Controls on dissolved inorganic carbon and δC in cave waters from DeSoto Caverns: Implications for speleothem δC assessments

Unraveling the factors controlling the carbon chemistry and transport of carbon within extant karst systems has important implications concerning the assessment of time-series δ¹³C records of speleothems. Here we report the results of a 3-year study of total dissolved inorganic carbon [DIC] and δ¹³C_DIC from cave waters at DeSoto Caverns (Southeastern USA) that offer valuable insight on carbon transport and the accompanied isotope fractionations from end-member sources to speleothems.[DIC] and δ¹³C_DIC values of cave waters range from 0.2 to 6.0 mM and 2.7 to −12.9 (‰ VPDB), respectively. [DIC] and δ¹³C_DIC of “seasonal drips” show seasonal, albeit noisy, variability and are inversely related (δ¹³C_DIC = −2.49[DIC] + 0.64, r² = 0.84). A shallow pool fed by multiple drips shows a bimodal δ¹³C_DIC distribution with an isotopically heavier mode during winter (−4‰ to −5‰ VPDB) relative to summer months (−9‰ to −10‰ VPDB). A multi-year trend of decreasing water availability during the study period is not reflected in a response of cave water carbon chemistry suggesting that rainfall amount may not be a significant controlling factor of the carbon chemistry. Coupled cave air winter ventilation/summer stagnation and varying CO₂ fluxes through the soil horizon and epikarst exert the strongest influence on seasonal [DIC] and δ¹³C_DIC variability. Measured values of high [DIC] and low δ¹³C_DIC from cave waters collected during the summer/early fall closely approximate isotopic equilibrium conditions. Conversely, low [DIC] and high δ¹³C_DIC values during winter/early months indicate kinetically enhanced isotopic fractionations within the cave waters. The kinetically enhanced isotopic fractionation of partitioned between degassed CO₂ and precipitated CaCO₃(1000lnα_{[(CO2-HCO3)+(CaCO3(AR)-HCO3)]/2}) is greater by about a factor of two (−6.7 ± 0.3‰) relative to the same isotopic fractionation under equilibrium conditions (−3.1‰).On the basis of ¹⁴C mass balance and paired ¹⁴C-U/Th measurements we estimate that on average about ∼23% of C delivered annually by the drips to the aragonite stalagmites is derived from ¹⁴C-dead dolomite cap while the remainder of ∼77% is derived from ¹⁴C-live biomass. δ¹³C measurements of aragonite (n = 12) sampled from the tips of active speleothems during the summer months are consistent with theoretical aragonite δ¹³C values calculated using the shallow pool summer/early fall data thus confirming the δ¹³C seasonality in both drips and coeval aragonite. δ¹³C values of an active stalagmite section spanning the last 200 years show a normal distribution with a mean of −7.1 ± 1.2‰ (n = 81) and a mode of −7‰ to −8‰ that are statistically indistinguishable from the annual mean and mode of all dripwaters. Thus secular time-series δ¹³C records of stalagmites at DeSoto Caverns with resolving power >10⁻¹ year will likely carry the imprints of drip annual means that record climate-driven δ¹³C seasonal biases.     

Phases of the Fe–C–N system as hosts of mantle carbon and nitrogen: Experimental studies at 7.8 GPa and 1350°C

Parts of the Fe–C–N system were studied in experiments at 7.8 GPa and 1350°C. It was shown that the admixture of nitrogen extends considerably the domain of melt stability in the system at temperatures close to the Fe–Fe₃C eutectic temperatures. Nitrogen solubility in cementite in equilibrium with the nitrogen- rich melt is below the detection limit of the EMPA technique applied. The metal melt is the only nitrogen concentrator (up to 4 wt % of N) in the range of compositions considered. The data obtained permit the conclusion that, in the case of complete dissolution of carbon and nitrogen, which might occur in the enriched mantle, native iron at ~250 km depth should either be completely molten or consist of a melt and carbide of iron.     

