Stable Carbon Isotope Ratios Research Articles

A novel method for tracing gasoline using GC-IRMS and Relief-Stacking fusion model

Due to China’s vast geographical expanse and the complexity of its natural environment, traditional methods are not suitable for tracing the origins of gasoline samples from different regions of China. The aim of this study is to trace the origins of gasoline samples through the analysis of carbon stable isotopic characteristics from 60 gasoline samples collected across four major regions in China. In this study, a novel method that combines gas chromatography-isotope ratio mass spectrometry (GC-IRMS) with Relief-Stacking was proposed for the first time, significantly enhancing the precision of the provenance results. Firstly, eight characteristic components were identified by Relief feature selection model for the first time and applied to the assessment of carbon stable isotope ratios across different regions. The discovery of these components effectively reduces data redundancy, thereby enhancing the accuracy of provenance analysis. Subsequently, five effective source tracing models (XGBoost, Random Forest, CatBoost, LightGBM, and KNN) were selected based on the CEI values. To further enhance the learning efficiency of the sourcing models, this study integrated the five selected source tracing models using three different methods(voting, stacking, and blending) and validated the performance of the optimal sourcing model. The results indicated that the Stacking fusion model achieves a CEI value of 0.923, significantly outperforming other fusion models. This advantage is attributed to the Stacking fusion model combining the s trengths of Boosting and Bagging ensemble methods and leveraging the advantages of individual classifiers within the model. The method proposed in this study can effectively address the limitations of previous tracing methods and offer valuable insights for the development of platforms related to stable isotope source tracing. In future research, through appropriate parameter adjustments and feature adaptations, the Relief-Stacking model can likewise be applied to source tracing studies in other countries characterized by extensive geographic ranges and variable environmental conditions.

A biogeochemical approach to examining sub-adult diet and the weaning process at Neolithic Tepecik-Çiftlik, Türkiye

Tepecik-Çiftlik, a Neolithic settlement located in the Cappadocia region of Central Anatolia, within the boundaries of Niğde province in modern Türkiye is crucial for helping us to better understand social behaviour and human mobility in the Neolithic, as well as relations between different groups. To investigate dietary habits, subsistence practices, and intra-societal variations stable carbon and nitrogen isotope ratio analysis has been conducted on the Neolithic human and faunal population. Further to this, 21 sub-adults were also sampled for stable carbon and nitrogen isotope ratio analysis to examine sub-adult diet, complementary feeding, and the cessation of breastfeeding as part of the weaning process. This isotopic investigation into the weaning process is complemented by a previously conducted study using Sr/Ca ratios from bone apatite of the same population. The δ13C values of the sampled sub-adults range from −19.8 ‰ to −19.0 ‰ and the δ15N values range from 8.0 ‰ to 15.2 ‰. The isotopic data suggest a very early onset of complementary feeding (ca. 0.2 years of age) and a brief breastfeeding period, relative to other prehistoric populations. The cessation of breastfeeding and this very brief weaning process was likely completed by ca. 1–1.5 years old. This early commencement of complementary feeding was most probably a deliberate social and cultural choice, supported by the presence of bowls and feeding spoons in the graves of very young babies and infants. However, this cultural choice may also have affected the mortality profile of the Neolithic population.

Utilization of stable isotopes in teeth to investigate pygmy sperm whales (Kogia breviceps) in the southeastern United States

AbstractThe pygmy sperm whale (Kogia breviceps) is currently the second‐most stranded cetacean in the southeastern United States (SEUS), but information concerning their population structure is severely limited. This study used stable isotope analysis to investigate the isotopic niches and population structure of K. breviceps among three regions in the SEUS determined by the distance of the continental shelf break and a fourth region in the Gulf of Mexico. Teeth from stranded individuals were subsampled via dental drill at four separate areas on each tooth, representing four different age classes: calf, juvenile, subadult, and adult. Stable isotope ratios of carbon and nitrogen were measured in the organic component of 42 teeth, and oxygen isotope ratios were measured in the inorganic (hydroxyapatite) component of 19 teeth. No differences were found in δ13C, δ15N, or δ18O values between regions. However, differences between age classes were significant for adults and subadults for δ13C and adults and juveniles for δ15N. Differences between males and females were also significant for δ15N. Results from this study provide the first carbon and nitrogen isotope values from different age classes of pygmy sperm whales as well as the first reported oxygen isotope values for this species.

