Stable isotope signatures provide unique tools to identify, quantify, and predict biogeochemical element cycling through and across boundaries of all geo spheres, and on extremly different scale dimensions. Mechanistic approaches, however, require careful approaches wrt. analytical methods, standardization, experimental verification, and theoretical evaluation. Stay tuned for the latest achievements in the field of stable isotope biogeosciences.
Orals: Wed, 6 May, 08:30–12:25 | Room 1.31/32
Isotopic analyses of carbon (δ¹³C) and oxygen (δ¹⁸O) are widely applied in biogeosciences to investigate biogeochemical cycles, ecosystem functioning, and environmental dynamics. Elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) represents one of the most widely applied systems for bulk samples. The laser ablation-IRMS (LA-IRMS) provides the possibility to resolve spatial and temporal variability at high resolution, but also presents some limitations due to gas handling, signal stability, and analytical comparability with conventional approaches.
For this study, we present a methodological comparison between δ¹³C and δ¹⁸O measurements obtained using EA-IRMS and an improved LA-IRMS configuration. In our configuration, the LA is coupled with the IRMS through a greenhouse gas (GHG) analyzer specifically modified to concentrate, purify, and stabilize CO₂ and CO generated during ablation to improve the gas signal for isotope measurements.
Analyses were conducted on hazelnut (Corylus avellana L.) wood slices for EA-IRMS and tree-ring increments for LA-GHG-IRMS. The comparison between the two methods showed main differences related to sampling resolution and analytical configuration. The LA-GHG-IRMS system provided high-resolution isotope measurements that allowed investigations of intra-seasonal patterns.
The application of the LA-GHG-IRMS system extends the analytical utility of laser-based stable isotope measurements in biogeosciences, providing new opportunities for high-resolution studies of ecological processes in terrestrial ecosystems.
How to cite: Tunno, I., Portarena, S., Carlino, P., Stremtan, C., Papale, D., and Calfapietra, C.: Application of EA-IRMS and a LA-GHG-IRMS approach for high-resolution carbon and oxygen isotope analysis in woody biomass, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21817, https://doi.org/10.5194/egusphere-egu26-21817, 2026.
Quantifying the relative contributions of evolutionary mechanisms to tree water-use strategies is critical for predicting species’ responses to climate change and supporting forest management strategies. Common garden experiments can explicitly address the contributions of genetics and plasticity in physiological-related traits. However, these experiments typically focus on young trees, and long-term physiological measurements from common garden experiments are largely lacking. Stable isotope analysis of tree rings bridges this gap by enabling the reconstruction of long-term water-use strategies of mature trees growing in long-term common garden experiments.
In this study, we investigate the evolutionary mechanisms underlying long-term water-use strategies in Quercus petraea across its distribution range by analysing annually-resolved stable isotope ratios (δ¹³C, δ¹⁸O, δ²H) from tree-ring cellulose. We sampled 234 individuals originating from nine provenances grown in four European common gardens (Denmark, France, Poland, and the United Kingdom). For the period 2012–2021, we derived annual carbon isotope discrimination (∆¹³C), intrinsic water-use efficiency (iWUE), and isotopic enrichment relative to precipitation (∆¹⁸O and ∆²H). Linear mixed-effects models were used to quantify the contributions of genetic variation, phenotypic plasticity, and its interaction (i.e. genetically-based plasticity) to variation in iWUE, ∆¹⁸O, and ∆²H. The dual-isotope approach (δ¹³C and ∆¹⁸O) was applied to investigate the provenance-specific adjustments in photosynthetic rate and stomatal conductance across sites.
Our results revealed significant genetic and genetically-based plasticity effects on all isotope ratios whereas phenotypic plasticity had a significant effect only on ∆²H. ∆¹⁸O and ∆²H exhibited distinct patterns related to genetics and phenotypic plasticity effects. Notably, ∆²H variability across sites exceeded provenance-level variation. These results could be indirectly related to the link of ∆²H to primary C metabolism. The dual-isotope analysis (δ¹³C and ∆¹⁸O) further identified adjustments in stomatal conductance as the main plastic response to contrasting environments. The provenance with the least plasticity (originally from the United Kingdom) also showed reductions in photosynthetic rates, indicating a limited capacity to adjust to contrasting environments. Overall, these findings highlight strong genetic and plastic control in water-use traits and demonstrate the potential of stable isotopes in tree rings to unravel evolutionary mechanisms in tree water-use strategies.
How to cite: Martínez-Sancho, E., Vitasse, Y., Treydte, K., Saurer, M., Argelich Ninot, M., Benito-Garzón, M., Bigler, C., Fonti, P., Miranda, J. C., Pålsson, A., Verstege, A., and Rellstab, C.: Stable isotopes in tree rings reveal the role of genetics and phenotypic plasticity in shaping water-use strategies of sessile oak across Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14404, https://doi.org/10.5194/egusphere-egu26-14404, 2026.
Carbon use efficiency (CUE), defined as the ratio of net primary production (NPP) to gross primary production (GPP), reflects the efficiency of carbon conversion into plant biomass after accounting for respiratory losses. As a key parameter in plant carbon budgeting and terrestrial carbon sequestration assessments, CUE is difficult to measure directly due to the challenges in quantifying gross CO₂ fixation and total respiration. Thus, many carbon cycle models rely on simplified empirical values (e.g., 0.5). Although climate warming may influence CUE due to the widely observed temperature‐sensitivity of respiration, the responses of CUE to warming remain unclear.
In this study, we grew wheat (T. aestivum) and upland rice (O. sativa) in controlled chambers under two temperatures: 25°C (control) and 29°C (+4°C warming). We took advantage of a gas exchange and 13C-labelling facility to estimate the gross photosynthetic rate of individual plants and trace the allocation of fixed carbon to shoot and root growth. A compartment model was fit to the data of tracer dynamic during the chase period to analyze the turnover features of carbon pools.
Both species exhibited physiological acclimation to warming: increased leaf‐level maximum carboxylation rate and specific leaf area, but decreased basal respiration rate. Consequently, whole‐plant CUE did not differ significantly between temperature treatments. ¹³C dynamics further revealed that warming did not alter the turnover rates of carbon pools supporting respiration and growth. These results indicate that +4°C warming did not affect CUE in wheat or upland rice, demonstrating a coordinated acclimation of photosynthesis and respiration to elevated temperature.
How to cite: Gong, X., Yang, Z., Liu, Q., and Li, L.: Plant carbon-use efficiency under warming: insights from a ¹³CO2 pulse-chase experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9124, https://doi.org/10.5194/egusphere-egu26-9124, 2026.
Gross primary production (GPP) describes ecosystem-scale canopy photosynthesis and provides the foundation of the ecosystem carbon budget. It is often derived from eddy covariance data based on models of the component processes. At several sites in Sweden and the Czech Republic, we have quantitatively tested these GPP estimates against independent empirical data based on stem-scale measurements of xylem water flux and intrinsic water-use efficiency (iWUE), where iWUE is estimated from the stable isotope composition of phloem contents. With one exception, these comparisons have agreed well in the middle of the growing season. On the other hand, at several sites, the methods showed distinct discrepancies either at the beginning or the end of the growing season. We discuss possible causes of these seasonal discrepancies ,including the decoupling of phloem contents from gas-exchange, the scaling of sap flux, mesophyll conductance, decoupling of air masses above and below the canopy, and the inference of GPP from eddy covariance data. Quantitative tests of these methods against independent data will be critical as our need to quantify carbon sources and sinks continues to grow.
How to cite: Marshall, J., Tarvainen, L., Vernay, A., Stojanović, M., Stangl, Z. R., and Rütting, T.: Comparing eddy covariance estimates of gross primary production to estimates from stem sap flux and phloem d13C across sites., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10665, https://doi.org/10.5194/egusphere-egu26-10665, 2026.
Quantifying labile soil carbon (C) pools and their stable isotope composition (δ¹³C) is fundamental for elucidating microbially mediated C cycling, soil organic matter turnover, and isotope fractionation during biogeochemical transformations. Extractable C and microbial biomass C are commonly obtained using salt solutions (e.g., 0.25–0.5 M K₂SO₄); however, subsequent determination of C concentrations and isotope ratios typically requires labor-intensive sample preparation steps, including freeze-drying, oven-drying, or desalting by dialysis. These procedures are time-consuming and may result in substantial losses of dissolved organic C, potentially biasing isotopic signatures.
Here, we present a novel analytical method that enables the simultaneous determination of C concentrations and stable isotope composition (δ¹³C) directly from liquid 0.5 M K₂SO₄ soil extracts without any prior sample preparation. This approach allows direct quantification of extractable and microbial biomass C, substantially reducing sample handling and associated analytical uncertainty.
Method validation across contrasting soil types demonstrates high precision and reproducibility for both elemental concentrations and isotope ratios, while avoiding C losses associated with dialysis or concentration procedures. The method facilitates rapid, high-throughput analysis and enhances the temporal and mechanistic resolution of studies on microbial turnover, rhizosphere processes, and soil C dynamics.
Overall, this approach provides a robust new tool for biogeoscience research, enabling integrated assessments of labile C pools and their isotopic signatures and supporting improved process-based understanding of soil biogeochemical cycling.
How to cite: Adnew, G. A., de Castro, M., and Ambus, P. L.: A novel method for simultaneous quantification and isotope analysis of labile soil carbon directly from liquid extracts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6598, https://doi.org/10.5194/egusphere-egu26-6598, 2026.
