Secondary mineral prevalence in Ryugu samples, similar to primitive carbonaceous-Ivuna type (CI) chondrites, suggests that aqueous alteration was a key factor in its formation. However, this general consensus masks our limited understanding of the specific mechanisms and environmental conditions involved in water-rock interactions on primitive asteroids. Highresolution cathodoluminescence (CL) analysis of the ubiquitous dolomite crystals in Ryugu samples reveals concentric epitaxial overgrowths with varying levels of Mn 2+ -activated luminescence. CL panchromatic images and spectral deconvolution provide compelling evidence for the evolution of aqueous fluids toward highly saturated brines. Given the close association of dolomite with widespread intergrowths of serpentine and saponite in the matrix, we propose that brine formation occurs as a byproduct of serpentinization. Unlike large-scale evaporation or freezing, this process can locally cause the hydrothermal fluid to dry out, significantly increasing its salinity over time. This leads to the sporadic precipitation of an evaporite mineral sequence, with dolomite forming at an early stage. This serpentinizationdriven brine formation model offers a convincing alternative to a purely prograde alteration history for Ryugu. It may also provide a better explanation for the alteration processes of Bennu and other CI chondrite parent bodies.

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 (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 the increasing adoption of Li-ion batteries for electric vehicles and energy storage systems. Among all metals, lithium exhibits the most significant growth in demand over the past 15 years. Consequently, current lithium consumption already surpasses the natural oceanic input from rivers, while recycling rates remain notably low (less than 5% globally). Recent studies have documented instances of lithium pollution in riverine systems, raising concerns about potential contamination of littoral zones, which serve as the ultimate sink for various pollutants. At the interface between continents and the ocean, littoral environments provide critical ecosystem services and their natural biodiversity is exceptional. While microplastics, organic pollutants and other trace metals such as Cu, Hg, and Zn are widely monitored and investigated in ecotoxicological studies, lithium has received little attention yet.To address this emerging issue, the ERC SeaLi2Bio project investigates the biogeochemical cycling of lithium in coastal environments and assess its potential risks for marine species and human health. We develop new and automated geochemical and isotopic techniques for measuring Li levels and Li isotopes in environmental, biological and marine samples, using last generation TQ-ICP-MS and MC-ICP-MS instruments. Lithium contamination and its recent evolution is determined on different continents through the study of estuarian waters and sentinel species. Ecotoxicologists experimentally determine Li bioaccumulation rates in coastal species and seafood. Biologists work on the Li transfer in cells and in tissues and identify the role of membrane transporters at play in marine species. Modelers use environmental and biological data to anticipate Li environmental risks related to future consumption and recycling scenarios.By combining these approaches, we aim to quantify the extent of lithium pollution in coastal ecosystems, identify vulnerable species and habitats, and predict future trends. Our findings will provide crucial insights for developing effective strategies to mitigate the environmental risks associated with lithium and ensure the sustainability of coastal ecosystems facing increasing anthropogenic pressures.

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.

This study presents lithium (Li) and magnesium (Mg) elemental and isotopic compositions in the clay-and silt-sized fractions of sediments from major rivers worldwide. Combined with previously published silicon (Si) isotope data, these results are used to reassess their potential as large-scale silicate weathering proxies and to characterize the soil state at the global scale. Among the three isotopic systems studied, Li isotopes exhibit the largest variations and differences between clays and silts, whereas Mg isotopes show no significant size-dependent differences. River clays are significantly enriched in Li and Mg compared to silts, indicating higher abundances than the upper continental crust (UCC). This enrichment is consistent with the preferential incorporation of Li and Mg into neoformed secondary phases. In contrast, siltsized fractions contain substantial amounts of quartz and other Li-and Mg-depleted primary minerals. In line with recent research, we show that a provenance proxy is required for deconvolving the weathering signal from measured clay d 7 Li values, using either Nd isotopes or average estimates for bedrock d 7 Li compositions. Unlike silicon isotope ratios (δ³⁰Si) in fluvial clays, which correlate with environmental parameters, the weathering signal derived from Li isotopes appears independent of both clay mineralogy and climate. This challenges previous interpretations linking the evolution of claybound δ⁷Li to Late Quaternary climate variations. We also provide the first global estimates for average Si, Mg and Li isotope compositions and concentrations in the clay-and silt-size fractions of fluvial sediments entering the ocean. Compared to the UCC, our estimates indicate systematic imbalance away from steady-state driven by an excess of elemental dissolved fluxes to the ocean. The excess supports the hypothesis that continental weathering is currently in disequilibrium, potentially due to lingering elevated mineral dissolution rates following the last deglaciation. It also indicates that anthropogenic contribution to the riverine dissolved load remains to be elucidated at the global scale.

During the TONGA cruise (2019), seawater samples were collected to assess the effect of volcanic eruption versus submarine hydrothermal system on the water column. For this purpose, two locations were investigated, the first one located directly under the influence of the New Late'iki island (eruption in October 2019), and the second one showing ongoing submarine hydrothermal activity. At both locations, the total strontium (TSr) and lithium (TLi) concentrations vary between 94.4 and 152.3 µmol/L and 13.2 and 203.5 µmol/L, respectively. When combined, TSr and TLi concentrations of all samples in the water column are higher than those of the oligotrophic water. Both volcanic eruption and submarine hydrothermal activity (e.g. volcanic ashes, particles, gas condensate) can deliver substantial amount of TSr and TLi to the water column. The distribution of TSr versus TLi evidences linear trends either with a negative or positive slope. The negative correlation is observed in the water column at both sites, directly under the influence of the eruption and in the vicinity of the volcano with hydrothermal activity. The positive TSr versus TLi correlation is observed at site under submarine hydrothermal influence and is in line with black smokers related hydrothermal plumes. The 87 Sr/ 86 Sr ratios vary between 0.709147 and 0.709210 and d 7 Li values vary between +10.1 and +37.6 ‰. While 92% of the measured 87 Sr/ 86 Sr ratios are in line with the mean value of oligotrophic waters, once combined with the d 7 Li values, only 20% of them remains within this field. The wide range of d 7 Li values decreases from sea-surface down to ~140 mbsl, before increasing at greater depth, while defining different linear trend according to the dissolved inorganic carbon concentrations. The variability of d 7 Li values reflect hydrothermal contribution, mineral-seawater interaction and potentially biology-environment interaction. In the particular geological setting of the study, where both hydrothermal and volcanic activities were at play, disentangling both contributions on water column implies a combined use of elemental and isotopic signatures of Sr and Li tracers.

감태(Ecklonia cava; E. cava)는 자연 및 인위적 영향으로 인해 개체 수가 점차 감소하고 있다. 현재까지 감태의 생태학적 특징에 관 한 연구는 활발하게 수행되었으나, 자연 생육 및 인공 이식 감태의 화학 및 동위원소적 특성에 관한 연구는 이루어지지 않은 실정이 다. 따라서 이번 연구에서는 동해안 해역에서 채취한 자연 생육 및 인공 이식 감태에 대한 무기화학조성(Na, K, Ca, Mg, and Sr) 및 스트론튬 동위원소 비( 87 Sr/ 86 Sr) 분석을 통해 두 개체군의 부위별 지화학적 특성을 비교 분석하고, 분류 가능성을 조사하였다. 각 감 태 개체군의 원소 함량은 줄기(2.90 ± 3.17%) > 잎(2.65 ± 2.98%) > 뿌리 (2.30 ± 2.04%) 순이며, 87 Sr/ 86 Sr 비는 잎(0.709198 ± 0.000013) > 줄기(0.709181 ± 0.000009) ≈ 뿌리(0.709181 ± 0.000017) 순서로 나타났다. 모든 부위에서 해수보다 높은 87 Sr/ 86 Sr 비 를 나타내 87 Sr/ 86 Sr 비가 높은 암석과 시멘트에서 Sr가 흡수되었음을 지시한다. t-test 결과, 두 개체군 간의 원소 조성은 유의한 차이 가 없는 것으로 나타났지만(p-value > 0.05, n = 30), 87 Sr/ 86 Sr 비는 유의미한 차이가 있는 것으로 나타났다(p-value < 0.05, n = 30). 이 번 연구에서 제시한 것처럼 87 Sr/ 86 Sr 비는 자연 발생 감태와 인공 이식 감태를 분류하는 유용한 추적자가 됨을 시사한다.

Non-conventional stable isotopes have received increasing attention in the past decade to investigate multi-level ecological connections from individuals to ecosystems. More recently, isotopes from trace and non-nutrient elements, potentially toxic (i.e., Hg), have also been recognized of great significance to discriminate sources, transports, and bioaccumulation, as well as trophic transfers. In contrast, lithium (Li) concentrations and its isotope compositions (δ 7 Li) remain poorly documented in aquatic ecosystems, despite its possible accumulation in marine organisms, its increasing industrial production, and its demonstrated hazardous effects on biota. Here, we present the first Li isotope investigation of various soft tissues, organs or whole organisms, from marine plankton, bivalves, cephalopods, crustaceans, and fish of different biogeographical regions [North Mediterranean Sea, North Atlantic Ocean (Bay of Biscay), South East Pacific Ocean (New Caledonia), and Southern Indian Ocean (Kerguelen Islands)]. Independently of the considered organisms, δ 7 Li values range widely, from 4.6‰ (digestive gland of bivalves) to 32.0‰ (zooplankton). Compared to homogeneous seawater (δ 7 Li ∼ 31.2‰ ± .3‰), marine organisms mostly fractionate Li isotopes in favor of the light isotope ( 6 Li). Within the same taxonomic group, significant differences are observed among organs, indicating a key role of physiology on Li concentrations and on the distribution of Li isotopes. Statistically, the trophic position is only slightly related to the average Li isotope composition of soft tissues of marine organisms, but this aspect deserves further investigation at the organ level. Other potential influences are the Li uptake by ingestion or gill ventilation. Overall, this work constitutes the first δ 7 Li extensive baseline in soft tissues of coastal organisms from different large geographic areas mostly preserved from significant anthropogenic Li contamination.

