Stable Carbon Isotope Composition Research Articles

Tracking hydrothermal infiltration within light oil reservoirs using organic geochemical proxies in the Shunbei area of Tarim Basin in China

Deep oil reservoirs are becoming increasingly significant fields of hydrocarbon exploration in recent decades. Hydrothermal fluid flow is deemed as a potentially crucial factor affecting the occurrence of deep oil reservoirs, such as enhancing porosity/permeability of reservoirs, accelerating oil generation and thermal cracking, and modifying organic properties of crude oils. Understanding the interplay between hydrothermal fluids and crude oils would provide useful constraints for reconstructing hydrocarbon accumulation processes and predicting the distribution patterns of crude oils. Voluminous crude oils have been discovered in the deeply buried Ordovician carbonate reservoirs within the Shunbei area of the northern Tarim Basin. Previous studies revealed that the Early Permian Tarim Large Igneous Province (LIP) has affected the Shunbei area, whereas it is still debated whether the LIP-related hydrothermal infiltration affected hydrocarbons within the Ordovician reservoirs. To resolve this puzzle, this study was designed to unravel the potential thermal impact of hydrothermal infiltration on hydrocarbons according to molecular and stable carbon isotopic compositions of oils and associated natural gases, reflectance analysis of solid bitumen, and fluid inclusion thermometry. The studied crude oils are characterized by uniform organic indicators of paraffin, terpanes, steranes, and light hydrocarbons, implying that crude oils are derived from the same source rock. Genetic binary diagrams, such as dibenzothiophene/phenanthrene (DBT/P) vs. Pr/Ph (pristane/phytane), Pr/n-C17 alkane vs. Ph/n-C18 alkane, C31R/C30hopane vs. C26/C25tricyclic terpane (TT), and C24/C23 TT vs. C22/C21 TT, indicate that marine shales deposited in a reducing-weakly oxidized environment are major source rocks. Natural gases are associated with oil reservoirs and are mainly generated via the decomposition of kerogen and crude oil. Solid bitumen with abnormally high reflectance values (2.17–2.20%) occurred in the studied area, suggesting their formation temperatures were 252–254 °C. The abnormally high temperatures may be caused by hydrothermal infiltration related to the Tarim LIP. Hydrothermal infiltration is supported by the presence of high contents of CO2 (30–48%) with enriched δ13C ratios (between − 2.5‰ and − 2.3‰), enriched n-alkane δ13C ratios, and incongruent temperatures estimated by multiple indicators, such as light hydrocarbon compositions, homogenization temperatures of fluid inclusions, and bitumen reflectance. Outcomes of this study support the interpretation that hydrothermal infiltration indeed occurred and may have facilitated hydrocarbon generation in the Shunbei area, and possibly elsewhere in the cratonic regions of the northern Tarim Basin.

Otolith stable isotopes highlight the importance of local nursery areas as the origin of recruits to yellowfin tuna (Thunnus albacares) fisheries in the western Indian Ocean

Yellowfin tuna (Thunnus albacares) supports the second largest tuna fishery worldwide, and in the Indian Ocean, it is overfished and subject to overfishing. This situation presents a significant challenge to fisheries management, requiring effective measures to rebuild and then maintain the stock at sustainable levels. A single stock of yellowfin is currently assumed by the Indian Ocean Tuna Commission (IOTC) for stock assessments in the Indian Ocean. However, the relative contribution of different spawning components to the total catches, and the degree of mixing rates of yellowfin tuna in the Indian Ocean by individuals from different production zones, are still unknown. This study uses otolith core oxygen and carbon stable isotope composition (δ18O and δ13C) of young-of-the-year yellowfin tuna from nursery areas located in the western (FAO Area 51) and eastern (FAO area 57) Indian Ocean, either side of 80ºE, to establish a reference baseline of isotopic signatures. Then, a mixed population program (HISEA) and Random Forest (RF) assignment approaches were used to predict the most likely origin (west or east) of sub-adult and adult yellowfin tuna captured from four fishery areas of the western Indian Ocean (offshore Pakistan, Seychelles, Reunion, and South Africa) by comparing their otolith core values to that of the baseline. Both approaches show that the western Indian Ocean fisheries are mainly composed of west origin fish (>95%). We also found some individuals with an otolith isotopic signature that was not characteristic of either of the samples available in the baseline. We simulated an alternative baseline group formed by individuals with mean and standard deviation δ13C and δ18O values above the maximum ranges of the original baseline. We then used RF to infer again the most likely origin of fish in the mixed sample considering 3 possible sources (west, east, alternative). About one third of the samples were assigned to the alternative group, possibly indicating that they differ in geographical or temporal terms with the origins represented in the original baseline. Findings of otolith stable isotope composition of yellowfin tuna in the western Indian Ocean can provide a more comprehensive understanding of the species’ spatial structure and connectivity beyond the current assumption of an ocean basin single stock.