Geographic variability of carbon and nitrogen isotope ratios of nonvolant terrestrial small mammals (Rodentia) across 3 Brazilian biomes

Abstract In this study, we investigated landscape variability of the carbon and nitrogen isotopic composition of nonvolant small mammals in the 3 main Brazilian biomes (Amazon, Atlantic Forest, and Cerrado) while also considering the differential spatial distribution of C4 plants in these biomes. We compiled a subset of data on stable carbon and nitrogen isotope ratios from nonvolant small mammals of the order Rodentia and compared the aggregated isotopic variability at the biome level using classical δ13C–δ15N biplot. The concept of isotopic niche width was used to test whether different foraging attributes drive their isotopic composition, while a Bayesian isotopic mixing model was used to estimate the proportion of 3 main food categories available to these small mammals. We also developed isoscapes in the Brazilian biomes, interpolating animals δ13C and δ15N based on the geographic coordinates of each sample and “sourcescapes” considering geographic variation of the dietary sources. The findings of this study advance our understanding of the foraging ecology of small mammals in biodiversity-rich regions of the Neotropics. Classical methodologies such as stomach content confirmed dietary choices revealed by the stable isotopic composition and also highlighted the importance of C3 and C4 plants in the diet of this group of animals, especially in biomes such as the Atlantic Forest and Cerrado, where there is a predominance of highly altered landscapes. These results confirm that replacing the original vegetation with C4 crops has altered the feeding patterns of small mammals, which could lead to critical ecological changes in the trophic structure of these areas. Vertical stratification of the dietary niche and the interaction between biome and foraging lifestyle were also observed. However, in each biome, there was significant intraspecific and interspecific variation caused by preferences for ingestion of plant and animal material, leading to different degrees of omnivory. Finally, the high local variability between individuals and species requires a larger sampling design that may also contribute to improved spatial resolution of the isoscapes.

Monitoring weekly δ 13С variations along the cambium-xylem continuum in the Canadian eastern boreal forest.

Intra-annual variations of carbon stable isotope ratios (δ13C) in different tree compartments could represent valuable indicators of plant carbon source-sink dynamics, at weekly time scale. Despite this significance, the absence of a methodological framework for tracking δ13C values in tree rings persists due to the complexity of tree ring development. To fulfill this knowledge gap, we developed a method to monitor weekly variability of δ13C in the cambium-xylem continuum of black spruce species [Picea mariana (Mill.) BSP.] during the growing season. We collected and isolated the weekly incremental growth of the cambial region and the developing tree ring from five mature spruce trees over three consecutive growing seasons (2019-2021) in Simoncouche and two growing seasons (2020-2021) in Bernatchez, both located in the boreal forest of Quebec, Canada. Our method allowed for the creation of intra-annual δ13C series for both the growing cambium (δ13Ccam) and developing xylem cellulose (δ13Cxc) in these two sites. Strong positive correlations were observed between δ13Ccam and δ13Cxc series in almost all study years. These findings suggest that a constant supply of fresh assimilates to the cambium-xylem continuum may be the dominant process feeding secondary growth in the two study sites. On the other hand, rates of carbon isotopic fractionation appeared to be poorly affected by climate variability, at an inter- weekly time scale. Hence, increasing δ13Ccam and δ13Cxc trends highlighted here possibly indicate shifts in carbon allocation strategies, likely fostering frost resistance and reducing water uptake in the late growth season. Additionally, these trends may be related to the black spruce trees' responses to the seasonal decrease in photosynthetically active radiation. Our findings provide new insights into the seasonal carbon dynamics and growth constraints of black spruce in boreal forest ecosystems, offering a novel methodological approach for studying carbon allocation at fine temporal scales.

QUALITY EVALUATION OF PINE AND BLOSSOM HONEY SAMPLES PRODUCED IN TURKEY: CORRELATION BETWEEN PHYSICOCHEMICAL CHARACTERISTICS

This study presents physicochemical characteristics of 39 honey samples (21 blossom and 18 pine honey) collected during two years from three different geographical regions of Türkiye that differs vastly in climatic conditions and thus plant species. The samples were analysed for δ13C/δ12C stable carbon isotope ratios of honey (δ13Ch) and its protein fraction (δ13Cp), moisture, free acidity, proline and 5-hydroxymethyl furfural (HMF) content, diastase activity and sugar composition. The results showed that C4 sugar content, proline content, diastase activity, acidity values of pine honeys were higher than that of blossom honeys whereas, higher moisture and HMF content were detected for blossom honeys. Besides, geographical region mainly affected the moisture and C4 sugar contents. High correlations between HMF and δ13Ch and δ13Cp; proline and acidity values; fructose and glucose content were determined, and this indicated the robustness of the analysis and quality evaluation among different honey types and regions.

