge). Surprisingly, respiration processes generate more DIC than weathering in this carbonate‐based catchment. These findings underscore the importance of vertical connectivity between the shallow and deep subsurface, highlighting the overlooked role of deep carbon processing and export.

Possible Effects of Changes in Carbonate Concentration and River Flow Rate on Photochemical Reactions in Temperate Aquatic Environments.

In temperate environments, climate change could affect water pH by inducing enhanced dissolution of CaSO4 followed by biological sulphate reduction, with the potential to basify water due to H+ consumption. At the same time, increased atmospheric CO2 could enhance weathering of carbonate rocks (e.g., dolomite) and increase the total concentration of dissolved carbonate species. Both processes enhance phototransformation by the carbonate radical (CO3•-), as shown for the non-steroidal anti-inflammatory drug paracetamol, provided that the dissolved organic carbon of water does not undergo important fluctuations. Climate change could also affect hydrology, and prolonged drought periods might considerably decrease flow rates in rivers. This is a substantial problem because wastewater pollutants become less diluted and, as a result, can exert more harmful effects due to increased concentrations. At the same time, in low-flow conditions, water is also shallower and its flow velocity is decreased. Photochemical reactions become faster because shallow water is efficiently illuminated by sunlight, and they also have more time to occur because water takes longer to cover the same river stretch. As a result, photodegradation of contaminants is enhanced, which offsets lower dilution but only at a sufficient distance from the wastewater outlet; this is because photoreactions need time (which translates into space for a flowing river) to attenuate pollution.

Influence of Carbonate Speciation on Hydrated Electron Treatment Processes.

Advanced reduction processes (ARPs) that generate hydrated electrons (eaq-; e.g., UV-sulfite) have emerged as a promising remediation technology for recalcitrant water contaminants, including per- and polyfluoroalkyl substances (PFASs). The effectiveness of ARPs in different natural water matrices is determined, in large part, by the presence of non-target water constituents that act to quench eaq- or shield incoming UV photons from the applied photosensitizer. This study examined the pH-dependent quenching of eaq- by ubiquitous dissolved carbonate species (H2CO3*, HCO3-, and CO32-) and quantified the relative importance of carbonate species to other abundant quenching agents (e.g., H2O, H+, HSO3-, and O2(aq)) during ARP applications. Analysis of laser flash photolysis kinetic data in relation to pH-dependent carbonate acid-base speciation yields species-specific bimolecular rate constants for eaq- quenching by H2CO3*, HCO3-, and CO32- ( = 2.23 ± 0.42 × 109 M-1 s-1, = 2.18 ± 0.73 × 106 M-1 s-1, and = 1.05 ± 0.61 × 105 M-1 s-1), with quenching dominated by H2CO3* (which includes both CO2(aq) and H2CO3) at moderately alkaline pH conditions despite it being the minor species. Attempts to apply previously reported rate constants for eaq- quenching by CO2(aq), measured in acidic solutions equilibrated with CO2(g), overpredict quenching observed in this study at higher pH conditions typical of ARP applications. Moreover, kinetic simulations reveal that pH-dependent trends reported for UV-sulfite ARPs that have often been attributed to eaq- quenching by varying [H+] can instead be ascribed to variable acid-base speciation of dissolved carbonate and the sulfite sensitizer.

Correlation of Stainless Steel Pit Morphology to Humidity-Specific Sea Salt Brine Constituents

Immersion exposures of 304 stainless steel ground to a #4 finish were conducted in brines representative of the chemistry of sea salt aerosols at low (40%) and high (76%) relative humidity (RH). Low-RH-equivalent brines resulted in cross-hatched pits, whereas high-RH-equivalent brines produced ellipsoidal, faceted pits. Distinct surface microcracking was observed to be associated only with cross-hatched pits and appeared to correlate with a high concentration of dissolved carbonate species in low-RH-equivalent solutions while being absent in the high-RH-equivalent brines. Correlating these results to brine composition suggested that the concentrations of MgCl2 and dissolved carbonate species in the brines could, in the presence of machining-induced surface microstructure and residual stress, determine pit morphology in marine atmospheres, thereby potentially impacting stress corrosion cracking susceptibility and lifetime prediction.

