Preparation and purification of organic samples for selenium isotope studies

Selenium (Se) is an important micronutrient but also a strong toxin with a narrow tolerance range for many organisms. As such, a globally heterogeneous Se distribution in soils is responsible for various disease patterns (i.e. Se excess and deficiency) and environmental problems, whereby plants play a key role for the Se entrance into the biosphere. Selenium isotope variations were proved to be a powerful tracer for redox processes and are therefore promising for the exploration of the species dependent Se metabolism in plants and the Se cycling within the Critical Zone. Plant cultivation setups enable systematic controlled investigations, but samples derived from them–plant tissue and phytoagar–are particularly challenging and require specific preparation and purification steps to ensure precise and valid Se isotope analytics performed with HG-MC-ICP-MS. In this study, different methods for the entire process from solid tissue preparation to Se isotope measurements were tested, optimized and validated. A particular microwave digestion procedure for plant tissue and a vacuum filtration method for phytoagar led to full Se recoveries, whereby unfavorable organic residues were reduced to a minimum. Three purification methods predominantly described in the literature were systematically tested with pure Se solution, high concentrated multi-element standard solution as well as plant and phytoagar as target matrices. All these methods efficiently remove critical matrix elements, but differ in Se recovery and organic residues. Validation tests doping Se-free plant material and phytoagar with a reference material of known Se isotope composition revealed the high impact of organic residues on the accuracy of MC-ICP-MS measurements. Only the purification method with no detectable organic residues, hydride generation and trapping, results in valid mass bias correction for plant samples with an average deviation to true δ82/76Se values of 0.2 ‰ and a reproducibility (2 SD) of ± 0.2 ‰. For phytoagar this test yields a higher deviation of 1.1 ‰ from the true value and a 2 SD of ± 0.1 ‰. The application of the developed methods to cultivated plants shows sufficient accuracy and precision and is a promising approach to resolve plant internal Se isotope fractionations, for which respective δ82/76Se values of +2.3 to +3.5 ‰ for selenate and +1.2 to +1.9 ‰ for selenite were obtained

Evidence for local carbon-cycle perturbations superimposed on the Toarcian carbon isotope excursion

A Jurassic negative carbon isotope excursion (CIE), co-evolved with Toarcian Oceanic Anoxic Event (OAE) at ~183 Ma, is suggested to be linked to a global carbon-cycle perturbation and is well documented for Toarcian terrestrial fossil woods and marine sediments around the globe. A theoretically coupled δ13Ccarb-δ13Corg pattern due to such dubbed global carbon-cycle event from the negative CIE in Dotternhausen Toarcian stratigraphic profile (southwest Germany) is unexpectedly disturbed by two-step δ13Ccarb-δ13Corg decoupling in which the last step, upper in the stratigraphic order, is of higher magnitude. However, the trigger(s) for these sudden decoupling disturbances are still poorly constrained. Here, connecting new carbon and oxygen isotope data with documentary lipid biomarkers shows that the global carbon cycle during the Toarcian OAE was disturbed by enhanced green sulfur bacteria (GSB) metabolisms and early diagenesis at local scales. The first step δ13Ccarb-δ13Corg decoupling was induced in the initial stage of the GSB bloom. The second step of much larger δ13Ccarb-δ13Corg decoupling arising from a GSB prosperity was, however, exaggerated by early diagenesis through the respiration of sulfate-reducing bacteria (SRB). Paleo-geographically distinct localities of the Tethys region show contrasting decoupled δ13Ccarb-δ13Corg patterns, which implies that the second-order carbon-cycle perturbations have pervasively and independently impacted the global carbon event during the Toarcian OAE

Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: new multi-proxy constraints from the Cooper Lake paleosol

