The distribution of sulfur isotopes in geological materials reveals information about Earth history and biogeochemical processes. Research during the last several decades has used sulfur isotope ...geochemistry as a tool to better understand microbial processes (
Harrison and Thode, 1958; Kaplan, 1975; Monster et al., 1979; Peck, 1959, 1962; Rees, 1973) and sediment diagenesis (
Berner, 1969, 1982; Canfield et al., 1993b). Earth historians also realized this potential, as there exists a rich record of environmental change within the sedimentary records (
Canfield and Teske, 1996; Claypool et al., 1980; Goodwin et al., 1976; Habicht et al., 2002; Kah et al., 2004; Monster et al., 1979; Shen et al., 2001; Strauss, 1993; Thode and Goodwin, 1983). These applications have championed the use of the two most abundant sulfur isotopes
32S and
34S, and provide a rich introduction to what the sulfur isotope record has to offer see (
Canfield, 2004; Canfield and Raiswell, 1999). Within the last decade, this information has been supplemented by new data derived from the less abundant isotopes
33S and
36S. The measurement of all four stable sulfur isotopes – multiple sulfur isotope geochemistry – has expanded our understanding of biological evolution and activity, atmospheric chemistry and transport, crustal recycling, and many more fields related to Earth surface processes see (
Farquhar and Wing, 2003). Here, I present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and Earth surface evolution.
We present a framework for interpreting the carbon isotopic composition of sedimentary rocks, which in turn requires a fundamental reinterpretation of the carbon cycle and redox budgets over Earth's ...history. We propose that authigenic carbonate, produced in sediment pore fluids during early diagenesis, has played a major role in the carbon cycle in the past. This sink constitutes a minor component of the carbon isotope mass balance under the modern, high levels of atmospheric oxygen but was much larger in times of low atmospheric O 2 or widespread marine anoxia. Waxing and waning of a global authigenic carbonate sink helps to explain extreme carbon isotope variations in the Proterozoic, Paleozoic, and Triassic.
Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate fluctuations, a potential rise in atmospheric oxygen or re-organization of the seafloor redox ...landscape, and the initial diversification of animals. It is widely assumed that the inferred redox change facilitated the observed trends in biodiversity. Establishing this palaeoenvironmental context, however, requires that changes in marine redox structure be tracked by means of geochemical proxies and translated into estimates of atmospheric oxygen. Iron-based proxies are among the most effective tools for tracking the redox chemistry of ancient oceans. These proxies are inherently local, but have global implications when analysed collectively and statistically. Here we analyse about 4,700 iron-speciation measurements from shales 2,300 to 360 million years old. Our statistical analyses suggest that subsurface water masses in mid-Proterozoic oceans were predominantly anoxic and ferruginous (depleted in dissolved oxygen and iron-bearing), but with a tendency towards euxinia (sulfide-bearing) that is not observed in the Neoproterozoic era. Analyses further indicate that early animals did not experience appreciable benthic sulfide stress. Finally, unlike proxies based on redox-sensitive trace-metal abundances, iron geochemical data do not show a statistically significant change in oxygen content through the Ediacaran and Cambrian periods, sharply constraining the magnitude of the end-Proterozoic oxygen increase. Indeed, this re-analysis of trace-metal data is consistent with oxygenation continuing well into the Palaeozoic era. Therefore, if changing redox conditions facilitated animal diversification, it did so through a limited rise in oxygen past critical functional and ecological thresholds, as is seen in modern oxygen minimum zone benthic animal communities.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Ediacaran reorganization of the marine phosphorus cycle Laakso, Thomas A.; Sperling, Erik A.; Johnston, David T. ...
