Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland

We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO₂) and hydrogen sulfide (H₂S) from Hengill volcanic system, Iceland. Soil CO₂ and H₂S efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722?g?m^?2?day^?1, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO₂ degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW?CNNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H₂S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO₂ efflux and soil temperatures were also measured. The total diffuse CO₂ emission estimated for this volcanic system was about 1,526?±?160?t?day^?1 of which 453?t?day^?1 (29.7?%) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO₂ output, we used the average H₂O/CO₂ mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4?C240.2) as a representative value of the H₂O/CO₂ mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154?t?day^?1. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07?×?10¹⁴?J?day^?1 or to a total heat flow of 1,237?MW_t.     

A reassessment of current volcanic emissions from the Central American arc with specific examples from Nicaragua

The Central American volcanic arc supplies a significant proportion of the persistent annual global sulphur dioxide emissions from volcanoes. In November/December 2003, we completed a survey of the arc section from Mombacho to San Cristóbal in Nicaragua recording individual mean fluxes of 800, 530 and 220 Mg day^− 1 in the plumes from San Cristóbal, Telica and Masaya, respectively. An assessment of fluxes published since 1997 along the entire Central America arc yields a mean total arc flux of SO₂ of 4360 Mg day^− 1 or 8–16% of the annual estimated global volcanic SO₂ flux to the troposphere. New field data shows that Masaya volcano continues to show stable HCl/SO₂ and HF/SO₂ ratios, suggesting a sustained flux of these components of ∼ 220 and 30 Mg day^− 1, respectively (1997 to 2004). Masaya's plume composition also appears to have been stable, between 2001 and 2003, with respect to all the particulate species measured, with significant fluxes of SO₄²⁻ (4 Mg day^− 1), Na⁺ (0.9–1.3 Mg day^− 1) and K⁺ (0.7 Mg day^− 1). Extrapolating the Masaya plume species ratios to the entire Central American arc gives mean HCl and HF fluxes of 1300 and 170 Mg day^− 1 and a particulate sulphate flux of 40 Mg day^− 1 for 1997 to 2004, although without further understanding of the degassing processes and sources at depth of these different volatiles, these arc-scale estimates should be treated with caution. Combining our arc scale mean SO₂ flux with published measurements of volcanic gas compositions with respect to CO₂ and H₂O allows us to estimate mean CO₂ fluxes of 4400–9600 Mg day^− 1 and H₂O fluxes of 70,000–78,000 Mg day^− 1 for the arc. Preliminary comparisons of these estimates of outgassing rates with published volatile input fluxes into the Central American subduction zone, suggest that Cl is more efficiently recycled through the subduction zone than CO₂. The results for H₂O are inconclusive.     

Carbon isotopes in the rivers from the Lesser Antilles: origin of the carbonic acid consumed by weathering reactions in the Lesser Antilles

In this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO₂) involved in the neutralization reactions during water–rock interactions. The δ¹³C data span a large range of variations, from –19‰ to –5 · 2‰ for DIC (dissolved inorganic carbon) concentrations ranging from 11 μM to 2000 μM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO₂ (enriched in heavy carbon (δ¹³C ≈ –3 · 5‰) and biogenic CO₂ produced in soils (enriched in light carbon (δ¹³C < –17‰)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO₂ consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first‐order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO₂, either under hydrothermal (hot) or surficial (cold) weathering regimes. This study shows that the contribution of magmatic CO₂ to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO₂ to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone. Copyright © 2013 John Wiley & Sons, Ltd.     

Carbon isotopic compositions of organic matter across continental Cretaceous–Tertiary (K–T) boundary sections: Implications for paleoenvironment after the K–T impact event