Carbon isotope ratios of C3 plants can been used to infer intrinsic water-use efficiency. Several transects have been established across Australia to study the sensitivity of intrinsic-water use efficiency to mean annual precipitation. These investigations showed a surprising divergence in the sensitivity of carbon-isotope discrimination to mean annual precipitation among sub-continental regions. Here, we combine previous observations with measurements along a new transect in northeastern Australia to show that such sub-continental scale sensitivity in the response of intrinsic water-use efficiency to precipitation depends on regional-scale soil phosphorus concentrations. The influence of soil phosphorus appears to operate through modulation of stomatal conductance, rather than, or in addition to, photosynthetic capacity. We hypothesize that Australian woody plant species have evolved to use high transpiration rates to facilitate phosphorus foraging in phosphorus-impoverished, ancient soils. Our analyses suggest that this strategy interacts with the well know strategy of increasing intrinsic water-use efficiency in response to decreasing mean annual precipitation.
How to cite: Cernusak, L., Alam, I., Farquhar, G., Givnish, T., De Kauwe, M., Schulze, E.-D., Westerband, A., Wright, I., and Cheesman, A.: Sub-continental patterns of carbon-isotope discrimination across Australia in relation to precipitation and soil nutrients, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15760, https://doi.org/10.5194/egusphere-egu26-15760, 2026.
Volcanic hydrocarbon reservoirs are distributed across more than 40 basins in 13 countries globally. In recent years, significant exploration prospects have been identified in Mesozoic volcanic strata within China’s offshore basins, including the Bohai Bay, East China Sea, Pearl River Mouth, and Qiongdongnan basins. The study of volcanic reservoirs remains a frontier topic in petroleum geology. Characterized by strong heterogeneity resulting from the superposition of multiple diagenetic processes and subsequent reformation, these reservoirs pose significant challenges for favorable reservoir prediction. Furthermore, the pronounced intra-volcanic heterogeneity leads to significant variations in hydrocarbon properties within single volcanic edifices, complicating the determination of hydrocarbon sources and the reconstruction of accumulation histories.Taking the BZ8S-A area in the Bozhong Sag of the Bohai Bay Basin as a case study, this research addresses these challenges. The study area is currently drilled by four exploration wells, revealing distinct variations in hydrocarbon composition, reservoir temperature and pressure, gas-oil ratios (GOR), and hydrocarbon column heights. Notably, two of these wells have tested high-yield oil and gas flows. To delineate the hydrocarbon accumulation process, a comprehensive multi-disciplinary approach was adopted, integrating geological background analysis, source rock distribution, hydrocarbon generation evolution in adjacent sags, and seismic interpretation.Advanced geochemical analyses were employed, including compound-specific carbon isotope analysis of oil and gas, monomeric hydrocarbon carbon isotopes, and organic matter stable carbon isotopes. These were combined with biomarker analysis (saturated hydrocarbons, aromatics, and adamantanes) and numerical simulation of hydrocarbon migration pathways. By establishing carbon isotopic cross-plots for source rocks at different stratigraphic levels in the hydrocarbon-generating sags and comparing them with typical generated hydrocarbon samples, the study conclusively determines that the hydrocarbons in the BZ8S-A volcanic reservoir are primarily sourced from the Shahejie Formation. Moreover, the geochemical evidence indicates that hydrocarbons in different well locations originated from distinct hydrocarbon-generating sags, revealing a complex, multi-source charging model for this volcanic reservoir.
How to cite: Shiyang, Z. and Qi, W.: Tracing Multi-Source Mixing in Volcanic Reservoirs Using Biomarkers and Carbon Isotopes: A Case Study of the Bozhong Sag, Bohai Bay Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11279, https://doi.org/10.5194/egusphere-egu26-11279, 2026.
Stable isotope analysis of organic materials is essential in environmental, geochemical, and food authenticity research, offering insights into carbon sources and product origins. Traditional Picarro Combustion Module–Cavity Ring-Down Spectroscopy (CM-CRDS) systems provide reliable, cost-effective δ¹³C analysis; furthermore, enabling simultaneous δ²H measurement greatly expands their utility for many applications.
We present a straightforward extension of the CM-CRDS system, integrating two dedicated analyzers: the Picarro G2201-i for δ¹³C and the Picarro L2130-i for δ²H. Key modifications include removing the water trap, heating the transfer tubing, and adding a heated buffer volume, enabling direct isotopic analysis of water vapor alongside carbon dioxide. This setup maintains the original sample delivery for carbon isotope analysis, while a simple software adjustment allows precise peak integration for hydrogen isotopes.
Performance was validated using a range of international standards representing diverse organic materials: USGS88 (marine collagen), USGS89 (porcine collagen), USGS90 (millet flour), USGS91 (rice flour), and IAEA CH7 (polyethylene foil). The system demonstrated excellent δ²H linearity (with slopes of 1.040, 1.074 and 1.017 on three separate days and R² values exceeding 0.99) while maintaining the high accuracy of δ¹³C measurements. Precision was assessed with hexamethylenetetramine (HMT), yielding a δ²H standard deviation of 0.26‰ and δ¹³C of 0.04‰ over 50 replicates. We chose HMT to determine the precision because it does not exchange hydrogen isotopes during storage and analysis and is used to determine the carbon-bound non-exchangeable hydrogen in fructose and glucose in honey [1]. Calibration procedures and best practices for hydrogen isotope analysis are discussed.
Our findings highlight the potential of combining the G2201-i and L2130-i analyzers with a CM in a coordinated analytical workflow for dual isotope analysis. This methodology opens new opportunities for isotope studies for environmental as well as food authenticity and food origin studies, and is a low-cost, easy to use alternative to IRMS analysis.
Reference
[1] Li et al., 2024, A new approach to detecting sugar syrup addition to honey: Stable isotope analysis of hexamethylenetetramine synthesised from honey monosaccharides (fructose and glucose). Food Chemistry 434.
How to cite: Wozniak, J., Roy, S., Hofmann, M. E. G., Bhattacharya, J., and Hemenway, T.: Simple, Fast, and Highly Precise δ¹³C and δ²H Analysis of Organics via Dual Picarro CRDS Integration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14109, https://doi.org/10.5194/egusphere-egu26-14109, 2026.
Oxygen (O), the most abundant element in the Earth's crust, has an underexplored isotope system in plant and soil sciences compared to carbon and nitrogen, despite its strong potential to serve as a robust proxy for climate, ecohydrology and biogeochemical studies. The stable isotope ratio of O (δ18O) in bulk soil organic matter (SOM) might reflect the isotope composition of soil water during SOM formation. However, this signal is blurred by the presence of O from inorganic minerals and a dynamic exchangeable O fraction that can quickly equilibrate with ambient water. To address these challenges, the O in SOM must be isolated from interfering O-containing inorganic compounds in plant OM and minerals. Moreover, the exchangeable O fraction must be accounted for. Although we hypothesise that the exchangeable O fraction in SOM is smaller than that of H, it can likely not be ignored.
We evaluated two alternative methods to separate organic and inorganic O from the soil: demineralisation (i.e., removal of inorganic compounds using HF and HCl) and removal of the organic compounds by muffling combined with a KCl treatment to remove oxyanions. After isolating the organic fraction, we applied a steam equilibration procedure, in which we equilibrated the samples with different water vapours of known O-isotopic composition to determine the δ18O value of the nonexchangeable O fraction, as has already been similarly established for H. We used standard materials like ethylene glycol, p-Nitro aniline, and Aldrich humic acid (AHA) for the demineralisation method and two O-containing minerals (Goethite and Apatite), both pure and mixed with AHA as model substances for the organic matter removal method and also 18O-spiked chemicals to select the procedure with no (or minimal) alterations of the original O isotope ratios. Our preliminary data reveal an exchangeable O fraction of 1-1.5% in AHA and excluding its effect by using mass balance calculation, the resulting δ18O value of the nonexchangeable fraction of AHA was ~15.2‰, which is significantly depleted relative to the humic acid extracted from natural soil (18.4-24.6‰), a discrepancy attributable to the absence of microbial decomposition and associated isotopic fractionation in our synthetic model compound (AHA). Thus, by quantifying the exchangeable O fraction and assessing the stability of the non-exchangeable O fraction against our treatments, this study provides a methodological prerequisite for the accurate determination of oxygen isotope ratios of the nonexchangeable O fraction in plant and soil science.
How to cite: Ghosh, D., Wilcke, W., and Oelmann, Y.: Decoding the stable isotope signature of the non-exchangeable oxygen fraction of bulk soil organic matter: methodological prerequisites , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1885, https://doi.org/10.5194/egusphere-egu26-1885, 2026.
Against the backdrop of climate change, the destructive power of tropical cyclones (TCs) has intensified, highlighting the urgent need for a more comprehensive understanding of tropical cyclone activity beyond the records provided by meteorological observations and historical documents. In this study, we compiled TC events affecting the Hong Kong region of South China since 1980 and investigated their isotopic imprints in precipitation and tree rings. We compared the hydrogen isotopic composition of precipitation (δ2Hppt) during TC-affected and TC-free months. After accounting for the rainfall amount effect and seasonal influences, we demonstrate that δ2Hppt consistently captured the anomalously depleted isotopic signals associated with TC rainfall. Furthermore, robust regression analysis indicated that TC-related precipitation isotopic variability explained approximately 30.5% of the variance in lignin methoxy stable hydrogen isotopes (δ2HLM) of tree-ring latewood in Pinus elliottii Engelm. at the Hong Kong site. Additionally, TC precipitation (TCP) exerted the strongest positive control on TC signals recorded in latewood δ2HLM, with additional contributions from TC intensity (MaxInte) and a significant negative seasonal effect (SeasonalIdx), while storm duration (Days) and distance (MinDist) showed limited independent influence. Overall, TC signals preserved in latewood δ2HLM reflect the integrated hydroclimatic effects of multiple storm characteristics at the annual scale, rather than being controlled by any single statistical descriptor of tropical cyclone activity. Our findings demonstrate that tree-ring latewood δ2HLM in P. elliottii can serve as a robust recorder of tropical cyclone signals. This work broadens the application of tree-ring lignin hydrogen isotopes and provides a novel proxy for improving interpretations of historical TC variability.