CHARACTERIZATION OF FINE CARBONACEOUS AEROSOLS FROM THE EASTERN MEDITERRANEAN: CONTRIBUTIONS OF FOSSIL AND NON-FOSSIL CARBON SOURCES

ABSTRACT In order to better characterise carbonaceous components in atmospheric aerosols and to assess the contributions of fossil carbon (FC) and non-fossil carbon (NFC) sources and their seasonality in the Eastern Mediterranean, we collected fine (PM1.3) aerosols at a remote marine background site, the Finokalia Research Station, Crete, Greece, over a period of one-year. PM1.3 samples were analysed for elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC), and stable carbon isotope ratio (δ13CTC) and radiocarbon content (14CTC) (pMC) of total carbon (TC). All the parameters, i.e., PM1.3, δ13CTC and 14CTC showed a clear temporal pattern with higher values in summer and lower values in autumn. The 14CTC ranged from 54.7 to 99.1 pMC with an average of 74.5 pMC during the entire year. The FC content in TC (FCTC) was found to be slightly lower in winter and almost stable in other seasons, whereas the NFC contents (NFCTC) showed a clear seasonality with the highest level in summer followed by spring and the lowest level in winter. Based on these results together with the seasonal distributions of organic tracers, we found that biomass burning (BB) and soil dust are two major sources of the fine aerosols in winter. Although biogenic emissions of VOCs followed by subsequent secondary oxidation processes are significant in summer followed by spring and autumn, pollen is a significant contributor to TC in spring. This study showed that emissions from fossil fuel combustion are significant (25.5%) but minor compared to NFC sources in the eastern Mediterranean.

Stable isotope analysis of western Lake Superior predatory fishes, part one: Trophic niche overlap

Characterizing food web interactions between introduced and native fish predators is important to quantify niche overlap, assess predator–prey balance, and support fisheries management. Lake Superior provides an ideal setting to investigate potential trophic overlap between native top predators, lake trout (Salvelinus namaycush) and walleye (Sander vitreus), and a diverse assemblage of introduced salmonids. Angler-caught fish were used to measure trophic position and niche overlap between predatory fishes in the western arm of Lake Superior based on carbon and nitrogen stable isotope ratios (δ13C, δ15N). Within a species, we did not find consistent differences in either δ13C or δ15N values by sex, collection year, capture location, or length. Among species, the range in δ15N values was >5 ‰, indicating that these species occupy ∼2 trophic positions, with dietary reliance ranging from primarily invertebrates to primarily fish, whereas the range in δ13C values indicated dietary reliance on a mix of pelagic and benthic prey. Combined, the δ13C and δ15N values revealed siscowet lake trout as the apex predator having a distinct trophic niche, while walleye and lean lake trout were intermediate trophic position predators with overlapping isotopic niches, and introduced salmonids were the lowest trophic position predators with overlapping trophic niches. Overlapping trophic niches indicated similar resource reliance and habitat occupancy among native lake trout and walleye, as well as among introduced salmonids, but less so between native and introduced predators.

Анализ отношений стабильных изотопов легких элементов в отдельных компонентах мёда

