InterCarb: a community effort to improve interlaboratory standardization of the carbonate clumped isotope thermometer using carbonate standards

Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale

Influence of mangrove zonation on CO2 fluxes at the sediment-air interface (New Caledonia)

Mangroves are the major ecosystems of tropical and subtropical coastlines. They are considered as a sink for atmospheric CO2 because they are characterized both by high net primary production, and by low rates of organic matter decomposition. However, a recent reassessment of the global mangrove budget suggests that organic carbon sinks have been underestimated, notably CO2 efflux from sediments and creek waters, and tidal export of dissolved inorganic carbon. Our objective was to understand the influence of mangrove zonation on the magnitude of CO2 fluxes at the sediment-air interface. Transparent and opaque dynamic closed chamber systems, coupled with an infra-red gas analyzer were used to measure CO2 fluxes. In addition, the physico-chemical properties (salinity, redox potential) of pore waters were determined, as well as the carbon content and the origin of surface sediments (Chlorophyll-a and delta C-13). Depending on the type of measurement (in the dark with or without biofilm, in the light with biofilm) and mangrove stand (saltflat, Avicennia sp., or Rhizophora spp.), mean surface sediment CO2 fluxes ranged between 40 +/- 56 and 199 +/- 95 mmol.m(-2).d(-1). We suggest that these differences mainly result both from the organic content and the redox conditions of the sediments, which are influenced by the physiological activities of the root system, and by the position and the elevation of the stand in the intertidal zone. In addition, the quality and abundance of biofilm, which also vary with the mangrove stand, also appear to strongly affect sediment CO2 fluxes as a result of chemical (metabolism) and also physical (barrier) processes

Transport dynamics and morphology of a high mountain stream during the peak flow season: the Ürümqi river (Chinese Tian-Shan)

International audienceno abstrac

Evidence of polygenetic carbon trapping in the Oman Ophiolite: Petro-structural, geochemical, and carbon and oxygen isotope study of the Wadi Dima harzburgite-hosted carbonates (Wadi Tayin massif, Sultanate of Oman)

International audienceThe Wadi Dima area (Oman Ophiolite) exposes partially altered to highly serpentinized harzburgites that are cross-cut by intense (>20 Vol%) carbonate veining. We identified a sequence of 3 types of carbonate veins with compositions ranging from calcite to dolomite (Mg/Ca = 0-0.85). Type 1 carbonates occur as a fine diffuse vein network, locally replacing olivine cores, penetrative into the serpentinized harzburgites. They have depleted trace elements abundances (e.g., Yb < 0.2 × C1-chondrite) relative to other Wadi Dima carbonates, exhibit negative Ce and positive Y, U anomalies and a broad range in δ13CV-PDB (-5 to -15‰) and δ18OSMOW (18 to 31‰). These compositions are consistent with precipitation after seawater-derived fluids and/or fluids in equilibrium with mantle rocks and serpentines during cooling of oceanic lithosphere (110 to 15°C). Type 2 carbonates are localized in veins, which acted as main flow paths for fluids interacting with peridotites in the exhumed Oman mantle lithosphere (50°C-10°C). The orientation of these veins is controlled by the crystallographic anisotropy of Oman mantle peridotites. Type 2 carbonates record two stages. The first involved the formation of large calcite crystals of composition similar to Type 1 carbonates (trace element depleted; δ13CV-PDB B = -4 to -9‰ and δ18OSMOW = 26 to 30‰), which during the second stage were recrystallized to form dolomite and calcite microcrystals (trace element enriched; δ13CV-PDB = -7 to -13‰ and δ18OSMOW = 29 to 32‰), after fluids sampling different sources including contributions of sediment-derived components. They were most likely formed at shallow depths and record the transition from oceanic to continental settings during late Cretaceous ophiolite obduction. Type 3 veins reactivate Type 2 veins. They comprise dominantly calcite and dolomite microcrystals (Light REE enriched patterns) with isotopic compositions (δ13CV-PDB B ~ -7 to -8‰; δ18OSMOW~ 28 to 32‰) consistent with precipitation at low temperatures (T°<30°C) from surface/meteoric fluids. Type 3 veining is probably triggered by ophiolite uplift during the Oligocene to early Miocene. Our study presents new insights into the role of the initial mantle anisotropy in the orientation of the vein network and of principal flow paths during serpentinization and carbonatization of mantle peridotites. It also highlights the highly variable carbon isotope composition of carbonates and suggest different origins for these heterogeneities: the carbon isotope composition of the early Type 1 carbonates dispersed in the poorly connected peridotites is locally modified by serpentinization reactions whilst the carbon isotope compositions of Type 2 and 3 carbonates record mixing of fluids from different sources in high flow veins

An explanation for the 18O excess in Noelaerhabdaceae coccolith calcite.