Climate, soil, and viticultural factors differentially affect the sub-regional variations in biochemical compositions of grape berries

Terroir leaves its influence on the flavor build-up in grape berries by triggering biochemical reactions that ultimately shape the typicality of the produced wines. However, the complex relationship between terroir, carbon stable isotopic composition, and the biochemical composition of grapes remains poorly understood. To fill these gaps, grape berries were harvested at maturity from two grape cultivars, Cabernet Sauvignon and Merlot (Vitis vinifera L.), across 32 sites within the Eastern Foothills of the Helan Mountains region over two vintages. The climate and soil data for these sites were collected, and cultivation practices were surveyed. In parallel, the grape quality indicators were measured at maturity to explore their variations among sub-regions and the correlations between terroir factors and grape quality. Moreover, the carbon stable isotopes (δ¹³C) were measured to evaluate the water status of vines at different sites. Results indicated that organic acids and anthocyanins exhibited a strong vintage effect, with the cooler vintage exhibiting higher levels of these compounds relative to the warmer vintage. Specifically, the Hongsipu sub-region, with a cooler climate, consistently demonstrated higher anthocyanin concentrations than other sub-regions in both vintages of the study. Further analysis revealed that the cultivar Cabernet Sauvignon displayed a higher ratio of di-hydroxylated to tri-hydroxylated anthocyanins in the cooler year, whereas Merlot exhibited the opposite trend. The Mantel test identified several critical factors influencing anthocyanin concentration, including total soil phosphorus (Tp), total soil potassium (Tk), soil thickness (Thickness), precipitation (April-September precipitation, Pre4–9), April-September average temperature (4–9 Tave), April-September active accumulated temperature (4–9 Aa), April-June active accumulated temperature (4–6 Aa), July-September active accumulated temperature (7–9 Aa), temperature diurnal range (May, July, August, September, DR-5 and DR 7–9), trellis system, vine density, and δ13C. Finally, structural equation modeling (SEM) was used to analyze and summarize the relationships between terroir factors, anthocyanin concentration, and δ¹³C. The results indicated that June and September precipitation had a positive impact on anthocyanin concentrations, while soil total potassium content had a negative impact. On the other hand, the July to September temperature diurnal range, trellis system, vine perimeter, and canopy height were the main drivers of δ¹³C, which further influenced grape anthocyanin concentrations. This research contributes to a scientific foundation for grape cultivation in the Eastern Foothills of the Helan Mountains and provides valuable insights for practices in other regions.

Carbon translocation within land snails affects the carbon isotopic fractionation

Stable carbon isotope composition (δ13C) of land snail materials is widely used as a proxy for reconstructing past vegetation and environmental changes. Interpretation δ13C data is challenging due to the complexities of snail physiology. This study cultured Lissachatina fulica (Bowdich, 1822) snails to investigate δ13C of their soft tissues and excrement under various plant types and dietary carbonate content. Our results show that snails primarily assimilate organic matter (OM), with limited use of dietary carbonates. δ13C of organic matter in excrement correlates positively with that in the diet, but exhibits deviations due to variable carbon isotopic fractionation during assimilation. Tissue δ13C (δ13Ctissue) is positively related to the δ13C of OM (δ13COM) in the diet, varying by turnover rates, with faster turnover rate, such as the digestive gland, exhibiting more negative δ13Ctissue values. Moreover, carbon isotopic fractionation between tissues and diet (Δ13Ctissue-OM) differs based on plant type. Snails fed with C3 plants show positive Δ13Ctissue-OM values, whereas those fed with C4 plants exhibit negative values. These Δ13Ctissue-OM values are far from equilibrium (Δ13Ctissue-OM = 0) with conditions of rapid snail growth. Our findings indicate that the snails fed with C3 and C4 plants result in distinct carbon isotopic fractionation, leading to the deviation in δ13C between plants and land snail materials (e.g., excrement, tissues, shells and shell-bound organic matter). A comprehensive model of carbon metabolism and isotopic fractionation in snails is proposed including the assimilation process from diet to soft tissues and excretion. This study highlights the importance of physiological factors such as growth rates and turnover rates when interpreting δ13C of land snail materials for paleoenvironmental reconstructions.