Honey possesses excellent sensory and nutritional properties, which makes it a valuable food ingredient. However, the same qualities make it one of the most often adulterated products in the world. Constant violations of processing technology threaten the beekeeping industry. In this regard, new authenticity criteria are a popular area of honey studies. The article introduces a method for establishing ratios of light stable isotopes in honey. The study featured 36 samples of honey of various geographical origins and botanical profiles, as well as five samples of sugar syrups from various raw materials. The quantitative profiles were obtained using a Delta Advantage V isotope mass spectrometer (USA – Germany) with additional Flash IRMS and Conflo IV modules. The experiment involved the ratios of stable carbon isotopes in honey δ13C (gross) and nitrogen δ15N in its protein fraction, as well as the values of δ13C, δ18O, and δ2H of ethanol isolated from fermented honey. The values of δ13C (gross) and δ13C of honey proteins made it possible to calculate the amount of added sugar of corn and cane origin. Exogenous sugars in the amounts of 6.5% and 18% cane sugar were detected in two samples. Isotope mass spectrometry was able to identify honey samples with exogenous sugars of C4-plant origin. However, the method failed to detect sugar-containing substances from C3-type plants. The δ18O index demonstrated some prospects as an identification criterion for sugars from C3-plants in honey. Nitrogen isotope ratios in honey proteins proved to be an efficient tool for determining honey authenticity and an additional criterion for identifying bee products. The research resulted in a patent (RU2809285C1) for a new method of determining exogenous sugar-containing substances in honey

River-estuary continuum highlighted by variabilities in carbon and nitrogen stable isotope ratios of the catadromous eel Anguilla japonica.

Estuaries exhibit high physicochemical variability and the properties of estuaries and the constituent segments are not yet systematically understood. This study aims to reveal the spatial heterogeneity of predominant organic sources using carbon and nitrogen stable isotope ratios (δ13C and δ15N, respectively) of Japanese eels (Anguilla japonica), one of the ideal natural samplers. In the Miyakoda River, Japan, our study site, the effectiveness of eel δ13C and δ15N values as standard indices of predominant organic sources was tested by employing the River Continuum Concept. This study then extended the application of these indices to the estuary, i.e., the Hamana Lake system, into which the Miyakoda River flows. Once in the upper estuary, eel δ13C and δ15N values became high, with the latter peaking in this river-estuary continuum, indicating that artificial labile subsidies (nutrients and organic matter) with high δ15N values were rapidly assimilated into the food web. Eel δ15N values decreased again in the middle estuary. Nevertheless, the influence of terrestrial organic subsidies extended into this segment, as evidenced by the low δ13C values of eels. These results suggest that refractory organic matter with low δ15N values, such as plant-derived ones, is slowly assimilated into the food web in the downstream estuarine segments. The higher δ13C values in the lower estuary suggested that the contribution of eelgrass or macroalgae occurred in addition to benthic microalgae. Thus, our results emphasize the need to consider the multiple energy flows to understand the estuary as a continuum.

Differentiating Pond-Intensive, Paddy-Ecologically, and Free-Range Cultured Crayfish (Procambarus clarkii) Using Stable Isotope and Multi-Element Analysis Coupled with Chemometrics.

The farming pattern of crayfish significantly impacts their quality, safety, and nutrition. Typically, green and ecologically friendly products command higher economic value and market competitiveness. Consequently, intensive farming methods are frequently employed in an attempt to replace these environmentally friendly products, leading to potential instances of commercial fraud. In this study, stable isotope and multi-element analysis were utilized in conjunction with multivariate modeling to differentiate between pond-intensive, paddy-ecologically, and free-range cultured crayfish. The four stable isotope ratios of carbon, nitrogen, hydrogen, and oxygen (δ13C, δ15N, δ2H, δ18O) and 20 elements from 88 crayfish samples and their feeds were determined for variance analysis and correlation analysis. To identify and differentiate three different farming pattern crayfish, unsupervised methods such as hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used, as well as supervised multivariate modeling, specifically partial least squares discriminant analysis (PLS-DA). The HCA and PCA exhibited limited effectiveness in classifying the farming pattern of crayfish, whereas the PLS-DA demonstrated a more robust performance with a predictive accuracy of 90.8%. Additionally, variables such as δ13C, δ15N, δ2H, Mn, and Co exhibited relatively higher contributions in the PLS-DA model, with a variable influence on projection (VIP) greater than 1. This study is the first attempt to use stable isotope and multi-element analysis to distinguish crayfish under three farming patterns. It holds promising potential as an effective strategy for crayfish authentication.

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Investigation of isotopic linkages between raw materials and black powder.