Geochemists have long considered Li isotope composition of marine carbonates as one of the most straightforward oceanic archives, tracing climate regulation by continental silicate weathering. However, despite an isotopically homogenous ocean, a large range of δ7Li values were reported in the literature for modern biogenic carbonates. Additionally, laboratory studies highlighted variable Li isotope fractionations during foraminifera growth and during precipitation of inorganic carbonates. Despite an increasing interest in this topic, there is still limited understanding of Li isotopic fractionation and of Li incorporation mechanisms in carbonates. The present review aims to filling this gap by compiling and meta-analyzing the past findings from the literature. More specifically, Li/Ca and δ7Li data concerning the influence of mineralogy, temperature, pH, growth rate and biological processes have been exhaustively reviewed and statistically examined, including by PCA (Principal Component Analysis). For inorganic carbonate, we demonstrate that (1) the influence of mineral type is insufficiently explored (2) the effect of temperature on Li isotopes is negligible, although temperature changes can affect calcite Li/Ca ratio, and (3) calcite δ7Li and Li/Ca are primarily influenced by pH and growth rate. For marine modern biogenic carbonates, our cartography highlights an uneven geographical distribution, and further studies are required in the Pacific, Indian, and Southern Oceans. Also, for both Li/Ca and δ7Li, there are statistically significant and systematic differences between ‘bulk carbonates’ and all studied marine biogenic groups (i.e. foraminifera, mollusks, brachiopods). A detailed examination of foraminifera data reveals that planktic species display δ7Li values statistically higher than benthic ones, and both anti-correlate with Li/Mg ratios. Overall, this review underlines the necessity of filling the identified gaps of knowledge and of attentively considering the impact of environmental parameters and biological processes for interpreting past δ7Li variations displayed by fossil shells.

Lithium (Li) has a wide range of uses in science, medicine, and industry, but its isotopy is underexplored, except in nuclear science and in geoscience. 6 Li and 7 Li isotopic ratio exhibits the second largest variation on earth's surface and constitutes a widely used tool for reconstructing past oceans and climates. As large variations have been measured in mammalian organs, plants or marine species, and as 6 Li elicits stronger effects than natural Li ($95% 7 Li), a central issue is the identification and quantification of biological influence of Li isotopes distribution. We show that membrane ion channels and Na +-Li + /H + exchangers (NHEs) fractionate Li isotopes. This systematic 6 Li enrichment is driven by membrane potential for channels, and by intracellular pH for NHEs, where it displays cooperativity, a hallmark of dimeric transport. Evidencing that transport proteins discriminate between isotopes differing by one neutron opens new avenues for transport mechanisms, Li physiology, and paleoenvironments.

The objective of the TONGA oceanographic expedition was to study the control of productivity and carbon sequestration by micronutrients of shallow hydrothermal origin in the Western Tropical South Pacific (WTSP) Ocean. The 37-day oceanographic survey took place on board the R/V L’Atalante in 2019 between Oct. 31 to Dec. 6 (Nouméa-Nouméa). Over a large area of the WTSP the team acquired numerous results on both the entire water column (up to the sediment) and the atmosphere. Specific task are represented on figure 1: (task 1) to characterize chemically and optically shallow hydrothermal fluids and to compare the source from below (shallow hydrothermal fluids) with the source from above (atmospheric deposition); (task 2) to quantify the dynamical dispersion of the fluids at small and regional scale; (task 3) to investigate the impact of the shallow hydrothermal sources on the biological activity and diversity, and the feedback to the atmosphere via the oceanic emissions of primary and secondary aerosols. (Task 4) to communicate about the campaign (see for example our Tweeter account (https://twitter.com/tongaproject) and the movie (26’) both in French (https://www.youtube.com/watch?v=e5kAd0i6Dck) and English (https://www.youtube.com/watch?v=UeABf-cVR-k). A long west to east (up to the blue waters of the gyre) transect allowed to characterize the different biogeochemical provinces crossed and a focus in the region of the Lau Basin allowed to investigate the impact of shallow hydrothermal sources. A series of short and long stations allowed to fully characterize the stocks and the fluxes in the different provinces. Short-term (up to 10 days) processes studies have been conducted (drifting moorings and minicosms experiments). Part of these results will feed into important modeling work. A fixed mooring line launched at the end of the campaign and recovered in Nov. 2020 as well as the 7 ARGO floats and 20 drifting buoys that were dropped during the campaign provide a broader temporal context of the acquisitions done during the campaign. An important focus of the campaign was the trace metal characterization of the entire water column. For this, TONGA has been labeled by the international program GEOTRACES (https://www.geotraces.org/). The impact on biological communities of fluids is supported by the international IMBER program (https://imber.info/). The TONGA project is also part of the LEFE program (funding by LEFE-CYBER and LEFE-GMMC), the ANR (Appel à projets génériques) and the Fondation A-MIDeX of the Aix-Marseille Université.

Human-induced environmental disturbances during the Holocene have provided support for the Early Anthropogenic Hypothesis (EAH), which proposes that with the advent of agro-pastoralism and associated deforestation, humans have modified CO2 and CH4 concentrations into the atmosphere. However, only limited evidence exists for human driven chemical alteration of the Earth’s Critical Zone (ECZ) in early antiquity. Here, we explore the impact of human activities on both erosion and chemical weathering patterns in the Nile basin during a time interval that includes the rise of the Aksumite Kingdom and Late Antique Egypt (∼3–∼1kaBP). By coupling lithium and neodymium isotopes (δ7Li, εNd) in clay-size fractions of two marine sediment cores from the Nile Deep Sea Fan (NDSF), we reconstruct the variability of sediment provenance and silicate weathering intensity in the Nile basin over the last 9000 years. Our high temporal resolution data show that for the last 3000 years, the Rosetta Nile Deep Sea Fan has been increasingly fed with clays delivered from the Ethiopian basaltic highlands (εNd = ∼−1), despite the absence of hydrological intensification and major climatic drivers over that region. Concomitantly, the clay Li isotopic composition shifted towards lower values δ7L1 values (δ7L1=1 to −2), yielding unprecedented negative values for at least the last 100,000 years. Combined with other archaeological, paleo-pedological and organic chemistry inferences, the L1–Nd isotope proxy records indicate a link between the intensification of continental weathering and intensified land-use and water management during the Pre-Aksumite (∼3to∼2kaBP) and Aksumite (∼2to∼1kaBP) periods. Therefore, our results provide direct support to the hypothesis of an early and large scale anthropogenic forcing on continental chemical weathering. A comparison with previously published records for Central Africa, Central Europe and China suggests that the impact of the intensification of early agriculture on the ECZ may have operated at a global scale starting around four thousand years ago.

The vertebrate fossil record documents a plethora of transitions between aquatic and terrestrial environments but their causes are still debated. Quantifying the salinity of living environments is therefore crucial for precising the sequence of ecological transitions. Here, we measured lithium stable isotope composition of mineralized tissues (δ 7 Limt) of extant and extinct vertebrates from various aquatic environments: seawater, freshwater/terrestrial, and "transitional environments" (i.e. brackish waters, or seasonal access to freshwater and seawater). We report statistically higher δ 7 Limt values for seawater vertebrates than freshwater ones, taxonomic groups considered separately. Moreover, vertebrates living in transitional environments have intermediate δ 7 Limt values. Therefore, we show that δ 7 Limt values of both extant and extinct vertebrates can discriminate their aquatic habitat.

SUMMARY Lithium (Li) has a wide range of uses in science, medicine and industry but its isotopy is underexplored, except in nuclear science and in geoscience. 6 Li and 7 Li isotopic ratio exhibits the second largest variation on Earth’s surface and constitutes a widely used tool for reconstructing past oceans and climates. As large variations have been measured in mammalian organs, plants or marine species, and as 6 Li elicits stronger effects than natural Li (~95% 7 Li) a central issue is the identification and quantification of biological influence of Li isotopes distribution. We show here that membrane ion channels and Na + -Li + /H + exchangers (NHEs), strongly fractionate Li isotopes. This systematic 6 Li enrichment is driven by membrane potential for channels, and by intracellular pH for NHEs, where it displays cooperativity, a hallmark of dimeric transport. Evidencing that transport proteins discriminate between isotopes differing by one neutron, opens new avenues for transport mechanisms, Li physiology, and paleoenvironments.

Lithium (Li) has two stable isotopes, 6 Li and 7 Li, whose large relative mass difference is responsible for significant isotopic fractionation during physico-chemical processes, allowing Li isotopes to be a good tracer of continental chemical weathering. Although physical erosion is dominant in the Polar regions due to glaciers, increasing global surface temperature may enhance chemical weathering, with possible consequences on carbon biogeochemical cycle and nutriment flux to the ocean. Here, we examined elemental and Li isotope geochemistry of meltwaters, suspended sediments, soils, and bedrocks in the Barton Peninsula, King George Island, Antarctica. Li concentrations range from 8.7 nM to 23.3 μM in waters, from 0.01 to 1.43 ppm in suspended sediments, from 9.56 to 36.9 ppm in soils, and from 0.42 to 28.3 ppm in bedrocks. δ 7 Li values are also variable, ranging from +16.4 to +41.1‰ in waters, from −0.4 to +13.4‰ in suspended sediments, from −2.5 to +6.9‰ in soils, and from −1.8 to +11.7‰ in bedrocks. Elemental and Li isotope geochemistry reveals that secondary phase formation during chemical weathering mainly control dissolved δ 7 Li values, rather than a mixing with sea salt inputs from atmosphere or ice melting. Likewise, δ 7 Li values of suspended sediments and soils lower than those of bedrocks indicate modern chemical weathering with mineral neoformation. This study suggests that increasing global surface temperature enhances modern chemical weathering in Antarctica, continuing to lower δ 7 Li values in meltwater with intense water-rock interactions.

Li isotope compositions of soft tissues and bones from six international reference materials of biological origin has been characterized with MC-ICP-MS.

Trace metals such as Cu, Hg, and Zn have been widely investigated in marine ecotoxicological studies considering their bioaccumulation, transfer along trophic webs, and the risks they pose to ecosystems and human health. Comparatively, Li has received little attention, although this element is increasingly used in the high-tech, ceramics/glass, and medication industries. Here, we report Li concentrations in more than 400 samples, including whole organisms and different organs of bivalves, cephalopods, crustaceans, and fish. We investigated species from three contrasting biogeographic areas, i.e. temperate (Bay of Biscay, northeast Atlantic Ocean), tropical (New Caledonia, Pacific Ocean), and subpolar climates (Kerguelen Islands, southern Indian Ocean), among diverse trophic groups (filter-feeders to meso-predators) and habitats (benthic, demersal, and pelagic). Although Li is homogeneously distributed in the ocean (at 0.18 μg/mL), Li concentrations in soft tissues vary greatly, from 0.01 to 1.20 μg/g dry weight. Multiple correspondence analyses reveal two clusters of high and low Li concentrations. Li distributions in marine organisms appear to be mostly geographically independent, though our results highlight a temperature dependency in fish muscles. Li is consistently bio-reduced through the trophic webs, with filter-feeders showing the highest concentrations and predatory fish the lowest. Strong variations are observed among organs, consistent with the biochemical similarity between Na and Li during transport in the brain and in osmoregulatory organs. Fish gills and kidneys show relatively high Li concentrations (0.26 and 0.15 μg/g, respectively) and fish brains show a large range of Li contents (up to 0.34 μg/g), whereas fish liver and muscles are Li depleted (0.07 ± 0.03 and 0.06 ± 0.08 μg/g, respectively). Altogether, these results provide the first exhaustive baseline for future Li ecotoxicology studies in marine coastal environments.