Reclamation-induced tidal restriction increases dissolved carbon and greenhouse gases diffusive fluxes in salt marsh creeks

Intertidal creeks play an important role in transporting nutrients between coastal ecosystems and ocean. Reclamation is a predominant anthropogenic disturbance in coastal regions; however, the influence of reclamation on carbon and nitrogen species and greenhouse gas (GHG) fluxes in creek remains unclear. In a subtropical salt marsh of eastern China, the seasonal patterns of dissolved carbon (DOC, DIC, CO2, and CH4) and inorganic nitrogen (NH4+-N, NO2−-N, and NO3−-N and N2O) species, and the diffusive fluxes of CO2, CH4, and N2O, were compared between the natural tidal creeks and the reclaimed creeks. Due to notably changed hydrological and biological conditions in the reclaimed creeks, concentrations of all dissolved carbon species, NH4+-N and NO2−-N increased significantly by 60.2–288.2%, while NO3−-N and N2O decreased slightly, compared to the natural tidal creeks. DIC and NO3−-N were the primary components of the total dissolved carbon and inorganic nitrogen in both creek types; however, their proportions decreased as a result of elevated DOC, CO2, CH4, NH4+-N, and NO2−-N following reclamation. Significantly higher global warming potential (0.58 ± 0.15 g CO2-eq m−2 d−1) was found in the reclaimed creeks, making them hotspot of greenhouse effects, compared to the natural tidal creeks. Our results indicated that changes in flow velocity, salinity, Chlorophyll a, and pH were the main factors controlling the dissolved carbon and nitrogen and consequent GHG emissions, due to reclamation. This study is helpful in understanding of carbon and nitrogen sink-source shifts resulting from land use changes in coastal wetlands.

Preservation methods for the isotopic composition of dissolved carbon species in non-ideal conditions.

The stable carbon isotope compositions of dissolved inorganic carbon (δ13CDIC) and dissolved organic carbon (δ13CDOC) are readily affected by post-sampling microbial activity if not adequately preserved. Existing preservation methods require rapid chilling, analysis, and/or toxic chemicals, all challenging to use safely in the field and during remote field seasons. Therefore, a preservation method that is safe but also effective over a range of storage times is needed when sampling waters at very remote sites. Two samples, with different dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations, were filtered with a 0.2-μm filter and preserved with six different methods, mercuric chloride, copper sulfate, phosphoric acid, benzalkonium chloride, zinc chloride, hydrochloric acid, and a filter-only control. These samples were held at 4°C, 22°C, or 35°C. Regular measurement of the DIC and DOC δ13C values were made over the following 60 days for δ13CDIC and 66 days for δ13CDOC. RESULTS: Over the course of the experiment, mercuric chloride, copper sulfate, zinc chloride, and benzalkonium chloride resulted in δ13CDIC fractionation at both 4°C and 22°C. Only filtering to 0.2 μm at the time of collection, with or without acidification with phosphoric acid, resulted in minimal isotopic fractionation at both 4°C and 22°C and over the entirety of the experiment. For δ13CDOC values, only filtering to 0.2 μm minimized fractionation for both bulk and vial storage over 66 days at 22°C. Filtering to 0.2 μm at the time of collection is more effective than the use of toxic chemicals for measuring δ13CDIC and δ13CDOC values. Phosphoric acid is as effective as only filtering for δ13CDIC and may be ideal depending on sampling considerations. These results demonstrate not only that water samples can be preserved for δ13CDIC and δ13CDOC analysis for long periods, but that preservation is best accomplished with non-toxic or low-toxicity methods.

CO2 release to the atmosphere from thermal springs of Sperchios Basin and northern Euboea (Greece): The contribution of “hidden” degassing

Greece is a region characterised by intense geodynamic activity that favours the circulation of hydrothermal fluids in the crust transporting volatiles from either the deep crust or the mantle to the surface. Elevated heat flow values are detectable at Sperchios Basin and North Euboea (central Greece), two areas defined by a system of deeply rooted extensional faults and Quaternary volcanic activity. This setting contributed to the formation of numerous hydrothermal systems, which are mostly expressed as CO2-rich thermal springs with intense bubbling.The CO2 output from six bubbling pools has been determined by flux measurements with the use of the floating chamber method. The highest bubbling CO2 output has been found at Thermopyles and Psoroneria (0.6 and 0.84 t/d, respectively), where the outgoing channels have an elevated flow (>250 l/s) of gas-charged water (>15 mmol/l of CO2). Although no bubbling is noticed along the stream, the CO2 content decreases by an order of magnitude after few hundreds of metres, indicating an intense degassing from the water. Taking into account the water flow and the amount of CO2 lost to the atmosphere, the CO2 output of the outgoing channels is quantified in 12.5 t/d for Thermopyles and 9.23 t/d for Psoroneria. Output estimation has also been made for the other springs of the area. The diffuse CO2 release from the outgoing channels has always been higher respect to that of the visible bubbling, suggesting that most of the degassing is “hidden”. Furthermore, the loss of CO2 from the water has determined a shift in dissolved carbonate species as demonstrated by the pH increase along the channel that led eventually to an oversaturation in carbonate minerals and therefore travertine deposition.The total CO2 output to the atmosphere of the study area is estimated at ~27 t/d, with the major contribution deriving from the degassing along the outflow channels of the thermal springs. Such output is comparable to that of the single active volcanic systems along the South Aegean Active Volcanic Arc and highlights the importance of “hidden” degassing along CO2-oversaturated streams.

