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Strontium isotopes (87Sr/86Sr) were evaluated as a potential method for studying the geographical origin of populations and movements patterns of migratory fish from the La Plata Basin (Paraná, Uruguay and Bermejo Rivers and Río de la Plata Estuary, South America). Surface water samples were collected at 43 sites during austral summer and winter (2018) while, Surubí (Pseudoplatystoma corruscans), Patí (Luciopimelodus pati), dorado (Salminus brasiliensis) and sábalo (Prochilodus lineatus) fishes were collected at seven locations. Water 87Sr/86Sr ratio was analysed by MC‐ICP‐MS (N = 74) and otolith core‐to‐edge 87Sr/86Sr transects (N = 50) were measured by LAfs‐MC‐ICP‐MS. Several water bodies presented significantly different (p < 0.05) water 87Sr/86Sr values. A ~ 1:1 relationship was found between 87Sr/86Sr measured in edge otolith and water. Data provide novel perspectives about migratory behaviour for all species, such as potential cross‐border migrations between countries of more than 1,000 km recorded for L. pati, S. brasiliensis and P. lineatus. These species seem to move between the Paraná and Uruguay rivers, which imply using the delta or the estuary as a corridor between them. Discriminant analysis based on otolith core 87Sr/86Sr suggested that the four species studied originate in sub‐basins different from those that were collected and revelled the presence of several potential spawning/nursery areas. The otolith 87Sr/86Sr profiles also suggested movements between different environments such as reservoirs, large plain rivers, mountain streams, floodplain valleys and estuaries. These results show the potential of 87Sr/86Sr as a tool for tracking the life history of fishes, and depict for the first time a complex use of the La Plata basin by the fishes, providing new information for management plans at the regional level. [ABSTRACT FROM AUTHOR]

The demand for large and reliable data sets on isotopic composition has increased in geochemistry and environmental sciences over recent years. We present an automated ion chromatographic separation method using a robotic pipetting arm, termed 'ChemCobOne', to reduce sample separation time. Its performance was tested for lithium isotope separation in geological reference materials using a single‐step separation with HCl (0.2 mol l−1) and a 2 ml resin volume. This refined lithium purification method does not forfeit precision, accuracy or purity compared with manual sample processing. In addition, a δ7Li value for NASS‐6 of 30.99 ± 0.50‰ (2s) (95% CI = 0.14‰, n = 44) was determined and the first δ7Li values for the granite rock reference material GS‐N (−0.57 ± 0.25‰ (2s), 95% CI = 0.15‰, n = 15), and for the soil reference material NIST SRM 2709a (−0.37 ± 0.67‰ (2s), 95% CI = 0.15‰, n = 63) are proposed. [ABSTRACT FROM AUTHOR]

The impact of intensive farming on chemical weathering in the Critical Zone is still an open question. Extensively instrumented and monitored over the last 50 years, the Orgeval Critical Zone Observatory (CZO) in France is an observation site impacted by intensive farming since the 1960s. The Orgeval observatory represents an ideal place to study the response and resilience capability of the Critical Zone under agricultural stress. This paper investigates the chemical composition of different water bodies in two nested catchments of the Orgeval CZO, including rainfall, springs, rivers, and rocks, over one and half hydrological year. We show that elemental and strontium isotopic ratios are powerful to constrain the origin of the elements. The results show that the river chemistry at the outlet of the two nested catchments is dominated by rain inputs (particularly atmospheric dust dissolution) and the chemical weathering of limestone and gypsum. Fertilizer input is clearly visible, although the distinction between gypsum dissolution and fertilizer inputs needs more investigation. The mixtures of water masses inferred from our data are in good agreement with the hydrological context of the watershed, that is, a multilayered aquifer structure. At the main outlet of the CZO, we estimate that the input of ocean‐derived solutes through rainfall represents 7 t km−2 year−1, on the same order of magnitude as the net fertilizer input (10 t km−2 year−1), and that rock weathering releases 50 t km−2 year−1. Including previously published physical erosion rates, we estimate that the total denudation rate (physical and chemical) of the Orgeval CZO is 20 mm (1,000 year)−1, which, along with the entire Seine watershed, is among the lowest chemical denudation rates for carbonate terrains under temperate climate. Chemical denudation is about 10 times higher than physical erosion in the Orgeval CZO. The consumption of CO2 by rock weathering is estimated to be between 265.103 and 360.103 molC km2 year−1, similar for the two nested catchments. Compared with the rivers, the springs show a higher CO2 consumption rate that suggests, as pointed out earlier, a enhancement of carbonate dissolution linked to nitrification and thus fertilizer application. The hyporheic zone appears to be a hot spot in the carbon cycle at the Orgeval CZO. This study sheds light on the complex, anthropocenic, interplay between geology, climate, and human activities that characterize and that take place in intensive agriculture regions. [ABSTRACT FROM AUTHOR]