Lithium production has dramatically increased over the past decade, and the first cases of environmental Li pollution have been recently reported in urban and mining regions. While elevated Li concentrations may be toxic for living organisms, tools to monitor Li in the environment have not yet been developed. Consequently, its impact on key biota and human health is still poorly known. The present laboratory-based study shows that the soft tissues of blue mussels (Mytilus edulis) can be used to quantify Li contamination in coastal waters. Stable Li isotope ratios (7 Li/ 6 Li) measured in these soft tissues correlate positively with seawater Li concentrations and show precisely the threshold above which mussels shift their depuration mechanism. Combined with other data from the natural environment, the experimental results have profound implications for the fate of coastal ecosystems and shellfish consumption living under a high Li environmental level. We also highlight the need to develop innovative tools to extract Li from wastewaters before its release into rivers and, ultimately, the ocean.

The characterization of particles in suspension in river plumes contributes to the assessment of net particulate organic carbon (POC) fluxes and to a better understanding of the anthropogenic and climatic impact on blue carbon. Prior to POC analysis in natural waters, inorganic carbon (in the form of carbonates) must be removed. This step is generally carried out by acid leaching. However, the presence of mineral matrices (in turbid waters) may hinder total decarbonation, which may result in biased measurements. This work checks the quality of decarbonation through the analysis of carbon stable isotope ratio (δ 13 C), considering suspended particles discharged by three rivers into coastal waters under flooding conditions. Carbonates were removed by adding variable volumes of 2N hydrochloric acid (HCl) to filters. Carbon concentrations and stable isotopic ratios were analyzed. Values of δ 13 C org (stable isotope ratio of organic carbon) allow the identification of incompletely decarbonated samples. If a small amount of detrital carbonates resists the usual decarbonation treatment, δ 13 C org can be significantly shifted towards less negative values, suggesting the need of more efficient decarbonation methods in order to improve the accuracy of organic carbon measurements. Even in the case of a high C org /C total ratio, the impact of remaining carbonates on the δ 13 C org value is strong because δ 13 C inorg is significantly different. The sensitivity of δ 13 C org measurement might therefore be used to validate POC measurements in estuarine and coastal waters.

Lithium (Li) has two stable isotopes, 6Li and 7Li, whose large relative mass difference is responsible for significant isotopic fractionation during physico-chemical processes. Thus Li isotopes are a good tracer of continental chemical weathering. Although physical erosion is dominant in the Polar regions due to cold climate and limited river systems, increasing global surface temperature may enhance chemical weathering, with possible consequences on carbon cycle and nutriment flux to the ocean. Fine fractions of soils have been forming during the last 6000 yr since the last deglaciation under warmer and more humid climate than other parts of Antarctica. Here, we examined elemental and Li isotope geochemistry of meltwaters, suspended sediments, soils and bedrocks in the Barton Peninsula, King George Island, Antarctica. Li concentrations range from 8.7 nM to 23.3 μM in water, from 0.01 ppm to 1.43 ppm in suspended sediment, from 9.56 ppm to 36.9 ppm in soil, and from 0.42 ppm to 28.3 ppm in bedrock. δ7Li values are also variable, ranging from +16.4 to +41.1‰ in water, from -0.4 to +13.4‰ in suspended sediment, from -2.5 to +6.9‰ in soil, and from -1.8 to +11.7‰ in bedrock. Correlation between elemental and Li isotope geochemistry reveals that both congruent and incongruent dissolution controls δ7Li values of water, rather than seasalt inputs from atmosphere or ice melting. Furthermore, PHREEQC modeling indicates that Fe-oxyhydroxides are oversaturatued in some meltwater, explaning their high δ7Li values that resulted from preferential uptake of 6Li. Likewise, δ7Li values of suspended sediment indicate are mostly caused by modern weathering . These results confirm that increasing global surface temperature enhances mordern chemical weathering in Antarctica, which therefore is expected to be stronger with time.

Chemical weathering plays an important role in sequestering atmospheric CO2, but its potential influence on global climate over geological timescales remains debated. To some extent, this uncertainty arises from the difficulty in separating the respective contribution of sedimentary and crystalline silicate rocks to past weathering rates in the geological record; two types of rocks having presumably different impact on the long-term carbon cycle. Here, we present a novel method for tracing the origin of weathered rocks on continents, based on the measurement of REE and Nd isotopes (eNd) in leached iron oxide fractions of river sediments [1,2]. We show that the degree of mid-REE enrichment in leached sediment phases provides information on the source of Fe oxides, indicating the presence of ancient marine Fe oxides derived from the erosion of sedimentary rocks or more recent secondary oxides formed in soils via silicate weathering. We also demonstrate that the e Nd difference between paired Fe-oxide and detrital fractions in river sediments (DeNd Feox-Det) reflects the relative contribution of sedimentary vs crystalline silicate rocks during weathering. Rivers draining old cratons and volcanic provinces display near-zero DeNd Feox-Det values indicative of dominant silicate weathering (0.5 ± 1.1), while multi-lithological catchments hosting sedimentary formations yield systematically higher values (2.7 ± 1.2). Taken together, these findings show that sedimentary rock weathering can be traced by the occurrence of riverine Fe oxides having more radiogenic Nd isotope signatures compared to detrital fractions. Finally, the influence of climate and geomorphic parameters on the Nd isotopic composition of sedimentary Fe oxides will be discussed, together with future perspectives.

Lithium isotopes in marine authigenic or detrital sedimentary archives have been recently used to trace continental weathering over geologic timescales. However, interpretations are predominantly based on the assumption that riverine Li isotopic signals can be propagated through estuaries without modification. Here, we verify this hypothesis by investigating the behaviour of Li isotopes in the Changjiang (Yangtze) River estuary. We observe a conservative mixing of dissolved Li and its isotopes between the Changjiang River water and seawater. The dissolved δ 7 Li yields a non-linear increase with salinity, and a significant increase occurs during the initial water mixing. Through the studied transect, estuarine flocculation and resuspension processes cause the homogenisation of offshore particulate δ 7 Li values, which are close to the average composition of upper continental crust. This study provides clear and direct evidence that the riverine dissolved Li isotopic signal is not modified during estuarine processes in large rivers, but caution should be exercised when using detrital δ 7 Li in marginal seas to investigate past continental weathering.

The present study investigates the processes controlling the elementary and isotopic cycle of the lithium over the Amazon basin. A numerical model is developed to simulate two major processes that have been proposed as key controls of the river lithium isotopic composition: weathering reactions inside the regolith, accounting for secondary phase formation, and interactions between riverine water and secondary phases in floodplain. Both processes generate fractionation of lithium isotopes ("batch" fractionation and "Rayleigh" distillation respectively) that potentially control the riverine isotopic composition of the Amazon and its tributaries. A study of the model parameters shows that two different regimes are impacting the lithium isotopic composition of the rivers within the Amazon catchment. In the South (Madeira and its tributaries), the lithium isotopic signature of river waters can be explained by lithium release and fractionation during weathering reactions in the regolith, followed by "Rayleigh distillation" in the floodplain increasing progressively the lithium isotopic composition, in agreement with a previously published hypothesis. In contrast, the lithium isotopic composition of rivers located in the northern part of the Amazon watershed (Solimoes and tributaries) cannot be simulated by the model assuming the same processes than in the southern part. Model optimization suggests than the nature of the material being eroded and weathered is important. In the North, fresh source rocks of volcanic origin releases large amount of Li and promotes rapid smectite precipitation, allowing the riverine δ 7 Li to rise before flowing through floodplains. This result suggests that the environments able to generate high riverine δ 7 Li (higher than 25‰) are complex and not firmly identified yet.

Chemical weathering plays an important role in sequestering atmospheric CO2, but its potential influence onglobal climate over geological timescales remains debated. To some extent, this uncertainty arises from thedifficulty in separating the respective contribution of sedimentary and crystalline silicate rocks to past weath-ering rates in the geological record; two types of rocks having presumably different impact on the long-termcarbon cycle. In this study, we investigate the use of rare earth element (REE) and neodymium isotopes (εNd)inleached iron oxide fractions of river sediments for tracing the origin of weathered rocks on continents. A newindex, called‘concavity index’(CI), is defined for measuring the degree of mid-REE enrichment in geologicalsamples, which enables the determination of the source of iron oxides in sediments, such as seawater-derived Fe-oxyhydroxide phases, ancient marine Fe oxides derived from the erosion of sedimentary rocks, and recentsecondary oxides formed in soils via alteration of crystalline silicate rocks or pyrite oxidation. Using this index,we demonstrate that theεNddifference between paired Fe-oxide and detrital fractions in river sediments (definedhere asΔεNd Feox-Det) directly reflects the relative contribution of sedimentary versus crystalline silicate rocksduring weathering. While rivers draining old cratons and volcanic provinces display near-zeroΔεNd Feox-Detvalues indicative of dominant silicate weathering (0.5 ± 1.1;n= 30), multi-lithological catchments hostingsedimentary formations yield systematically higher values (2.7 ± 1.2;n= 44), showing that sedimentary rockweathering can be traced by the occurrence of riverine Fe oxides having more radiogenic Nd isotope signaturescompared to detrital fractions. This assumption is reinforced by the evidence that calculatedΔεNd Feox-Detvaluesagree well with previous estimates for carbonate and silicate weathering rates in large river basins.Examining the influence of climate and tectonics on measured Nd isotopic compositions, wefind thatΔεNdFeox-Detis strongly dependent on temperature in lowlands, following an Arrhenius-like relationship that reflectsenhanced alteration of silicate rocks and formation of secondary Fe oxides in warmer climates. In contrast, inhigh-elevation catchments,ΔεNd Feox-Detdefines striking correlation with maximum basin elevation, which wealso interpret as reflecting the intensification of silicate weathering and associated Fe oxide formation as ele-vation decreases, due to the combined effects of thicker soils and warmer temperature.Overall, our newfindings are consistent with previous assertions that the alteration of sedimentary rocksprevails in high-elevation environments, while silicate weathering dominates infloodplains. This novel approachcombining REE and Nd isotopes opens new perspectives for disentangling the weathering signals of sedimentaryand crystalline silicate rocks in the geologic record, which could be used in future studies to reassess the causalrelationships between mountain uplift, erosion and climate throughout Earth's history.