To assess the environmental perturbation induced by the impact event that marks the Cretaceous–Tertiary (K–T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K–T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record δ¹³C values of plant-derived organic matter, reflecting the δ¹³C value of atmospheric CO₂, whereas siliceous sedimentary rocks record the δ¹³C values of organic matter derived from plants and microbiota. The microbiota δ¹³C value reflects not only the δ¹³C value of atmospheric CO₂, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds.Across the freshwater K–T boundary at Brownie Butte, the δ¹³C values decrease by 2.6‰ (from − 26.15‰ below the boundary clay to − 28.78‰ above the boundary clay), similar to the trend in carbonate at marine K–T sites. This means that the organic δ¹³C values reflect the variation of δ¹³C of atmospheric CO₂, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in δ¹³C values is observed across the K–T boundary at Dogie Creek (from − 25.32‰ below the boundary clay to − 26.11‰ above the boundary clay), the degree of δ¹³C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate.About 2‰ decrease in δ¹³C of atmospheric CO₂ was expected from the δ¹³C variation of marine carbonate at the K–T boundary. This δ¹³C-decrease of atmospheric CO₂ should affect the δ¹³C values of organic matter derived from plant tissue. As such a decrease in δ¹³C value was not observed at Dogie Creek, a process that compensates the δ¹³C-decrease of atmospheric CO₂ should be involved. For example, the enhanced contribution of ¹³C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The δ¹³C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO₃⁻ becomes an important carbon source, as well as dissolved CO₂. As the δ¹³C-decrease of atmospheric CO₂ reflected a reduction of marine productivity, the compensation of the δ¹³C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment.A distinct positive δ¹³C excursion of 2‰ in the K–T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K–T boundary clays include ¹³C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K–T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K–T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10 yr) respond to the impact-related environmental perturbations.     

Diffuse Emission of CO2 from Showa-Shinzan, Hokkaido, Japan: A Sign of Volcanic Dome Degassing

Two soil CO₂ efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO₂ degassing and estimate the total CO₂ output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO₂ efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO₂ efflux data showed a wide range of values up to 552 g m^-2 d^-1. Carbon isotope signatures of the soil CO₂ ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO₂ efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m^-2 d^-1, respectively). The spatial distribution of CO₂ efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan. The total diffuse CO₂ output of Showa-Shinzan was estimated to be about 14.0–15.6 t d^-1 of CO₂ for an area of 0.53 km².     

Anomalous Diffuse CO2 Emissions at the Masaya Volcano (Nicaragua) Related to Seismic-Volcanic Unrest

Anomalous changes in the diffuse emission of carbon dioxide within the Masaya caldera have been observed before two seismic events that occurred at 10 and 30 km from the observation site. Their epicenters are located, respectively, south of Managua in Las Colinas (4.3 magnitude) and the Xiloa caldera (3.6 magnitude), in 2002 and 2003, recorded by the geochemical station located at El Comalito, Masaya volcano (Nicaragua). Anomalous increases were observed, which occurred around 50 and 8 days before the main seismic event that took place in Las Colinas, and 4 days before the seismic swarm at the Xiloa caldera, with a maximum CO₂ efflux of 9.3 and 10.7 kg m^?2 day^?1, respectively. The anomalous CO₂ efflux increases remained after filtering with multiple regression analysis was applied to the CO₂ efflux time series, which indicated that atmospheric variables, during the first 4 months, explained 23 % CO₂ variability, whereas, during the rest of the time series, CO₂ efflux values are poorly controlled with only 6 %. The observed anomalies of the diffuse CO₂ emission rate might be related to pressure changes within the volcanic–hydrothermal system and/or to geostructural changes in the crust due to stress/strain changes caused before and during the earthquakes’ formation, and seem not to be related to the activity of the main crater of Masaya volcano.     

Spatial and temporal variations of pCO2, dissolved inorganic carbon and stable isotopes along a temperate karstic watercourse

This study investigated CO₂ degassing and related carbon isotope fractionation effects in the Wiesent River that drains a catchment in the karst terrain of the Franconian Alb, Southern Germany. The river was investigated by physico‐chemical and stable isotope analyses of water and dissolved inorganic carbon during all seasons along 65‐km long downstream transects between source and mouth. Calculated pCO₂ values at the source were 21 400 ± 2400 µatm. The pCO₂ rapidly decreased in the river water and dropped to an average of 1240 ± 330 µatm near the mouth. About 90% of this decrease occurred within the first 6 km of the river. The river was supersaturated with respect to CO₂ over its entire course and must have acted as a continuous year‐round CO₂ source to the atmosphere. The average CO₂ flux from the karst river was estimated with 450 mmol m^?2 day^?1 with higher fluxes up to 5680 mmol m^?2 day^?1 at the source. At the source, δ¹³C_DIC values showed no seasonal variations with an average of ?14.2 ± 0.2‰. This indicated that groundwater retained high pCO₂ mainly from soil CO₂. The contribution of soil CO₂ to dissolved inorganic carbon was estimated at 65% to 72%. The downstream CO₂ loss caused a positive shift in δ¹³C_DIC values of 2‰ between source and mouth because of the preferential loss of the ¹²C isotope during degassing. Considering the findings of this study and the fact that carbonate lithology covers a significant part of the earth's surface, CO₂ evasion from karst regions might contribute notably to the annual carbon dioxide release from global freshwater systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Correlations between13C and ΣCO2 in surface waters and atmospheric CO2

¹³C and ΣCO₂ data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ¹³C of the ΣCO₂ in the deep water (～3000m) decreases from 1.7‰ in the North Atlantic to ?0.10‰ in the North Pacific. This change is attributed to the addition of about 158 μmoles of CO₂ per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO₂, while the remainder is attributed to dissolution of calcium carbonate.The δ¹³C of the dissolved CO₂ in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO₂ at a mean temperature of 16°C. The δ¹³C and ΣCO₂ values of Antarctic surface water samples suggest that these waters are derived from a mixture of North Atlantic deep water and equilibrated surface water.     

