Lithium (Li) isotopes ratios (expressed as δ⁷Li) are increasingly utilized as tracers for environmental and biological processes, including recent studies on Li uptake by living organisms and its emerging role as a contaminant. However, the typically low Li concentrations in natural samples and sentinel species used for monitoring present significant analytical challenges, particularly in generating efficiently high-precision and accurate isotopic data. In this study, we present the results of multiple tests and an optimized protocol for Li isotopic analysis at ultra–trace levels (< 3 ng Li) using the Neoma MC-ICP-MS. We also provide long–term, high-precision isotopic data for marine and biological reference materials. First, we demonstrate that memory effects remain significant when analyzing low–concentration Li solutions. However, reducing the sample volume to 550 µL effectively minimizes these effects to just 3% of the ⁷Li signal. Our findings confirm that the Standard Sample Bracketing (SSB) method is effective for low–level Li isotopic measurements, though several precautions are necessary. Specifically, the molarity of nitric acid used for sample and LSVEC (bracketing standard) dilution must be carefully matched, with deviations of less than 0.3%. Additionally, the relative difference in ⁷Li voltages between standards and samples needs to be within ± 20% to avoid significant isotopic bias. Furthermore, we directly compared two desolvating systems (Apex Ω and Aridus III) for Li isotopic analysis under dry plasma conditions. This comparison enabled us to propose an optimized introduction system for nanogram–level analyses with minor memory effects. We then applied our protocol to multiple analyses of four reference materials (Li7–N, AEL, EDMM–1–H, Seawater, NIST SRM–1400, and PLK–VLFR), demonstrating efficient data acquisition with excellent long–term accuracy and precision for both marine and biological matrices. Future efforts should focus on reducing the time required for Li dissolution and purification from samples used in high-frequency environmental and bio–monitoring applications.

Lithium consumption has surged dramatically since 2010, primarily driven by the boost of high-tech devices like mobile phones and laptops, as well as Li-ion batteries for electric vehicles and energy storage systems. Current Li consumption surpasses the natural river flux to the ocean (70 kt/yr), while recycling rates remain notably low. Recent studies document instances of lithium pollution in riverine systems [1], raising concerns about potential contamination of soils and littoral zones, which serve as the ultimate sink for various pollutants released on land. Littoral environments provide critical ecosystem services and their natural biodiversity is exceptional. While microplastics, organic pollutants and several trace metals have been widely monitored and investigated in ecotoxicological studies, lithium has received little attention yet. To address this emerging issue, we investigate the biogeochemical cycling of lithium and assess its potential risks for ecosystems using its isotopic ratio (delta7Li). For this, we develop optimized and automated geochemical and isotopic techniques for measuring Li levels and Li isotopes in environmental and in biological samples using respectively last generation TQ-ICP-MS (iCap MTX) and MC-ICP-MS (NeomaTM) (ThermoFischer Sci.). Lithium contamination and its recent evolution is being determined for various parts of France and the European continent through the study of river waters sampled at their outlets and through the study of sentinel species bioaccumulating lithium. The transfer of lithium from the environment to aquatic organisms is being investigated experimentally [2], and cell cultures targeting ionic transporters of interest are employed to quantify kinetics effects [3]. Using sentinel species, we find that some of the large rivers display an increase of Li levels since 1990’s while others not. Lab experiments and related Li isotope variations demonstrate that the excretion rate is rapid and depends on the Li environmental level and on the organism metabolism. These first results open new questions concerning the impact of anthropogenic lithium on its global cycle and its fate in the critical zone. [1] Choi et al. (2019) Nature Communications 10, 5371. [2] Thibon et al. (2021) ACS Earth & Space Chem. 5, 6, 1407-1417. [3] Poet, Vigier, Bouret et al. (2023) iScience 26, 106887