The use of lithium (Li) has dramatically increased during the last two decades due to the proliferation of mobile electronic devices and the diversification of electric-powered vehicles. Lithium is also prescribed as a medication against bipolar disorder. While Li can exert a toxic effect on living organisms, few studies have investigated the impact of anthropogenic inputs on Li levels in the environment. Here we report Li concentrations and Li isotope compositions of river, waste and tap water, and industrial products from the metropolitan city of Seoul. Results show that the large increase in population density in Seoul is accompanied by a large enrichment in aqueous Li. Lithium isotopes evidence a major release from Li-rich materials. Water treatment protocols are also shown to be inefficient for Li. Our study therefore highlights the need for a global Li survey and adequate solutions for minimizing their impact on ecosystems and city dwellers.

During the Pleistocene, tropical Africa was the site of significant hydrologic changes related to variations in the intensity of the African monsoon. The socalled African Humid Period (AHP) has been known for some time, the AHP is being revisited today with the aid of innovative geochemical and organic tools such as lithium isotope and molecular biomarkers which allow variations in precipitation and their impact on the formation of soil to be quantified. Recent studies conducted at a high temporal resolution (10-1000 years) in lake and deltaic sedimentary records in Africa have suggested that gradual long-term monsoon intensity oscillations were often punctuated by millennial-scale episodes of hyperaridity. It is suspected that these rapid episodes had (and will have) an impact on human populations, but this remains to be conclusively demonstrated. Deltas are mainly fed by the influx of terrigenous material from flooded rivers and are extremely sensitive to changes in precipitation, vegetal cover, and their catchment areas. The spatio-temporal study of the Nile delta’s sediments has demonstrated that approximately 90% of the herrigenous material deposited in the Nile deep sea fan originates from erosion of the Ethiopian Highlands, especially during wet periods. The geochemical (Nd, Li isotopes and Ti/Ca ratio) and molecular biomarker tracers have revealed the rapid development of centennial hyperarid episodes occurred contemporaneously with cold intervals recorded in Greenland ice cores (i.e. Greenland stadials or Heinrich Stadials recorded in North Atlantic sediment. The nature of the links between weathering and these hyperarid episodes are still under debate. In particular, the timescale over which chemical weathering may respond to hydroclimate change is yet to be determined at the continental scale. We will present a synthesis of works recently performed in the Nile Basin, which strongly suggests rapid and significant variations of silicate weathering, and a dominant role of monsoon-precipitation variations in this region. We used Li & Nd isotope and GDGT tracers in a study that investigated sediment records from the Nile delta and Lake Tana (in the Ethiopian Highlands) for the last 110 and 16 thousand years, respectively. Our approach thus opens new perspectives for understanding hydro-climate variations in tropical Africa (long-term arid/humid periods and millennial-scale episode of aridity), and for determining their impact on sediment transport, continental weathering and soil development.

Chemical composition of river sediments and dissolved load is classically used to infer controls on continental weathering and, therefore, exert an important role on the understanding of the global carbon and biogeochemical cycles. To date, most studied river basins are strongly impacted by dam constructions; however, the effects of dams on sediment chemical compositions are little known. The Three Gorges Dam is one of the largest dams in the world and began impounding water in 2003 in the Changjiang basin. In order to investigate the impact of this dam on downstream sediment chemistry, temporal variation of sediment weathering intensity is reported here based on analyzed and compiled data between 1997 and 2018. Downstream sediments collected before 2003 are characterized by weak weathering intensity, in agreement with the overwhelming flux and fast transfer of sediments derived from the mountainous upper watershed. After the Three Gorges Dam operation, strong midlower riverbed erosion changed the roles of the midlower reaches from important sinks to major sources of sediments delivered to the East China Sea. This resulted in a progressive change of the sediment chemistry because the eroded midlower riverbed sediments were more deeply weathered, as confirmed by 150-year-old sediment cored in the lower mainstream and by mass-balance calculations. This more intensive weathering may be explained by warmer climate and longer water-rock interaction time in the midlower basin. Thus, this study suggests the need to quantify potential bias in weathering intensity and controls caused by damming activity in large river systems.

Silicate weathering of basaltic rocks constitutes a non-negligible sink of atmospheric CO2 but the role it plays in the regulation of past and future global climate is still matter of debate. In this study, silicate weathering rates for various sub-basins of the Ethiopian Traps, emplaced 30 million years ago, and the corresponding atmospheric CO2 consumption rates are evaluated. For this, major and trace elements were measured in the dissolved phases and in the sedimentary particles carried and deposited by the main rivers flowing through this steep region. Lithium isotopes and major elements were also measured in the extracted clay fractions in order to infer complementary information on weathering processes in this region. Clay δ7Li values correlate positively with Mg/Ti ratios, and are best explained by varying ratios of leaching versus clay formation rate.Although located in a region annually submitted to monsoon, average silicate weathering rate (16.1 tons/km2/year) and CO2 consumption rate (0.65 × 1012 mol/year) are estimated to be low when compared to other basaltic regions such as the Deccan Traps, and volcanically active islands of the tropical zone. This is surprising since the concentrations of Total Dissolved Solids of the Ethiopian rivers are among the highest ones. With a 2D rainfall model that takes into account the detailed topography of the region, annual occurrence of the Monsoon, and monitoring station data, we show that runoff intensity is a key parameter that explains this difference. We determine that, at present, the weathering of the Ethiopian Traps plays a negligible role in the carbon cycle. However, simple calculations, which integrate recent knowledge on African climate variations and on weathering controls, illustrate that during the African Humid Period (14–8 kyr), a significant increase of Monsoon precipitation may have resulted in much higher weathering rates and related CO2 consumption (0.91–1.5 × 1012 mol/year). This study therefore evidences the potential importance of this region in the past, and the need to quantify more precisely the variations of the monsoon intensity and its impact on tropical watersheds for reconstructing past CO2 levels.

In this study, the accuracy and the precision corresponding to Li isotopic measurements of low level samples such as marine and coastal carbonates are estimated. To this end, a total of fifty‐four analyses of a Li‐pure reference material (Li7‐N) at concentrations ranging from 1 to 6 ng ml−1 were first performed. The average δ7Li values obtained for solutions with and without chemical purification were 30.3 ± 0.4‰ (2s, n = 19) and 30.2 ± 0.4‰ (2s, n = 36), respectively. These results show that the chosen Li chemical extraction and purification procedure did not induce any significant isotope bias. Two available carbonate reference materials (JCt‐1 and JCp‐1) were analysed, yielding mean δ7Li values of 18.0 ± 0.27‰ (2s, n = 6) and 18.8 ± 1.8‰ (2s, n = 9), respectively. Small powder aliquots (< 15 mg) of JCp‐1 displayed significant isotope heterogeneity and we therefore advise favouring JCt‐1 for interlaboratory comparisons. The second part of this study concerns the determination of δ7Li value for biogenic carbonate samples. We performed a total of twenty‐nine analyses of seven different tropical coral species grown under controlled and similar conditions (24.0 ± 0.1 °C). Our sample treatment prior to Li extraction involved removal of organic matter before complete dissolution in diluted HCl. Our results show (a) a constant δ7Li within each skeleton and between the different species (δ7Li = 17.3 ± 0.7‰), and (b) a Li isotope fractionation of −2‰ compared with inorganic aragonite grown under similar conditions. Comparison with literature data suggests a significant difference between samples living in aquaria and those grown in natural conditions. Finally, we investigate ancient (fossil) carbonate material and foraminifera extracted from marine sedimentary records. Different leaching procedures were tested using various HCl molarities. Results indicate that carbonate preferential dissolution must be carried out at an acid molarity < 0.18 mol l−1. Possible contamination from silicate minerals can be verified using the Al/Ca ratio, but the threshold value strongly depends on the carbonate δ7Li value. When the silicate/carbonate ratio is high in the sediment sample (typically > 2), contamination from silicates cannot be avoided, even at low HCl molarity (⪡ 0.1 mol l−1). Finally, bulk carbonate and foraminifera extracted from the same core sample exhibited significant discrepancies: δ7Li values of foraminifera were more reproducible but were significantly lower. They were also associated with lower Sr/Ca and higher Mn/Ca ratios, suggesting a higher sensitivity to diagenesis, although specific vital effects cannot be fully ruled out.

Soils are key to ecosystems and human societies, and their critical importance requires a better understanding of how they evolve through time. However, identifying the role of natural climate change versus human activity (e.g. agriculture) on soil evolution is difficult. Here we show that for most of the past 12,300 years soil erosion and development were impacted differently by natural climate variability, as recorded by sediments deposited in Lake Dojran (Macedonia/Greece): short-lived ( < 1,000 years) climatic shifts had no effect on soil development but impacted soil erosion. This decoupling disappeared between 3,500 and 3,100 years ago, when the sedimentary record suggests an unprecedented erosion event associated with the development of agriculture in the region. Our results show unambiguously how differently soils evolved under natural climate variability (between 12,300 and 3,500 years ago) and later in response to intensifying human impact. The transition from natural to anthropogenic landscape started just before, or at, the onset of the Greek ‘Dark Ages’ (~3,200 cal yr BP). This could represent the earliest recorded sign of a negative feedback between civilization and environmental impact, where the development of agriculture impacted soil resources, which in turn resulted in a slowdown of civilization expansion.

Li isotopes have been proven to be a powerful proxy for indicating silicate weathering over the geologic past. However, sediment provenance change and sedimentary recycling during source-to-sink transport processes can impose serious biases on the recognition of weathering signals registered in the siliciclastic sediments in shale-rich large basins. The Changjiang (Yangtze River) is featured by complex lithologies and monsoon climate regimes in its vast catchment. During the past 14 kyr, the different tempo-spatial variations of Indian Summer Monsoon and East Asia Summer Monsoon might have imprinted the changes of sediment provenance and silicate weathering. These aspects will be investigated using Li isotopes measured in the clay fractions, together with Nd isotopes, mineralogy, major and trace elements, from Core CM97 located in Changjiang Delta. First results indicate that clay δ 7 Li values vary within a restricted range during the last 14 kyr, from-2.7 to-1.1 ‰, with an average value of-1.6 ‰. It is noteworthy that Li isotopes in the core clay fraction responded directly and rapidly to climate changes in cold period, showing obvious co-variations with climate proxy at 14-11 ka. In contrast, δ 7 Li values remain constant during the early and mid-Holocene warm period. With the robust constraint of sediment provenance changes by Nd isotopes and clay minerals, we infer that sediments from the upper reaches was further weathered in the mid-lower reaches during the transportation/deposition process in cold peroid, responding to climate fluctuation. However, during the warm period, strong rainfall and higher leachaing rates might explain the smoothing of the Li signals in clays (Bastian et al., 2017), mostly inherited from the upper mountainous catchment. We will refine these interpretations based on additional analyses on river sediments.

Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth's climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region. Erosion processes on continents include mechanical erosion and chemical weathering, both of which shape the Earth's surface and contribute to substantial drawdown of atmospheric carbon via export of organic-rich clay fractions and alteration of silicate minerals. However, while the links between climate and physical erosion rates have been well documented from river chemistry data 1 and sedimentary records 2 , the response of continental chemical weathering to climate change is not well understood and requires further investigation. At the large scale, the relative importance of physical erosion, temperature, rainfall, vegetation and lithology on chemical weathering over both long (> 10 6 yr) and short (≪ 10 4 yr) periods of time is still under debate. Most studies that have established links between climate and silicate weathering were based on the analysis of dissolved phases in modern river basins 3 or on the reconstruction of past ocean chemistry during the Cenozoic 4 from marine carbonates or deep-sea ferromanganese deposits. To date, only a few studies have investigated past variations in silicate weathering over short timescales and these have yielded contradictory results 5–9. However, this information is important for predicting the evolution of the short-term carbon cycle and its impact on the Earth's vital resources. Sediments formed in weathering profiles, exported by large rivers and accumulated on margins, can provide invaluable information on the short-term evolution of weathering at the sub-continental scale. To provide constraints on the links between hydro-climate and weathering, we have reconstructed the Late Quaternary evolution of rock chemical weathering in the Nile basin, using a marine sediment record recovered from the Nile deep-sea fan, off the coast of Egypt (Fig. 1). Tropical Africa is known to have experienced major hydrological changes during the Quaternary period, which dramatically affected fluvial discharge and particle delivery to the surrounding ocean margins 10–12. The onset of past humid periods was related to increased summer insolation in the Northern Hemisphere associated with northward migration of the Inter Tropical Convergence

This study presents the carbon, oxygen, and magnesium isotope compositions of two modern brachiopods, Terebratalia transversa and Frieleia halli, and one fossil specimen (2.3 Ma), Terebratula scillae. The aim of this study is to investigate the variability of these isotopic compositions and to evaluate the potential of brachiopods as a proxy of past seawater delta Mg-26 values. The two investigated brachiopod shells present the same range of delta(26)Mgvariation (up to 2%). This variation cannot be ascribed to changes in environmental parameters (temperature or pH). As has been previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the delta Mg-26 value of the primary layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends can be explained by kinetic effects linked to changes in growth rate during the brachiopod life. The innermost calcite layer of T. transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past delta Mg-26 values of seawater. (C) 2016 Elsevier B.V. All rights reserved.

Silicate minerals are a major Mg source to seawater through rivers and therefore it is important to determine the impact of dissolution and formation of Mg-rich primary and secondary minerals on the Mg isotope signature of natural waters. We dissolved biotite mineral in a plug flow reactor at controlled pH and T =25[degrees]C and synthesized TO- and TOT-phyllosilicates (lizardite and kerolite, respectively) at T =90, 150, and 250[degrees]C. All leaching solutions during biotite dissolution are enriched in light isotopes compared to the biotite sample, with a 1.1a[degrees] range of [DELTA].sup.26Mg.sub.biotite-solution. At pH=1, Mg isotopic steady-state between the solution and biotite is established after 600h, while at pH=5, it is never reached, even after 4months. A sequential leaching suggests that the solution [delta].sup.26Mg values depend mostly on a balance between the relative proportions of labile and structural Mg with different [delta].sup.26Mg values. Ca concentrations and elementary ratios measured in output solutions during the incipient stage of dissolution indicate non-negligible Mg contribution from small amount of disseminated carbonate phases present within the biotite sample. During synthetic clay formation, both TO and TOT clays are significantly enriched in heavy isotopes and follow Rayleigh fractionation equations for specific values of isotope fractionation factors. At T =250[degrees]C, a single isotope fractionation factor of 1.00059[+ or -]0.00014 can explain the Mg isotope evolution of both TO and TOT clays. A similar isotope fractionation factor of 1.00054[+ or -]0.00014 can be inferred from all TOT synthesized at T =90-250[degrees]C. A compilation of Mg isotope fractionation factors during secondary phase formation highlights a difference between field and experimental investigations at low temperature. More experiments are now necessary to determine the role of clay crystallochemistry at temperatures below 50[degrees]C

Past ocean pH and pCO2 are critical parameters for establishing relationships between Earth's climate and the carbon cycle. Previous pCO2 estimates are associated with large uncertainties and are debated. In this study, laboratory cultures of the foraminiferan genus Amphistegina were performed in order to examine the possible factors that control the Li isotope composition (δ7Li) of their shells. δ7Li is insensitive to temperature and pH variations but correlates positively with the Dissolved Inorganic Carbon (DIC) of seawater. Li/Ca ratio in the shells shows negative correlation with δ7Li, consistent with published data for planktonic foraminifera from core tops and from short periods during the Cenozoic. We propose that the sensitivity of δ7Li and Li/Ca ratio to DIC is a biological phenomenon and is related to biomineralization mechanisms in foraminifera. We used the published foraminiferal δ7Li records, and our experimental results, to determine the paleo-ocean DIC and pH for the last glacial–interglacial cycle. The results are consistent with published estimates of pH and pCO2 based on boron isotopes and ice cores. We suggest Li and its isotopes may serve as a new complementary proxy for the paleo-ocean carbonate chemistry.

In order to better constrain the geochemical budget of Si in the ocean, and potentially other elements released by the dissolution of silicates, the alteration of riverine particulate material in estuaries and seawater needs to be estimated. For this, a series of alteration experiments of basaltic glass were performed at various degrees of salinity (from 0 to 3.5 g L−1) in far-from-equilibrium conditions. The solution used is a filtered natural seawater standard from the Atlantic Ocean. The forward dissolution rates increase from 2.1 · 10-7 mol Si m-2 s-1 (S = 0g L-1) to 7.7 · 10-7 mol Si m-2 s-1 (S = 3.5g L-1) at 90 °C and were extrapolated at 16 °C (from 2.9 · 10-10 mol Si m-2 s-1 at S = 0g L-1 to 1.1 · 10-9 mol Si m-2 s-1 at S = 3.5g L-1) . This positive relationship between glass dissolution rate and salinity degree is consistent with published investigations concerning the role of specific cations and ligands present in seawater, which can promote dissolution at the glass surface. These results illustrate the potential of river basaltic glass particles to dissolve quickly in the water column after entering into the brackish waters of estuaries, and before sinking on continental margins. Based on these dissolution rates and on assumptions on the particulate solid flux of fresh basaltic glass exported by rivers towards the ocean, the corresponding flux of dissolved Si is estimated to range between 2 and 8 · 1012 mol Si yr-1 . This is of the same order of magnitude as the estimated river dissolved Si flux, which represents therefore a significant input of Si into the ocean. Additionally, if the glass dissolution process remains congruent during the residence time of suspended particles into the water column, the K flux to the ocean could also be significantly affected.

Over 1400 electron probe and 700 ion probe microanalyses were performed on eleven mineral separates to evaluate their potential as reference materials for in situ Li isotopic determination. Our results suggest the homogenous distributions of major elements, Li and its isotopes for each sample. Hence, these samples are suitable to be used as reference materials for in situ measurements of Li abundance and Li isotopes by secondary ion mass spectrometry (SIMS) or laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). These samples have the advantage of mitigating probable matrix effects during calibration owing to the wide range of compositions. The effect of composition on the δ7Li of olivine measured by SIMS is a linear function of composition, with δ7Li increasing by 1.0‰ for each mole per cent decrease in forsterite component.

Chemical weathering of continental rocks plays a central role in regulating the carbon cycle and the Earth's climate (Walker et al., 1981; Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon dioxide globally (Beaulieu et al., 2012). However, the role of climate variability on chemical weathering is still strongly debated. Here we focus on the Himalayan range and use the lithium isotopic composition of clays in fluvial terraces to show a tight coupling between climate change and chemical weathering over the past 40 ka. Between 25 and 10 ka ago, weathering rates decrease despite temperature increase and monsoon intensification. This suggests that at this timescale, temperature plays a secondary role compared to runoff and physical erosion, which inhibit chemical weathering by accelerating sediment transport and act as fundamental controls in determining the feedback between chemical weathering and atmospheric carbon dioxide.

The marine record of ocean lithium isotope composition may provide important information constraining the factors that control continental weathering and how they have varied in the past. However, the equations establishing links between the continental flux of Li to the ocean, the continental Li isotope composition and the ocean Li isotope composition are under-constrained, and their resolution are related to significant uncertainties. In order to partially reduce this uncertainty, we propose a new approach that couples the C and Li cycles, such that our proposed reconstruction of the Cenozoic Li cycle is compatible with the required stability of the exospheric carbon cycle on geological timescales. The results of this exercise show, contrary to expectations, that the Cenozoic evolution of the Li isotope composition of rivers did not necessarily mimic the oceanic δ7Li rise. In contrast, variations in the continental flux of Li to the ocean are demonstrated to play a major role in setting the ocean δ7Li. We also provide evidence that Li storage in secondary phases is an important element of the global Li cycle that cannot be neglected, in particular during the early Cenozoic. Our modeling of the published foraminifera record highlights a close link between soil formation rate and indexes recording the climate evolution during the Cenozoic, such as foraminifera δ18O and pCO2 reconstructions. This leads us to conclude that the Li isotope record does not provide persuasive, unique evidence for erosional forcing of Cenozoic change because it could alternatively be consistent with a climatic control on soil production rates.

The Li isotope signatures of hydrothermal fluids are remarkably constant (View the MathML sourceδLi7=8.0±1.9‰) irrespective of the water/rock ratio (W/RW/R), permeability, temperature or fluid involved (seawater or meteoric). High temperature hydrothermal fluids represent the second most significant source of Li to the ocean, yet the homogeneity of the Li isotopic signatures of this source remains to be explained and in this context, the lack of data for the corresponding altered phases is problematic. We measured Li contents and Li isotope signatures (as well as mineralogy, composition and local fluid temperature) in hyaloclastites collected from a borehole in the Hellisheidi geothermal system (Iceland) which have been altered by high temperature aqueous fluids (from 170 to 300 °C). Li is more enriched in the solid phases than the other alkali metals, highlighting its greater ability to be incorporated into secondary phases, especially at high temperatures (>250 °C). Mass balance calculations show that the low Li concentrations in hydrothermal fluids are best explained by a high water/rock ratio and a high permeability of this system. The Li isotopic signature of the altered hyaloclastites (View the MathML sourceδLi7 between +1.9 and +4.0‰+4.0‰) remains close to the fresh basalt at deep levels and high temperatures (290–300 °C) (as measured View the MathML sourceδLi7 range between +3.7 and +4.0‰+4.0‰), and decreases at shallower depths and lower temperatures (150–270 °C) (View the MathML sourceδLi7 between +1.9 and +3.1‰+3.1‰). A mass balance model involving basalt dissolution, secondary phase formation, and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed. The corresponding apparent mineral-fluid Li isotope fractionation factors resulting from precipitation of secondary phases (View the MathML sourceΔLiminerals-fluid7) range between 0‰ at 300 °C and −8.5‰−8.5‰ at 170 °C and highlight a key role of chlorite. Applying the same approach to mid-ridge oceanic hydrothermal systems allows the relatively homogeneous isotope signatures of high temperature fluids of various locations to be explained.