Variation of carbon and nitrogen stable isotope composition in leaves and roots of Littorella uniflora (L.) Asch. in relation to water pH and nutrient availability

In a phytotron experiment, the effects of pH variation and eutrophication on isoetids plants from soft-water lakes specifically the submerged form of Littorella uniflora (L.) Asch. was investigated by analyzing stable carbon and nitrogen isotopes (δ13C and δ15N). Conducted in late October 2020, 200 specimens from Lake Zawiad, near Gdansk, Poland, were examined over 75 days. The study tested three pH levels (∼4.5, ∼7.0, and ∼8.5) and a detailed 12-step nutrient gradient (nitrogen: 0–10 mg/l; phosphorus: 0–0.3 mg/l). The analysis focused on isotopic composition in leaves and roots, revealing that acidic conditions favored higher δ13C values (leaves: −22.67 ‰; roots: −23.23 ‰), suggesting a preference for lighter carbon forms in photosynthesis and intensive use of limited sources of CO2. The neutral pH variant showed the lowest δ13C values (leaves: −25.53 ‰; roots: −25.47 ‰), indicating less optimal conditions. δ15N values exhibited minimal fluctuation across pH levels, with slight variations in acidic and alkaline environments compared to neutral conditions. An observed decrease in δ13C across all pH levels with increased nutrients, alongside a rise in δ15N values, indicates a complex interaction between isotopic composition and environmental factors. Our findings suggest that L. uniflora shows a distinct isotopic response to varying pH levels, with higher δ13C values under acidic conditions potentially indicating enhanced CO2 uptake through a specialized carbon assimilation strategy. This highlights the species' adaptive mechanisms to environmental stressors, suggesting that the isotopic composition of aquatic vegetation can serve as a sensitive indicator of changes in lake ecosystems.

Impact of elevated CO2 on the δ13C of n-alkane biomarkers

The stable carbon isotopic composition of n-alkane biomarkers is a commonly used proxy for studying plant community change and palaeohydrology in the geologic record. However, interpretations of n-alkane δ13C tend to assume that all variation is due to changes in bulk plant δ13C, reflecting a signal of fractionation due to photosynthesis, and that the biosynthetic fractionations which occur after photosynthesis (εn-alkane) are constant. However, this untested assumption may overlook environmental influences on εn-alkane which can offer alternative explanations for n-alkane δ13C trends, thereby allowing for the reconstruction of plant biochemistry in geological records. In this study, we use the Free Air CO2 Environment experiment at the Birmingham Institute of Forest Research to investigate the impact of elevated CO2 concentrations on the response of εn-alkane. We measured the δ13C levels of bulk and n-alkanes in two plant species, Acer pseudoplatanus (European sycamore) and Corylus avellana (common hazel), over four years. Our findings indicate that the εn-alkane levels in both species increased under elevated CO2 compared to ambient levels. However, the seasonal variation in εn-alkane suggests that this increase is due to separate mechanisms. In A. pseudoplatanus, this increase occurs consistently throughout the growth season, suggesting that changes in carbon allocation to different tissue types within the plant is responsible. Conversely, in C. avellana, the effect becomes more pronounced as the growth season progresses, indicating that altered timing of n-alkane synthesis under elevated CO2 may influence εn-alkane. Collectively, this suggests that εn-alkane should not be assumed constant in the geologic record, and highlights that biosynthetic processes should be considered when interpreting compound-specific isotopes of carbon.

Stable carbon isotopic composition of particulate organic matter in the Cosmonaut and Cooperation Seas in summer

This study examined particulate organic carbon (POC) and its isotopic composition (δ13CPOC) in the Cosmonaut and Cooperation Seas in the Antarctica during the summer of 2019. Our results show that the spatial variation of POC concentration in summer surface water generally mirrors that of δ13CPOC, with higher POC and δ13CPOC values in the Cosmonaut Sea compared to the Cooperation Sea. The δ13CPOC values in both seas were positively correlated with the proportion of Chl-a in smaller particles (< 20 μm). However, the relationship with the proportion of biogenic POC in smaller particles (< 20 μm) differed between the two seas. This discrepancy is attributed to differences in the dominant phytoplankton species. In the Cosmonaut Sea, smaller phytoplankton (nano- and pico-phytoplankton) were dominated by Phaeocystis antarctica, whereas in the Cooperation Sea, they were dominated by pennate diatoms. The δ13CPOC in deep waters of both seas increased with depth, reflecting the effects of organic remineralization. The carbon isotope fractionation factors during remineralization, estimated using Rayleigh model, were 1.5 ± 0.2‰ and 1.6 ± 0.2‰ in the Cosmonaut Sea and the Cooperation Sea, respectively. These small isotope effects indicate that the isotope signals of organic matter exported from the upper layer are well preserved in the deep ocean. Additionally, anomalously high δ13CPOC values were observed in the bottom water outside the Cape Darnley polynya in the Cooperation Sea, reflecting the input of ice algae-derived organic matter from the shelf during AABW formation. A simple isotopic mass balance estimate suggests that 6–19% of the POC in the AABW of the Cooperation Sea is contributed by ice algae. Our study highlights the complexity of factors affecting δ13CPOC in the Southern Ocean, emphasizing the importance of phytoplankton community composition.