Ordovician-Silurian Boundary Extinction and Its Relationship to Iridium and carbon Isotope Anomalies

The abundance distributions of more than 40 elements in the No. 502 Ordovician-Silurian (O/S) bounda-ry section at Fenxiang, Yichang have been studied by RNAA and INAA. The results show that in the bounda-ry bed, there is a distinctive Ir anomaly because the Ir concentration abruptly increases to 0.64 ppb.Furthermore, the Ir is positively correlated in abundance variation with some siderophile and sulphophile ele-ments. In the same bed of the O/S boundary section at Huanghuachang, Yichang, there is also a δ~(13)C excur-sion. These geochemical signs support the hypothesis that the terminal Ordovician mass extinction was proba-bly related to extraterrestrial event, and provide new evidence for defining the O/S boundary between theHirnantia-Kinnella and G. persculptus Zones.     

Terrestrial carbon sequestration in southeast and south-central United States

Analyses of regional carbon sources and sinks are essential technologies in mitigating the accumulation of CO2 in the for assessing the economical feasibility of various carbon sequestration atmosphere and in preventing global warming. Such an inventory is a prerequisite for the regional trading of CO2 emission. As a U.S. Department of Energy Southeast Regional Carbon Sequestration Partner, we have estimated the state-level terrestrial carbon pools in the southeast and south-central US, and have projected the potential for terrestrial carbon sequestration in the region. This region includes： Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas, and Virginia. The total terrestrial carbon storage in southeast and south-central US （11 states） was estimated to be 21.1 Pg C. Total annual terrestrial carbon sink in the region was calculated to be 189.1 Tg C/a. Of the various carbon sinks, the annual forest carbon sink （estimated as 76 Tg C g/a） could compensate for 13% of the total annual greenhouse gas emission in the region in the early 1990s. Through proper policies and the use of best management practices, a further 9.3% of the total greenhouse gas emission could be offset by terrestrial sequestration （53.9 Tg C/a）.     

Stable nitrogen and carbon isotope (δN and δC) variability in shallow tropical Pacific soft coral and black coral taxa and implications for paleoceanographic reconstructions

Soft corals and black corals are useful proxy tools for paleoceanographic reconstructions. However, most work has focused on deep-water taxa and few studies have used these corals as proxy organisms in shallow water (<200 m). To facilitate the use of stable nitrogen and carbon isotope (δ¹⁵N and δ¹³C) records from shallow-water soft coral and black coral taxa for paleoceanographic reconstructions, quantification of the inherent variability in skeletal isotope values between sites, across depth, and among taxa is needed. Here, skeletal δ¹⁵N and δ¹³C values were measured in multiple colonies from eleven genera of soft corals and two genera of black corals from across a depth transect (5-105 m) at two sites in Palau located in the tropical western Pacific Ocean. Overall, no difference in skeletal δ¹⁵N and δ¹³C values between sites was present. Skeletal δ¹⁵N values significantly increased and δ¹³C values decreased with depth. This is consistent with changes in isotope values of suspended particulate organic matter (POM) across the photic zone, suggesting that the primary food source to these corals is suspended POM and that the stable isotopic composition of POM controls the skeletal isotopic composition of these corals. Thus, to compare the isotope records of corals collected across a depth range in the photic zone, first order depth corrections of −0.013‰ m⁻¹ and +0.023‰ m⁻¹ are recommended for δ¹⁵N and δ¹³C, respectively. Average depth-corrected δ¹⁵N values were similar between black corals and soft corals, indicating that corals in these orders feed at a similar trophic level. In contrast, average depth-corrected δ¹³C values of black corals were significantly lower than that of soft corals, potentially resulting from metabolic processes associated with differing skeletal compositions among the orders (i.e., gorgonin vs. chitin based). Thus, a correction of +1.0‰ is recommended for black corals when comparing their δ¹³C-based proxy records to soft corals. After correcting for both the depth and order effects, variability in δ¹⁵N values among corals within each genera was low (standard deviation (SD) of the mean <±0.5‰), with the exception of Acanthorgorgia. The calculated SD of <±0.5‰ provides a first order guideline for the amount of variability that could be expected in a δ¹⁵N record, and suggests that these corals may be useful for δ¹⁵N-based paleoceanographic reconstructions. Variability in δ¹³C values among corals within genera was also low (standard deviation of the mean <±0.5‰) with the exception of Rhipidipathes and Villogorgia. Similar to δ¹⁵N, records from the genera studied here with the exception of Rhipidipathes and Villogorgia may be useful for δ¹³C-based paleoceanographic reconstructions. Overall, using the recommendations developed here, stable isotope records from multiple sites, depths and taxa of these corals can be more rigorously compared.     