Mantle-derived carbon in Hercynian granites. Stable isotopes signatures and C/He associations in the thermomineral waters,N-Portugal

Na–HCO₃–CO₂-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO₂-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO₂-rich waters. The δ²H and δ¹⁸O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO₂ (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO₂ inorganic origin for the gas. δ¹³C_CO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO₂. Such an assumption is supported by the ³He/⁴He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression).     

The hydrothermal system of Mendeleev Volcano,Kunashir Island,Kuril Islands: The geochemistry and the transport of magmatic components

This paper reports a detailed geochemical study of thermal occurrences as observed in the edifice and on the flanks of Mendeleev Volcano, Kunashir Island in August and September 2015. We showed that three main types of thermal water are discharged there (neutral chloride sodium, acid chloride sulfate, and acid sulfate types); these waters exhibit a zonality that is typical of volcano-hydrothermal island arc systems. Spontaneous and solfataric gases have relatively low ³He/⁴He ratios, ranging between 5.4Ra and 5.6Ra, and δ¹³C-CO₂ between –4.8‰ and –3.1‰, and contain a light isotope of carbon in methane (δ¹³C ≈ –40‰). Gas and isotope geothermometers yield relatively low temperatures around 200°C. The isotope compositions in all types of water are similar to that of local meteoric water. The distribution of microcomponents varies among different types. The isotope composition of dissolved Sr varies considerably, from 0.7034 as observed in Kunashir rocks on an average to 0.7052 in coastal springs, which may have resulted from admixtures of seawater. The total hydrothermal transport rates of magmatic Cl and SO₄, as observed for Mendeleev Volcano, are 7.8 t/d and 11.6 t/d, respectively. The natural outward transport of heat by the volcano’s hydrothermal system is estimated as 21 MW.     

Evaluation of the carbon isotopic effects of NDIR and CRDS analyzers on atmospheric CO2 measurements

Non-dispersive infrared(NDIR) and cavity ring-down spectroscopy(CRDS) CO_2 analyzers use 12CO_2 isotopologue absorption lines and are insensitive to all or part of other CO_2-related isotopologues. This may produce biases in CO_2 mole fraction measurements of a sample if its carbon isotopic composition deviates from that of the standard gases being used. To evaluate and compare the effects of carbon isotopic composition on NDIR and CRDS CO_2 analyzers, we prepared three test sample air cylinders with varying carbon isotopic abundances and calibrated them against five standard cylinders with ambient carbon isotopic composition using CRDS and NDIR systems. We found that the CO_2 mole fractions of the sample cylinders measured by G1301(CRDS) were in good agreement with those measured by Lo Flo(NDIR). The CO_2 values measured by both instruments were higher than that of a CO_2 isotope measured by G2201i(CRDS) analyzer for a test cylinder with depleted carbon isotopic composition δ~(13)C =-36.828‰, whereas no obvious difference was found for other two test cylinders with δ~(13)C=-8.630‰ and δ~(13)C=-15.380‰, respectively. According to the theoretical and experimental results, we concluded that the total CO_2 mole fractions of samples with depleted isotopic compositions can be corrected on the basis of their 12CO_2 values calibrated by standard gases using Lo Flo and G1301 if the δ~(13)C and δ18O values are known.     

Anomalous Diffuse CO2 Emission prior to the January 2002 Short-term Unrest at San Miguel Volcano, El Salvador, Central America

On January 16, 2002, short-term unrest occurred at San Miguel volcano. A gas-and-steamash plume rose a few hundred meters above the summit crater. An anomalous microseismicity pattern, about 75 events between 7:30 and 10:30 hours, was also observed. Continuous monitoring of CO₂ efflux on the volcano started on November 24, 2001, in the attempt to provide a multidisciplinary approach for its volcanic surveillance. The background mean of the diffuse CO₂ emission is about 16 g m^-2 d^-1, but a 17- fold increase, up to 270 g m^-2 d^-1, was detected on January 7, nine days before the January 2002 short-term unrest at San Miguel volcano. These observed anomalous changes on diffuse CO₂ degassing could be related to either a sharp increase of CO₂ pressure within the volcanic-hydrothermal system or degassing from an uprising fresh gas-rich magma within the shallow plumbing system of the volcano since meteorological fluctuations cannot explain this observed increase of diffuse CO₂ emission.     