A cross-regional examination of camelid herding practices in Peru from 900 BCE to 1450 CE: Insights from stable isotopes in camelid bone collagen and fiber.

The economic, socio-political, and cultural significance of camelids in the Andean region is well-recognized, yet an understanding of their management evolution over pre-historical periods remains limited. This study aims to fill this gap by conducting the first cross-regional assessment of camelid pastoralism in Peru from 900 BCE to 1470 CE, using stable carbon and nitrogen isotopic compositions from the bone collagen and fibers of 577archaeological camelids across 21 sites. This research investigates the spatio-temporal shifts in camelid dietary habits, focusing on how the rise of intensive agriculture may have influenced change and led to the evolution of distinct roles for camelids in coastal versus non-coastal Andean economies. Our analysis indicates an increase in δ13C values over time on the coast, suggesting a shift towards maize-based camelid diets. Conversely, δ13C values decrease over time in highland environments, suggesting camelids consumed relatively more wild C3 forage and/or cultivated crops such as tubers. The study also reveals a significant positive relationship between latitude and δ15N values, suggesting increasing environmental aridity enriches δ15N in bone collagen. After controlling for this latitudinal effect, we observe a rise in δ15N values in both coastal and non-coastal camelids, suggesting that in later periods camelids may have been foddered in agricultural fields that were enriched with guano or dung fertilizer used to intensify production. Importantly, this research uncovers a distinct dietary divergence between coastal and inland camelids. The observed divergence in diets suggests contrasting socio-economic uses of camelids, where coastal camelids were predominantly involved in ceremonial and political activities, while those in non-coastal areas were crucial to the subsistence economy.

Intra-tooth isotopic analysis shows seasonal variability in the high-elevation context of Melka Kunture (Upper Awash Valley, Ethiopia) during the Early Pleistocene

In order to investigate seasonal changes in diet, environment and climate, we analyzed the stable carbon and oxygen isotopic composition of intra-tooth sequential profiles (14 teeth, 282 enamel samples) of Hippopotamidae, Equidae, Bovidae and Suidae from Melka Kunture, Upper Awash Valley, central Ethiopian Highlands (2000–2200 m a.s.l.).We found that during the Early Pleistocene, between 1.95 and 1 Ma, most of the analyzed hippos display a seasonally stable C4 diet, even if the δ13C values within hippos show a degree of variability that we interpret as the outcome of feeding on plants that use different C4 photosynthetic pathways. Several hippo specimens display a seasonal shift from C4 to mixed C3-C4 diets. The sampled equid, bovid and suid specimens recorded both stable C4 diets and mixed C3-C4 feeding with a seasonal progressive increase of δ13C values. When affected by seasonal changes, the serially analyzed taxa show different niche partitioning: hippos increase the consumption of C3 vegetation, whereas equids and suids include more C4 vegetation in their diets. The intra-individual δ18O variability in the analyzed taxa is interpreted as the outcome of different water sources, depending on animal habitat, behavior and mobility patterns.Our data are placed in controlled stratigraphic and chronological sequences and combined with the outcome of other proxies, allowing us to evaluate the site paleoecology comprehensively. We suggest that the central Ethiopian Highlands, where MK is located, possibly acted as a refugium-like area during the Early and Middle Pleistocene, characterized by a specific type of montane vegetation (DAF) and diverse faunal and hominin species that demonstrated their resilience and adaptability to changing environments and climates.

Mercury Stable Isotopes Reveal the Vertical Distribution and Trophic Ecology of Deep-Pelagic Organisms over the North-East Atlantic Ocean Continental Slope.

Deep-pelagic species are central to marine ecosystems and increasingly vulnerable to global change and human exploitation. To date, our understanding of these communities remains limited mainly due to the difficulty of observations, calling for complementary innovative tools to better characterize their ecology. We used mercury (Δ199Hg, δ202Hg, Δ201Hg, and Δ200Hg), carbon (δ13C), and nitrogen (δ15N) stable isotope compositions to segregate deep-pelagic species caught on the continental slope of the Bay of Biscay (NE Atlantic) according to their foraging depth and trophic ecology. Decreasing fish Δ199Hg values with corresponding depth estimates from the surface to down to 1,800 m confirmed that mercury isotopes are able to segregate deep species over a large vertical gradient according to their foraging depth. Results from isotopic compositions also identified different mercury sources, likely reflecting different trophic assemblages over the continental slope, in particular, the demersal influence for some species, compared to purely oceanic species. Overall, our results demonstrate how mercury stable isotopes can inform the vertical foraging habitat of little-known species and communities feeding in the deep.