Lithium isotopic composition of marine specie’s soft tissues give key information on mechanisms of biological isotopic fractionation in the ocean. It has been shown that lithium isotopic composition of bivalve’s soft tissues can help modeling the impact of Li in the environment. These approaches concern low Li - organic rich - samples, which often require multiple analyses for reliable data treatment. The field of isotope geochemistry needs to develop appropriate methods to fulfill biological constraints. In this study, we propose new methods for biological sample’s preparation prior Li isotopic analyses by MC-ICP-MS (NEOMA, Thermo Fisher Sci.). Lithium purification is performed manually using cation-exchange resin columns, which is efficient, but time-consuming[1]. We are developing an automated procedure using prepFAST MCTM (ESI) with a specific column geometry for lithium. We tested two acids (HCl, HNO3) at different molarities and flow rates. Test were performed using solutions of 10 ppm Na and 200 ppb Li. First results show that 3 hours per sample is required (including column washing) and that the memory effect is negligible for both Li and Na. The dissolution of biological matrices using acids may be time consuming, and inefficient, while a 100% yield is required to avoid isotopic bias. We incinerated different biological tissues, with known Li isotopic ratio[2]. At 600 °C and using HNO3, the dissolution is rapidly 100% efficient for 50-150 mg dry weight. Temperature effect on lithium isotopes will now be evaluated. These preliminary results provide different techniques to optimize chemical protocols for Li isotopes analyses of biological materials, which should facilitate interdisciplinary approaches.

Lithium isotopes (δ7Li) are key tracers in Earth and Environmental Sciences, used for studying continental weathering, past climate, hydrothermal systems, and biogeochemical processes. High-precision δ7Li measurements rely on MC-ICP-MS, but analyzing low Li samples remain challenging. This study evaluates the Thermo Fischer Sci. Neoma MC-ICP-MS (without MS/MS) operational since Sept. 2024 at LOV. Two setups were tested: with (1) Apex Omega and (2) Cetac Aridus III desolvator. Samples were introduced via a microFAST Isotope DualLoop (ESI) locally configured to reduce overnight evaporation. Each desolvator was assessed with and without the Dual Loop system. Measurements were performed on unpurified 3 ppb lithium standards: LSVEC (δ⁷Li = 0‰) and Li7-N (δ⁷Li = 30.2 ± 0.3‰)1 using a standard bracketing technique. Analyses were performed in low-resolution mode, achieving Li sensitivity up to 6000V/ppm. With the Apex Omega, repeated LSVEC and Li7-N measurements without the dual loop yielded average δ7LiLSVEC = -0.02‰ ± 0.1‰ (2SD, n=16) and δ7LiLi7-N = 30.01‰ ± 0.2‰ (2SD, n=28). Using the Dual Loop injector, we get similar values, with δ7LiLSVEC = -0.003‰ ± 0.1‰ (2SD, n=33) and δ7LiLi7N = 30.35‰ ± 0.3‰ (2SD, n=75). In both cases a persistent memory effect (1%-6% of the ⁷Li signal) remains challenging. Despite this, the data accuracy and reproducibility for pure Li solutions are correct compared to data published for low-Li reference materials2. For the Aridus III desolvator, sensitivity matched that of Apex Omega, but the Dual Loop is crucial to maintain precision: δ7LiLSVEC = 0.03‰ ± 0.1‰ (2SD, n=24), δ7LiLi7N = 30.7‰ ± 0.2‰ (2SD, n=19). Efforts are ongoing to lower Li concentration and mitigate memory effects. Overall, the NeomaTM MC-ICP-MS enables rapid, high-precision δ7Li values at the ppb level. Future work will focus on biological reference materials and further configuration assessments.

The Mesozoic-Cenozoic transition is a period of biogeochemical cycle perturbations. The strongest of them is the Cretaceous-Paleogene boundary (K-Pg) crisis, characterized by one of the most important extinctions of planktonic marine calcifiers in Earth's history. One of the primary drivers of this biocalcification crisis is thought to be the increase in atmospheric CO₂ concentration and ocean acidification triggered by the Chicxulub Impact, and/or Deccan volcanism. Because it reflects changes of the calcium cycle and/or depends on parameters of the carbonate system, the Ca isotope composition of carbonate minerals precipitated from seawater (^{δ 44 / 40}Ca) offers the potential to reconstruct some of the environmental changes that occurred. Here we present new high-resolution planktonic and benthic foraminiferal ^{δ 44 / 40}Ca, δ¹⁸O, δ¹³C, and Sr/Ca records across the K-Pg transition from Shatsky rise (Leg 198; ODP Site 1209, Hole C). The ^{δ 44 / 40}Ca record displays a succession of rapid shifts of ca. - 0.4 ‰ across the K-Pg transition. They are similar though not identical between the planktonic and benthic records. These shifts took place on a timescale significantly shorter than the residence time of Ca in the oceans and are therefore unlikely to result from global disequilibrium in the oceanic Ca budget. Instead, changes in the fractionation factor between carbonate minerals and seawater in response to changes in precipitation rates may explain the observed ^{δ 44 / 40}Ca and Sr/Ca record. The benthic and planktonic ^{δ 44 / 40}Ca records show a late Maastrichtian and an early Danian negative excursions best explained by a succession of episodes of ocean alkalinity increase related to increased continental weathering caused by CO₂ emissions from Deccan volcanism and the aftermath of the K-Pg biocalcification crisis. Carbonate compensation via carbonate sediment dissolution, biological carbonate compensation via reduction of biocalcification, and/or an increase in continental weathering must have occurred to offset the excess CO₂, ultimately resulting in rapid changes in ocean carbonate chemistry, in combination with reduced surface alkalinity export in response to the early Paleogene planktonic biomineralization crisis.