How to cite: Wang, Y., Li, W., and Song, X.: Extremely low δ2H signatures in tropical cyclone precipitation recorded by tree-ring lignin methoxy hydrogen isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4359, https://doi.org/10.5194/egusphere-egu26-4359, 2026.
This study examines the stable oxygen and hydrogen isotopic composition of gypsum (CaSO4·2H2O) hydration water (GHW) preserved in sediments from the Laguna de la Ratosa playa lake (Málaga Province, southern Iberian Peninsula). The objective was to reconstruct the lake water isotopic composition between 18.5 and 7.5 ka, reflecting hydroclimate variability in the southern Iberian Peninsula during the Pleistocene-Holocene transition. The GHW proxy relies on the fact that during crystallization, gypsum incorporates water from the solution, allowing the isotopic composition of the paleo-lake water to be directly inferred from that of GHW. This is possible because the oxygen and hydrogen isotope fractionation factors between aqueous solutions and GHW are well constrained and largely insensitive to temperature and salinity. The reconstructed lake-water isotopic values show a progressive decrease (from mean values of 6 to 0‰ for δ¹⁸O and from 10 to –5‰ for δ²H) between 18.5 and 11 ka, coincident with the deglaciation. This trend indicates a transition toward less evaporative conditions associated with increasingly humid climate. Superimposed on this overall trend, however, are three arid intervals centered at ca. 18 ka, 16 ka, and 12–13 ka, during which both δ¹⁸O and δ²H values increased. These arid phases are interpreted as reflecting the influence of the Last Glacial Maximum, Heinrich Stadial 1 (HS1), and the Younger Dryas on lake hydrology. During the Early-Mid Holocene (11–7.5 ka), isotopic values stabilized at the lowest levels of the record (ca. 0‰ for δ¹⁸O and ca. –5‰ for δ²H), suggesting persistently reduced evaporation and the establishment of a more permanent lacustrine system under sustained wetter conditions. Overall, these results demonstrate that gypsum hydration water preserved in playa-lake sediments constitutes a robust proxy for reconstructing paleohydrological variability and associated climatic changes.
Acknowledgments: This study was funded by the GYPCLIMATE (PID2021-123980OA-I00) and PID2021-125619OB-C21 projects of the Spanish Ministry of Economy and Competitiveness and FEDER European Regional Development Funds. J.C.P. acknowledges the Research Teaching Training contract PRE2022-103493 Ministry of Economy and Competitiveness of Spain. L.M. was funded by the FPU21/06924 grant of the Spanish Ministerio de Educación y Formación Profesional. C.V. was funded by the European Comission (Marie Curie postdoctoral fellowship, grant no. 101063961). F.G acknowledges the Ramón y Cajal contract (RYC2020-029811-I) and the PPIT-UAL grant from the Andalusian Regional Government -FEDER2022-2026 (RyC-PPI2021-01).
How to cite: Cañada-Pasadas, J., Gázquez, F., Martegani, L., Voigt, C., Sánchez-Villanueva, A. I., García-Alix, A., and Jiménez-Moreno, G.: Reconstructing hydroclimate across the Pleistocene–Holocene transition in southern Iberia using stable isotopes of gypsum hydration water, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5528, https://doi.org/10.5194/egusphere-egu26-5528, 2026.
The strontium isotope ratio 87Sr/86Sr is a key tracer with wide-ranging applications in geochemistry, hydrology, paleoclimatology and migration research. To make sound interpretations of 87Sr/86Sr isotope ratios in the context of biogeosciences, researchers need high quality data. In this contribution, we critically evaluate the accuracy of two conceptually different analytical protocols for 87Sr/86Sr determination on the example of a large dataset (n = 135) comprising biogenic and abiogenic materials.
Water, soil extracts, and hydroxyapatites (tooth enamel) were prepared according to established procedures and analyzed by solution-based multi-collector inductively coupled plasma mass spectrometry (MC ICP-MS). For the calibration we used two protocols: internal normalization (also termed internal mass bias correction or internal calibration) and standard-sample-bracketing (external calibration). Isotope dilution mass spectrometry was not considered suitable, because this calibration approach becomes very time- and cost-intensive when applying to a large sample set.
Analysis of water, soil extracts and hydroxyapatites showed that the majority of 87Sr/86Sr isotope ratios which were determined by internal normalization shifted towards higher values in comparison to data determined by standard-sample-bracketing. Extensive evaluations ruled out sample preparation or measurement errors. Instead, internal normalization yielded biased data, because it is based on the assumption that all samples have the same 88Sr/86Sr isotope ratio, which can be used for normalization. However, in 90% of the investigated samples the 88Sr/86Sr significantly deviated from the assumed invariant value; in particular, the 88Sr/86Sr that is conventionally expressed as δ(88Sr/86Sr)SRM987 ranged from -1.01‰ to 0.20‰. As a consequence, internally normalized 87Sr/86Sr data biased by up to 0.00043, which was 2-times larger than previously predicted by theoretical calculations. These results demonstrate that the choice of calibration method has a much higher impact on the accuracy of 87Sr/86Sr isotope ratios than initially expected. The implication of these findings in biogeoscience applications will be discussed.
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n°856453 ERC-2019-SyG).
How to cite: Tchaikovsky, A., Braeuer, S., Pohl, W., and Hann, S.: Critical evaluation of internal normalization and standard-sample-bracketing for accurate ⁸⁷Sr/⁸⁶Sr analysis , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5954, https://doi.org/10.5194/egusphere-egu26-5954, 2026.
Winter is a critical yet understudied phase in the annual cycle of Arctic seabirds, largely due to logistical challenges of polar fieldwork. While geolocators have advanced our understanding of migration and overwintering behavior, their cost and technical limitations constrain widespread use. As a complementary and scalable alternative, feather analysis offers integrated insights into both ecology and contaminant exposure at individual and population levels.
In this study, we examined head feathers from thick-billed murres (Uria lomvia) collected at seven colonies spanning West Greenland, the Canadian Arctic, and Svalbard. This species breeds widely across the circumpolar Arctic, but several Atlantic populations are in decline. Because head feathers are grown during the non-breeding season, they reflect mercury exposure at overwintering sites. We measured total mercury concentrations, stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N), and mercury isotope compositions (δ²⁰²Hg, Δ¹⁹⁹Hg) to assess variation in winter foraging habitats and mercury exposure pathways. Our results reveal distinct spatial patterns in δ²⁰²Hg that align with known west-to-east gradients in the Hg isotopic composition of North Atlantic prey fish, suggesting region-specific foraging areas during winter. Intra-colony variation in δ²⁰²Hg further highlights individual-level differences in winter habitat use, consistent with patterns derived from geolocator data. Additionally, the strong positive correlation between total Hg concentration and Δ¹⁹⁹Hg suggests that foraging depth significantly influences mercury uptake. These findings demonstrate that an integrated isotopic-tracking approach advances ecological biogeochemistry by tracing both contaminant pathways and seabird movement using natural isotopic tracers.
How to cite: Li, M.-L., Janssen, S., Tate, M., Choy, E., Elliot, K., and Gousy-Leblanc, M.: Integrating Geolocator Tracking and Isotopic Tools to Reveal Winter Foraging Ecology and Mercury Exposure in Arctic Seabirds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2458, https://doi.org/10.5194/egusphere-egu26-2458, 2026.
Stable isotope approaches are rapidly transforming how we investigate trace-element cycling in living systems, offering information that goes far beyond concentration measurements. Mercury (Hg) stable isotopes, in particular, have proven highly informative across a broad range of environments, and marine studies have highlighted their value for disentangling sources and in vivo processing. Studies on apex marine predators (e.g., seabirds) show that Hg isotopes can track internal processing and trophic transfer. In contrast, selenium (Se) isotopic characterization in biota, more specifically in animals, is still limited and technically challenging, but it opens promising perspectives, especially given Se’s recognized antagonistic role in Hg toxicity.
Key gaps persist in the Brazilian Amazon, where complex Hg (and Se) exposure scenarios call for higher-resolution tracers. Translating Hg and Se isotope approaches to Amazonian freshwater systems, from fish to riverside populations, may clarify bioaccumulation pathways and fate. Recent progress achieved in marine organisms, including compound-specific strategies, will be presented, together with the main analytical challenges and opportunities for extending these approaches to the Amazon.
How to cite: Pedrero Zayas, Z., Marchan Moreno, C., Queipo Abad, S., Neves, G., Barbosa Jr., F., Corns, W., Cherel, Y., Bustamante, P., Amouroux, D., Louvat, P., and Bueno, M.: Mercury and selenium stable isotopes across contrasting food webs: marine insights, amazon priorities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20589, https://doi.org/10.5194/egusphere-egu26-20589, 2026.
