The suitability of the soils of the Netherlands for arable land and grassland

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Multi-collector Inductively Coupled Plasma Mass Spectrometry: New Developments and Basic Concepts for High-precision Measurements of Mass-dependent Isotope Signatures

Due to the development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) around 25 years ago, the isotopes of a large range of elements (masses from Li to U) are now analyzed with high enough precision and accuracy to resolve subtle natural variations. These so-called 'non-traditional stable isotope systems' opened many new research avenues and are applied at an increasing rate in research and industry projects and in a broad range of different disciplines, including archeology, biology, physics, cosmochemistry and geology. Here, we briefly summarize the most basic concepts of MC-ICP-MS, introduce new technical developments and address important points on how to acquire accurate high-precision isotope measurements of non-traditional stable isotopes

Hydrothermal circulation and oil migration at the root of the heterogeneous micro-structure of carbonaceous material in the 2.0 Ga Zaonega Formation, Onega Basin, Russia

Organic-rich rocks of the 2.0 Ga Zaonega Formation, Karelia, Russia, have been studied extensively to gain understanding of the global carbon cycle and reconstruction of paleo-environments, directly after the Great Oxidation Event (GOE). This formation has a complex history of alteration, involving pervasive hydrothermal circulation, hydrocarbon generation/migration, and mineral authigenesis. Several previous studies have focused on the description of these secondary effects, and the identification of primary geochemical signals in the carbonaceous phases. Migration and infiltration of organic-rich fluids appear to have had only limited effect on the primary carbon isotope record (δ13Corg). However, the structural variability of carbonaceous material (CM) appears to have been strongly affected, with a range of reported structures including carbon onion-shaped nanostructures and mineral-templated graphite films. Here we present a systematic Raman spectroscopy-based study of the structural variability of CM in a drill core representing the middle and upper strata of the Zaonega Formation. The Raman spectra of CM show a systematic difference in structural order between the bulk carbonaceous matrix (Matrix-CM) and the CM occurring near mineral contacts (Contact-CM), indicating that mineral templating was an important process affecting structural order in the formation. The templating effect was observed on the surface of a wide range of minerals. The difference in structural order between Matrix-CM and Contact-CM can be traced throughout the ca. 400 m stratigraphy. The structural order varied with the degree of alteration and hydrothermal circulation, from highly ordered structures directly above a large gabbro intrusion at the bottom of the stratigraphy to less ordered structures higher up in the sequence. This trend directly correlates with the δ18O trend of secondary calcite, and can be attributed to the decreasing influence and temperature regime of hydrothermal circulation upward in the stratigraphy. The results presented here suggest that organic-rich hydrothermal fluids can locally strongly enhance graphitization of carbonaceous materials, and cause sample-scale heterogeneities in the structural order of organic materials. This has implications for the interpretation of carbonaceous materials in other ancient rocks experiencing circulation of organic-rich hydrothermal fluids.publishedVersio

Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures

Variations in barium (Ba) stable isotope abundances measured in low and high temperature environments have recently received increasing attention. The actual processes controlling Ba isotope fractionation, however, remain mostly elusive. In this study, we present the first experimental approach to quantity the contribution of diffusion and adsorption on mass-dependent Ba isotope fractionation during transport of aqueous Ba²+ ions through a porous medium. Experiments have been carried out in which a BaCl₂ solution of known isotopic composition diffused through u-shaped glass tubes filled with silica hydrogel at 10 °C and 25 °C for up to 201 days. The diffused Ba was highly fractionated by up to -2.15 ‰ in δ¹³⁷⁄¹³⁴Ba, despite its high atomic mass. The time-dependent isotope fractionation can be successfully reproduced by a diffusive transport model accounting for mass-dependent differences in the effective diffusivities of the Ba isotope species (D₁₃₇Ba ⁄D₁₃₄Ba =(m₁₃₄⁄m₁₃₇ )β ). Values of β extracted from the transport model were in the range of 0.010 to 0.011. Independently conducted batch experiments revealed that adsorption of Ba onto the surface of silica hydrogel favoured the heavier Ba isotopes (α = 1.00015 ± 0.00008). The contribution of adsorption on the overall isotope fractionation in the diffusion experiments, however, was found to be small. Our results contribute to the understanding of Ba isotope fractionation processes, which is crucial for interpreting natural isotope variations and the assessment of Ba isotope ratios as geochemical proxies

Barium isotope (re-)equilibration in the barite-fluid system and its implications for marine barite archives

Variations in the Ba isotopic composition of seawater are largely driven by the extent of barite precipitation in the marine photic zone and replenishment of Ba by upwelling and/or continental inputs. Pelagic barites offer a robust tool for tracing sources and sinks of Ba in the (paleo)ocean as they record these isotopic variations. Knowledge of the Ba isotope fractionation between barite and ambient waters is therefore imperative. Here, the Ba isotope fractionation between barite and Ba2+ (aq) under equilibrium conditions has been estimated by the three-isotope method with a 135Ba-enriched reactive fluid. The estimated Ba isotope fractionation was Δ137/134BaBarite-Ba2+ = −0.07 ± 0.08‰. Textural observations of barite crystals recovered up to 756 days of reaction reveal smoothing of solid surfaces but also typical dissolution features such as development of pits and cracks. Thus, dissolution/re-precipitation is likely the mechanism controlling the observed isotope exchange that is facilitated by the further development of porosity in the crystals. Additionally, the isotope exchange in the experimental runs fits a second-order law yielding a surface normalized isotope exchange rate of ∼2.8 × 10−10 mol/m2/s. This exchange rate could theoretically result in complete isotope exchange between pelagic barite with a typical edge size of 1 μm and ambient seawater or pore fluid within years, altering the barite's Ba isotopic composition during settling towards the seafloor and/or after deposition in marine sediments. Although there is considerable uncertainty in extrapolating experimental results to natural conditions and longer time scales, the rapid rates of exchange observed experimentally over short timescales suggest that isotope exchange in pelagic barite should be considered during interpretation of the Ba isotope composition as a paleoarchive.</p

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