The adsorption of boron on detrital particles like clay or metal oxides is thought to be a major mechanism driving changes in the boron isotopic composition of seawater on geologic timescales. However, the sensitivity of adsorption parameters to long-term changes in the seawater concentration of major ions (Mg2+, Ca2+, SO42-) and dissolved inorganic carbon (HCO3-, CO32-) is not known. We conducted multiple sets of adsorption experiments that consist of suspending pretreated clay minerals (either kaolinite, smectite or illite) in artificial seawater with a modified chemical composition. Specifically, we investigate adsorption in seawater with a major ion composition resembling that of the Cretaceous (100 Ma) and the Eocene (50 Ma), as well as modern seawater with either reduced or elevated concentrations of dissolved inorganic carbon. We finally combine the results with modeled values for the mineral assemblage of detrital sediment to constrain boron adsorption fluxes in the past. The dataset consists of two sheets that store (1) the results of our adsorption experiments and (2) the modeled sediment properties. Experiments were performed on KGa-1b kaolinite, SWy-3 smectite and IMt-2 illite obtained from the Clay Mineral Society. For each of these clays, a consistent particle size fraction of 2 – 0.2 μm was extracted by repeated centrifugation and decantation. As a result, clay samples used in the experiments have a high mineralogical purity of 95% (in the case of kaolinite and illite) and 50% (in the case of smectite). Pretreated clays were submerged in one of four different boron-containing artificial seawater solutions. These seawater solutions were prepared by mixing trace element-grade salts with ultrapure water according to the recipe of Millero (2013). Specifically, the amounts of added MgCl2, CaCl2, Na2SO4 and NaHCO3 were varied to produce four different seawater stock solutions that have (i) a major ion concentration similar to Eocene seawater; (ii) a major ion concentration similar to Cretaceous seawater; (iii) a DIC concentration half as high as in modern seawater; (iv) a DIC concentration twice as high as in modern seawater. Clay and seawater were allowed to interact for 48h through continuous agitation, after which solution samples were extracted.
Adsorption and isotopic fractionation of boron on clastic sediment is one process responsible for the heavy boron isotopic composition of the modern ocean. However, the mechanism by which boron complexes to the surface of clay minerals and the cause of its isotopic fractionation are still unclear. We performed two sets of experiments, using solutions of pure water with added boron and seawater, to explore the isotope behavior during adsorption of boron onto kaolinite, smectite and illite. The dataset consists of an excel file with four sheets that store (1) the NIST RM 803 measurements we used to establish the long-term reproducibility of our isotope measurements, (2) results of our pure experiment, (3) results of our seawater experiments and (4) a global compilation of XRD-based riverine clay mineral assemblages.
The dataset presented here encompasses the results of the geochemical analyses of water and recent carbonate samples collected in the El Peinado basin located in the Southern Puna Plateau in Catamarca, Argentina. This system formed by the hypersaline lake Laguna del Peinado, numerous hydrothermal springs, and the small hypersaline lake Laguna Turquesa, provides a natural laboratory to study carbonate formation and the mechanisms that control the incorporation of various elements and isotopes into their structure under a broad range of geochemical conditions. Geochemical analyses include data on the physicochemical parameters, elemental, and isotopic (δ18O, δ2H, δ11B) composition of the waters, and data on the elemental and isotopic (δ18O, δ13C, δ11B) composition of the carbonates. These data allowed us to calculate element partition coefficients and isotopic fractionation between coupled water-carbonate samples from this natural setting, which are also included here. This dataset also includes the results of water modelling using the software PHREEQC, which contains data on the chemical speciation of carbon and boron, the species contributing to total alkalinity, and mineral saturation indices. This information is useful for all those dealing with geochemistry of hypersaline lakes, geochemistry of continental carbonates, as well as paleoenvironmental and paleoclimatic studies using lake carbonates as archives. These data correspond to the research article “On the origin and processes controlling the elemental and isotopic composition of carbonates in hypersaline Andean lakes”. The full description of the data is provided in the data description file.