Non-traditional trace metals are increasingly utilized to evaluate potential microbial processes in the search for evidence of ancient life. Recent investigations of modern terrestrial hot spring silica deposits (sinter), as analogs for early life on Earth or Mars (e.g. Homeplate, Gusev crater), have highlighted unique gallium enrichments associated with silicified microbial filaments and microbially mediated rock textures, such as stromatolites. We used new analytical methodologies for in situ and bulk analysis of gallium isotopes in sinter to better understand the observed Ga enrichment. In situ analysis, by Cameca 1280 ion probe, provides the necessary spatial resolution to target individual microbial filaments with a 10 μm ion beam, but with a lesser precision of ~±3 ‰, compared to the ±0.06 ‰ precision via MC-ICPMS bulk analysis. In situ results indicate heterogeneity of δ71Ga (>10 ‰ variation overall) with silicified microbial filaments on average isotopically lighter than adjacent silica. Multiple processes may influence the Ga isotopic ratio in sinter including preferential microbial selection, changes in fluid chemistry, and silicification processes. Ongoing experiments on Ga-Si spiked microbial growth and abiotic silica precipitation may further elucidate the cause of isotopic variability as we continue to refine this in situ isotopic methodology and its utility in planetary biosignature detection.
How to cite: Rowe, M. C., Kunihiro, T., Tanaka, R., Dao, N. V., Ota, T., Campbell, K. A., Ruff, S. W., Nersezova, E. E., Stallard, D., Lyon, B., and Langendam, A.: Gallium isotopes in silicified microbial hot spring deposits: a potential geochemical biosignature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15347, https://doi.org/10.5194/egusphere-egu26-15347, 2026.
Stable silicon isotopes have emerged as powerful tracers of marine biogeochemical processes, yet their application in high-latitude environments remains comparatively underexplored. Here we synthesize silicon isotope observations from the Eurasian Arctic Ocean to show how isotope patterns help disentangle physical transport, including open-ocean circulation, shelf–basin exchange, and river influence, from biological utilization across ice-covered and seasonally ice-free regimes. Using published case studies from the Siberian shelves and the Transpolar Drift, we illustrate how Si isotope signatures resolve coupled physical and biogeochemical controls on nutrient pathways. We then outline key methodological challenges for extending Si isotope work into sea ice, including defining open versus closed brine habitats, linking isotope signals to brine-network connectivity, and avoiding sampling artifacts that integrate unknown source volumes. Finally, we discuss how ongoing Arctic observing efforts, including large international campaigns, open new avenues for applying Si isotope techniques to questions of nutrient availability, ecosystem change, and ice–ocean coupling in a rapidly transforming Arctic system.
How to cite: Laukert, G., Hendry, K., and Horner, T. J.: Stable silicon isotopes as tracers of Arctic sea ice–ocean macronutrient cycling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14259, https://doi.org/10.5194/egusphere-egu26-14259, 2026.
Effective management of river pollution is often limited by low-frequency monitoring approaches that fail to resolve the spatiotemporal dynamics of nutrient sources, hydrodynamic transport, and in-stream biogeochemical processing. To address this, we applied a high-resolution Lagrangian sampling framework to a well-characterised reach of the River Thames, enabling continuous tracking of water parcels downstream of key nutrient inputs. This approach combined nutrient concentration data, optical characterisation, and stable isotope tracers with detailed hydrodynamic measurements to resolve nutrient sources, mixing behaviour, and short-reach processing. Water samples were collected for conventional nutrient analysis, excitation–emission matrix (EEM) fluorescence, and isotopes of nitrate and phosphate. Field measurements were supported by drone-based infrared imaging to characterise surface flow structure and a remote-controlled survey vessel equipped with Acoustic Doppler Current Profiler, Single Beam Echo Sounder, and GPS to resolve hydrodynamics and channel morphology. In situ sondes and large-volume sampling further captured water-quality variability. Phosphate oxygen isotopes (δ¹⁸Op) were used to directly trace wastewater-derived phosphorus downstream of a wastewater treatment works (WWTW) outfall. Nineteen river samples collected at ~20 m intervals were compared with upstream river and WWTW effluent end members. Effluent phosphate exhibited a distinctly lower δ¹⁸Op value than background river phosphate, enabling a two-endmember isotope mixing model. Results indicate that WWTW-derived phosphate contributed approximately 20–55% of riverine phosphate across most of the reach, with localized zones of near-complete effluent dominance. A pronounced low-δ¹⁸Op anomaly coincident with elevated phosphorus concentrations is interpreted as a localized hydrodynamic pulse of wastewater phosphate superimposed on progressive biological reprocessing. Together, these results demonstrate that wastewater phosphorus can exert strong, spatially heterogeneous control on riverine phosphate over very short distances, even under conditions of active mixing and biological cycling. More broadly, this integrated Lagrangian-hydrodynamic-isotopic framework provides a powerful new basis for quantifying nutrient sources, transport, and transformation in rivers, with direct implications for more effective nutrient management strategies.
How to cite: Gooddy, D., O'Brien, A., Bowes, M., Everard, N., Laize, C., Rameshwaran, P., Pesso, C., Harrison, P., Sorensen, J., Smith, A., and Krause, S.: Taking the Pulse: Tracking Wastewater Nutrients Through a River Using Lagrangian Sampling and Isotopic Tracers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3089, https://doi.org/10.5194/egusphere-egu26-3089, 2026.
The identification of phosphorus (P) sources is critical for implementing effective eutrophication mitigation strategies. Lake Baldegg (Switzerland) has a history of excessive phosphorus inputs leading to severe eutrophication. Here, we utilise the oxygen isotopic composition of inorganic phosphate (δ¹⁸O(PO4)) to discriminate soil-bound phosphate sources (orchard, arable, grasslands and forest; effluents from the local wastewater treatment plant and manure).
Previously, source apportionment using δ¹⁸O(PO4) has been limited by the number of sources exceeding the number of tracers. In attempt to resolve this issue, additional tracers (C, N and geochemical elements) have been incorporated into the mixing models. As these tracers may originate from different sources and/or undergo different biogeochemical cycling than phosphate, their use for phosphate apportionment can potentially lead to erroneous results.
To overcome this issue, we analysed the δ¹⁸O(PO4) values in multiple inorganic phosphate pools: NaOH-extractable (Fe/Al-bound), HCl-extractable (Ca/Mg-bound) and HNO₃-extractable residual inorganic P (modified Hedley sequence). The pools were purified using a zirconium-loaded resin, precipitated as Ag₃PO₄ and analysed for δ¹⁸O(PO₄) via high-temperature pyrolysis based isotope ratio mass spectrometry (TC/EA-IRMS).
Preliminary results show that δ¹⁸O(PO4) values discriminate in each pool between land-uses: forest (NaOH: +10.2‰; HCl: +10.6‰), orchards (NaOH: +15.6‰; HCl: +14.7‰), arable fields (NaOH: +16.0‰; HCl: +14.9‰) and grassland soils (NaOH: +17.0‰; HCl: +16.8‰). As such, multiple pools can be potentially used as tracers for phosphate apportionment and remove the need for additional non-phosphate-specific tracers. While this study demonstrates the discrimination between different sources, analysis of the lake sediments is currently ongoing. We aim to reconstruct 130 years of inorganic phosphate sources and identify key moments the catchment’s history.
How to cite: Heinrich, R., Cox, T., Jaisi, D., Tamburini, F., and Alewell, C.: Using δ¹⁸O(PO4) for historical source apportionment of inorganic phosphates in the eutrophic lake Baldegg, Switzerland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1857, https://doi.org/10.5194/egusphere-egu26-1857, 2026.
The discovery of heterotrophic nitrification has expanded our view of nitrification beyond the canonical chemolithoautotrophs. Yet, the role of heterotrophic bacteria in nitrification across environmental and engineered systems remains unclear, partly due to limited physiological characterization and the absence of robust diagnostic tools. The analysis of nitrogen (N) isotope fractionation effects has been used for tracing biogeochemical N cycle processes and offers the potential to resolve underlying biochemical pathways. While autotrophic nitrification is known to generate substantial N isotope effects during ammonia (NH₃) oxidation to nitrite (NO₂⁻), comparable constraints for heterotrophic nitrifiers are lacking. Here, we report for the first time the N isotope effects associated with heterotrophic nitrification by Alcaligenes faecalis, an organism capable of converting NH₃ into several nitrogenous products. In batch incubations with 2.2 mM ammonium (NH₄⁺) as the sole N source, A. faecalis produced up to 0.67 ± 0.04 mM NH₂OH, 0.11 ± 0.01 mM NO₂⁻, and 12 ± 1.2 µM N₂O, while the remaining NH₄⁺ was assimilated into biomass. Therefore, the main NH4+consumption pathway of A. faecalis is, in fact, best described by ammonium assimilation, which supports previous findings. Total NH₄⁺ consumption showed an isotope effect of 13.8 ± 0.4‰, exceeding that of biomass formation (4.8 ± 0.2‰). Both values fall within the known range for bacterial NH₄⁺ assimilation, but the disparity suggests additional fractionating steps beyond assimilation alone. NH₂OH, NO₂⁻, and N₂O were initially strongly ¹⁵N-depleted relative to the NH₄⁺ source, and became progressively enriched as NH₄⁺ was consumed. N₂O exhibited a variable site preference (24–38‰), indicating contributions from at least two production pathways. Overall, our findings show that heterotrophic nitrification produces N-isotopic signatures fundamentally distinct from canonical ammonia oxidation. These characteristic patterns in both NH₄⁺ and NO₂⁻ pools highlight the diagnostic potential of stable isotopes for identifying heterotrophic nitrification in complex systems.
How to cite: Frey, C., Lenferink, W. B., von Kessel, M. A. H. J., Magyar, P. M., Jetten, M. S. M., Lehmann, M. F., and Lücker, S.: Isotopic fingerprint of heterotrophic nitrification by Alcaligenes faecalis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13059, https://doi.org/10.5194/egusphere-egu26-13059, 2026.