La limite Crétacé-Paléogène (KPg, -66 Ma) est associée à l'une des plus grandes perturbations environnementale de l'histoire récente de la Terre. Cette crise, liée à la mise en place d'une province magmatique de premier ordre (traps du Deccan) et/ou à un impact météoritique (formation du cratère de Chixculub) se traduit entre autres par une perturbation profonde de la bioproduction carbonatée océanique. Si de nombreuses questions subsistent quant à l'importance relative de l'impact et du volcanisme dans les perturbations de la limite KPg, la modification de la composition chimique du système océan-atmosphère par l'émission d'énormes quantités d'acide sulfurique et carbonique d'origines volcaniques a probablement joué un rôle clé dans la crise Crétacé-PaléogèneDurant ce projet de thèse j'ai réalisé des enregistrements isotopiques à haute résolution des isotopes stables du soufre et du calcium à travers la transitons Crétacé-Paléogène. Ces enregistrements sont basés sur des échantillons monospécifiques de foraminifères planctoniques et benthiques issue du pacifique équatorial.Les enregistrements de δ44/40Ca benthiques et planctoniques avant et après la limite K-Pg nous ont permis de mettre en évidence une succession d'épisodes de changements de l'alcalinité océanique liés à l'augmentation de l'altération continentale et à la crise de biocalcification causée par les émissions de CO2 du volcanisme du Deccan. La compensation des carbonates par la dissolution des sédiments carbonatés, la réduction de la biocalcification et/ou l'augmentation de l'altération continentale ont dû se produire pour compenser l'excès de CO2. Par conséquence, cela a entraîné des changements rapides dans la chimie des carbonates océaniques, en combinaison avec une réduction de l'exportation de l'alcalinité de surface en réponse à la crise de biominéralisation planctonique du Paléogène précoce.L'examen de la perturbation du cycle du soufre quant lui, soutient plutôt l'idée que l'extinction de masse à travers la transition K-Pg n'est pas être associée à une expansion globale de conditions anoxique, contrairement aux différents événements d'extinction de masse du Phanérozoïque, où il existe des preuves multiples du de développement de condition anoxique associé aux perturbations du cycle du carbone. Ces conclusions est en accord avec les observations micropaléontologiques qui ne montrent pas d'extinction de masse des foraminifères benthiquesCette approche géochimique multiproxies a l'avantage de permettre donc une évaluation plus pousser de certains paramètres clés tel que la chimie des carbonates et l'anoxie océanique à travers la transition Crétacé -Paléogène permettant ainsi d'avoir un schéma global plus clair des perturbations biogéochimiques autour de cette période.

The rapid response of benthic foraminifera to environmental factors (e.g. organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such an approach, however, requires a thorough knowledge of their modern ecology in such extreme settings. To this aim, seven stations along a north–south transect across the Storfjorden (Svalbard archipelago) have been sampled using an interface multicorer. This fjord is an area of intense sea ice formation characterised by the production of brine-enriched shelf waters (BSW) as a result of a recurrent latent-heat polynya. Living (rose bengal-stained) foraminiferal assemblages were analysed together with geochemical and sedimentological parameters in the top 5 cm of the sediment. Three major biozones were distinguished. (i) The “inner fjord” zone, dominated by typical glacier proximal calcareous species, which opportunistically respond to fresh organic matter inputs. (ii) The “deep basins and sill” zone, characterised by glacier distal agglutinated fauna; these are either dominant because of the mostly refractory nature of organic matter and/or the brine persistence that hampers the growth of calcareous species and/or causes their dissolution. (iii) The “outer fjord” zone, characterised by typical North Atlantic species due to the intrusion of the North Atlantic water in the Storfjordrenna. The stressful conditions present in the deep basins and sill (i.e. acidic waters and low food quality) result in a high agglutinated ∕ calcareous ratio (A∕C). This supports the potential use of the A∕C ratio as a proxy for brine persistence and overflow in Storfjorden