Climate-driven peatlands development and vegetation dynamics in Northeastern China since the mid-Holocene: New evidence from Huanan peatlands

Studying peatland evolution and vegetation patterns in response to climate change provides valuable insights into future ecosystem trends. This study focuses on the Huanan peatland located in Changbai Mountain regions in Northeast China, utilizing phytolith analysis and stable carbon isotope composition (δ13C) to reconstruct late Holocene vegetation dynamics. Additionally, grain size, total organic carbon (TOC), and total nitrogen (TN) analyses were conducted to understand peatland development and paleoclimate since the late Holocene. The research identifies three distinct climate periods since 5500 cal yr BP: an initial warm, humid phase (5500–4000 cal yr BP) characterized by high river levels that formed lacustrine sediments; a subsequent transition to cold, dry conditions (4000–1500 cal yr BP) that initiated peat formation; and continued dry, cold conditions (1500 cal yr BP to the present) with sustained peat growth. Phytolith data reveal a dominant forest vegetation type since 2000 cal yr BP, further divided into three periods: 2000–1300 cal yr BP, marked by diverse and dense vegetation; 1300–750 cal yr BP, with declining plant cover; and 750 cal yr BP to the present, characterized by an increase in woody plants but a reduction in local grass cover.

The use of combined C[sbnd]Mg isotope compositions of carbonates from orogenic Sb[sbnd]Au deposits as a tracer of fluid interaction with sea-floor altered crust

The Mesoarchaean Murchison Greenstone Belt is composed of a strongly deformed volcano-sedimentary succession metamorphosed up to amphibolite facies and surrounded by metaluminous and peraluminous granitoids in the north of the Kaapvaal Craton of southern Africa. A circa 40 km-long shear-zone of strongly carbonatised rocks (the Antimony Line, or Sb-Line) oriented along the main trend of the greenstone belt (WSW–ENE) hosts important Sb deposits with accessory Au. These commodities mostly occur as stibnite and native gold hosted by quartz‑carbonate rocks at the centre of the Sb-Line, underlining the importance of CO2-rich fluid flow for mineralisation during deformation and metamorphism.In this study, we compare the elemental and stable isotope (C-O-Mg) composition of carbonates from the Sb-Line with regionally distributed carbonates hosted by the volcano-sedimentary succession distal to mineralisation. The carbonates of the Sb-Line and regional rocks have overlapping major element compositions. Both magnesite and dolomite in most Sb-Line samples have marked light-REE-depleted patterns with variable positive Eu anomalies. Carbon isotope ratios define two clusters, with marked δ13C peaks at ca. -5 ‰ for Sb-Line rocks and ca. -2 ‰ for regional rocks, implying separate C-sources. The peak at ca. -2 ‰ likely represents early carbonatisation through sea-floor alteration, whereas the first peak at ca. -5 ‰ is indicative of deep CO2 (mantle, or magma-derived) introduced during tectonic activity of the Sb-Line. Magnesium isotope ratios of regional rocks reveal limited fractionation (bulk δ26Mg = −0.27 ± 0.10 ‰) that overlap with mantle values, but some carbonate-bearing veins present 26Mg-depleted compositions (bulk δ26Mg = −1.91 to −0.40 ‰). Sb-Line carbonated rocks have more fractionated Mg isotope compositions (bulk δ26Mg = −0.8 to 0.0 ‰) and carbonates display marked negative 26Mg values (δ26Mg from −1.46 to −0.31 ‰). We interpret these results in terms of preferential remobilisation of isotopically light Mg during fluid-rock interaction and dissolution of carbonate in the host-rocks. The lack of correlation between δ13C and δ26Mg indicates decoupling of these isotopic systems, implying contribution from isotopically distinct sources of C and Mg to the mineralised zone.Similar to other structurally controlled AuSb mineralisation in Archaean greenstone belts, metal transport and ore deposition in the Murchison Greenstone Belt was closely related to the deep cycle of carbon, linking C-draw-down during sea-floor alteration, carbonate re-mobilisation during metamorphism and CO2 degassing from deep sources along major crustal discontinuities. In contrast to models for orogenic AuSb deposits invoking a purely intra-crustal, metamorphic origin of mineralising fluids, our results underline the importance of deep-sourced fluids originating from an external source from the volcano-sedimentary succession.