Oceanic element inventories derived from marine sedimentary rocks place important constraints on oxidative continental weathering in deep time, but there remains a scarcity in complementary observations directly from continental sedimentary reservoirs. This study focuses on better defining continental weathering conditions near the Archean-Proterozoic boundary through the multi-proxy (major and ultra-trace element, Fe and Cr stable isotopes, μ-XRF elemental mapping, and detrital zircon U-Pb geochronology) investigation of the ca. 2.45 billion year old (giga annum, Ga) Cooper Lake paleosol (saprolith), developed on a sediment-hosted mafic dike within the Huronian Supergroup (Ontario, Canada). Throughout the variably altered Cooper Lake saprolith, ratios of immobile elements (Nb, Ta, Zr, Hf, Th, Al, Ti) are constant, indicating a uniform pre-alteration dike composition, lack of extreme pH weathering conditions, and no major influence from ligand-rich fluids during weathering or burial metasomatism/metamorphism. The loss of Mg, Fe, Na, Sr, and Li, a signature of albite and ferromagnesian silicate weathering, increases towards the top of the preserved profile (unconformity) and dike margins. Coupled bulk rock behaviour of Fe-Mg-Mn and co-localization of Fe- Mn in clay minerals (predominantly chlorite) indicates these elements were solubilized primarily in their divalent state without Fe/Mn-oxide formation. A lack of a Ce anomaly and immobility of Mo, V, and Cr further support pervasively anoxic weathering conditions. Subtle U enrichment is the only geochemical evidence, if primary, that could be consistent with oxidative element mobilization. The leaching of ferromagnesian silicates was accompanied by variable mobility and depletion of transition metals with a relative depletion order of Fe≈Mg≈Zn\u3eNi\u3eCo\u3eCu (Cu being significantly influenced by secondary sulfide formation). Mild enrichment of heavy Fe isotopes (δ56/54Fe from 0.169 to 0.492 ‰) correlating with Fe depletion in the saprolith indicates loss of isotopically light aqueous Fe(II). Minor REE+Y fractionation with increasing alteration intensity, including a decreasing Eu anomaly and Y/Ho ratio, is attributed to albite breakdown and preferential scavenging of HREE\u3eY by clay minerals, respectively. Younger metasomatism resulted in the addition of several elements (K, Rb, Cs, Be, Tl, Ba, Sn, In, W), partly or wholly obscuring their earlier paleo-weathering trends. The behavior of Cr at Cooper Lake can help test previous hypotheses of an enhanced, low pH-driven continental weathering flux of Cr(III) to marine reservoirs between ca. 2.48-2.32 Ga and the utility of the stable Cr isotope proxy of Mn-oxide induced Cr(III) oxidation. Synchrotron μ- XRF maps and invariant Cr/Nb ratios reveal complete immobility of Cr despite its distribution amongst both clay-rich groundmass and Fe-Ti oxides. Assuming a pH-dependent, continental source of Cr(III) to marine basins, the Cr immobility at Cooper Lake indicates either that signatures of acidic surface waters were localized to uppermost and typically unpreserved regolith horizons or were geographically restricted to acid-generating point sources. However, in given detrital pyrite preservation in fluvial sequences overlying the paleosol, we propose that the oxidative sulphide corrosion required to drive surface pH(δ53/52Cr: -0.321 ± 0.038 ‰, 2sd, n=34) that cannot be linked to Cr(III) oxidation and is instead interpreted to have a magmatic origin. The combined chemical signatures and continued preservation of detrital pyrite/uraninite indicate low atmospheric O2 during weathering at ca. 2.45 Ga preserved in the rift-related sedimentary rocks of the Lower Huronian. The aqueous flux from the reduced weathering of mafic rocks was characterized by a greater abundance of transition metals (Fe, Mn, Zn, Co, Ni) with isotopically light Fe(II), as well as higher Eu/Eu* and Y/Ho. In most models of Precambrian ocean element inventories, hydrothermal fluids are viewed as the main supplier of several metals (e.g., Fe, Zn), although the results herein suggest that a riverine metal supply may have been substantial and that using Eu-excess as a strict proxy for hydrothermal flux may be misleading in near-shore marine sedimentary environments

Depth-dependent δ13 C trends in platform and slope settings of the Campbellrand-Malmani carbonate platform and possible implications for Early Earth oxygenation

Highlights • Carbon cycle of Neoarchean carbonate platform and potential oxygen oasis. • Carbon isotopes reveal a shift to aerobic biosphere and increasing oxidation state. • Rare earth element patterns reveal decrease in open ocean water influx. • Rimmed margin architecture was crucial for evolution of aerobic ecosystems. Abstract The evolution of oxygenic photosynthesis is widely seen as the major biological factor for the profound shift from reducing to slightly oxidizing conditions in Earth’s atmosphere during the Archean-Proterozoic transition period. The delay from the first biogenic production of oxygen and the permanent oxidation of Earth’s atmosphere during the early Paleoproteorozoic Great Oxidation Event (GOE) indicates that significant environmental modifications were necessary for an effective accumulation of metabolically produced oxygen. Here we report a distinct temporal shift to heavier carbon isotope signatures in lagoonal and intertidal carbonates (δ13Ccarb from -1.6 to +0.2 ‰, relative to VPDB) and organic matter (δ13Corg from about -40 to -25 ‰, relative to VPDB) from the 2.58–2.50 Gy old shallow–marine Campbellrand-Malmani carbonate platform (South Africa). This indicates an increase in the burial rate of organic matter caused by enhanced primary production as well as a change from an anaerobic to an aerobic ecosystem. Trace element data indicate limited influx of reducing species from deep open ocean water into the platform and an increased supply of nutrients from the continent, both supporting primary production and an increasing oxidation state of the platform interior. These restricted conditions allowed that the dissolved inorganic carbon (DIC) pool in the platform interior developed differently than the open ocean. This is supported by coeval carbonates from the marginal slope setting, which had a higher interaction with open ocean water and do not record a comparable shift in δ13Ccarb throughout the sequence. We propose that the emergence of stable shallow-water carbonate platforms in the Neoarchean provided ideal conditions for the evolution of early aerobic ecosystems, which finally led to the full oxidation of Earth’s atmosphere during the GOE