Carbon isotopic evolution of aqueous fluids in CM chondrites: Clues from in-situ isotope analyses within calcite grains in Yamato-791198

We report the variability in carbon and oxygen isotopic compositions, chemical compositions, and cathodoluminescence intensities within calcite grains in the Yamato-791198 CM chondrite measured by secondary ion mass spectrometry. To understand the change in carbon isotopic compositions during calcite formation, the carbon isotope-analyses were performed on a series of crystal growth bands of each calcite grain. The crystal growth of calcite grains was inferred from comprehensive analyses of oxygen isotopes, chemical compositions, and cathodoluminescence characteristics.The observed δ18O variations within individual grains are as large as 13‰. The oxygen-isotope data plot on a single straight line with a slope of 0.61 ± 0.06 (2σ) in an oxygen three-isotope diagram. This slope steeper than that of the terrestrial fractionation line indicates that the oxygen isotopic compositions of aqueous fluids evolved from higher δ18O and Δ17O to lower δ18O and Δ17O compositions due to the oxygen-isotope exchange between water and anhydrous silicates in the parent body. Thus, calcite crystals grew from higher Δ17O to lower Δ17O areas. The crystal growth inferred from oxygen isotopic compositions is corroborated by the morphology and cathodoluminescence characteristics of the calcite grains. The minor element concentrations of the calcite grains did not increase/decrease monotonically during calcite formation.The δ13C variations within individual grains are no more than 4‰ except for one grain. The intra-grain δ13C variations observed here are much smaller than inter-grain δ13C variations of ∼80‰ previously reported. These observations indicate that the carbon isotopic compositions of dissolved carbon species did not change during calcite formation and that they were locally heterogeneous which reflects variable proportions of carbon reservoirs with different isotopic compositions.

Large Presence of Carbonic Acid in CO2-Rich Aqueous Fluids under Earth's Mantle Conditions.

The chemistry of carbon in aqueous fluids at extreme pressure and temperature conditions is of great importance to Earth's deep carbon cycle, which substantially affects the carbon budget at Earth's surface and global climate change. At ambient conditions, the concentration of carbonic acid in water is negligible; therefore, aqueous carbonic acid was simply ignored in previous geochemical models. However, by applying extensive ab initio molecular dynamics simulations at pressure and temperature conditions similar to those in Earth's upper mantle, we found that carbonic acid can be the most abundant carbon species in aqueous CO2 solutions at ∼10 GPa and 1000 K. The mole percent of carbonic acid in total dissolved carbon species increases with increasing pressure along an isotherm, while its mole percent decreases with increasing temperature along an isobar. In CO2-rich solutions, we found significant proton transfer between carbonic acid molecules and bicarbonate ions, which may enhance the conductivity of the solutions. The effects of pH buffering by carbonic acid may play an important role in water-rock interactions in Earth's interior. Our findings suggest that carbonic acid is an important carbon carrier in the deep carbon cycle.

Examining the Distribution and Variation of Dissolved Carbon Species and Seasonal Carbon Exports within the Jiulongjiang River Basin (Southeast China)

ABSTRACT Liu, J.; Han, G.; Liu, X.; Yang, K.; Li, X., and Liu, M., 2019. Examining the distribution and variation of dissolved carbon species and seasonal carbon exports within the Jiulongjiang Riv...