Despite the occurrence of highly variable lithium (Li) elemental distribution and isotopic fractionation in mantle mineral, the mechanism of Li heterogeneity and fractionation remains a controversial issue. We measured Li contents and isotopic compositions of olivine and clinopyroxene xenocrysts and phenocrysts from kamafugite host lavas, as well as minerals in melt pockets occurring as metasomatic products in peridotite xenoliths from the Western Qinling, central China. The olivine xenocrysts in the kamafugites show compositional zonation. The cores have high Mg# (100 × Mg/(Mg+Fe); 91.0–92.2) and Li abundances (5.63–21.7 ppm), low CaO contents (≤0.12 wt%) and low δ7Li values (−39.6 to −6.76‰), which overlap with the compositional ranges of the olivines in the melt pockets as well as those in peridotite xenoliths. The rims of the olivine xenocrysts display relatively low Mg# (85.9–88.2), high CaO contents (0.19–0.38 wt%) and high δ7Li values (18.3–26.9‰), which are comparable to the olivine phenocrysts (Mg#: 86.4–87.1; CaO: 0.20–0.28 wt%; Li: 12.4–36.8 ppm; δ7Li: 18.1–26.0‰) and the silicate-melt metasomatized olivines. The clinopyroxene phenocrysts and clinopyroxenes in the melt pockets have no distinct characteristics with respect to the Li abundances and δ7Li values, but show higher and lower CaO contents, respectively, than the clinopyroxenes from silicate and carbonatite metasomatized samples. These features indicate that Li concentration and isotopic signatures of the cores of the xenocrysts recorded carbonatite melt-peridotite reaction (carbonatite metasomatism) at mantle depth, and the variations in the rims probably resulted from xenocryst–host magma interaction during ascent. Our results reveal that the interaction with carbonatite and silicate melts gave rise to an increase in Li abundance in minerals of peridotite xenoliths at mantle depth or during transportation. In terms of δ7Li, the carbonatite and silicate melts produced remarkably contrasting δ7Li variations in olivine. Based on the systematic variations of Li abundances and Li isotopes in olivines, we suggest that the δ7Li value of olivine is a more important indicator than that of clinopyroxene in discriminating carbonatite and silicate melt interaction agents with peridotites.

Lithium isotopes are a potential tracer of silicate weathering but the relationship between lithium isotope compositions and weathering state still need to be established with precision. Here, we report Li concentrations and Li isotope compositions of soils developed along a 4 million year humid-environment chronosequence in the Hawaiian Islands. Li concentrations are variable with depth and age, ranging from 0.24 to 21.3 ppm, and significant Li depletions (up to 92%) relative to parent basalts are systematically enhanced towards the surface. Our calculations show that the relative contribution from atmospheric deposits to the Li soil budget remains small, with a maximum contribution from dust Li of 20% at the oldest site. This is explained by the capacity of the weathering products to retain, within the profiles, the Li coming from basalt alteration, and allows us to explore more specifically the role of alteration processes on soil Li isotope signatures. The delta Li-7 values display a large range between -2.5 parts per thousand and + 13.9 parts per thousand. The youngest soils (0.3 ka) display the same delta Li-7 value as fresh basalt, regardless of depth, despite similar to 30% Li loss by leaching, indicating that there is little Li isotope fractionation during the incipient stage of weathering. delta Li-7 values for the older soils (>= 20 ka) vary non-linearly as a function of time and can be explained by progressive mineral transformations starting with the synthesis of metastable short-range order (nano-crystalline) minerals and followed by their transformation into relatively inert secondary minerals. Results highlight significant Li isotope fractionation during secondary mineral formation and in particular during Li uptake by kaolinite. Finally, we suggest that the non-monotonous evolution of the regolith delta Li-7 value over the last 4 Ma is consistent with climatic variations, where congruent release of Li isotopes occurs during warmer periods. (C) 2014 Elsevier Ltd. All rights reserved.

To investigate the effects of silicate and carbonatite metasomatism on mantle heterogeneity, we report lithium (Li) concentrations and isotopic compositions for olivine (Ol), orthopyroxene (Opx) and clinopyroxene (Cpx) from two suites of mantle xenoliths (Hannuoba, the North China Craton, and Haoti, the Western Qinling Orogen). The Hannuoba xenoliths range from lherzolite to pyroxenite and were affected by silicate metasomatism, whereas the Haoti xenoliths vary from harzburgite to wehrlite and were affected by carbonatite metasomatism. Lithium concentrations and isotopic compositions display a dichotomy between Hannuoba and Haoti xenoliths, and the overall variation exceeds what was previously reported. The minerals from Haoti xenoliths are more enriched in Li (Ol: 1.23–13.2 ppm; Opx: 3.00–82.8 ppm; Cpx: 1.39–112 ppm) than those from Hannuoba samples (Ol: 1.34–5.52 ppm; Opx: 0.23–16.1 ppm; Cpx: 1.18–79.8 ppm). Lithium isotopic compositions of these samples are highly variable in both suites of samples. δ7Li ranges from + 3.0‰ to + 41.9‰ in Ol, from − 21.0‰ to + 20.2‰ in Opx and from − 17.4‰ to + 18.9‰ in Cpx for Hannuoba samples. Haoti minerals display a similar degree of variation with δ7Li ranging from − 29.1‰ to + 19.9‰ in Ol, − 16.9‰ to + 18.0‰ in Opx and − 45.1‰ to + 19.6‰ in Cpx. On average, Li isotopic compositions of minerals from Hannuoba xenoliths follow the sequence of δ7LiOl > δ7LiOpx > δ7LiCpx, whereas those from Haoti xenoliths are characterized by the opposite sequence of δ7LiCpx > δ7LiOpx > δ7LiOl; in particular there is considerable difference in δ7Li values of Ol. The Li elemental and isotopic data suggest that mantle metasomatism by distinct agents is an important process for generating the large heterogeneity of Li abundances and isotopic distribution in the lithospheric mantle. The distinct geochemical characteristics of Li isotopes in silicate and carbonatite metasomatism are closely related to the preferential incorporation of Li into minerals from distinct melts. These findings further demonstrate that the Li isotopic systematics may in turn help to discriminate between silicate and carbonatite metasomatism.

We combines Mg isotopic analyses with soil characterization methods to determine Mg isotopic compositions of bulk soils, basalts, and carbonate fractions at an arid (∼30 cm MAP) soil chronosequence on the Island of Hawaii. This chronosequence is developed on Pololu (350 ka) and Hawi (170 ka) lava flows. Both profiles contain pedogenic carbonates and secondary alumino- silicate and sequioxide phases. Bulk soil horizons at these sites range in δ26Mg from -0.21±0.31 ‰ to -1.75±0.22 ‰ for the Hawi and -0.01±0.31 ‰ to -0.21±0.31 ‰ for the Pololu. Basalts underlying the soil profiles have average δ26Mg values of - 0.25±0.06 ‰. Pedogenic carbonate δ26Mg values at these sites vary from -1.05±0.22‰ to -2.31±0.22‰. Integrating the soils as a whole yields bulk soil isotopic compositions of -1.35±0.16 ‰ for the Hawi and -0.12±0.12 ‰ for the Pololu. These differences in overall δ26Mg between total soils may be explained by the relative abundance of Mg in carbonate; in the Hawi soil 69±11% of Mg is hosted by carbonate phases, while in the Pololu soil 16±2% of Mg is in carbonate phases. Estimates of Mg input to the soils through time, through rainfall estimates as well as rock weathering estimates provided by the immobile index element Zr, allows the calculation of the δ26Mg of Mg exported from these systems. The isotopic composition Mg exported from the Hawi soil is not tightly constrained but must be significantly isotopically heavier than the basalt parent material. The Pololu soil is much better constrained and has exported Mg with a δ26Mg of -0.36±0.26 ‰, close to the weighted mean value of inputs to the soil from weathering and atmospheric deposition. The evolution of the soil mineralogy and morphology during progressive development of the weathering profile result in significant changes in the isotopic composition of Mg exported through time.

Calcium isotopic compositions () were measured in Icelandic rivers draining a range of catchment types. The values of the rivers ranged from 0.45‰ to 0.67‰, which in all cases was higher than the value of basaltic rock standards (0.42±0.03‰). A single explanation was unable to satisfactorily explain the values of all rivers, rather it was found that the rivers formed three distinct groups based on the extent of glacial coverage in each catchment. The Ca isotopic composition of rivers draining catchments with less than 10% glacial cover could be explained by the mixing of water sources: basalt-derived solutes, meltwater (taken to represent meteorological precipitation inputs) and hydrothermal water. However, fractionation of in these catchments cannot unequivocally be ruled out. In catchments with greater than 22% glacial cover, Ca isotopic compositions could not be explained by a mixture of water sources and instead reflected a fractionation process, most likely the precipitation of Ca-bearing secondary minerals or the adsorption/ion-exchange of Ca onto mineral surfaces. The fractionation factor () for this process was calculated to be 0.9999. The third group of rivers, with partially glaciated (10–21%) catchments, grouped with glaciated catchments with respect to their Sr geochemistry and with non-glaciated catchments with respect to their Ca geochemistry. The difference in the controls of Ca isotope fractionation between glaciated and unglaciated catchments was attributed to different weathering regimes.