When rock is converted to weathering products, the involved processes can be fingerprinted using the stable isotope ratios of metals (for example Li, Mg, Ca, Fe, Sr) and metalloids (B, Si). Here we construct a framework for interpreting these "novel" stable isotope ratios quantitatively in the compartments of the weathering zone in a geomorphic context. The approach is applicable to any novel stable isotope system and is based on a simple steady-state mass balance model that represents the weathering zone from the scale of a soil column to that of entire continents. Our model is based on the assumption that the two main processes associated with isotope fractionation are formation of secondary precipitates such as clays, and uptake of nutrients by plants. The model results show that the isotope composition of a given element in the weathering zone compartments depends on (1) the ratio between the release flux to water through primary mineral dissolution and the erosion flux of isotopically fractionated solid material, consisting of secondary precipitates and organic matter; (2) the isotope fractionation factors associated with secondary mineral precipitation and uptake by plants. A relationship is established between isotope ratios, isotope fractionation factors, and indexes for chemical weathering [such as chemical depletion fractions (CDF) and elemental mass transfer coefficients (7)] derived from simple elemental concentration measurements. From this relationship, isotope fractionation factors can be calibrated from chemical and isotope data measured on field material. Furthermore, we show how the ratio of solid export to dissolved export of a given element from the weathering system can be estimated from the comparison of the isotope composition between bedrock, water, and sediment. This calculation can be applied to samples from soils, from rivers, and from the sedimentary record, and does not require knowing the isotope fractionation factors involved in the reactions. Finally, we apply the model to the oceanic Li isotope record reconstructed from marine carbonate sediments in order to discuss changes in global geomorphic regimes through the Cenozoic. [ABSTRACT FROM AUTHOR]

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d-DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi-collector inductively coupled plasma-mass spectrometer (MC-ICP-MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP-MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2-5 times higher with d-DIHEN and wash times up to ten times shorter. Repeatability of B/B sample-calibrator bracketing measurements reached 0.25‰ (2 s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δB values in the ranges −90 to +40‰ and −2 to +2.5‰, demonstrating our ability to distinguish δB values with differences of only 0.25‰. The international seawater reference material NRCC NASS-5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10-month period, yielded an average δB value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δB determined by d-DIHEN MC-ICP-MS and positive-TIMS (P-TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰). [ABSTRACT FROM AUTHOR]

The two long-term sources of atmospheric carbon are CO2 degassing from metamorphic and volcanic activity, and oxidation of organic carbon (OC) contained in sedimentary rocks, or petrogenic organic carbon (OCpetro). The latter flux is still poorly constrained. In this study, we report particulate organic carbon content and 14C activity measurements in Amazon River sediments, which allow for estimates of the OCpetro content of these sediments. A large decrease of OCpetro content in riverine sediments is observed from the outlet of the Andes to the mouth of the large tributaries. This loss reveals oxidation of OCpetro during transfer of sediments in the floodplain, and results in an escape of ∼0.25 Mt C/yr to the atmosphere, which is on the same order of magnitude as the CO2 consumption by silicate weathering in the same area. Raman microspectroscopy investigations show that graphite is the most stable phase with respect to this oxidation process. These results emphasize the significance of OCpetro oxidation in large river floodplains in the global carbon cycle. [ABSTRACT FROM AUTHOR]