Isotopic seasonality of fluvial-derived greenhouse gases implies active layer deepening

Abstract Climate change in the northern circumpolar regions is rapidly thawing organic-rich permafrost soils, releasing substantial dissolved CO2 and CH4 into fluvial systems. This mobilization impacts local ecosystems and global climate feedback loops, playing a crucial role in the Arctic carbon cycle. Here, we analyze the stable carbon (δ13C) and radiocarbon (F14C) isotopic composition of dissolved CO2 and CH4 in the Sagavanirktok and Kuparuk River watersheds on the North Slope, Alaska. By examining spatial and seasonal variations in these isotopic signatures, we identify patterns of carbon release and transport along the river continuum. We find consistent CO2 isotopic signatures across the fluvial continuum, reflecting a mixture of geogenic and biogenic sources integrated throughout the watershed. Bayesian mixing models further demonstrate a systematic depletion in 13C and 14C signatures of dissolved CO2 sources from spring to fall, indicating increasing contributions of aged carbon as the active layer deepens seasonally. This seasonal deepening allows percolating groundwater to access deeper, older soil horizons, transporting CO2 produced by aerobic and anaerobic soil respiration to streams and rivers. In contrast, we observe no clear relationships between the 13C and 14C compositions of dissolved CH4 and landscape properties. Given the reduced solubility of CH4, which facilitates outgassing and limits its transport in aquatic systems, the isotopic signatures are likely indicative of localized contributions from streambeds, adjacent water saturated soils, and lake outflows. Our study demonstrates that dissolved greenhouse gases are sensitive indicators of the release of old carbon from thawing permafrost and serve as early warning signals for permafrost carbon feedback. It establishes a crucial baseline for understanding their role in regional carbon cycling and Arctic environmental change.&amp;#xD;

Carbon Isotopic Composition Reflects Intrinsic Water Use Efficiency But Not its Component Traits in Sugarcane

Water is the most important resource in plant growth and is a major limiting factor in sugarcane productivity worldwide. Improving water use efficiency (WUE) can increase sugarcane productivity relative to available water resources by increasing photosynthetic capacity relative to transpiration and stomatal conductance instead of decreasing stomatal conductance. Leaf carbon stable isotopic composition (δ13Cleaf) can serve as a proxy for intrinsic WUE (WUEi) because WUEi and δ13Cleaf are theoretically related through the link between intracellular and ambient CO2 concentrations (Ci/Ca) and leaf CO2 discrimination (Δ13Cleaf). In this study we surveyed 55 sugarcane genotypes for WUEi, leaf WUE (WUEleaf), Ci/Ca, and δ13Cleaf by gas exchange measurements and stable isotope analysis. We hypothesized that significant genotypic variation was found in WUEi, WUEleaf, and δ13Cleaf within the sugarcane population in Louisiana. We also hypothesized that both WUEi and δ13Cleaf and Δ13Cleaf and Ci/Ca were correlated and that δ13Cleaf could be used as a proxy for WUEi in sugarcane. Here WUEi and WUEleaf had a genetic effect and were controlled mostly by water loss (stomatal conductance or transpiration). WUEi, WUEleaf, Ci/Ca, and δ13Cleaf were correlated, but δ13Cleaf was not correlated with the component traits of WUEi (photosynthetic rate and stomatal conductance). δ13Cleaf shows promise as a proxy for WUEi to at least be able to select the tails of the distribution, but the relationship between WUEi and δ13Cleaf may not be sufficiently strong to select WUE at a finer scale.

Unveiling spatial variations in atmospheric CO2 sources: a case study of metropolitan area of Naples, Italy

In the lower atmosphere, CO2 emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. The atmospheric concentration of CO2 is crucial in urban areas due to its connection with air quality, pollution, and climate change, becoming a pivotal parameter for environmental management and public safety. In volcanic zones, geogenic CO2 profoundly affects the environment, although hydrocarbon combustion is the primary driver of increased atmospheric CO2 and global warming. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO2 concentration measurements alone. This study presents survey results on the stable isotope composition of carbon and oxygen in CO2 and airborne CO2 concentration in Naples’ urban area, including the Campi Flegrei caldera, a widespread hydrothermal/volcanic zone in the metropolitan area. Over the past 50 years, two major volcanic unrests (1969–72 and 1982–84) were monitored using seismic, deformation, and geochemical data. Since 2005, this area has experienced ongoing unrest, involving the pressurization of the underlying hydrothermal system as a causal factor of the current uplift in the Pozzuoli area and the increased CO2 emissions in the atmosphere. To better understand CO2 emission dynamics and to quantify its volcanic origin a mobile laboratory was used. Results show that CO2 levels in Naples’ urban area exceed background atmospheric levels, indicating an anthropogenic origin from fossil fuel combustion. Conversely, in Pozzuoli's urban area, the stable isotope composition reveals a volcanic origin of the airborne CO2. This study emphasizes the importance of monitoring stable isotopes of atmospheric CO2, especially in volcanic areas, contributing valuable insights for environmental and public health management.