Ultra-trace element characterization of the central Ottawa River basin using a rapid, flexible, and low-volume ICP-MS method

Ultra-trace (<1 ng g-1) rare earth elements and yttrium (REE+Y) and high field strength element (HFSE) geochemistry of freshwater can constrain element sources, aqueous processes in hydrologic catchments, and the signature of dissolved terrestrial fluxes to the oceans. This study details an adapted method capable of quantifying ≥38 elements (including all REE+Y, Nb, Ta, Zr, Hf, Mo, W, Th, U) with minimal sample preparation in natural water aliquots as low as ≤2 mL. The method precision and accuracy are demonstrated using measurement of the National Research Council – Conseil national de recherches Canada (NRC-CNRC) river water certified reference material (CRM) SLRS-6 sampled from the Ottawa River (OR). Data from SLRS CRM are compared to those of new, filtered (HREE-enriched REE+Y patterns, small natural positive Y and Gd anomalies, and negative Eu and Ce anomalies. These REE+Y features are coherent downstream in the OR apart from amplification of Eu and Ce anomalies during REE removal/dilution. The OR samples capture a downstream decrease in sparingly soluble HFSE (Th, Nb, Ta, Zr, Hf), presumably related to their colloid-particulate removal from the dissolved load, accompanied by crustal Zr/Hf (32.5 ± 5.1) and supercrustal Nb/Ta (25.1 ± 7.7) ratios. Subcrustal Th/U (0.17-0.96) and supercrustal Mo/W (12.0-74.5) ratios in all ORB waters indicate preferential release and aqueous solubility of U>Th and Mo>W, with the latter attributed primarily to preferential W adsorption on soil or upstream aquatic (oxy)(hydr)oxide surfaces

Moderate levels of oxygenation during the late stage of Earth's Great Oxidation Event

FOO and RS acknowledge financial support from the University of Tübingen and the German Research Foundation (DFG Grant SCHO1071/11-1). FOO and MBA are thankful for support from the Natural Environment Research Council (NERC grant NE/V004824/1). The stable isotope facilities at IDYST were funded by the University of Lausanne. SK, YA and MIV-R acknowledge European Research Council (ERC) Starting Grant 636808 (O2RIGIN). AH and FOO acknowledge support from National Research Foundation of South Africa (NRF Grant 75892). SK also acknowledges the Ramon y Cajal contract (RYC2020-030014-I). Participation by AB was supported by Discovery and Accelerator Grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and ACS PF grant (624840ND2). EES acknowledges funding from a NERC Frontiers grant (NE/V010824/1). SWP acknowledges support from a Royal Society Wolfson Research Merit Award. MIV-R additionally acknowledges funding support from the German Research Foundation (DFG Grant VA 1568/1-1).The later stages of Earth's transition to a permanently oxygenated atmosphere during the Great Oxidation Event (GOE; ∼2.43–2.06 Ga) is commonly linked with the suggestion of an “oxygen overshoot” during the ∼2.22–2.06 Ga Lomagundi Event (LE), which represents Earth's most pronounced and longest-lived positive carbon isotope excursion. However, the magnitude and extent of atmosphere-ocean oxygenation and implications for the biosphere during this critical period in Earth's history remain poorly constrained. Here, we present nitrogen (N), selenium (Se), and carbon (C) isotope data, as well as bio-essential element concentrations, for Paleoproterozoic marine shales deposited during the LE. The data provide evidence for a highly productive and well-oxygenated photic zone, with both inner and outer-shelf marine environments characterized by nitrate- and Se oxyanion-replete conditions. However, the redoxcline subsequently encroached back onto the inner shelf during global-scale deoxygenation of the atmosphere-ocean system at the end of the LE, leading to locally enhanced water column denitrification and quantitative reduction of selenium oxyanions. We propose that nitrate-replete conditions associated with fully oxygenated continental shelf settings were a common feature during the LE, but nitrification was not sufficiently widespread for the aerobic nitrogen cycle to impact the isotopic composition of the global ocean N inventory. Placed in the context of Earth's broader oxygenation history, our findings indicate that O2 levels in the atmosphere-ocean system were likely much lower than modern concentrations. Early Paleoproterozoic biogeochemical cycles were thus far less advanced than after Neoproterozoic oxygenation.Publisher PDFPeer reviewe

Zinc enrichment and isotopic fractionation in a marine habitat of the c. 2.1 Ga Francevillian Group: A signature of zinc utilization by eukaryotes?