Differences in stable isotope compositions of freshwater snails from surface sediments of two Polish shallow lakes

The study reports and discusses the differences in δ¹³C and δ¹⁸O values of shells between several species of freshwater snails. Shells were derived from sediment samples collected from depths of 0.5, 1, 2 and 3 m along transects in two shallow eutrophic lakes located in mid-western Poland. Mean δ¹³C values of the shells ranged between −7.5 and −3.8‰ in Lake Jarosławieckie and between −8.1 and −5.2‰ in Lake Rosnowskie Duże, whereas mean δ¹⁸O values ranged between −2.2 and −0.2‰ and between −2.2 and 0.4‰ respectively in the studied lakes. A similar order of species in terms of shell isotope values, from least to most ¹³C and ¹⁸O-depleted was observed in both lakes and seems to indicate constancy of the factors controlling the stable isotope compositions of snail shells. We postulate that the nearly 4‰ difference in the mean carbon stable isotope values between the species was primarily controlled by the amount of metabolic carbon incorporated into the shells and the δ¹³C values of the snail food. Different growth cessation temperatures and microhabitats of the species studied result in temporally and spatially varied DIC δ¹³C values, water δ¹⁸O values and water temperature of shell precipitation, and may thus differentiate the δ¹³C and δ¹⁸O values of shells. The range of δ¹³C and δ¹⁸O values of individual shells from a sediment sample (mean 2.35 and 2.15‰, respectively) is interpreted as reflecting an intraspecific variability of isotope compositions in shells from a population and changes of the ambient conditions during the accumulation of the sediment layer. The species-specificity and intraspecific variability in C and O isotopic compositions of shells allow concluding that in palaeolimnological studies, stable isotope analyses should be performed on a set of mono-specific shells representing mean isotope compositions of the species for the interval studied rather than single shells or multispecific bulk shell material.     

Soil CO2 flux baseline in an urban monogenetic volcanic field: the Auckland Volcanic Field, New Zealand

The Auckland Volcanic Field (AVF) is a dormant monogenetic basaltic field located in Auckland, New Zealand. Though soil gas CO₂ fluxes are routinely used to monitor volcanic regions, there have been no published studies of soil CO₂ flux or soil gas CO₂ concentrations in the AVF to date or many other monogenetic fields worldwide. We measured soil gas CO₂ fluxes and soil gas CO₂ concentrations in 2010 and 2012 in varying settings, seasons, and times of day to establish a baseline soil CO₂ flux and to determine the major sources of and controlling influences on Auckland's soil CO₂ flux. Soil CO₂ flux measurements varied from 0 to 203 g m^?2 day^?1, with an average of 27.1 g m^?2 day^?1. Higher fluxes were attributed to varying land use properties (e.g., landfill). Using a graphical statistical approach, two populations of CO₂ fluxes were identified. Isotope analyses of δ¹³CO₂ confirmed that the source of CO₂ in the AVF is biogenic with no volcanic component. These data may be used to assist with eruption forecasting in the event of precursory activity in the AVF, and highlight the importance of knowing land use history when assessing soil gas CO₂ fluxes in urban environments.     

Dissolved inorganic carbon isotopes of a typical alpine river on the Tibetan Plateau revealing carbon sources,wetland effect and river recharge

The Nyangqu River, the largest right bank tributary of the Yarlung Zangbo River in the Qinghai–Tibet Plateau, was representative of an alpine riverine carbon cycle experiencing climate change. In this study, dissolved inorganic carbon (DIC) spatial and seasonal variations, as well as their carbon isotopic compositions (δ¹³C_DIC) in river water and groundwater were systematically investigated to provide constraints on DIC sources, recharge and cycling. Significant changes in the δ¹³C_DIC values (from −2.9‰ to −23.4‰) of the water samples were considered to be the result of different contributions of two dominant DIC origins: soil CO₂ dissolution and carbonate weathering. Three types of rock weathering (dissolution of carbonate minerals by H₂CO₃ and H₂SO₄, and silicate dissolution by H₂CO₃) were found to control the DIC input into the riverine system. In DIC cycling, groundwater played a significant role in delivering DIC to the surface water, and DIC supply from tributaries to the main stream increased from the dry season to the wet season. Notably, the depleted δ¹³C_DIC ‘peak’ around the 88.9° longitude, especially in the September groundwater samples, indicated the presence of ‘special’ DIC, which was attributed to the oxidation of methane from the Jiangsa wetland located nearby. This wetland could provide large amounts of soil organic matter available for bacterial degradation, producing ¹³C-depleted methane. Our study provided insights regarding the role of wetlands in riverine carbon cycles and highlighted the contribution of groundwater to alpine riverine DIC cycles.     