The stable isotope analysis of black powder (BP) is of great significance for its comparison and source inference. Previous studies have verified the feasibility of distinguishing different BP samples through stable isotopes. However, the impact of raw materials and synthesis processes on the stable isotopes of BP remains unclear. On the one hand, the raw materials of BP are widely sourced, and whether stable isotopes can distinguish different source materials remains to be studied. On the other hand, the synthesis of BP involves the physical mixing of raw materials, and whether this process leads to isotope fractionation also needs further investigation. To address these problems, stable isotope ratios of 27 charcoals, 15 potassium nitrates, 6 self-made and 10 commercial BP samples were analyzed. The results showed that the stable isotope ratios can be utilized to distinguish charcoals and potassium nitrates from different manufacturers and batches. No significant differences in the nitrogen and oxygen stable isotope ratios between the self-made BP and its raw materials were observed, indicating that the physical mixing process does not induce significant fractionation of stable isotopes. However, the carbon stable isotope ratios of charcoal increased (within 2SD) after being synthesized into BP. Due to the utilization of additives and variations in the synthesis process, the correlation between the stable isotope ratios of commercial BP and its raw materials was complex. The findings of this study provide a scientific reference for tracing the source of BP.

Stable carbon isotope ratios of pristine carbohydrates preserved within nannofossil calcite

The geochemical characterization of phytoplankton-derived organic compounds found in marine sediments has been widely used to reconstruct atmospheric pCO2 throughout the Cenozoic. This is possible owing to a well-established relationship between the carbon isotope ratios of phytoplankton biomass and CO2 concentration in the ambient seawater. An ideal molecular target for such proxy reconstructions would be degradation resistant on geologic timescales and unambiguously associated with known, experimentally tractable, organisms, so that species-specific models can be developed, calibrated, and applied to appropriate material. However, existing organic matter targets do not meet these criteria, primarily owing to ambiguity in the source species of recalcitrant compounds in deep time. Here we explore the potential of a novel organic carbon target for isotopic analysis: acidic polysaccharides extracted from the calcite plates (coccoliths) that are produced by all calcifying haptophytes. Carbohydrates are usually rapidly remineralized in sediments, but coccolith-associated polysaccharides (CAPs) are mechanically protected from diagenesis within the coccolith calcite lattice. Coccoliths can be taxonomically separated by size and identified, often to species level, prior to CAP extraction, providing a species-specific record. Coccolith morphology and composition are important additional sources of information, which are then unambiguously associated with the extracted CAPs. We found that carbon isotope ratios of CAPs changed in response to the environmental changes associated with a glacial cycle, which we attribute to temperature-driven changes in average growth rate. Once the underlying biosynthetic processes and the associated isotope effects are better understood, this archive of pristine organic matter has the potential to provide insight into phytoplankton growth rates and atmospheric pCO2 far beyond the Cenozoic, to when the first coccolithophores inhabited the surface ocean over 200 million years ago.

A long-term study of stable isotope ratios of fingernail keratin and amino acids in a mother-infant dyad.

To evaluate the potential of compound-specific isotope analysis of amino acids (CSIA-AA) for investigating infant feeding practices, we conducted a long-term study that compared infant and maternal amino acid (AA) nitrogen isotope ratios. Fingernail samples were collected from a single mother-infant dyad over 19 months postpartum. Carbon and nitrogen stable isotope ratios were measured in the bulk keratin of the fingernail samples. Selected samples were then hydrolyzed and derivatized for compound-specific nitrogen isotope analysis of keratin AAs. As in previous studies, infant bulk keratin nitrogen isotope values increased during exclusive breastfeeding and fell with the introduction of complementary foods and eventual cessation of breastfeeding. Infant trophic AAs had elevated nitrogen isotope values relative to the mother, while the source AAs were similar between the mother and infant. Proline and threonine appeared to track the presence of human milk in the infant's diet as the isotopic composition of these AAs remained offset from maternal isotope values until the cessation of breastfeeding. Although CSIA-AA is costly and labor intensive, it appears to hold potential for estimating the duration of breastfeeding, even after the introduction of complementary foods. Through the analysis of a full suite of AAs, it may also yield insights into infant physiology and AA synthesis.