Biogeochemistry of the rare sulfidic glaciovolcanic cave system on Mount Meager, British Columbia, Canada

The Mount Meager Volcanic Complex (Q̓welq̓welústen) is an active glacier-capped volcanic massif in the Garibaldi Volcanic Belt (British Columbia) and the only known glaciovolcanic cave system in North America steadily releasing sulfur-rich gases. In September 2022, leveraging specialized cave explorer expertise, the fumarole-carved ice cave at the Job Glacier on Mt. Meager was surveyed. Direct measurements of fumarolic gas concentrations were taken at the source, with H2S &amp;gt;200 ppm, SO2 &amp;gt;100 ppm, CO2 ∼5,200 ppm, and CO ∼230 ppm. Snowpack and fumarole-associated sediments were characterized for microbial diversity, functional potential, and biogeochemistry including measurements of nutrients, major ions, dissolved organic and inorganic carbon concentrations as well as the stable isotope compositions of carbon, sulfur, hydrogen and oxygen. Green algae (Chlorophyta) dominated the snowpack, consistent with other Pacific Northwest glaciers. Representatives of Firmicutes were the most abundant bacterial sequences detected in our samples, contrasting with other glacier and snowpack samples which harbor abundant Sphingobacteria, Betaproteobacteria, and Alphaproteobacteria. Sediments and water collected inside the cave were mostly high in SO42- (5.3–185.2 mg/L) and acidic (pH = 3.6–6.0), while most other major anions and cations were below detection of the method used. Snow at the cave entrance had more SO42- (0.08 mg/L) and lower pH (5.9) than snow collected at a distance (SO42- undetectable, pH 7.6), suggesting influence by fumarole exhalations. Negative δ13C values of organic matter (−29.0‰ to −26.1‰, respectively) in sediments suggest in-situ microbial carbon transformations, findings that are supported by the presence of genes encoding complete heterotrophic and autotrophic carbon transformation pathways. The δ34S value of H2S was ∼0‰, suggesting a deep magmatic origin; however, both sulfur-oxidizing and sulfate-reducing microbial phyla were present in the sediment samples as were genes encoding both dissimilatory sulfur-oxidizing and sulfate-reducing pathways. Metagenomic data suggest diverse chemosynthetic lifestyles in the cave microbial community. This study provides insight on the microbiomes associated with a sulfidic glaciovolcanic system and identifies unique analog features for icy celestial bodies like Saturn’s moon Enceladus, where cryovolcanic activity may carry biomarkers from the subsurface and deposit them on surface ice.

Thermally induced release and generation of CO2 and C1–C4 hydrocarbons in Opalinus Clay from Mont Terri (Switzerland)

Claystone formations are candidate host rocks for high-level heat-emitting nuclear waste (HLW). Temperatures from 90 to 150 °C at the canister surface are discussed internationally as potential emplacement and storage conditions. The thermal energy emitted from waste containers will be transported into the host rock formation, accelerating chemical reactions including the release of sorbed and dissolved gases and the generation of new gases. This study investigated gas release and generation in Opalinus Clay from Mont Terri (Switzerland) at elevated temperature and pressure conditions relevant for HLW storage and beyond. Hydrous pyrolysis experiments were conducted in Dickson-type flexible gold-titanium reaction cells and gold capsules in the temperature range of 80–345 °C and at 20 MPa. CO2(g) was the predominant product, followed by C1–C4 hydrocarbons, which decrease in abundance with increasing carbon atom number. Neither CO nor H2S was detected. H2 was generated only in high temperature experiments at 315 °C and 345 °C, respectively. A combination of CO2(g) quantification, stable carbon isotopic composition data, thermodynamic calculations and aqueous fluid composition (dissolved ions, pH) demonstrated that ≥80 % of the measured CO2(g) originated from carbonate mineral dissolution. The model calculations also suggest that the fraction of CO2(aq) in DIC increases from ∼50 % at 80 °C to nearly 100 % at higher temperatures. Thermal transformation of organic matter represented an additional source for CO2(g) and was the predominant process yielding the C1–C4 hydrocarbons. Our findings stress the importance of quantitative geochemical data for the safety assessment of potential host rocks for HLW storage. We demonstrated that two sources are involved in gas release and generation at temperatures relevant for HLW storage, e.g., in the Opalinus Clay – organic matter and carbonate minerals. Our data will contribute to numerical modelling studies and the refinement of feature, events, and processes (FEP) catalogues.