Advances in carboxylate collectors adsorption on monazite surface: Part 1 – Assessment of the hydroxylation and carbonation of surface lanthanide ions

The adsorption of carboxylate collectors is largely assumed to be affected by the monazite surface speciation. In order to provide key information for the understanding of this phenomenon, we propose in this study a thermodynamic model for the equilibrium of monazite-(La) crystal in an H2O-CO2 system. This model allows access to the speciation information of the dissolved lattice species. Based on this model, we identify potential chemical reactions that may affect, under certain conditions, lanthanide ions on monazite surface. Since these surface ions have vacant coordination sites, they may react with water molecules and media species to restore their coordination shells. Therefore, it has been suggested that surface lanthanide ions undergo hydroxylation and carbonation reactions under alkaline conditions.X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to analyse synthetic monazite-(La) samples treated in deionised water or sodium carbonate solutions. The spectroscopy results suggest that surface lanthanide ions do tend to hydroxylate under alkaline conditions. Furthermore, under the tested conditions, no significant monazite surface carbonation was observed. These results indicate that surface lanthanide ions have limited affinity for dissolved carbonate species, contrary to what is suggested by the thermodynamic model for free lanthanide ions in the bulk.

Effects of atom substitutions and dissolved carbonate species on monazite electrophoretic mobility

In this study, the atom substitutions that commonly affect the monazite lattice were considered as potential factors affecting the monazite electrophoretic mobility. The influence of light rare earth elements (LREE) substitutions and the presence of thorium, calcium, and silicate within the monazite crystal lattice was also examined using a natural monazite and synthetic cerium, lanthanum and neodymium monazite materials. Electrophoretic mobility measurements performed after treatment in an electrolyte solution equilibrated with air outline that LREE substitutions and other substitutions observed in the tested natural monazite did not affect the mineral surface properties.Conversely, the electrophoretic mobility of the synthetic monazites was found to be significantly affected by the amount of dissolved carbonate species present in the aqueous media. More precisely, carbonate species were found to decrease the electrophoretic mobility of monazite. Unlike tests performed with a solution equilibrated with air, the electrophoretic mobility of monazite treated in a CO2 depleted electrolyte solution, under controlled atmosphere, were found erratic. This highlights the difficulty in obtaining reliable electrophoretic mobility data when the carbonate content in the supporting electrolyte solutions is not controlled.

The B/Ca and Cd/Ca of a subsurface-dwelling foraminifera Pulleniatina obliquiloculata in the tropical Indo-Pacific Ocean: implications for the subsurface carbonate chemistry estimation

Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium (B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive relationship with [B(OH)4-] and the dissolved carbonate species at the apparent calcification depth of P. obliquiloculata. The boron partition coefficients (KD) between P. obliquiloculata B/Ca and seawater [B(OH)4-]/[HCO3-] distribute around 1.1×10-3–1.3×10-3 with a mean value of (1.19±0.12)×10-3, and are significantly related to the nutrient concentration, especially phosphate. The lack of any clear correlation between the P. obliquiloculata B/Ca and seawater carbonate chemical parameters suggests that the physiochemical controls on boron incorporation are masked by the complexity of natural seawater condition. But the significant dependence of KD on nutrient may likely be explained by a nutrient related growth-rate effect. Cd/Ca of P. obliquiloculata shows significant correlation with seawater phosphate concentration, and its partition coefficients (DCd) are significantly related to temperature. A first-principle methodology of P. obliquiloculata B/Ca is applied, with the aid of Cd/Ca as a phosphate proxy and a constraint on KD, to estimating sea water carbonate chemistry (e.g., pH). The results are fairly promising and allow us to propose the possibility to apply the combination of B/Ca and Cd/Ca proxies (and also Mg/Ca and δ18O for estimating temperature and salinity) for the paleoreconstruction of seawater carbonate chemistry.

Time-Dependent Physicochemical Changes of Carbonate Surfaces from SmartWater (Diluted Seawater) Flooding Processes for Improved Oil Recovery.