The Atacama Desert contains the largest natural nitrate accumulations on Earth. Yet, the processes controlling their formation and redistribution remain debated, particularly for nitrate veins hosted in bedrock. In this study, we combine field observations with chemical and stable isotope analyses (δ18O, Δ17O, δ15N) of nitrate from all major deposit types across the Atacama nitrate provinces. All nitrate occurrences display large positive Δ17O values (+13 to +22‰) and elevated δ18O (+43 to +65‰), confirming a unanimous atmospheric origin via ozone-driven photochemical oxidation of NOx.
Vein-hosted nitrates in volcanic and sedimentary rocks show suppressed Δ17O and δ18O values trending toward fossil hydrothermal waters, indicating partial oxygen isotope exchange during interaction with hot, saline, acidic fluids. Field relationships, fault-controlled mineralization, rhyolitic exsolution textures, and sulfate sulfur isotopes independently confirm hydrothermal dissolution, transport, and reprecipitation of originally atmospheric nitrate.
These results define a two-stage geological cycle: long-term atmospheric deposition, groundwater transport, and evaporative concentration under hyperaridity, followed by tectonically driven hydrothermal recycling linked to Andean magmatism. This two-mechanism framework reconciles the isotopic, mineralogical, and spatial diversity of nitrate deposits, demonstrating that the Atacama Desert records a coupled atmospheric–hydrothermal cycle linked to the tectonic and magmatic evolution of the central Andean margin, and providing a template for other nitrate-bearing deserts on Earth and potentially on other planets.
Nitrate deposit δ15N = −8 to +4‰ are slightly higher than in atmospheric nitrate and overlap with the Atacama soil nitrate profile compositions, but in contrast show a positive correlation with δ18O. This excludes humidity driven microbial denitrification and gaseous N loss as a major driver for local secondary composition contrasts.
How to cite: Riffo Contreras, C., Chong, G., Klipsch, S., E. Böttcher, M., Davies, A., and Staubwasser, M.: The Geologic Super-Cycle of Chilean Nitrate Deposition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11165, https://doi.org/10.5194/egusphere-egu26-11165, 2026.
Posters on site: Wed, 6 May, 16:15–18:00 | Hall X1
Identifying and quantifying the processes that control the carbon and nitrogen cycling in aquatic systems is important for mitigating urban and agricultural pollution, optimizing environmental policy and understanding global nutrient cycles. The isotopic analysis of dissolved organic carbon (TOC) and total bound nitrogen (TNb) are particularly important to elucidate the different sources, track nutrient cycling processes and help contamination identification.
Here, we present the δ13C performance of the Elementar iso TOC® cube for <5 mg/L carbon TOC concentrations in estuarine river water samples, highlighting a salinity gradient from 2g/L to 25g/L. We also present determination of TOC concentration and δ13C TOC in seawater, demonstrating the performance of the iso TOC® cube for the analysis of seawater samples.
The iso TOC cube® elemental analyser has been developed for fully integrated TOC/TNb isotope ratio analysis. Optimised for precise measurements of TC, TOC, TIC and TNb isotope ratios covering a wide range of applications areas. All types of liquids from drinking water, industrial wastewater, soil leachates, or marine samples are determined reliably and with the highest isotopic precision.
How to cite: Seed, M., Preece, C., Boocock, T., and De Reuss, M.: Fully integrated TOC and TNb analysis of estuarine and sea water samples with the Elementar iso TOC cube® , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11252, https://doi.org/10.5194/egusphere-egu26-11252, 2026.
Research on the nitrogen (N) cycle in agricultural ecosystem is key to better understand and manage N nutrition of crops and N losses to the environment. Stable isotope tools have been extensively used to identify and quantify N pathways and processes, but suitable methods typically require sophisticated and expensive instrumentation which is not always available and is rarely suitable for in situ analysis. A quadrupole mass spectrometer (GAM200, InProcess, Bremen) was modified to study 15N enrichment in N species and N2 in water and air in the lab and in the field. To establish a membrane inlet mass spectrometer (MIMS) a silicone tubing inlet was added to enable online analysis of dissolved gases. Four applications were established:
- The MIMS was used to analyze N2 and Ar in groundwater samples to determine excess-N2 from denitrification. In situ online analysis in the Fuhrberger Feld aquifer was conducted at multilevel groundwater monitoring wells, clearly identifying the steep rise in denitrification upon appearance of sulfides.
- To study N2 production by denitrification the in situ 15N push pull method [1] was used, where 15N labelled NO3- solution is injected to groundwater and subsequently samples containing 15N labelled N2 are analyzed, in this study by the MIMS. This method was automated and tested in lab mesocosms [2].
- An automated sample preparation unit for inorganic nitrogen (SPIN) was coupled to the MIMS for automated and sensitive determination of the 15N abundances and concentrations of nitrate, nitrite, and ammonium in aqueous solutions. It was based on the principle of the SPIN-MAS [3] but with the advantage to analyze samples online. It provides a wide dynamic range for all three N species for both isotope abundance and concentration measurements [4, 5]. We propose to use this method in conjunction with online sampling of dissolved N species in soil using dialysis membranes [6] which had not been performed until now to our knowledge.
- The improved 15N gas flux method to measure N2 fluxes from soils under N2 depleted atmosphere has been applied int the field [7] but was complicated by the difficulty to maintain stable background concentrations [8]. A capillary inlet was added to the GAM 200 and used for in situ monitoring of background N2 concentrations in flux chambers.
We conclude the used quadrupole mass spectrometer has been proven as a versatile, economic and easy to use detector for a wide range of applications in N cycle research and is promising for future applications.
References:
- Well, R. and D.D. Myrold, 1999. doi.org/10.1016/S0038-0717(99)00029-22.
- Eschenbach, W. and R. Well DOI: 10.1002/rcm.5066
- Stange, C.F. et al. ,2007 DOI: Doi 10.1080/10256010701550658
- Eschenbach, W. 2018, DOI: 10.1021/acs.analchem.8b02956
- Eschenbach, W. et al 2017 DOI: 10.1021/acs.analchem.7b00724
- Inselsbacher, E., et al. 2011, doi.org/10.1016/j.soilbio.2011.03.003
- Well, R., et al 2019 doi.org/10.1002/rcm.83638.
- Eckei, J., et al., 2024. DOI: 10.1007/s00374-024-01806-z
How to cite: Dyckmans, J. and Well, R.: Using a quadrupole mass spectrometer as versatile detector to study N transformations and fluxes in soils and aquatic systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21873, https://doi.org/10.5194/egusphere-egu26-21873, 2026.
The release of carbon dioxide and reactive nitrogen in various forms by humans disrupts the functioning of ecosystems around the world. In Europe, many valuable habitats, particularly wetlands and dry grasslands, are under threat due to eutrophication. However, contrasting water regimes mean that the uptake of anthropogenic nitrogen by plants in these ecosystems differs, and this is also interrelated with an increase in trophic level in both habitats.
In our study, we measured the δ15N and δ13C values, as well as the total nitrogen content (TN), of 99 pairs of foliar samples collected from seven species of vascular plants in dry grasslands and wetlands in Poland. Each pair consisted of a historical sample, collected from a herbarium voucher dating from before 1939 (i.e. before the widespread use of artificial fertilisers in agriculture), and a contemporary sample, collected in 2024, from the same species in a similar location.
We performed t-tests to determine whether there were significant differences in the means of δ15N, TN, and δ13C between samples from the two habitats. Next, we calculated the differences in δ15N, TN, and δ13C between the contemporary and historical samples for each pair. We then tested whether the difference for each species and habitat type was significantly different from zero using 90% confidence intervals. We analysed the relationships between differences in δ15N and TN over time and the following factors using multiple linear regression: habitat type, the proportion of farmland in the landscape, the consumption of synthetic nitrogen fertiliser and NOx deposition.
The δ15N and TN values were lower for dry grassland species than for wetland species in both the contemporary and historical subsets. For dry grassland species, the mean δ15N value was lower in contemporary samples than in historical ones. For wetland species, however, the opposite was true. The difference in δ15N values between pairs of samples was positively correlated with the proportion of farmland in the landscape. The mean TN value was higher in contemporary wetland samples than in historical ones, but not in dry grassland plants. The mean δ13C value, corrected for the Suess effect, was lower in contemporary samples than in historical ones. The mean difference was −0.51 ‰ for dry grassland species and −3.85 ‰ for wetland species.
Our study revealed that a century of carbon emissions, increased nitrogen input into the environment and the dominance of artificial fertilisers and combustion-derived nitrogen over biological nitrogen sources has not resulted in consistent responses across habitats and species. While the isotopic composition of nitrogen and carbon in plant tissues in Central Europe has undoubtedly changed, this change is context-dependent. Its magnitude and direction are impacted by the habitat and the identity and/or ecology of the species. As expected, man-made alterations appear to be more pronounced in wetland environments than in dryland habitats. Furthermore, the source of disruption may differ between the habitat types. Specifically, wetlands are exposed to a multitude of anthropogenic nitrogen and carbon sources, whereas dry grasslands seem to be predominantly affected by changes in atmospheric composition.
How to cite: Dembicz, I., Chojnowska, N., Chibowski, P., and Kozub, Ł.: Contrasting isotopic responses of dryland and wetland plants to a century of global anthropogenic changes in nutrient cycling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4432, https://doi.org/10.5194/egusphere-egu26-4432, 2026.
Closed-transient chamber systems are widely used to measure the transport of non-reactive greenhouse gases (GHGs) and their stable isotopes between the soil and atmosphere. Technologies used to measure GHGs in chamber-based systems have advanced since their first introduction. In many early systems, gas analysis was performed off-line using gas chromatography and/or mass spectrometry. The introduction of non-dispersive infrared gas analyzers suitable for field deployment allowed CO2 to be measured on-line, but for other GHGs on-line analysis was not possible until the more recent introduction of tunable diode laser absorption spectroscopy (TDLAS)- based gas analyzers. The most recent generations of TDLAS analyzers have extended measurement capabilities from reporting total concentration of a given GHG, to separating concentrations of its most abundant stable isotopologues. For CO2, this advancement makes possible near real-time estimation of isotopic signature (δ13C) of the carbon source pool.