Spatiotemporal variations of dissolved inorganic carbon and controlling factors in a small karstic catchment,Southwestern China

Dissolved inorganic carbon (DIC) is the most important carbon component in karst aquatic system where fluid is highly transmissive, but has rarely been examined in the subtropical karst critical zone (K-CZ). In this study, concentrations of dissolved solutes and isotopic compositions of DIC (δ¹³C_DIC) at 11 sites of a 73.4 km² karstic catchment in Southwestern China were analysed monthly in order to uncover the spatiotemporal variations of both DIC and its dominant sources, and to identify relevant controlling factors. Both DIC concentrations and δ¹³C_DIC were highly variable, ranging from 2.52 to 5.85 mmol l⁻¹ and from −15.7 to −4.5‰, respectively. DIC in underground water (UGW) was higher in concentration and more depleted in ¹³C compared to surface water (SFS). DIC concentrations showed an inconsistent seasonal trend with other solutes, with higher values in the wet season at some sites. δ¹³C_DIC values were lower in the wet season than in the dry season. The results of mixing model IsoSource revealed spatiotemporal patterns of DIC sources. During the dry season, carbonate weathering was the primary contributor to DIC in UGW (excluding in the middle reaches). However, during the wet season, soil CO₂ was the dominant source of DIC in both UGW and SFS, and it was higher than in the dry season. Overall, there are significant spatiotemporal disparities and highly transmissive characteristics of both DIC and its sources in the K-CZ, which are controlled by multiple factors. This study also highlights that rainfall may play a crucial role in accelerating carbon dynamics in the K-CZ. High-frequency sampling campaigns in high-flow periods and deep analyses are needed in future work to elucidate the related processes and mechanisms. © 2019 John Wiley & Sons, Ltd.     

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.     

Fumarole/plume and diffuse CO2 emission from Sierra Negra caldera, Galapagos archipelago

Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO₂ emission of 11?±?2?t day^?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H₂S/SO₂, CO₂/SO₂, and H₂O/SO₂ molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H₂O, CO₂, and H₂S emission rates were 562, 394, and 3?t day^?1, respectively. The total output of diffuse CO₂ emissions from the summit of Sierra Negra volcano was 990?±?85?t day^?1, with 605?t day^?1 being released by a deep source. The diffuse-to-plume CO₂ emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H₂O; the main noncondensable components amounted to 97.4?mol% CO₂, 1.5?mol% SO₂, 0.6?mol% H₂S, and 0.35?mol%?N₂. The higher H₂S/SO₂ ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. ³He/⁴He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25?R _A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively.     

Classification and origin of natural gases from Lishui Sag,the East China Sea Basin

Natural gases discovered up to now in Lishui Sag, the East China Sea Basin, differ greatly in gaseous compositions, of which hydrocarbon gases amount to 2%–94% while non-hydrocarbon gases are dominated by CO₂. Their hydrocarbon gases, without exception, contain less than 90% of methane and over 10% of C₂ ⁺ heavier hydrocarbons, indicating a wet gas. Carbon isotopic analyses on these hydrocarbon gases showed that δ ¹³C₁, δ ¹³C₂ and δ ¹³C₃ are basically lighter than −44‰, −29‰ and −26‰, respectively. The difference in carbon isotopic values between methane and ethane is great, suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation. δ ¹³ \( C_{CO_2 } \) values of nonhydrocarbon gases are all heavier than −10‰, indicating a typical abiogenic gas. The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit, consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter. Moreover, δ ¹³C₁ values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰ heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit while δ ¹³C₂ and δ ¹³C₃ values of the former are over 9‰ heavier than those of the latter. Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag, where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter, therefore, natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.

     

Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece

The chemical and isotopic compositions (δD_H2O, δ¹⁸O_H2O, δ¹⁸O_CO2, δ¹³C_CO2, δ³⁴S, and He/N₂ and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ¹⁸O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H₂–Ar, H₂–N₂, and H₂–H₂O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H₂O–H₂–CO₂–CO–CH₄ system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.