Over the past few decades, field- and laboratory-scale studies have shown enhancements in oil recovery when reservoirs, which contain high-salinity formation water (FW), are waterflooded with modified-salinity salt water (widely referred to as the low-salinity, dilution, or SmartWater effect for improved oil recovery). In this study, we investigated the time dependence of the physicochemical processes that occur during diluted seawater (i.e., SmartWater) waterflooding processes of specific relevance to carbonate oil reservoirs. We measured the changes to oil/water/rock wettability, surface roughness, and surface chemical composition during SmartWater flooding using 10-fold-diluted seawater under mimicked oil reservoir conditions with calcite and carbonate reservoir rocks. Distinct effects due to SmartWater flooding were observed and found to occur on two different timescales: (1) a rapid (<15 min) increase in the colloidal electrostatic double-layer repulsion between the rock and oil across the SmartWater, leading to a decreased oil/water/rock adhesion energy and thus increased water wetness and (2) slower (>12 h to complete) physicochemical changes of the calcite and carbonate reservoir rock surfaces, including surface roughening via the dissolution of rock and the reprecipitation of dissolved carbonate species after exchanging key ions (Ca2+, Mg2+, CO32-, and SO42- in carbonates) with those in the flooding SmartWater. Our experiments using crude oil from a carbonate reservoir reveal that these reservoir rock surfaces are covered with organic-ionic preadsorbed films (ad-layers), which the SmartWater removes (detaches) as flakes. Removal of the organic-ionic ad-layers by SmartWater flooding enhances oil release from the surfaces, which was found to be critical to increasing the water wetness and significantly improving oil removal from carbonates. Additionally, the increase in water wetness is further enhanced by roughening of the rock surfaces, which decreases the effective contact (interaction) area between the oil and rock interfaces. Furthermore, we found that the rate of these slower physicochemical changes to the carbonate rock surfaces increases with increasing temperature (at least up to an experimental temperature of 75 °C). Our results suggest that the effectiveness of improved oil recovery from SmartWater flooding depends strongly on the formation of the organic-ionic ad-layers. In oil reservoirs where the ad-layer is fully developed and robust, injecting SmartWater would lead to significant removal of the ad-layer and improved oil recovery.

A Kinetic Difference Between 12C‐ and 13C‐Bound Oxygen Exchange Rates Results in Decoupled δ18O and Δ47 Values of Equilibrating DIC Solutions

AbstractAccurate determination of paleotemperatures using carbonate δ18O and Δ47 values rely upon the assumption that the minerals in question formed close to expected isotopic equilibrium with their environment. If there is insufficient time for dissolved carbonate to equilibrate with water between the production of DIC and mineralization, the mineral may preserve a disequilibrated isotopic state. The equilibrium composition and rate of DIC equilibration are related to the temperature, pH, and salinity of the solution, and these have been quantified in previous studies which investigated this via the quantitative precipitation all dissolved carbonate species (∑DIC) as barium carbonate (BaCO3). Here we present a study wherein the equilibration over time of clumped isotopes (Δ47) is investigated at 5, 15, and 25 °C. Results show a significant non–first‐order behavior for this process, which can be explained with a kinetic isotope effect wherein oxygen bound to 12C will exchange more rapidly than oxygen bound to 13C. This difference in equilibration rates is minor, less than 2%; however, it results in Δ47 values paradoxically becoming initially less equilibrated during initial equilibration. The magnitude and direction of this effect is expected to vary depending on the direction from which δ18O values equilibrate, even in circumstances where the initial and final Δ47 values are identical. The implication of this finding is that carbonates which form rapidly can have decoupled δ18O and Δ47 values. This study presents a mathematical framework wherein this behavior can be described accurately to provide a predictive model for describing equilibrating aqueous systems.

Comparison of the burial rate estimation methods of organic and inorganic carbon and quantification of carbon burial in two high Arctic fjords

Summary Quantifying the burial of organic carbon (OC) and inorganic carbon (IC) species in marine sediments contribute to a better understanding of carbon cycle. This is especially important in the Arctic, where carbon deposition is relatively high and expected to change with climate warming. This study aimed to quantify the burial rates of OC and IC in the sediments of two high-latitude fjords – Hornsund and Kongsfjorden (European Arctic). Comparison of the results from three methods quantifying carbon burial in marine sediments was carried out. Sediment cores, pore water, and over-bottom water samples were analyzed for OC and IC. The burial rates were established by considering: carbon deposition to sediments minus carbon return flux, carbon deposited to sediments 80–100 years ago and carbon deposited to sediments recently. The radiolead method was employed for sediment dating. Carbon return flux was obtained using dissolved carbon species concentrations in pore water and over-bottom water. Sediment linear and mass accumulation rates in the fjords were 0.12–0.20 cm y−1 and 1160–2330 g m−2 y−1. The OC burial rates were 19.3–30.3 g OC m−2 y−1 in Hornsund and 5.7–10.0 g OC m−2 y−1 in Kongsfjorden. IC burial was taken as equal to IC deposition and ranged from 10.7 to 20.8 g IC m−2 y−1 in Hornsund and 19.4–45.7 g IC m−2 y−1 in Kongsfjorden. The “return flux” model seems most appropriate for carbon burial rate studies. The data demonstrated that OC burial dominates in Hornsund, while in Kongsfjorden, IC burial is more important.