Organic carbon isotope (δ13Corg) curve and extinction trends across the Triassic/Jurassic boundary at Mt. Sparagio (Italy): A tool for global correlations between peritidal and pelagic successions

The Triassic/Jurassic boundary (TJB, 201.3 Ma) is characterized by profound turnovers in both marine and terrestrial biota, known as end-Triassic mass Extinction event (ETE). During this severe event, distinct negative carbon isotope excursions (CIEs) have been globally observed, and they were linked to volcanogenic emissions or methane release by dissociation of clathrates. The triggering factor of the negative CIEs was attributed to the emplacement of the Central Atlantic Magmatic Province (CAMP) and the break-up of the Pangea. Specifically, three significant carbon-cycle disruptions named Precursor, Initial and Main CIE have been recorded in several stratigraphic successions deposited in terrestrial and pelagic environments. We investigated the organic carbon isotope curve from the subtidal facies of the Mount Sparagio section (Sicily, Italy), which is a continuous peritidal succession representing an Upper Triassic to Lower Jurassic carbonate platform edging the south-western side of the Tethys Ocean. For the first time, we achieved a complete profile of organic carbon stable isotopic composition (δ13Corg) during the end-Triassic mass Extinction event (ETE) in a carbonate shallow water environment. The δ13Corg profile highlights the 3 negative excursions that characterized the Triassic/Jurassic boundary time interval in pelagic and deep-water successions. The documented CIEs correspond to significant biotic turnovers recognized along the Mt. Sparagio section, suggesting that also the Upper Triassic-Lower Jurassic carbonate platforms were affected by the onset of the Central Atlantic Magmatic Province. Furthermore, although the Mt. Sparagio section has been studied in detail for microfacies associations and it is well biostratigraphically constrained with shallow marine macro- and microfossils, only the documented δ13Corg negative shifts allowed to correlate peritidal environments to pelagic successions, making the organic carbon curve (δ13Corg) a powerful tool for global correlations.

Minimally Invasive Vacuum-Aided Extraction Technique for the Lipid Analysis of Historic Parchment.

Parchment is an ancient writing support formed from dehaired animal skins. Its manufacture comprises a series of liming and scraping steps before being stretched and dried under tension. Historical parchment represents a valuable source of cultural heritage which, until now, has limited investigations to noninvasive analyses to infer ink composition, degradation, or physical changes over time. We highlight the prospect of the molecular and isotope compositions of animal lipids from parchment as an untapped record of its production and the animal's diet and environment. We report a minimally invasive, total lipid extraction aided by a vacuum for historical parchments. The quantitative and qualitative compositions of lipid extracts obtained using this method are compared with those obtained using invasive sampling for nine sacrificial membranes dated 1765-1825 CE. This extraction method is then applied to membranes from the Chancery Parliament Rolls (1814-1820 CE) held by The National Archives, UK to obtain lipids and derive taxonomic and dietary information using their stable carbon isotope compositions. This novel vacuum-aided extraction allows, for the first time, animal lipids to be obtained from parchment minimally invasively, paving the way for dietary and paleoclimate studies using this well-dated and common material.

Organic Matter Enrichment in Jurassic Hydrocarbon Source Rocks from the Turpan-Hami Basin: Insights from Organic and Elemental Geochemistry.

Petroleum can be generated by thermal cracking of organic matter within sediments, and the organic matter within sediments plays the dominant role in determining oil and gas generation. Organic matter within sediments is characterized by various sources, such as sapropelic organic matter from algal, microbial, and planktonic organisms and humic organic matter from higher plants. Paleo-productivity, terrestrial influx, and depositional environments could obviously influence the enrichment processes of the organic matter within sediments. Organic and elemental geochemical proxies can investigate the sedimentary process and reflect the enrichment characteristics of organic matter. In this study, hydrocarbon source rocks from the Shuixigou Group were collected from the Taibei Sag of the Turpan-Hami Basin, rock-eval pyrolysis was conducted, and stable carbon isotope composition of organic carbon and major and trace element distributions were measured. Based on this, the type and maturation of organic matter, paleo-productivity, terrestrial influx, and depositional paleo-environments were investigated. The results show that the Jurassic hydrocarbon source rocks are characterized by type III kerogen and are in the oil-window stage of maturation. The depositional paleo-environments of hydrocarbon source rocks in different formations are not remarkably different. The water bodies have freshwater oxidizing environments, and the paleo-climatic characteristics are warm and humid. However, the paleo-productivity of samples from the lower Jurassic Sangonghe Formation is higher than samples from other formations. Overall, the organic matter enrichment in Jurassic hydrocarbon source rocks of the Turpan-Hami Basin could be mutually controlled by the paleo-productivity and depositional paleo-environments. The results of this study could provide theoretical insight into deep petroleum exploration and resource evaluation in the Turpan-Hami Basin.