Linear mixing model-based approaches are used to separate the isotopic signature of a source pool from background condition observed during soil chamber measurements. The most common, those proposed by Keeling (1958) and Miller and Tans (2003), uses the relationship between the normalized isotopic ratio (δ) and total concentration, or some derivate term of either, to estimate the source pool conditions. Keeling’s methodology is widely cited but requires extrapolation well beyond measured conditions. The Miller-Tans approach is predicated on the same underlying mass balance as Keeling but uses a solution that estimates the source pool only over measured conditions, reducing uncertainty in final estimates. Both approaches require independent measurement of the total concentration and normalized isotopic ratio, which is not possible with TDLAS based analyzers. TDLAS analyzers measure individual isotopologue mole fractions and use the same set of individual measurements to calculate both total concentration and the normalized isotopic ratio, introducing an inherent autocorrelation between them. Additionally, the δ exhibits a bias as a function of total measured CO2 concentration, introducing an apparent concentration dependence error (CDE) in d reported from TDLAS.
We present an alternative approach to estimating the source pool isotopic composition specific to TDLAS measurements. This alternative approach relies only on measurements of individual isotopologue mole fractions, avoiding autocorrelation, and does not require extrapolation beyond measurement conditions. We include a sensitivity analysis of mixing model approaches and errors common to TDLAS based instruments, using a chamber dataset synthesized from field-based measurements of environmental conditions and physical properties of gas transport.
How to cite: Hupp, J., Belovitch, M., Lynch, D., and Vath, R.: An alternative approach to determine source stable carbon isotope composition for closed-transient chamber measurements using TDLAS analyzers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2823, https://doi.org/10.5194/egusphere-egu26-2823, 2026.
Dissolved inorganic carbon (DIC) - including aqueous CO2, carbonic acid, bicarbonate, and carbonate - is often the largest pool of carbon in aquatic systems. Biogeochemical processes result in exchanges of carbon between the various DIC components and may act to move carbon into or out of the DIC pool. The isotopic composition of carbon is a product of both its source and mass-dependent fractionation as carbon changes form through the processes acting on it. Consequently, measurement of the stable carbon isotope composition of DIC is a valuable tool for understanding biogeochemical processes in aquatic systems. However, differences in isotopic composition are small, and separating source contributions requires precise measurement.
Measurement of DIC can be done by conversion to CO2 in the presence of a strong acid and quantification of liberated CO2 by gas analysis. To determine isotopic composition of the liberated CO2 (δ13C) historical methods used isotope ratio mass spectrometry (IRMS). More recently, tunable diode laser absorption spectrometry (TDLAS) based gas analyzers have been adopted for these measurements but have continued to base methodological considerations on those developed for IRMS. While IRMS and TDLAS can both be used to determine δ13C, there are fundamental differences in the technology, which should be considered during application. In particular, this has meant δ13C - DIC measurements have been unable to take full advantage of TDLAS performance characteristics.
Here we describe methodological advancements from integration of a TDLAS (LI-7825 carbon isotope analyzer) with a DIC measurement system (LI-5370A), that include changes to the pneumatic and analytical approach used in the DIC system. Pneumatic modifications allow the TDLAS to operate at an independent flow rate from the DIC system and serve to manipulate the residence time for CO2 along the flow path. We describe use of a non-CO2 free carrier gas, which allows the DIC measurement to take full advantage of analyzer precision and minimize errors intrinsic to δ13C as determined by TDLAS. We present data demonstrating measurement precision over a range of conditions and show that under similar conditions, these methodological changes result in precision exceeding that published previously for TDLAS-DIC measurements.
How to cite: Griessbaum, F., Hupp, J., Lynch, D., Scaboo, M., Leclerc, A., and Cai, W.-J.: Methodological advancements for stable carbon isotope measurement of dissolved inorganic carbon using tunable diode laser absorption spectrometers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5063, https://doi.org/10.5194/egusphere-egu26-5063, 2026.
Rapidly expanding biogeochemical applications based on compound specific isotope ratios require instrumentation versatility to meet different analytical challenges. Here we present features and benefits of using the following GC injection techniques: on-column injection, Large Volume Injection (LVI) Programmed Temperature Vaporization (PTV) technique, Static Headspace Sampling (SHS) injection and conventional Split/Splitless injection. We will demonstrate capability of Thermo Scientific™ GC IsoLink™ II IRMS System to support these injection techniques to properly transfer a representative portion of the sample to the analytical column while avoiding discrimination and isotopic effects.
On-column injection is applied for analysis of thermally labile or unstable compounds, as well as for samples with large analyte-boiling-point differences. It can be advantageous in a wide area of applications, i.e. for investigations of alkenones and alkanes from soils and sediments. We will present an optimized GC-IRMS analytical setup for stable carbon isotope ratios analysis of saturated hydrocarbons.
The LVI PTV is an injection technique which allows the introduction of larger volumes of samples in the GC injector which can be particularly useful for analysis of organic pollutants present in very small quantities. Here we present an optimized methodology for analysis of very small amounts of saturated hydrocarbons.
The SHS injection via split/splitless injector eliminates the need for direct liquid sample injection, reducing column contamination and improving analyte separation and reproducibility of isotope data. Here we demonstrate excellent precision and accuracy for GC-C-IRMS analysis of VOCs by using an optimized method for SHS, including improved sensitivity and lower detection limits.
Finally, we also present an optimized workflow for the analysis of PAHs by GC-IRMS with conventional Splitless injection, including characterization of PAHs standards and data evaluation.
How to cite: Milano, S., de Castro, M., and Tuthorn, M.: GC-IRMS: optimization of injection techniques for analysis of saturated hydrocarbons, VOCs and PAHs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3304, https://doi.org/10.5194/egusphere-egu26-3304, 2026.
Marine macroalgae are central to coastal carbon cycling and represent a significant portion of global primary production and organic matter export. Giant kelp (Macrocystis pyrifera) forests, in particular, serve as major carbon sinks and influence regional nutrient dynamics. However, the isotopic and biochemical pathways that define these contributions remain poorly constrained. While hydrogen isotope (δ²H) analyses are widely utilised in terrestrial ecology to integrate environmental water signals and metabolic fractionation, their application in marine macroalgae, particularly at the compound-specific level, currently remains underutilised.
Our previous research demonstrated that δ²H values in the soluble sugars of M. pyrifera are highly sensitive to light intensity, which indicates a distinct metabolic imprint tied to photosynthetic carbohydrate supply. We have now expanded this investigation to include lipid biomarkers, specifically focusing on fatty acids (analysed as methyl derivatives) and sterols (analysed as acetate derivatives). Samples were collected across six kelp forest sites in Carmel Bay, California. Preliminary Gas Chromatography-Mass Spectrometry results from three fully processed sites show complex profiles of C12–C26 saturated and unsaturated fatty acids, alongside a range of cholest-, ergost-, and stigmast-based sterols. These molecular distributions vary systematically with site and depth, offering early evidence of biochemical partitioning between photosynthetic and post-photosynthetic pathways under varying natural light regimes.
This presentation will explore new compound-specific δ²H measurements performed on the aforementioned compounds. By doing so, we aim to determine whether δ²H signatures in fatty acids and sterols primarily track photosynthetic fractionation or are shaped by downstream metabolic adjustments. By synthesising isotopic and molecular data, we seek to disentangle external environmental drivers, such as light and water isotopic composition, from intrinsic biochemical controls on compound-specific δ²H values. Refining these relationships is vital for the development of robust δ²H-based paleoenvironmental proxies and for assessing the role of modern and ancient kelp forests as dynamic carbon sinks.
How to cite: Salik, M. A., Cormier, M.-A., Steller, D., Lehmann, M., Al-Sid-Cheikh, M., and Gagnon, P.: Hydrogen Isotope Dynamics in Macrocystis pyrifera: Implications for Compound-Specific Isotope Analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21521, https://doi.org/10.5194/egusphere-egu26-21521, 2026.
Archaeological wood holds value not only as a source of information on how people used to live centuries or millennia ago, it is also a valuable proxy for reconstructing past climatic and environmental changes. When the sample amount available for destructive analytical methods is limited it forces the research team to judiciously prioritize what information to extract and which method to use. When it comes to light stable isotope analyses, the most widely used instrumentation requires rather intensive manual sample preparation and the prepared sample cannot be recuperated after analyses.
The elemental analyzer is currently the go-to sample introduction peripheral for stable isotope analyses of tree rings, but as any analytical method it has its draw-backs and limitations. A key limitation is that each growth ring must be individually separated mechanically and prepared for analysis; this challenge can be managed with sufficient time and manpower. However, very narrow growth rings (<1mm) are a clear limiting factor when each ring needs to be manually removed or when multiple analysis are required for each growth ring. Both issues can easily be circumvented by using a laser ablation (LA) module as sample introduction peripheral. Core segments or wood slices of up to 4.5 cm length can be analyzed in situ (including duplicates and triplicates) without further preparation. For archaeological wood, this method has the added benefits of being minimally invasive, the ablation tracks being practically invisible, and circumventing the need to sacrifice a portion of the artifact for analyses.
Our case study is a fragment of oak wood (Quercus sp.) provided by the National Museum of Denmark. The wood originates from construction timber found during an archaeological excavation of wells located near The Wadden Sea in south-west Denmark. The whole sample contains 199 growth rings and has been dendrochronologically dated to AD 407-605, covering the mid-sixth century where a global climate crisis caused a longer period of cold and wet growth seasons; this is also expressed in archaeological wood by the formation of extremely narrow growth rings. Because of growth ring widths down to 0.49 mm, it is challenging to separate and prepare wood material from each ring for stable isotope analyses using the traditional EA IRMS method.