This study investigates the potential of Mg isotopes as tracers of biogeochemical processes in a small-forested catchment located on sandstones extremely poor in Mg-bearing minerals. The average delta Mg-26 is -0.63 +/- 0.12 parts per thousand and 0 +/- 0.14 parts per thousand for local rainwater and bedrock, respectively. From the C horizon to the upper eluvial (E) horizon, soil delta Mg-26 (from 0.0 +/- 0.14 parts per thousand to 0.25 +/- 0.14 parts per thousand) is close to the bedrock value, while more than 70% of Mg is lost, suggesting a small isotopic shift during illite dissolution. The surface soil horizon (A(h)) delta Mg-26 is close to plant delta Mg-26, and especially to the grass delta Mg-26 value (-0.49 parts per thousand). The bulk delta Mg-26 of trees and grass (-0.32 parts per thousand and -0.41 parts per thousand, respectively) are higher than the average delta Mg-26 values of the soil exchangeable fraction (-0.92 parts per thousand to -0.42 parts per thousand), and of rainwater (-0.65 parts per thousand). Within plants, roots are enriched in heavy isotopes, whereas light isotopes are preferentially translocated and stored in the above ground parts. In Norway spruce, the older needles, forming the annual litterfall, are isotopically lighter and strongly depleted in Mg compared to more recent needles. Soil solution delta Mg-26 shifts seasonally, from low values, lower than rainwater and close to litterfall during a high rainfall period in spring, to higher values, close to soil delta Mg-26 in dryer periods of winter or summer. At the watershed scale, streamwater delta Mg-26 varies between -0.85 perpendicular to 0.14 parts per thousand and -0.08 perpendicular to 0.14 parts per thousand and delta Mg-26 values decrease linearly with discharge. The high streamwater delta Mg-26 at low flow, close to bedrock delta Mg-26, most likely reflects dissolution processes in the deep saprolite in relation to the very long water residence time. Conversely, we suggest that low stream level delta Mg-26 values are at least partly related to the contribution of surface flows from wet areas. Using a simple mass and isotopic balance approach, we compute that mineral dissolution rates in the soil (0.35 kg Mg ha(-1) year(-1)) presently compensate for Mg losses from the soil. (C) 2012 Elsevier Ltd. All rights reserved.

Li, B, Mg and Ca isotopes became of increasing interest during the last decade due to their potential for better constraining the carbon cycle and nutrient cycling. At the soil-water-plant scale, Li and B isotopes are powerful tools for the understanding of processes leading to clay mineral formation in soils. Ca and Mg isotopes allow, for their part, to identify plant-mineral interactions and recycling by vegetation. At the scale of monolithological silicate watersheds, Li and B isotope fractionations are mainly controlled by the degree of mineral leaching and the amount of clay mineral formation. Ca and Mg isotope signatures in soil and waters vary seasonally, depending on the vegetation growth cycle and rain events. In mixed-lithology basins, B and Li isotopes are controlled by alteration rates of silicate minerals and the residence time of waters within the watershed. Ca and Mg isotope ratios of river waters appear to be also lithology-controlled.

There has been much debate as to whether 210 Pb-226 Ra disequilibria in young volcanic rocks result from partial melting, cumulate interaction or magma degassing. Here we present new data from basalts erupted in 1978 from Ardoukoba volcano in the Asal Rift. The (210 Pb/ 226 Ra) t ratios are very low (0.2 to 0.6) and appear to correlate negatively with (226 Ra/ 230 Th). Invariant (230 Th/ 238 U) and (231 Pa/ 235 U) ratios require similar melting rates, porosities, and extents for all parental magmas. Thus, the range in (226 Ra/ 230 Th), which is negatively correlated with Th concentration, reflects fractional crystallization over millennia after the magmas were emplaced into the crust. This precludes the 210 Pb deficits from resulting from partial melting. Instead, the 210 Pb deficits must have formed subsequent to magma differentiation and are interpreted to reflect several decades of magma degassing. Many young basalts erupted in a variety of tectonic settings are similarly depleted in 210 Pb with respect to 226 Ra, suggesting that they continuously degas over a period of a few to several decades, perhaps reflecting the time required to rise to the surface from deeper reservoirs. In some of these basalts, gas accumulation leads to the shallowest, most evolved, and earliest erupting magmas having the highest (210 Pb/ 226 Ra) ratios and sometimes 210 Pb excesses.

Experimental precipitations of calcite and other carbonate minerals were performed under various conditions of pH, temperature and solution Mg/Ca to determine the Mg partition coefficient and Mg isotope fractionation. Fifteen experiments were performed at pH ranging from 7.41 ± 0.07 to 8.51 ± 0.39, temperature ranging from 16.2 ± 0.7 to 26.5 ± 0.3°C and Mg/Ca solution ranging from 0.11 to 0.52 mol/mol. The apparent Mg partition coefficient between calcite and solution (D Mg) spans a large range of values from 0.018 ± 0.014 to 0.15 ± 0.11 and carbonate Mg isotope fractionation (D 26 Mg) ranges from À2.53 ± 0.25& to À1.33 ± 0.14& and does not correlate with either pH or temperature. The range in D Mg and D 26 Mg suggests non-equilibrium partitioning controlled by the processes of calcite growth, i.e. mixing between calcite grown at equilibrium and fluid inclusions, and entrapment of a surface Mg-rich calcite layer in isotopic equilibrium with the solution. The equilibrium Mg isotope fractionation between inorganic calcite and solution is estimated to be À2.13 ± 0.24&. Additional Mg elemental and isotopic fractionations are observed to occur during biogenic formation of calcite due to variable removal of Mg by the organisms (high-Mg calcite corals, foraminifera) of seawater Mg from their calcification medium.

This chapter relates recent developments concerning the use of several U-series nuclides, in particular 234 U-238 U and 230 Th-238 U disequilibria, for constraining physical and chemical erosion rates and sediment age. Indeed, the ability to measure these disequilibria with an extremely high precision, even in samples with low concentrations such as natural waters, has opened new avenues for investigating erosional processes. This chapter is articulated in three main parts: a brief introduction and presentation of modern technical methods is followed by a description of how 234 U-238 U and 230 Th-238 U disequilibria measured in dissolved (water) and solid (sediment) river phases can be used to provide quantitative constraints on physical and chemical erosion rates at the basin scale. In parallel, recoil effects occurring during sediment formation can now be modelled and used to estimate the residence time of a sediment within a basin. Finally, the last part of this chapter presents the latest findings concerning the study of weathering profiles and the modelling of U and Th migration within an aquifer system.

Assessing the origin and behaviour of lithium and the distribution of Li isotopes in hydro-systems is of major importance in order to increase our knowledge of the lithium cycling at the Earth's surface. Lithium is a fluid-mobile element and due to the large relative mass difference between its two stable isotopes, it is subject to significant low and high temperature mass fractionation which provides key information on the nature of water/rock interaction processes. The main objective of the present work is to constrain the behaviour of Li and its isotopes by focusing on three different hydrosystems: rainwaters, river waters and deep geothermal waters.

In order to use lithium isotopes as tracers of silicate weathering, it is of primary importance to determine the processes responsible for Li isotope fractionation and to constrain the isotope fractionation factors caused by each process as a function of environmental parameters (e.g. temperature, pH). The aim of this study is to assess Li isotope fractionation during the dissolution of basalt and particularly during leaching of Li into solution by diffusion or ion exchange. To this end, we performed dissolution experiments on a Li-enriched synthetic basaltic glass at low ratios of mineral surface area/volume of solution (S/V), over short timescales, at various temperatures (50 and 90°C) and pH (3, 7, and 10). Analyses of the Li isotope composition of the resulting solutions show that the leachates are enriched in 6Li (δ7Li = +4.9 to +10.5‰) compared to the fresh basaltic glass (δ7Li = +10.3 ± 0.4‰). The δ7Li value of the leachate is lower during the early stages of the leaching process, increasing to values close to the fresh basaltic glass as leaching progresses. These low δ7Li values can be explained in terms of diffusion-driven isotope fractionation. In order to quantify the fractionation caused by diffusion, we have developed a model that couples Li diffusion with dissolution of the glassy silicate network. This model calculates the ratio of the diffusion coefficients of both isotopes (a=D7/D6), as well as its dependence on temperature, pH, and S/V. a is mainly dependent on temperature, which can be explained by a small difference in activation energy (0.10 ± 0.02 kJ/mol) between 6Li+ and 7Li+. This temperature dependance reveals that Li isotope fractionation during diffusion is low at low temperatures (T < 20°C), but can be significant at high temperatures. However, concerning hydrothermal fluids (T > 120°C), the dissolution rate of basaltic glass is also high and masks the effects of diffusion. These results indicate that the high δ7Li values of river waters, in particular in basaltic catchments, and the fractionated values of hydrothermal fluids are mainly controlled by precipitation of secondary phases.

We report osmium concentrations and isotopic compositions of 40 groundwater samples from the Bengal plain. Groundwaters have Os concentrations (16.9-191.5 pg/kg), about 5-10 times higher than those published for most rivers or seawater. 187Os/188Os varies widely (from 0.96 to 2.79) and is related to the isotopic signatures of the sediments constituting local aquifers. Os contents are correlated with those of soluble elements such as Sr, Mg, and Ca, suggesting that differing extents of solid-solution interaction explain most of the variation in measured Os concentrations. The covariation between Os and Sr allows us to estimate the mean Os content of Bengal groundwater (70 pg/kg). This concentration is too low to allow Bengal groundwater to significantly influence the marine Os isotopic composition, if likely fresh groundwater discharge rates to the Bay of Bengal are assumed. However, if Bengal groundwater Os concentrations are typical, the global Os groundwater flux would be expected to be around 180 kg/year, making it the second largest input of Os to the ocean after the river flux. Including this flux in the current Os marine budget, and assuming that this and other fluxes have remained constant with time, would decrease the calculated residence time of Os in the ocean by about 30%.

Over the last decade it has become apparent that Li isotopes may be a good proxy to trace silicate weathering. However, the exact mechanisms which drive the behaviour of Li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy. In this study, we analysed the Li concentrations and isotopic compositions in the various surface reservoirs (soils, rocks, waters and plants) of a small forested granitic catchment located in the Vosges Mountains (Strengbach catchment, France, OHGE http://ohge.u-strasbg.fr). Li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin, atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals (which together represent a minimum of 70% of dissolved Li). Li isotope ratios in soil pore waters show large depth dependent variations. Average dissolved d7Li decreases from _1.1&to _14.4& between 0 and _30 cm, but is +30.7&at _60 cm. This range of Li isotopic compositions is very large and it encompasses almost the entire range of terrestrial Li isotope compositions that have been previously reported. We interpret these variations to result from both the dissolution and precipitation of secondary phases. Large isotopic variations were also measured in the springs and stream waters, with d7Li varying from +5.3& to +19.6&. d7Li increases from the top to the bottom of the basin and also covaries with discharge at the outlet. These variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks. We suggest that the dissolved d7Li increases with increasing residence time of waters through the rocks, and so with increasing time of interaction between waters and solids. A dissolution precipitation model was used to fit the dissolved Li isotopic compositions. It was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of _5&to _14& (best fit _10.8&), in agreement with Li incorporation into clay. In soil solutions, it was found that isotopic fractionation during secondary precipitation is larger (at least _23&), suggesting a major role for different secondary phases, such as iron oxides that maybe incorporate Li with a higher isotope fractionation.