The Fe–C–O–H–N system at 6.3–7.8 GPa and 1200–1400 °C: implications for deep carbon and nitrogen cycles

Interactions in a Fe–C–O–H–N system that controls the mobility of siderophile nitrogen and carbon in the Fe⁰-saturated upper mantle are investigated in experiments at 6.3–7.8 GPa and 1200–1400 °C. The results show that the γ-Fe and metal melt phases equilibrated with the fluid in a system unsaturated with carbon and nitrogen are stable at 1300 °C. The interactions of Fe₃C with an N-rich fluid in a graphite-saturated system produce the ε-Fe₃N phase (space group P6₃/mmc or P6₃22) at subsolidus conditions of 1200–1300 °C, while N-rich melts form at 1400 °C. At IW- and MMO-buffered hydrogen fugacity (fH₂), fluids vary from NH₃- to H₂O-rich compositions (NH₃/N₂?>?1 in all cases) with relatively high contents of alkanes. The fluid derived from N-poor samples contains less H₂O and more carbon which mainly reside in oxygenated hydrocarbons, i.e., alcohols and esters at MMO-buffered fH₂ and carboxylic acids at unbuffered fH₂ conditions. In unbuffered conditions, N₂ is the principal nitrogen host (NH₃/N₂?≤?0.1) in the fluid equilibrated with the metal phase. Relatively C- and N-rich fluids in equilibrium with the metal phase (γ-Fe, melt, or Fe₃N) are stable at the upper mantle pressures and temperatures. According to our estimates, the metal/fluid partition coefficient of nitrogen is higher than that of carbon. Thus, nitrogen has a greater affinity for iron than carbon. The general inference is that reduced fluids can successfully transport volatiles from the metal-saturated mantle to metal-free shallow mantle domains. However, nitrogen has a higher affinity for iron and selectively accumulates in the metal phase, while highly mobile carbon resides in the fluid phase. This may be a controlling mechanism of the deep carbon and nitrogen cycles.     

Adsorption and stabilization of organic carbon by mineral surfaces in soils

Soils are the largest carbon reservoir in the terrestrial system. Soils contain about three times more carbon than vegetation and twice as much as that present in the atmosphere. Soil organic matter （SOM） is very complex in composition and structure, formed of heterogeneous substances and generally associated with minerals in soils. SOM is classified as labile and stable fractions on the basis of residence time, determined not only by the chemical composition of SOM, but also by types of protection or bonds within soils. The stable carbon fraction is protected either physically or chemically. To understand the process of SOM stabilization, physicochemical properties of organic-mineral complexes were determined by Fourier transformed infrared （FTIR） with attenuated total reflectance （ATR） and diffuse reflectance （DRIFT）, atomic force microscopy （AFM）, and nuclear magnetic spectroscopy （NMR）. Humic acids and carboxylic acids with relatively short carbon chains were used as sorbates, and goethite, kaolinite, and montmorillonite as adsorbents. Humic acid was fractionated during adsorption on the minerals, which was highly influenced by the characteristics of minerals. For instance, long-chain aliphatic carbon was likely to be adsorbed onto the surface of kaolinite and montmorillonite, while goethite surface attracted carboxylic functional groups of humic acid.     

Oxygen and carbon isotope and cation geochemistry of metasomatic carbonates and fluids—Bergell aureole,Northern Italy

Oxygen and carbon isotope geochemistry and Ca-Mg geothermometry are used to investigate temperatures, fluid compositions, and mechanisms of vein formation in dolomitic marble roof pendants of the Bergell intrusive complex, northern Italy. Ca-Mg and oxygen isotope geothermometry suggests that the mineralogically zoned clinohumite-chondrodite-calcite, forsterite-calcite, diopside-calcite, and tremolite-calcite veins formed over a range of temperature of approximately 520 to 380°C. Most veins apparently formed near 400°C from H₂O-rich C-O-H fluids (X_Co2 = 0.1-0.25).Abrupt 5–14%. isotopic “discontinuities” over several millimeters across the vein front are coincident with the mineralogically indicated vein fronts, suggesting that mass transport was controlled by an infiltration mechanism. Decarbonation did not play a significant role in determining the isotopic composition of the vein calcite. The isotopic data suggest a metasomatic fluid of rather constant composition and fluid-rock ratios as high as 100. Such ratios are minimum estimates, but not inconsistent with fluid/rock ratios calculated for complete reaction of the dolomitic wall rock with a fluid which provides the required silica.     