The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (Corg) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble Corg respectively. In Himalayan and Amazon river sediments, the proportion of Corg solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the Corg content for the dissolved organic carbon content measured after decarbonation. Data presented here show that Corg dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment. [ABSTRACT FROM AUTHOR]

Large rivers integrate the products of physical erosion and chemical weathering in different forms (dissolved, fine to coarse particles). The geochemical composition of these products carry important informations on the mechanisms controlling erosion and weathering at the basin scale : sources of the products, vegetation, climate, anthropogenic and tectonic factors, timescale involed. In the framework of a large franco-chinese project, the four largest rivers in China (Changjiang, Huanghe, Zhujiang, Heilongjiang) were sampled : vertical profiles, surface tributaries, bedload sediments and surface monthly time series over a year were collected at different locations along the stream of these rivers. We report major and trace elements concentrations and Nd-Sr isotopes in the suspended particulate matter and bedloads. The four river basins cover a large diversity of climatic, lithologic, tectonic and anthropic settings, that our results put in perspective as controls on erosion-weathering mechanism and its associated timescales. [ABSTRACT FROM AUTHOR]

Chemical weathering of silicate rocks sustains long term solute cycling through water-rock interactions in the terrestrial subsurface that transforms pristine bedrock into the diverse landscapes that characterize the Earth's surface (i.e. the Critical Zone). The drawdown of CO2 via these weathering reactions serves as a major component in the long term cycling of carbon and is thought to play a key role in the regulation of Earth's climate over geologic timescales. Thus, understanding the silicate weathering feedback is critical for assessing regional and global scale responses to a rapidly changing climate. However, to accurately quantify silicate weathering rates, a better understanding of solute generation and transport in the subsurface is required. Stream solute concentrations and discharge are highly coupled, integrating various reaction pathways and fluid residence times and thus can provide key insight into the hydrogeochemical controls within the critical zone. Strong responses of solute export with "storm" (flood) events characterized by large variations in discharge over a short time, suggests that transient hydrologic processes could exert a predominant control on weathering reactions in the critical zone. To address this, we utilize stable isotopes of Si (designated δ30Si), a highly sensitive silicate weathering tracer, to gain insight into the hydrogeochemical processes taking place under transient hydrological conditions.Our study focuses on Si isotope analyzes performed on storm events from several small catchments spanning a range of different climates and lithologies as part of an international collaboration between U.S and French Critical Zone Observatory networks to better understand concentration-discharge relationships (SAVI). Our preliminary findings suggest that δ30Si – discharge relationships could provide unique insight into the balance between primary mineral dissolution and secondary mineral precipitation in the weathering zone and, thus, be a powerful complementary tool to frequently used C-Q relationships. [ABSTRACT FROM AUTHOR]

The Cambrian explosion, the rapid appearance of most animal phyla in the geological record, occurred concurrently with bottom seawater oxygenation. Whether this oxygenation event was triggered through enhanced nutrient supply and organic carbon burial forced by increased continental weathering, or by species engaging in ecosystem engineering, remains a fundamental yet unresolved question. Here we provide evidence for several simultaneous developments that took place over the Ediacaran-Cambrian transition: expansion of siliceous sponges, decrease of the dissolved organic carbon pool, enhanced organic carbon burial, increased phosphorus removal and seawater oxygenation. This evidence is based on silicon and carbon stable isotopes, Ge/Si ratios, REE-geochemistry and redox-sensitive elements in a chert-shale succession from the Yangtze Platform, China. According to this reconstruction, sponges have initiated seawater oxygenation by redistributing organic carbon oxidation through filtering suspended organic matter from seawater. The resulting increase in dissolved oxygen levels potentially triggered the diversification of eumetazoans.The Ediacaran-Cambrian oxygenation of seawater is thought to have been caused by lifeforms engaging in ecosystem engineering. Here, the authors show that siliceous sponges increased seawater dissolved oxygen concentrations by redistributing organic carbon oxidation through filtering suspended organic matter.