Constraining the timing of eukaryogenesis and the divergence of eukaryotic clades is a major challenge in evolutionary biology. Here, we present trace metal concentration and zinc isotope data for c. 2.1 billion-year-old Francevillian Group pyritized structures, previously described as putative remnants of the first colonial multicellular organisms, and their host black shales. Relative to the host rocks, pyritized structures are strongly enriched in zinc, cobalt and nickel, by at least one order of magnitude, with markedly lighter zinc isotope compositions. A metabolic demand for high concentrations of aqueous zinc, cobalt, and nickel combined with preferential uptake of lighter zinc isotopes may indicate metalloenzyme utilization by eukaryotes in marine habitats c. 2.1 billion years ago. Once confirmed, this would provide a critical calibration point for eukaryogenesis, suggesting that this major evolutionary innovation may have happened contemporaneously with elevated atmospheric oxygen levels during the latter part of the Great Oxidation Event, some 400 million years earlier than is currently widely accepted

Genetic analysis of hyperemesis gravidarum reveals association with intracellular calcium release channel (RYR2)

Hyperemesis Gravidarum (HG), severe nausea/vomiting in pregnancy (NVP), can cause poor maternal/fetal outcomes. Genetic predisposition suggests the genetic component is essential in discovering an etiology. We performed whole-exome sequencing of 5 families followed by analysis of variants in 584 cases/431 controls. Variants in RYR2 segregated with disease in 2 families. The novel variant L3277R was not found in any case/control. The rare variant, G1886S was more common in cases (p = 0.046) and extreme cases (p = 0.023). Replication of G1886S using Norwegian/Australian data was supportive. Common variants rs790899 and rs1891246 were significantly associated with HG and weight loss. Copy-number analysis revealed a deletion in a patient. RYR2 encodes an intracellular calcium release channel involved in vomiting, cyclic-vomiting syndrome, and is a thyroid hormone target gene. Additionally, RYR2 is a downstream drug target of Inderal, used to treat HG and CVS. Thus, herein we provide genetic evidence for a pathway and therapy for HG

Silicon and chromium stable isotopic systematics during basalt weathering and lateritisation: A comparison of variably weathered basalt profiles in the Deccan Traps, India

Global biomass production is fundamentally affected by the hydrological cycling of elements at the Earth's surface. Continental weathering processes are the major source for most bio-essential elements in marine environments and therefore affect primary productivity. In addition, critical zone biomass depends on energy and chemical exchange reactions in weathering profiles. The latter reservoirs are in turn influenced by different climatic conditions that control weathering and pore water parameters like pH and Eh, which regulate mineral break down rates and dictate the mobility and mass flux of elements. Two Deccan Traps basalt weathering profiles of contrasting age and alteration intensity provide a natural laboratory for investigating the effects of rock alteration on Si and Cr and their isotopic. systematics. The Quaternary Chhindwara profile has progressed to a moderate degree of alteration (saprolite), while the Paleogene Bidar example displays an extremely altered laterite. The Chhindwara saprolite profile shows a near uniform Cr and Si concentration and isotopic composition, whereas the Bidar laterite profile is characterised by an intense loss of Si, a large enrichment of Cr within the most altered uppermost levels, and a wide range of Cr stable isotope ratios (-0.85 to 0.36 parts per thousand delta Cr-53/52). A co-variation between Si and Cr isotopes, as well as their co-variation with iron content, provides empirical evidence that iron redistribution within the profile has a large effect on Cr mobility and Si isotopic fractionation. Therefore, it is concluded that iron oxides exert a primary control over the isotopic composition of both Cr and Si in pore waters of laterites. Since laterite formation is promoted by tropical climates, the results of this study provide new evidence to suggest that the hydrological Cr and Si fluxes originating from continental weathering have changed in accordance with large-scale, deep time climate variation and continental plate configuration. An increased flux of Si and greater magnitude of Cr mobility and isotopic fractionation are possibly amplified under CO2-rich, greenhouse episodes and/or when large landmasses were tectonically arranged at near equatorial latitudes