Relationship between fish traits and the methane‐derived carbon contribution to fish in a shallow lake

Abstract Although the transfer of methane‐derived carbon (MDC) to benthic macroinvertebrates such as chironomid larvae and oligochaetes has been well documented, knowledge of the transfer of MDC to fish is limited. We investigated the MDC contribution to 28 fish species through their growth stages and examined the relationship between fish traits including body size, and MDC contribution to fish within species in Lake Kasumigaura, Japan. We used carbon stable isotope ratios and a two‐source mixing model (methane‐oxidation bacteria [MOB] and particulate organic matter) to estimate the MDC contribution to fish. The MDC contribution to individual fish ranged from 0% to 21.5%. Anguilla japonica showed the highest MDC contribution (mean 3.8%). Fish species were classified into four groups according to two criteria: (a) whether the correlation between the MDC contribution and fish size (within species) was significantly negative (negative vs. not significant; ns); and (b) whether the 90th percentile of MDC contribution was 0% or not. The mean MDC contribution was highest (2.18% ± 2.93%, 12 species) for the group with (a)ns/(b)>0%, including the high contribution species such as Abbottina rivularis (mean 5.5%) and Biwia zezera (mean 9.8%). This group (12 species) included relatively high numbers of benthic habitat use (eight species) and omnivores (nine species). The mean MDC contributions were almost zero for the group with (a)ns/(b)=0% (seven species), which included only two species of benthic habitat use and one species of omnivores. The mean MDC contributions were intermediate for the other groups with (a)negative/(b)>0% (1.30% ± 1.17%, seven species) and (a)negative/(b)=0% (0.10%, two species). The negative correlation between fish size within species and MDC contribution in groups with (a)negative/(b)>0% and (a)negative/(b)=0% indicated that ontogenetic habitat and dietary shifts induced changes in MDC transfer. Our results suggest that 21 out of 28 fish species were involved in the MDC transfer in a shallow lake, but variation in MDC transfer could be explained by fish traits (trophic guild and habitat use). Although the mean MDC contribution to all fish species was low (0.61% ± 1.97%), the roughly estimated annual consumption rate of fish on MOB corresponded to approximately 10% of the MOB production in the sediment, suggesting that fish contribute to methane dynamics from the perspective of biogeochemical cycles.

Sourcing and long-range transport of particulate organic matter in river bedload: Río Bermejo, Argentina

Abstract. Fluvial transport of organic carbon from the terrestrial biosphere to the oceans is an important term in the global carbon cycle. Traditionally, the long-term burial flux of fluvial particulate organic carbon (POC) is estimated using river suspended sediment flux; however, organic carbon can also travel in river bedload as coarse particulate organic matter (POMBed). Estimates of fluvial POC export to the ocean are highly uncertain because few studies document POMbed sources, flux, and evolution during long-range fluvial transport from uplands to ocean basins. This knowledge gap limits our ability to determine the global terrestrial organic carbon burial flux. In this study we investigate the flux, sources, and transformations of POMBed during fluvial transport over a ∼1300 km long reach of the Río Bermejo, Argentina, which has no tributary inputs. To constrain sourcing of POMBed, we analyzed the composition and stable hydrogen and carbon isotope ratios (δ2H, δ13C) of plant wax biomarkers from POMBed at six locations along the Río Bermejo and compared this to samples of suspended sediment, soil, leaf litter, and floating organic debris (POMfloat) from both the lowland and headwater river system. Across all samples, we found no discernible differences in n-alkane average chain length or nC29 δ13C, indicting a common origin for all sampled POMBed. Leaf litter and POMfloat nC29 δ2H values decrease with elevation, making it a useful proxy for POMBed source elevation. Biomarker δ2H values suggest that POMBed is a mix of distally derived headwater and locally recruited floodplain sources at all sampling locations. These results indicate that POMBed can be preserved during transport through lowland rivers for hundreds of kilometers. However, the POMBed flux decreases with increasing transport distance, suggesting mechanical comminution of these coarse organic particles and progressive transfer into the suspended load. Our provisional estimates suggest that the carbon flux from POMBed comprises less than 1 % of the suspended load POC flux in the Río Bermejo. While this represents a small portion of the river POC flux, this coarse, high-density material likely has a higher probability of deposition and burial in sedimentary basins, potentially allowing it to be more effective in long-term CO2 drawdown relative to fine suspended particles. Because the rate and ratio of POMBed transport versus comminution likely vary across tectonic and climatic settings, additional research is needed to determine the importance of POMBed in the global carbon cycle.