We report Li isotopic compositions, for river waters and suspended sediments, of about 40 rivers sampled within the Mackenzie River Basin in northwestern Canada. The aim of this study is to characterize the behaviour of Li and its isotopes during weathering at the scale of a large mixed lithology basin. The Mackenzie River waters display systematically heavier Li isotopic compositions relative to source rocks and suspended sediments. The range in delta Li-7 is larger in dissolved load (from +9.3 parts per thousand to +29.0 parts per thousand) compared to suspended sediments (from 1.7 parts per thousand to +3.2 parts per thousand), which are not significantly different from delta Li-7 values in bedrocks. Our study shows that dissolved Li is essentially derived from the weathering of silicates and that its isotopic composition in the dissolved load is inversely correlated with its relative mobility when compared to Na. The highest enrichment of Li-7 in the dissolved load is reported when Li is not or poorly incorporated in secondary phases after its release into solution by mineral dissolution. This counterintuitive observation is interpreted by the mixing of water types derived from two different weathering regimes producing different Li isotopic compositions within the Mackenzie River Basin. The incipient weathering regime characterizing the Rocky Mountains and the Shield areas produces Li-7 enrichment in the fluid phase that is most simply explained by the precipitation of oxyhydroxide phases fractionating Li isotopes. The second weathering regime is found in the lowland area and produces the lower delta Li-7 waters (but still enriched in Li-7 compared to bedrocks) and the most Li-depleted waters (compared to Na). Fractionation factors suggest that the incorporation of Li in clay minerals is the mechanism that explains the isotopic composition of the lowland rivers. The correlation of boron and lithium concentrations found in the dissolved load of the Mackenzie Rivers suggests that precipitation of clay minerals is favoured by the relatively high residence time of water in groundwater. In the Shield and Rocky Mountains, Li isotopes suggest that clay minerals are not forming and that secondary minerals with stronger affinity for Li-7 appear. Although the weathering mechanisms operating in the Mackenzie Basin need to be characterized more precisely, the Li isotope data reported here clearly show the control of Li isotopes by the weathering intensity. The spatial diversity of weathering regimes, resulting from a complex combination of factors such as topography, geology, climate and hydrology explains, in fine, the spatial distribution of Li isotopic ratios in the large drainage basin of the Mackenzie River. There is no simple relationship between Li isotopic composition and chemical denudation fluxes in the Mackenzie River Basin

This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali-rich samples (granite, soil, plants). This protocol was based on a combination of two pre-existing methods: transition metals were first removed from the sample using an AG-MP1 anion-exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca 2+ , Mn 2+ and Sr 2+) using a AG50W-X12 cation-exchange resin. This procedure allowed Mg recovery of ~100 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC-ICP-MS instruments (Isoprobe and Nu Plasma). The long-term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE-N), limestone (Cal-S) and seawater (BCR-403) reference materials analysed in this study yielded δ 26 Mg mean values of-0.28 ± 0.08‰,-4.37 ± 0.11‰ and-0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR-N) and granite (GA), yielded δ 26 Mg mean values of-0.50 ± 0.08‰ and-0.75 ± 0.14‰, respectively. The weathering products, soil (TILL-1) and river water (NIST SRM 1640), gave δ 26 Mg values of-0.40 ± 0.07‰ and-1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR-381), sea lettuce (Ulva lactuva) (BCR-279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR-482) reference materials gave δ 26 Mg values of-1.10 ± 0.14‰,-0.90 ± 0.19‰,-0.50 ± 0.22‰ and-1.15 ± 0.27‰ respectively. Plant δ 26 Mg values fell within the range defined by published data for chlorophylls.

The lithium isotope compositions ((7)Li/(6)Li) and Li/Ca ratios of shallow-water and deep-sea corals (Porites lutea, Cladocora caespitosa, Lophelia pertusa and Desmophyllum cristagalli) were measured using a Cameca ims 1270 ion microprobe. The two C. caespitosa samples were grown under controlled conditions at CO(2) partial pressures (pCO(2)) of 416 +/- 29 mu atm and 729 +/- 30 mu atm, respectively. In situ analyses show that all samples are isotopically homogeneous (within analytical precision, +/- 1.1 parts per thousand, 1 sigma) and display significantly lower delta(7)Li values relative to seawater. indicating a significant isotope fractionation during aragonite formation. In contrast to all other elements analysed so far, there is no relationship between the Li isotopic compositions and the skeletal ultrastructure. However, Li/Ca does show variation correlated with ultrastructure, albeit with significant differences between species. This implies that the bio mineralization mechanisms, which are supposed to be different for the different skeletal components, do not influence the Li isotopic composition in corals. In particular, the model of Rayleigh fractionation in a semi-enclosed calcifying fluid is incompatible with the homogeneity of the Li isotope compositions at the micrometer scale We also. show that changes in pCO(2) (and pH) do not significantly affect the Li isotope signature. Nevertheless, a small but significant and systematic difference in Li isotopic composition is observed between deep-sea azooxanthellate and shallow-water zooxanthellate corals. The lack of dependence on pH and pCO(2) and on skeletal ultrastructure indicates that the U isotopic signature of corals could be used as a proxy for reconstructing the paleo-delta(7)Li of seawater and, potentially, for deconvolving past continental weathering rates. (C) 2009 Elsevier B.V. All rights reserved.

Magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the Moselle basin, northeastern France. This small basin is remarkable for its well-constrained and varied lithology on a small distance scale, and this is reflected in river water Sr isotope compositions. Upstream, where the Moselle River drains silicate rocks of the Vosges mountains, waters are characterized by relatively high 87Sr/86Sr ratios (0.7128-0.7174). In contrast, downstream of the city of Epinal where the Moselle River flows through carbonates and evaporites of the Lorraine plateau, 87Sr/86Sr ratios are lower, down to 0.70824. Magnesium in river waters draining silicates is systematically depleted in heavy isotopes (δ26Mg values range from −1.2 to −0.7‰) relative to the value presently estimated for the continental crust and a local diorite (−0.5‰). In comparison, δ26Mg values measured in soil samples are higher (∼0.0‰). This suggests that Mg isotope fractionation occurs during mineral leaching and/or formation of secondary clay minerals. On the Lorraine plateau, tributaries draining marls, carbonates and evaporites are characterized by low Ca/Mg (1.5-3.2) and low Ca/Sr (80-400) when compared to local carbonate rocks (Ca/Mg = 29-59; Ca/Sr = 370-2200), similar to other rivers draining carbonates. The most likely cause of the Mg and Sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer. δ26Mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year (from −1.4‰ to −1.6‰ and from −1.2‰ to −1.4‰, respectively), within the range defined for the underlying rocks. Downstream of Epinal, the compositions of the Moselle River samples in a δ26Mg vs. 87Sr/86Sr diagram can be explained by mixing curves between silicate, carbonate and evaporite waters, with a significant contribution from the Vosgian silicate lithologies (>70%). Temporal co-variation between δ26Mg and 87Sr/86Sr for the Moselle River throughout year is also observed, and is consistent with a higher contribution from the Vosges mountains in winter, in terms of runoff and dissolved element flux. Overall, this study shows that Mg isotopes measured in waters, rocks and soils, coupled with other tracers such as Sr isotopes, could be used to better constrain riverine Mg sources, particularly if analytical uncertainties in Mg isotope measurements can be improved in order to perform more precise quantifications

In situ measurement of Li isotope ratios in foraminifera has been developed using a Cameca ims 1270 ion microprobe. In situ d 7 Li analyses have been performed in biogenic calcite of planktonic foraminifera from various locations. Results show that for west Pacific mixed Globigerinoides and Globorotalia (22°S161°E), the isotopic variability between tests and within a single test, respectively, is not significantly greater than estimated analytical uncertainty ($1.5%). Mean d 7 Li for several planktonic foraminifera tests corresponds to the seawater value, strongly suggesting negligible Li isotope fractionation relative to seawater, as previously inferred by Hall et al. (2005) using thermo-ionization mass spectrometer and multicollector-inductively coupled plasma-mass spectrometry techniques. Combined with scanning electron microscopy and ion microprobe imaging, micron-sized grains, enriched in lithium, silica and aluminum have been found in the foraminifera calcite matrix. A simple mixing model shows that 0.3-2 wt % of marine clays incorporated within the analyzed calcite would lower the foraminifera d 7 Li value, by 3% to 10% relative to the isotopic composition of the pure calcite. By comparison, no such grains have been detected in corals. The presence of micron-sized silicate grains embedded within the foraminifera calcite is consistent with the Erez (2003) biomineralization model, involving calcite precipitation from seawater vacuoles. By contrast, coral calcium carbonate is instead precipitated from ions, which have been pumped or diffused through several membranes, impermeable to micrometric grains. Ion microprobe in situ d 7 Li measurements in biogenic calcite present new methods for investigating both biomineralization processes and the past record of the ocean composition by exploring geochemical variations at a scale that is smaller in space and in time.

An analytical procedure has been developed for the in situ measurement of calcium isotope composition of carbonates with a spatial resolution of 15-20 μm on a Caméca IMS 1270 ion microprobe. By using two Faraday cup detectors, the 40 Ca and 44 Ca can be measured simultaneously, improving the internal reproducibility. Instrumental mass fractionation (IMF) of calcium isotopes was observed to be independent of primary ion beam intensity and of the Mg content of the carbonate, but can depend on vacuum conditions. Three calcite reference materials were used in this study (ENS 0, MEX and BRET 105E) and their δ 44 Ca values relative to NIST915a were reproducible within a typical 1σ standard deviation of ≈0.15‰. This analytical procedure was applied to planktonic foraminifera, Globorotalia inflata, dated at 2.8 Ma from Shatsky Rise (ODP leg 198). The range of measured δ 44 Ca within a single test is 1.7‰. This intratest variation can be attributed to several processes such as temperature variation, ontogenic effects or differences between primary and secondary calcite (i.e. calcite precipitated by different biomineralization processes). Despite this intratest variation, the averages δ 44 Ca for each foraminifer are similar and are in agreement with published δ 44 Ca values measured for this age. This study shows that in situ δ 44 Ca measurements in tests of foraminifera are an appropriate tool for investigating biomineralization processes.

We report here a newly developed method for measurement of Li isotopes by use of multi-collector ICP-MS (Neptune) allowing rapid and high precision determination of Li isotope ratios at low levels of lithium (15–20 ng). The lithium reference sample solution IRMM-016 was analysed over a period of ten months with an external reproducibility of 0.24% (2s, n = 52). Chemical separation of Li from matrix was performed on the seawater sample IRMM BCR-403, for which a mean δ7Li value of + 31.0 ± 0.1 % (2s/√n, n = 31) was obtained. This mean value is in good agreement with those previously published for other seawater samples. BCR-403 seawater being readily available, we propose that this seawater sample be used as a reference sample for Li isotope measurements.