Understanding experts’ views and risk perceptions on carbon capture and storage in three European countries

The challenge of making the transition to a sustainable energy regime is not limited to engineering; it has important social and political dimensions. Therefore, implementation of new technologies, such as carbon capture and storage (CCS), requires not only economic and technical capacities but also an understanding of social factors. These factors include experts’ views and risk perceptions. Understanding them will contribute to the risk governance of CCS by demonstrating who is concerned about what and why with respect to CCS and how risk perception and stakeholders’ concerns vary in different countries. This research is based on analysis and mapping of data collected from case studies of three countries: Germany, Norway and Finland. Our analysis shows that in countries where opposition to CCS is the strongest, like Germany, risk perceptions can be driven by such factors such as the lack of trust and doubts about the need of the project. At the same time as in countries with moderate opposition, such as Norway or Finland, risk perceptions are more connected with the risk for investment. We also conclude that the strongest polarization in risk perceptions is among NGOs in different countries, followed by scientists. The positions of private sector stakeholders and government are more homogenous. Such large variation in risk perceptions of experts could be influenced by several factors, including cultural orientation, attitudes and views of stakeholders, and the social, political and technical settings for deployment of technology in each country.     

Land–sea carbon and nutrient fluxes and coastal ocean CO2 exchange and acidification: Past,present, and future

Epochs of changing atmospheric CO₂ and seawater CO₂–carbonic acid system chemistry and acidification have occurred during the Phanerozoic at various time scales. On the longer geologic time scale, as sea level rose and fell and continental free board decreased and increased, respectively, the riverine fluxes of Ca, Mg, DIC, and total alkalinity to the coastal ocean varied and helped regulate the C chemistry of seawater, but nevertheless there were major epochs of ocean acidification (OA). On the shorter glacial–interglacial time scale from the Last Glacial Maximum (LGM) to late preindustrial time, riverine fluxes of DIC, total alkalinity, and N and P nutrients increased and along with rising sea level, atmospheric PCO₂ and temperature led, among other changes, to a slightly deceasing pH of coastal and open ocean waters, and to increasing net ecosystem calcification and decreasing net heterotrophy in coastal ocean waters. From late preindustrial time to the present and projected into the 21st century, human activities, such as fossil fuel and land-use emissions of CO₂ to the atmosphere, increasing application of N and P nutrient subsidies and combustion N to the landscape, and sewage discharges of C, N, P have led, and will continue to lead, to significant modifications of coastal ocean waters. The changes include a rapid decline in pH and carbonate saturation state (modern problem of ocean acidification), a shift toward dissolution of carbonate substrates exceeding production, potentially leading to the “demise” of the coral reefs, reversal of the direction of the sea-to-air flux of CO₂ and enhanced biological production and burial of organic C, a small sink of anthropogenic CO₂, accompanied by a continuous trend toward increasing autotrophy in coastal waters.     

Modeling CO2 chemistry, δC, and oxidation of organic carbon and methane in sediment porewater: Implications for paleo-proxies in benthic foraminifera

I present a numerical diffusion-advection-reaction model to simulate CO₂ chemistry, δ¹³C, and oxidation of organic carbon and methane in sediment porewater. The model takes into account detailed reaction kinetics of dissolved CO₂ compounds, H₂O, H⁺, OH⁻, boron and sulfide compounds. These reactions are usually assumed to be in local equilibrium, which is shown to be a good approximation in most cases. The model also includes a diffusive boundary layer across which chemical species are transported between bottom water and the sediment-water interface. While chemical concentrations and δ¹³C_TCO2 at these locations are frequently assumed equal, I demonstrate that they can be quite different. In this case, shells of benthic foraminifera do not reflect the desired properties of bottom water, even for species living at the sediment-water interface (z = 0 cm). Environmental conditions recorded in their shells are strongly influenced by processes occurring within the sediment. The model is then applied to settings in the Santa Barbara Basin and at Hydrate Ridge (Cascadia Margin), locations of strong organic carbon and methane oxidation. In contrast to earlier studies, I show that a limited contribution of methane-derived carbon to porewater TCO₂ in the Santa Barbara Basin cannot be ruled out. Simulation of methane venting shows that at oxidation rates greater than , the δ¹³C of porewater TCO₂ at z > 1 cm is depleted by more than 15‰ relative to bottom water. Depletions of this magnitude have not been observed in living benthic foraminifera, even at methane vents with much higher oxidation rates. This suggests that foraminifera at these sites either calcify at very shallow sediment depth or during times when oxidation rates are much lower than ∼50 μmol cm⁻² y⁻¹.     