Isotope-based inferences of the trophic niche of short-finned pilot whales in the Webbnesia

Knowledge of predator-prey interactions is key in ecological studies and understanding ecosystem function, yet this is still poorly explored in the deep-sea environment. Carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope ratios of a deep-diving species, the short-finned pilot whale (Globicephala macrorhynchus), were used to explore knowledge gaps on its ecological niche and foraging habitats in the Webbnesia marine ecoregion (Tenerife Island, n = 27 animals vs. Madeira, n = 31; 500 km apart) where animals display distinct levels of site fidelity. Specifically, we tested whether intraspecific isotopic variation results from differences between geographic areas (due to possible foraging plasticity between regions), sexes, and/or years (2015–2020) using Generalized Linear Models. In general, significant differences (p < 0.05) were found in the stable isotope profiles of pilot whales between the two archipelagos, which were also reflected in their isotopic niche. The higher mean and wider range of δ15N values in Tenerife suggest that pilot whales consume prey of higher trophic levels and more diverse than Madeira. The higher mean and wider range of δ13C values in Madeira suggest that in that island, pilot whales rely on prey from more diverse habitats. There was significant variation between some years, but not between sexes. Finally, we discuss pilot whales' foraging strategies worldwide and infer the reliance on benthic or benthopelagic food sources in the Webbnesia.

Simultaneous onboard analysis of seawater dissolved inorganic carbon (DIC) concentration and stable isotope ratio (δ13C‐DIC)

AbstractDissolved inorganic carbon (DIC) and its stable carbon isotope (δ13C‐DIC) are valuable parameters for studying the aquatic carbon cycle and quantifying ocean anthropogenic carbon accumulation rates. However, the potential of this coupled pair is underexploited as only 15% or less of cruise samples have been analyzed for δ13C‐DIC because the traditional isotope analysis is labor‐intensive and restricted to onshore laboratories. Here, we improved the analytical precision and reported the protocol of an automated, efficient, and high‐precision method for ship‐based DIC and δ13C‐DIC analysis based on cavity ring‐down spectroscopy (CRDS). We also introduced a set of stable in‐house standards to ensure accurate and consistent DIC and δ13C‐DIC measurements, especially on prolonged cruises. With this method, we analyzed over 1600 discrete seawater samples over a 40‐d cruise along the North American eastern ocean margin in summer 2022, representing the first effort to collect a large dataset of δ13C‐DIC onboard of any oceanographic expedition. We evaluated the method's uncertainty, which was 1.2 μmol kg−1 for the DIC concentration and 0.03‰ for the δ13C‐DIC value (1σ). An interlaboratory comparison of onboard DIC concentration analysis revealed an average offset of 2.0 ± 3.8 μmol kg−1 between CRDS and the coulometry‐based results. The cross‐validation of δ13C‐DIC in the deep‐ocean data exhibited a mean difference of only −0.03‰ ± 0.07‰, emphasizing the consistency with historical data. Potential applications in aquatic biogeochemistry are discussed.

A multi-analytical approach for the identification of pollutant sources on black crust samples: Stable isotope ratio of carbon, sulphur, and oxygen

This study is focused on the identification of pollutant sources on black crust (BC) samples from the Monumental Cemetery of Milan (Italy), through a multi-analytical approach based on the determination of stable isotope ratios of carbon, sulphur, and oxygen. Six black crust samples, mainly developed on marble sculptures over a time span of 100–150 years, were analysed.For the first time, δ13C was measured for BC samples: δ13C values of the pulverized samples (from −1.2 to +1.3 ‰) are very close to the values obtained from the carbonate matrix, whereas after the removal of the matrix through acidification, δ13C values of BC samples from Milan range from −27.2 to −22.1 ‰, with no significant variation between samples with different ratios of organic carbon to elemental carbon. In sum, the δ13C values obtained for all BC samples fall within the range of anthropogenic emissions such as vehicle traffic, coal combustion and industrial emissions.δ34S and δ18O values of sulphate from BC samples range from −6.3 to +7.0 ‰ and from +7.6 to +10.5 ‰, respectively. Coupling the analysis of the oxygen isotope ratio with that of sulphur enables a more precise identification of the origin of sulphates: the observed isotopic composition falls in the range typical for anthropogenic emission of sulphur dioxide.Overall, in this study, C, S and O isotopes were combined for the first time to assess pollutant sources on black crust samples: this multi-stable isotope approach allowed to show that the BC formation on monuments from the Monumental Cemetery of Milan mostly results from anthropogenic emissions from fossil fuels combustion by road vehicles and factories, as well as domestic heating.