Coccoliths have dominated the sedimentary archive in the pelagic environment since the Jurassic. The biominerals produced by the coccolithophores are ideally placed to infer sea surface temperatures from their oxygen isotopic composition, as calcification in this photosynthetic algal group only occurs in the sunlit surface waters. In the present study, we dissect the isotopic mechanisms contributing to the “vital effect”, which overprints the oceanic temperatures recorded in coccolith calcite. Applying the passive diffusion model of carbon acquisition by the marine phytoplankton widely used in biogeochemical and palaeoceanographic studies, our results suggest that the oxygen isotope offsets from inorganic calcite in fast dividing species Emiliania huxleyi and Gephyrocapsa oceanica originates from the legacy of assimilated 18O-rich CO2 that induces transient isotopic disequilibrium to the internal dissolved inorganic carbon (DIC) pool. The extent to which this intracellular isotopic disequilibrium is recorded in coccolith calcite (1.5 to +3 ‰ over a 10 to 25 °C temperature range) is set by the degree of isotopic re-equilibration between CO2 and water molecules before intracellular mineralisation. We show that the extent of re-equilibration is, in turn, set by temperature through both physiological (dynamics of the utilisation of the DIC pool) and thermodynamic (completeness of the re-equilibration of the relative 18O-rich CO2 influx) processes. At the highest temperature, less ambient aqueous CO2 is present for algal growth, and the consequence of carbon limitation is exacerbation of the oxygen isotope vital effect, obliterating the temperature signal. This culture dataset further demonstrates that the vital effect is variable for a given species / morphotype, and depends on the intricate relationship between the environment and the physiology of biomineralising algae

An explanation for the 18O excess in Noelaerhabdaceae coccolith calcite

Coccoliths have dominated the sedimentary archive in the pelagic environment since the Jurassic. The biominerals produced by the coccolithophores are ideally placed to infer sea surface temperatures from their oxygen isotopic composition, as calcification in this photosynthetic algal group only occurs in the sunlit surface waters. In the present study, we dissect the isotopic mechanisms contributing to the "vital effect”, which overprints the oceanic temperatures recorded in coccolith calcite. Applying the passive diffusion model of carbon acquisition by the marine phytoplankton widely used in biogeochemical and palaeoceanographic studies, our results suggest that the oxygen isotope offsets from inorganic calcite in fast dividing species Emiliania huxleyi and Gephyrocapsa oceanica originates from the legacy of assimilated 18 O-rich CO2 that induces transient isotopic disequilibrium to the internal dissolved inorganic carbon (DIC) pool. The extent to which this intracellular isotopic disequilibrium is recorded in coccolith calcite (1.5 to +3‰ over a 10 to 25 °C temperature range) is set by the degree of isotopic re-equilibration between CO2 and water molecules before intracellular mineralisation. We show that the extent of re-equilibration is, in turn, set by temperature through both physiological (dynamics of the utilisation of the DIC pool) and thermodynamic (completeness of the re-equilibration of the relative 18O-rich CO2 influx) processes. At the highest temperature, less ambient aqueous CO2is present for algal growth, and the consequence of carbon limitation is exacerbation of the oxygen isotope vital effect, obliterating the temperature signal. This culture dataset further demonstrates that the vital effect is variable for a given species/morphotype, and depends on the intricate relationship between the environment and the physiology of biomineralising algae

Understanding Fluid Flow during Tectonic Reactivation: An Example from the Flamborough Head Chalk Oucrop (UK)

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Understanding Fluid Flow during Tectonic Reactivation: An Example from the Flamborough Head Chalk Outcrop (UK)

Flamborough Head chalks are located at the extremities of E-W and N-S trending fault systems along the Yorkshire coast (UK). Rock deformation is expressed in Selwicks Bay where a normal fault is exposed along with a high density of calcite veins. The fault mineralization is tested using geochemistry. Crosscutting relationships are used to differentiate between three vein generations: a network of parallel veins that are oriented perpendicular to stratigraphy (Group I), hydraulic breccia with typical jigsaw puzzle structure (Group II), and a third generation of calcite veins crosscutting the two previous generations (Group III). Geochemical analyses revealed that all three generations possess the same chemical signature and must reflect successive pulses from the same mineralizing fluid source. Strontium isotope analyses showed that the veins have elevated 87Sr/86Sr ratios, that is, up to 7.110, while ratios of the chalk matrix equal 7.707. The latter value is in agreement with the signature of Late Cretaceous seawater. Consequently, the source of the fluid is external, reflecting an open system. The radiogenic Sr-isotope ratios, combined with low iron concentration, suggest that fluids migrated through sandy deposits. Fluid inclusion salinities range from 0 to 12 eq. wt% NaCl equiv. with a dominance of very low salinity inclusions, reflecting a meteoric signal. This leads to a model where meteoric fluids stored in an underlying confined sandstone aquifer were remobilized. The wide range of salinities could result from mixing of the meteoric fluid with some more saline fluids present in the rock sequence or from the dissolution of salts in the subsurface. In addition to the understanding of the local paragenetic evolution of the veining in Flamborough Head chalks, this study offers an insight into the way how fluid flows and mineralizes along fault zones