Major contribution to carbon neutrality by China’s geosciences and geological technologies

In the context of global climate change, geosciences provide an important geological solution to achieve the goal of carbon neutrality, China’s geosciences and geological technologies can play an important role in solving the problem of carbon neutrality. This paper discusses the main problems, opportunities, and challenges that can be solved by the participation of geosciences in carbon neutrality, as well as China’s response to them. The main scientific problems involved and the geological work carried out mainly fall into three categories: (1) Carbon emission reduction technology (natural gas hydrate, geothermal, hot dry rock, nuclear energy, hydropower, wind energy, solar energy, hydrogen energy); (2) carbon sequestration technology (carbon capture and storage, underground space utilization); (3) key minerals needed to support carbon neutralization (raw materials for energy transformation, carbon reduction technology). Therefore, geosciences and geological technologies are needed: First, actively participate in the development of green energy such as natural gas, geothermal energy, hydropower, hot dry rock, and key energy minerals, and develop exploration and exploitation technologies such as geothermal energy and natural gas; the second is to do a good job in geological support for new energy site selection, carry out an in-depth study on geotechnical feasibility and mitigation measures, and form the basis of relevant economic decisions to reduce costs and prevent geological disasters; the third is to develop and coordinate relevant departments of geosciences, organize and carry out strategic research on natural resources, carry out theoretical system research on global climate change and other issues under the guidance of earth system science theory, and coordinate frontier scientific information and advanced technological tools of various disciplines. The goal of carbon neutrality provides new opportunities and challenges for geosciences research. In the future, it is necessary to provide theoretical and technical support from various aspects, enhance the ability of climate adaptation, and support the realization of the goal of carbon peaking and carbon neutrality.     

Experimental modeling of native carbon formation in a C–O–H fluid system

Integrated data are presented on structure–morphology features, as well as on the material and phase composition, of a fluid-produced carbonaceous substance (CS) formed under known thermodynamic conditions of the experiment (C–O–H system, 500–800°C, and 500–1000 atm). Solid products of the synthesis were examined by means of X-ray phase and thermal analyses, scanning electron microscopy combined with microprobe analysis, transmission electron microscopy, high-resolution Raman spectroscopy, IR spectroscopy, and CHN-analysis. The characteristics of the experimental CS may be applicable in genetic modeling of natural ore-bearing fluidal carbonaceous systems.     

Organic carbon isotope ratios (δ13C) of Arctic Amerasian Continental shelf sediments

Organic matter origins are inferred from carbon isotope ratios ('¹³C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in '¹³C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment '¹³C, OC/N, and '¹⁵N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C₃ plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C₄ and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment '¹³C values (-16.5 to -13.6‰) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial-interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO₂ and pCO₂ in the Arctic Basin halocline.     

Re-evaluation of linearity and precision of Gas Bench II-IRMS system and potential implications for carbon and oxygen isotope measurements on small-sized carbonate samples

In this study, the δ^13C and δ^18O values were systematically measured on NBS-18, NBS-19 and IAEA-CO-1 with different sample sizes, with the objective to examine the stability and reproducibility of previously developed linearity correction strategy especially for small-sized samples （e.g. 〈50 μg）. Firstly, the δ^13C and δ^18O values of NBS-19 standards （6-10 samples per run） with sample sizes scattered below -100 μg were determined in three different runs. The logarithmic regressions were performed on the plots of δ-values vs. peak area （sample size） for each run and the correction was applied using peak area of the first peak. Results show that two of the three data sets have almost the same regressive equations for both δ^13C and δ^18O values. The maximum difference in δ^13C values calculated by three equations when sample size varies between -10 and -100 μg is better than 0.15‰, compared with the maximum 0.82‰ for δ^18O values. Since alteration of phosphoric acids could not influence carbon isotope, the 〈0.15‰ difference in calculated δ^13C values should reflect the stability of mass spectrometer conditions. In contrast, the large difference in regressive equations for δ^18O values may be attributed to changed oxygen isotope in phosphoric acids due to exchange with atmosphere through time. It means that standards with sample sizes properly distributed should be arranged in every run for subsequent linearity correction of δ^18O values of small-sized samples （e.g. marine ostracode）.     