Volatiles and energy released by Puracé volcano

Total CO2 output of Purace volcano (Colombia) was estimated on the basis of fluids discharged by fumaroles, soil gases, and dissolved carbon species in the aquifer. The soil CO2 emission was computed from a field survey of 512 points of CO2 soil flux measurements at the main degassing areas of Purace volcano. The CO2 flux from Purace’s plume was estimated using an indirect method, that used the SO2 plume flux and CO2/SO2 ratio of the main high temperature fumarole. The total output of CO2 was estimated at ≅ 1500 t/day. The main contribution of CO2 comes from the plume (summit degassing) and from soil degassing that emit 673 and 812 t/day, respectively. The contributions of summit and soil degassing areas are comparable, indicating an intermediate degassing style partitioned between closed and open conduit systems. The estimated water vapor discharge (as derived from the chemical composition of the fumaroles, the H2O/CO2 ratio, and the SO2 plume flux) allowed calculation of the total thermal energy (fumarolic, soil degassing, and aquifer) released from the Purace volcanic system. This was 360 MW.

Fractionation processes affecting the stable carbon isotope signature of thermal waters from hydrothermal/volcanic systems: The examples of Campi Flegrei and Vulcano Island (southern Italy)

The carbon isotopic composition of dissolved C-bearing species is a powerful tool to discriminate the origin of carbon in thermal waters from volcanic and hydrothermal systems. However, the δ13C values of dissolved CO2 and TDIC (Total Dissolved Inorganic Carbon) are often different with respect to the isotopic signature that characterizes the potential carbon primary sources, i.e. deep hydrothermal reservoirs, magmatic gases and organic activity. The most commonly invoked explanation for such isotopic values is related to mixing processes between deep and shallow end-members. Nevertheless, experimental and empirical investigations demonstrated that isotopic fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to reproduce the measured isotopic values. In this paper, we investigated the chemistry of thermal waters, collected at Campi Flegrei and Vulcano Island (southern Italy), whose origin is related to interaction processes among magmatic gases, meteoric water, seawater and hosting rocks. A special focus was dedicated to the δ13C values of dissolved CO2 (δ13CCO2(aq)) and total dissolved inorganic carbon (δ13CTDIC). The δ13CCO2(aq) and δ13CTDIC values in the water samples from both these systems ranged from (i) those measured in fumarolic gases, likely directly related to the deep hydrothermal-magmatic reservoir, and (ii) those typically characterizing biogenic CO2, i.e. produced by microbially-driven degradation of organic matter. A simple mixing model of the two end-members, apparently explaining these intermediate carbon isotopic values, contrasts with the chemical composition of the dissolved gases. On the contrary, isotopic fractionation due to secondary processes, such as calcite precipitation, affecting hydrothermal fluids during their underground circulation, seems to exhaustively justify both the chemical and isotopic data. If not recognized, these processes, which frequently occur in volcanic and hydrothermal systems, may lead to an erroneous interpretation of the carbon source, causing an underestimation of the contribution of the hydrothermal/magmatic fluids to the dissolved carbon species. These results pose extreme caution in the interpretation of intermediate δ13CCO2(aq) and δ13CTDIC values for the assessment of the carbon budget of hydrothermal-volcanic systems.

The CO2 flux from hydrothermal systems of the Karymsky volcanic Centre, Kamchatka

The CO2 flux provided by the hydrothermal activity within the Karymsky Volcanic Centre, Kamchatka, was measured, and the CO2 balance of the Karymsky caldera lake was estimated in the framework of a Deep Carbon Observatory (DCO) project. The Karymsky Volcanic Centre located in the SE of the Kamchatka Peninsula, in the middle of the modern volcanic front, consists of two calderas, hosts a caldera lake and is characterized by hydrothermal activity that is manifested at several thermal fields. Within the Akademii Nauk (AN) caldera which is filled by a caldera lake, the Akademii Nauk springs discharge boiling water into the lake. The lake is drained by the Karymsky River that then crosses the caldera of the Karymsky volcano (Karymsky caldera) and drains the thermal field of CO2-rich Karymsky springs. The lake after the 1996 sublimnic eruption is in a steady-state condition with the total dynamic CO2 budget of about 4t/day, and has a total amount of CO2 stored inside of the lake of around 8000t. The thermal springs of the Karymsky caldera drained by the Karymsky River enrich the river in dissolved carbon species. A total CO2 output of 320t/day from both Karymsky Centre calderas was estimated, carrying around 130t/day carbon species (expressed as CO2) as dissolved species (HCO3 and CO2(aq)), and emitting to the atmosphere around 190t/day of CO2 as the diffusion flux from the soil and bubbling emanations from the springs.