Our LA IRMS setup comprises the isoScell Δ100 sample chamber (Terra Analitic), LSX 213 G2+ (Teledyne Photon Machines), CryoPrep and HS2022 IRMS (both Sercon). For δ13C a spatial resolution of 60μm is easily achievable, with precision on the QC of 0.08 ‰. Mean δ13C on the analyzed segment is -24.17 ‰ v. VPDB. The dataset is also in acordance with data from wider rings that could be analyzed via EA IRMS.
How to cite: Ellegaard Larsen, H. M., Stremtan, C. C., Puscas, C. M., and Olsen, J.: In situ δ13C analysis of <1mm thick annual growth rings in archaeological wood samples via LA IRMS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20124, https://doi.org/10.5194/egusphere-egu26-20124, 2026.
Temporal variability of tree-ring cellulose δ2H (δ2Hring-cel) can be a unique tool for understanding tree physiology and climate. However, we do not fully understand the drivers of temporal variability in δ2Hring-cel. Investigating seasonal δ2Hring-cel in boreal forests is particularly challenging. Previous studies on intra-annual tree-ring δ18Ohave shown that tree-ring isotope variability can result from the combined but opposing effects of source water and leaf assimilates, a dynamic likely relevant for δ2Hring-cel as well. To be able to use δ2Hring-cel as a standalone and reliable bioindicator, it is important to understand the variable hydrogen isotope fractionation between source water and tree rings. Our study aimed to provide context to this variability in a natural forest by tracing intra-annual δ2Hring-cel to the δ2H of its sources (water, sugars & starch), and comparing δ2Hring-cel to physiological and climatic factors.
The δ2H of source water, leaf water and carbohydrate pools (i.e. water-soluble carbohydrates, starch) were analysed from five pine (Pinus sylvestris) trees during 2019 at Hyytiälä forest, Finland. Their δ2H were used to model continuous δ2H of source water (δ2Hsource) and bulk leaf water (δ2Hleaf-water) and photosynthetic water (δ2Hphoto-water). Intra-annual δ2Hring-cel were analysed in 2018 and 2019 at a resolution of 5-10 timepoints per year, and they were allocated to xylogenetic timepoints. They were then compared to time-integrated δ2Hsource, δ2Hleaf-water, δ2Hleaf-sug, net assimilation rate, and various other physiological and climatic factors.
Carbohydrate δ2H was significantly different among leaves, branches and stems. δ2Hring-cel had strong time-integrated relationships to modelled δ2Hsource, net leaf assimilation rate and evapotranspiration, but the direction of their relationships was different between years. At monthly resolution, water-soluble carbohydrate δ2H measured from one year-old needles had a strong, positive relationship to δ2Hring-cel. δ2Hring-cel also had strong relationships to Standardized Soil Moisture Index (SSMI) in both years.
We show that δ2Hring-cel has a potential as an indicator of soil drought conditions, and that this signal is likely mediated by the leaf-level response to soil drought. This clearly support the growing body of evidence that δ2Hring-cel is strongly mediated by physiological processes, while also opening a new avenue for δ2Hring-cel interpretations. Our results show promise for δ2Hring-cel functioning as a bioindicator of soil drought related physiological stress signals in long-term tree ring chronologies.
How to cite: Angove, C., Lehmann, M., Saurer, M., Tang, Y., Sahlstedt, E., Young, G., Treydte, K., Leppä, K., Schiestl-Aalto, P., Wiesenberg, G., and Rinne-Garmston, K.: Intra-annual tree-ring cellulose δ2H as an indicator of soil drought, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3928, https://doi.org/10.5194/egusphere-egu26-3928, 2026.
Stable carbon isotope compositions (δ13C) in plant materials are an important tool to study variations in the environment that plants live in. δ13C in resin has been less explored than in other extensively studied materials, e.g. tree rings, leaves and n-alkanes, with its temporal and spatial variability poorly quantified. Here, we sampled resin from the breast-height stem and leaves at the lower canopy across 80 pine forest plots in Southwestern China (~ 800,000 km2), and examined the climatic signal recorded in δ13C in resin and leaves. Our results show a clear humidity signal (e.g. precipitation and aridity index) recorded in resin δ13C, much stronger than that preserved in leaf δ13C. The climatic signal was strongest when averaged over the previous two growing seasons, suggesting an average turnover time of two years in the stem resin pool. Our results highlight that resin δ13C is a promising indicator for spatial variability in climatic signals, so resin can serve as a practical alternative to leaves for δ13C-based studies.
How to cite: Tang, Y., Cui, J., Rinne-Garmston, K. T., and Piao, S.: Humidity Signal Recorded in δ¹³C of Pine Resin and Leaves in Southwestern China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15473, https://doi.org/10.5194/egusphere-egu26-15473, 2026.
Lignin is a major component of plant-derived organic matter in soils, and the stable carbon isotopic composition of lignin-derived methoxyl (δ 13C LMeO) groups provides a distinct molecular fingerprint for identifying sources and their relative contributions to soil organic matter. This study investigates δ 13C LMeO values in soil profiles from surface horizons to bedrock in a deciduous and coniferous forest in Switzerland, with the aim of estimating the relative contributions of lignin from photosynthetic and non-photosynthetic plant tissues. Analyses were conducted on two particle-size fractions (<63 µm and 63–200 µm), and the influence of ¹³C isotopic fractionation during lignin degradation was evaluated for both size fractions.
Preliminary source apportionment results, not accounting for isotopic fractionation during degradation, indicate that the coarse fraction at the coniferous site is dominated by lignin derived from non-photosynthetic plant tissues, approaching a 100% contribution. In contrast, the fine fraction at the coniferous site and both particle-size fractions at the deciduous site comprise approximately 60% lignin from non-photosynthetic tissues.
In contrast to bulk δ¹³C and other compound-specific stable isotope tracers, δ 13C LMeO values exhibited a systematic isotopic depletion in the fine (<63 µm) fraction. This depletion suggests preferential stabilization of the more easily degradable lignin from photosynthetic tissues. In the coarse (63–200 µm) fraction, δ 13C LMeO values showed a clear relationship with the extent of degradation, consistent with isotopic fractionation during lignin loss. In contrast, no systematic degradation-related trend was observed in the fine fraction. Together, these results highlight contrasting controls of degradation and stabilization on lignin across soil particle-size fractions and underscore the importance of accounting for isotopic fractionation when applying δ 13C LMeO for soil organic matter source attribution.
How to cite: Cox, T., mharchat, F., and Alewell, C.: Lignin Methoxyl δ¹³C Reveals Particle-Size–Dependent Sources and Degradation in Forest Soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10623, https://doi.org/10.5194/egusphere-egu26-10623, 2026.
The biological pump is a fundamental component of the oceanic carbon cycle, in which export production from the euphotic zone and subsequent organic carbon remineralization in the twilight zone jointly regulate carbon sequestration in the ocean interior. However, the magnitude, spatial variability, and tracers of these coupled processes remain incompletely understood. Here, we investigate the linkage between export production, twilight zone remineralization, and particulate barium in the western North Pacific (wNP) and the South China Sea (SCS). Organic carbon remineralization fluxes in the twilight zone (150-600 m) are quantified using a newly developed transfer function relating particulate excess barium (PBaxs) to oxygen utilization rates, revealing pronounced spatial heterogeneity, with PBaxs concentrations and remineralization fluxes increasing from the subtropical gyre to the North Pacific transition zone. Satellite-derived net primary production (NPP) and export production (EP) exhibit spatial patterns broadly consistent with the inferred remineralization fluxes, indicating a strong association between upper-ocean productivity and mesopelagic carbon degradation. Estimates of the e-ratio and r-ratio based on NPP, EP, and remineralization fluxes demonstrate contrasting biological pump efficiencies, with low e-ratios and high r-ratios in the subtropical gyre reflecting weak carbon sequestration, and high e-ratios and low r-ratios in the transition zone indicating a more efficient biological pump. We further evaluate the potential of particulate barium isotopes as tracers of EP by establishing a calibration between twilight zone particulate barium isotopic composition and euphotic-zone EP in the modern ocean, which reveals a significant negative relationship. However, this relationship does not persist in sedimentary archives: barium isotopic compositions show no systematic response to glacial-interglacial variations in paleoproductivity, and EP reconstructed using the modern calibration exhibits no correlation with sedimentary total organic carbon fluxes. Overall, this study provides an integrated assessment of the applicability and limitations of barium-based proxies from the water column to sediments, highlighting the tight association between Ba, export production, and twilight zone remineralization while emphasizing the challenges and limitations in extending modern barium-based proxies to reconstruct past biological pump dynamics.
How to cite: Yuan, Y., Zhao, S., Zhang, Z., Frank, M., and Cao, Z.: Tracing twilight zone organic carbon remineralization and paleoproductivity with particulate barium proxies: insights and limitations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9004, https://doi.org/10.5194/egusphere-egu26-9004, 2026.