Environmental changes and carbon cycle perturbations at the Triassic–Jurassic boundary in northern Switzerland

The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ¹³C of the total organic carbon (δ¹³C_TOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ¹³C_TOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ¹⁵N_TN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.     

Transformation of organic carbon and its potential impact on lead weathering in firing range soils

Lead （Pb） is normally considered as a trace element in soils and sediments for geochemical study. However, the concentration of Pb in firing range soils is generally so high that it should be considered as a major element during the evaluation of the soil geochemical properties. Soil organic matter （SOM） has been reported as one of the major factors to expedite the corrosion of metallic lead （Pb） in acidic and organic-rich soils. The main impacts of SOM on the fate and transport of Pb in firing range soils lie in the following two aspects; （1） the complexation of organic matter with Pb, which has received lots of attention, and; （2） changes in soil redox potential due to the transformation of SOM and its subsequent impact on Pb speciation, which has rarely been investigated. Soils from 6 different firing ranges are selected for this study. These samples have been stored under a closed condition for more than 3 years. The soil moisture contents were well-retained, as all the samples were kept in closed plastic buckets. The analytical data showed that the summation of the soil total organic carbon content （TOC） and inorganic carbon contents （TIC） were consistent with soil total carbon contents （TC） measured in previous years, although the TOC and TIC contents have changed respectively after years of storage. In general, it is observed that the soil TOC decreased against an increase of TIC. The mass balance on such a transformation suggested a major conversion of organic carbon （Corg） to inorganic carbon （CO3^2-） in the stored soils.     

Club convergence and spatial distribution dynamics of carbon intensity in China’s construction industry

Climate change caused by carbon emissions continuously threatens sustainable development. Due to China’s immense territory, there are remarkable regional differences in carbon emissions. The construction industry, which has strong internal industrial differences, further leads to carbon emission disparity in China. Policymakers should consider spatial effects and attempt to eliminate carbon emission inequality to promote the sustainable development of the construction industry and realize emission reduction targets. Based on the classic Markov chain and spatial Markov chain, this paper investigates the club convergence and spatial distribution dynamics of China’s carbon intensity in the construction industry from 2005 to 2014. The results show that the provincial carbon intensity in the construction industry is characterized by “convergence clubs” during the research period, and very low-level and very high-level convergence clubs have strong stability. Moreover, the carbon intensity class transitions of provinces tend to be consistent with that of their neighbors. Furthermore, the transition of carbon intensity types is highly influenced by their regional backgrounds. The provinces with high carbon emissions have a negative influence on their neighbors, whereas the provinces with low carbon emissions have a positive influence. These analyses provide a spatial interpretation to the “club convergence” of carbon intensity.     

Hydrological budget,carbon sources and biogeochemical processes in Lac Pavin (France): Constraints from δO of water and δC of dissolved inorganic carbon

Lac Pavin (French Massif Central) is a permanently stratified lake: the upper water layers (mixolimnion, from 0 to 60 m depth) are affected by seasonal overturns, whereas the bottom water layers (monimolimnion, from 60 to 90 m depth) remain isolated and are never mixed. Hence, they are capable of storing important quantities of dissolved gases, mainly CO₂. With the aim of better constraining the water balance and of gaining new insights into the carbon cycle of Lac Pavin, an isotopic approach is used. The δ¹⁸OH₂O$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}$ profiles lead the authors to give a new evaluation of the evaporation flow rate (8 L s⁻¹), and to propose and characterize two sub-surface springs. The sub-surface spring located at the bottom of the lake can be deduced from the 1% isotopic difference between the upper water layers (mean δ¹⁸OH₂O$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}$ value: −7.3‰) and the bottom water layers (δ¹⁸OH₂O=-8.4‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}=-8.4‰$). It is argued that this sub-surface spring has isotopic and chemical characteristics similar to those of the magmatic CO₂-rich spring (i.e. Fontaine Goyon, δ¹⁸OH₂O=-9.4‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}=-9.4‰$), and we calculate its flow rate of 1.6 L s⁻¹. The second sub-surface spring is located around 45 m depth, with a composition close to those of the water surface streams (δ¹⁸OH₂O<-7.6‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}<-7.6‰$).