A low blank, high-precision, and highly reproducible technique for Boron (B) isotope analysis performed by Multi-Collector-Inductively Coupled Plasma-Mass Spectrometer (MC-ICP-MS), Thermo Scientific Neptune PlusTM was developed and is presented here. We show data on a set of international certified standard materials (NIST SRM 951) and various kind of matrices (B1-IAEA, B2-IAEA, B3-IAEA, B4-IAEA, B5-IAEA, and JB-2) measured with MC-ICP-MS Neptune Plus, focusing on the accuracy and reproducibility of the analyses performed in the Neptune-TIMS Laboratory
In the Western Tauern Window, Zillertal Alps (Austria/Italy), metasediments of a Mesozoic intra-montane basin ("Pfitsch-Mörchner basin"; Veselá and Lammerer, 2008) are exposed. The (me-ta)sediments were deposited on a Variscan basement, which comprises different types of meta-granitoids and their (Pre)-Variscan metamorphic country rocks. The chemical composition (major and trace elements) of these rocks is presented for 205 samples. In the metasediments (103 samples), we distinguish the following units (from base to top): metaconglomerate (14 samples) – mica schist (19) – carbonate-mica schist (9) – tourmaline gneiss (35) – lazulite quartzite (25) – marble (1). In the basement to the NW of the basin, we distinguish two different types of orthogneiss (both Zentralgneis of the Tux unit, in the local nomenclature two varieties Augenflasergneis and Schrammacher gneiss; 32 samples) and the roof pendant of these gneisses with serpentinite (10 samples), amphibolite, and paragneiss (no analyses presented). In the SE of the basin we distinguish orthogneiss from the Zillertal branch of the Zentralgneis (7 samples), biotite-chlorite-plagioclase gneiss (9 samples), amphibolite, and (Pre-)Variscan graphitic micaschist with the local name Furtschagl schist (no analyses presented), and at the base of the basin sediments a schistose pyrite quartzite (31) with lenses of magnetite-chloritoide-staurolite-chlorite rich rocks (13 samples MCSC-lenses, interpreted as paleosol, Barrientos and Selverstone, 1987). From a subset of these samples (23 samples), rare earth elements were determined, and from another subset of 25 samples 11B/10B boron isotope ratios and whole rock B-contents. This extends a previously published data set of B isotope ratios in tourmaline from the metasedimen-tary unit (Berryman et al. 2017). For a test of stratigraphic correlation, typical rocks from the meta-conglomerate, the carbonate-mica schist, lazulite quartzite, and marble (one sample each) were analyzed for 87Sr/86Sr isotope ratios.
The cause of changes in atmospheric carbon dioxide (CO₂) during the recent ice ages is yet to be fully explained. Most mechanisms for glacial–interglacial CO₂ change have centred on carbon exchange with the deep ocean, owing to its large size and relatively rapid exchange with the atmosphere. The Southern Ocean is thought to have a key role in this exchange, as much of the deep ocean is ventilated to the atmosphere in this region. However, it is difficult to reconstruct changes in deep Southern Ocean carbon storage, so few direct tests of this hypothesis have been carried out. Here we present deep-sea coral boron isotope data that track the pH—and thus the CO₂ chemistry—of the deep Southern Ocean over the past forty thousand years. At sites closest to the Antarctic continental margin, and most influenced by the deep southern waters that form the ocean's lower overturning cell, we find a close relationship between ocean pH and atmospheric CO₂: during intervals of low CO₂, ocean pH is low, reflecting enhanced ocean carbon storage; and during intervals of rising CO₂, ocean pH rises, reflecting loss of carbon from the ocean to the atmosphere. Correspondingly, at shallower sites we find rapid (millennial- to centennial-scale) decreases in pH during abrupt increases in CO₂, reflecting the rapid transfer of carbon from the deep ocean to the upper ocean and atmosphere. Our findings confirm the importance of the deep Southern Ocean in ice-age CO₂ change, and show that deep-ocean CO₂ release can occur as a dynamic feedback to rapid climate change on centennial timescales.
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