The content and stable isotopic (98Mo/95Mo) composition of bladder wrack (Fucus vesiculosus) were investigated for their potential as a sink for dissolved molybdate in coastal environments. The macrophytes were grown in mesocosms fed with brackish coastal waters from a temperate coastal bay (Kiel Bight) under ambient conditions of simulated environmental stress, e.g., enhanced temperature and/or CO2 partial pressure. Conditions were set up to simulate possible future climate change scenarios applying a delta-approach. Dissolved molybdate in brackish Baltic seawater was isotopically found to be close to the open North Sea, with a slight trend towards isotopically more negative values with decreasing salinity. This is in-line with a fresh water contribution originating from weathered minerals in the catchment area. It was found that the organic tissue of Fucus vesiculosus was substantially enriched in 95Mo compared to dissolved seawater molybdate by up to -1.5 mU. Isotope fractionation was slightly enhanced by increasing temperature but no effect was observed for the other or combined treatments. Seasonal effects in the contents and isotope signatures of the tissue were observed with diminished incorporation of Mo during summer time and an associated lowered isotope signature. No clear trend in the fractionation of the different Mo isotopes can be predicted for different complex climate change scenarios, considering an increase in carbon dioxide partial pressure, in combination with temperature. Mainly temperature seems to impact Mo incorporation and associated isotope signature. A mass balance approach indicates, that the impact of Fucus growth on the total Mo budget in the coastal bight is small due to a continuous water exchange. The results for Mo in seaweed are compared to other trace elements and stable isotope signatures (C, N, S) incorporated into the tissue, too. The results from the present study demonstrate the potential of seaweed to act as an environmental multi-element biomonitor.
How to cite: Böttcher, M. E., Winde, V., Neubert, N., Roeser, P., and Nägler, T. F.: Seaweed is a sink for isotopically light molybdenum in temperate coastal environments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14217, https://doi.org/10.5194/egusphere-egu26-14217, 2026.
The biogeochemical cycling of sulfur stands as a cornerstone in the regulation of the Earth's surface redox state, acting as a primary buffer for atmospheric oxygen and a critical player in the burial of organic matter. The formation and subsequent preservation of sedimentary pyrite represents the dominant sink of reduced sulfur from the global ocean. For decades, the sulfur-isotopic composition of pyrite has been utilized by geochemists as a proxy to reconstruct the chemical evolution of earth's oceans and atmosphere. However, the reliability of this isotopic archive is linked to the physical and chemical state of the sediment-water interface, a boundary layer that was radically transformed by the evolution and intensification of bioturbation - the mixing and ventilation of sediments by burrowing animals. While it is often assumed that the onset of benthic faunal activity had a profound effect on the preserved S-isotope ratio (e.g., (Canfield and Farquhar 2009), actual studies exploring the impact of bioturbation are scarce. (Riemer et al. 2023) show experimental data that suggests that bioturbation shifts the isotope ratio of dissolved H2S towards more negative values. This is in contrast to numerical studies that suggest that bioturbation has no effect on the pyrite S-isotope ratio (Mertens, Paradis, and Hemingway 2025). Here we extend the iron-redox shuttle model of (Van de Velde and Meysman 2016) to include iron-monosulfide and pyrite precipitation, dissolution and oxidation reactions. Our model explicitly tracks, O2, SO4, OM, S0, S2-, Fe3+, Fe2+ in liquid and sorbed state, FeS and FeS2 and their respective S-isotope ratios. Model results suggest that bioturbation has either no, or only a very small, impact. However the current model does not yet include sulfur disproportionation and organic sulfur, so these findings are preliminary.
References
Canfield, Donald E., and James Farquhar. 2009. “Animal Evolution, Bioturbation, and the Sulfate Concentration of the Oceans.” Proceedings of the National Academy of Sciences 106 (20): 8123–27. doi:10.1073/pnas.0902037106.
Mertens, Cornelia, Sarah Paradis, and Jordon D. Hemingway. 2025. “Sedimentary Conditions Drive Modern Pyrite Burial Flux to Exceed Oxidation.” Nature Geoscience. doi:10.1038/s41561-025-01855-5.
Riemer, Sydney, Alexandra V. Turchyn, André Pellerin, and Gilad Antler. 2023. “Digging Deeper: Bioturbation Increases the Preserved Sulfur Isotope Fractionation.” Frontiers in Marine Science 9 : 1039193. doi:10.3389/fmars.2022.1039193.
Velde, Sebastiaan van de, and Filip J. R. Meysman. 2016. “The Influence of Bioturbation on Iron and Sulphur Cycling in Marine Sediments: A Model Analysis.” Aquatic Geochemistry 22 (5-6): 469–504. doi:10.1007/s10498-016-9301-7.
How to cite: Wortmann, U.: The impact of bioturbation on pyrite sulfur isotope ratios: A numerical experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8048, https://doi.org/10.5194/egusphere-egu26-8048, 2026.
Cadmium (Cd) exhibits nutrient-type behaviour in the modern ocean and its isotope system has emerged as a promising tracer of primary productivity and carbon burial. Phytoplankton preferentially assimilate lighter Cd isotopes across a wide range of oceanic conditions, leaving surface waters comparatively enriched in heavier isotopes. This biologically-driven fractionation underlies the application of Cd-isotope ratios as a tracer for nutrient availability and the intensity of primary productivity in both modern marine settings and palaeo-oceans. However, Cd-isotope systematics are also strongly influenced by redox conditions, specifically through the formation and removal of isotopically light Cd sulphides under euxinic conditions. The extent to which sedimentary Cd-isotope signatures faithfully record overlying water-colum processes under such conditions remains poorly constrained.
Here we present new Cd-isotope data from both the water column and sediments of Framvaren Fjord in Norway, the most intensely reducing modern marine basin. Framvaren Fjord serves as a modern analogue for strongly euxinic marine conditions that prevailed during extreme climate events throughout Earth’s history. Notably, the redoxline separating oxic from anoxic waters is uniquely located within the photic zone, in close proximity to the depth of maximum biological productivity. These data allow us to deconvolve Cd-isotope fractionation associated with biological uptake from that linked to Cd sulphide precipitation, and to shed light on how these processes are transferred to and preserved in the underlying sediment.
How to cite: Gangl, S., Stirling, C., Porcelli, D., Druce, M., and Reid, M.: Cd isotopes under extreme euxinia: Tracing productivity and redox in palaeo-oceans, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20811, https://doi.org/10.5194/egusphere-egu26-20811, 2026.
Food fraud related to the geographical origin of high-value agricultural products represents a persistent challenge in regions where local production coexists with large volumes of imported material. In the Canary Islands, potatoes constitute a culturally and economically important crop, with locally grown and traditional cultivars commanding substantially higher market prices than imported varieties, creating clear incentives for mislabelling.
Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) represent a metal isotope system that directly links agricultural products to the geological and biogeochemical characteristics of their cultivation environment through soil–plant transfer processes. Applications to plant-based products grown under contrasting agronomic and water-management conditions demonstrate that geological substrates exert primary control on strontium isotopic signatures. Potatoes cultivated on Tenerife display tightly constrained ⁸⁷Sr/⁸⁶Sr ratios between ~0.7046 and ~0.7054, consistent with uptake from low-radiogenic ocean-island basalts characteristic of the island.
These isotopic values are well separated from those typically associated with continental European agricultural regions and remain coherent across different potato cultivars, despite variability in strontium concentrations (≈410–710 ppb/g). Even within a single basaltic island, small but reproducible variations in ⁸⁷Sr/⁸⁶Sr are observed, reflecting local geological heterogeneity and soil development.
The results highlight the suitability of strontium isotopes as a geology-driven fingerprint within terrestrial biogeoscience systems and demonstrate their potential for verifying the Canarian origin of potatoes. This approach provides a robust foundation for applied provenance studies and authenticity control in volcanic island agro-ecosystems.
How to cite: Perdomo-Sosa, O., C. Coldwell, B., Lodoso Ruíz, E., Cartaya Arteaga, S., Asensio Ramos, M., V. Melián, G., A. Hernández, P., and M. Pérez, N.: Strontium isotopes as geological fingerprints in potatoes cultivated on ocean-island basalts , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10602, https://doi.org/10.5194/egusphere-egu26-10602, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 2
EGU26-21380 | Posters virtual | VPS5
From Geochemical Fingerprints to Food Authentication: Integrating Explainable and Cost-Aware Machine Learning for Provenance AnalysisTue, 05 May, 15:27–15:30 (CEST) vPoster spot 2
The increasing demand for reliable food authentication highlights the need for scalable and innovative tools to link geochemical fingerprints in food products with their geographic provenance. Food authentication is not only essential for preventing fraud but also offers a unique opportunity to relate agricultural products to their underlying geochemical signatures. Here we present a unified framework that combines stable isotopes (e.g. ⁸⁷Sr/⁸⁶Sr) and trace-element fingerprints measured in food products with explainable and cost-aware machine learning to support provenance verification.
We first develop a cost-aware binary classification model for French sparkling wines, demonstrating how high-precision ⁸⁷Sr/⁸⁶Sr ratios can be partially substituted by low-cost elemental proxies (e.g. Rb) while maintaining strong discriminative power. To address scalability constraints, we extend this approach to a multiclass setting using cost-sensitive logistic regression to classify wines from multiple Portuguese and Chilean regions, explicitly handling class imbalance and feature redundancy. Finally, we introduce TeaPrint, an unsupervised multimodal clustering framework that jointly integrates isotopic, elemental and volatile organic compound data to uncover coherent regional geochemical patterns in international tea samples without requiring prior labels.
Across these case studies, we show that food products carry integrated geochemical signatures that can be exploited for robust provenance authentication across heterogeneous datasets. By bridging forensic geochemistry and explainable machine learning, our approach offers a cost-efficient and scalable pathway towards robust provenance authentication and transparent food supply chains.
How to cite: Lu, Y., Doerr, C., and Sebilo, M.: From Geochemical Fingerprints to Food Authentication: Integrating Explainable and Cost-Aware Machine Learning for Provenance Analysis , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21380, https://doi.org/10.5194/egusphere-egu26-21380, 2026.