Proceedings of the National Academy of Sciences - PNAS,
06/2020, Letnik:
117, Številka:
22
Journal Article
Recenzirano
Odprti dostop
The Ediacaran Period (635 to 541 Ma) marks the global transition to a more productive biosphere, evidenced by increased availability of food and oxidants, the appearance of macroscopic animals, ...significant populations of eukaryotic phytoplankton, and the onset of massive phosphorite deposition. We propose this entire suite of changes results from an increase in the size of the deep-water marine phosphorus reservoir, associated with rising sulfate concentrations and increased remineralization of organic P by sulfate-reducing bacteria. Simple mass balance calculations, constrained by modern anoxic basins, suggest that deep-water phosphate concentrations may have increased by an order of magnitude without any increase in the rate of P input from the continents. Strikingly, despite a major shift in phosphorite deposition, a new compilation of the phosphorus content of Neoproterozoic and early Paleozoic shows little secular change in median values, supporting the view that changes in remineralization and not erosional P fluxes were the principal drivers of observed shifts in phosphorite accumulation. The trigger for these changes may have been transient Neoproterozoic weathering events whose biogeochemical consequences were sustained by a set of positive feedbacks, mediated by the oxygen and sulfur cycles, that led to permanent state change in biogeochemical cycling, primary production, and biological diversity by the end of the Ediacaran Period.
The rise of atmospheric oxygen fundamentally changed the chemistry of surficial environments and the nature of Earth's habitability
. Early atmospheric oxygenation occurred over a protracted period ...of extreme climatic instability marked by multiple global glaciations
, with the initial rise of oxygen concentration to above 10
of the present atmospheric level constrained to about 2.43 billion years ago
. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago
, which represents the estimated timing of irreversible oxygenation of the atmosphere
. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron-sulfur-carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10
of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.
Microbial sulfate reduction has governed Earth's biogeochemical sulfur cycle for at least 2.5 billion years. However, the enzymatic mechanisms behind this pathway are incompletely understood, ...particulary for the reduction of sulfite—a key intermediate in the pathway. This critical reaction is performed by DsrAB, a widespread enzyme also involved in other dissimilatory sulfur metabolisms. Using in vitro assays with an archaeal DsrAB, supported with genetic experiments in a bacterial system, we show that the product of sulfite reduction by DsrAB is a protein-based trisulfide, in which a sulfite-derived sulfur is bridging two conserved cysteines of DsrC. Physiological studies also reveal that sulfate reduction rates are determined by cellular levels of DsrC. Dissimilatory sulfate reduction couples the four-electron reduction of the DsrC trisulfide to energy conservation.
A central tenant in microbial biogeochemistry is that microbial metabolisms follow a predictable sequence of terminal electron acceptors based on the energetic yield for the reaction. It is thereby ...oftentimes assumed that microbial respiration of ferric iron outcompetes sulfate in all but high-sulfate systems, and thus sulfide has little influence on freshwater or terrestrial iron cycling. Observations of sulfate reduction in low-sulfate environments have been attributed to the presumed presence of highly crystalline iron oxides allowing sulfate reduction to be more energetically favored. Here we identified the iron-reducing processes under low-sulfate conditions within columns containing freshwater sediments amended with structurally diverse iron oxides and fermentation products that fuel anaerobic respiration. We show that despite low sulfate concentrations and regardless of iron oxide substrate (ferrihydrite, Al-ferrihydrite, goethite, hematite), sulfidization was a dominant pathway in iron reduction. This process was mediated by (re)cycling of sulfur upon reaction of sulfide and iron oxides to support continued sulfur-based respiration--a cryptic sulfur cycle involving generation and consumption of sulfur intermediates. Although canonical iron respiration was not observed in the sediments amended with the more crystalline iron oxides, iron respiration did become dominant in the presence of ferrihydrite once sulfate was consumed. Thus, despite more favorable energetics, ferrihydrite reduction did not precede sulfate reduction and instead an inverse redox zonation was observed. These findings indicate that sulfur (re)cycling is a dominant force in iron cycling even in low-sulfate systems and in a manner difficult to predict using the classical thermodynamic ladder.
Highest reported efficiency cesium lead halide perovskite solar cells are realized by tuning the bandgap and stabilizing the black perovskite phase at lower temperatures. CsPbI2Br is employed in a ...planar architecture device resulting in 9.8% power conversion efficiency and over 5% stabilized power output. Offering substantially enhanced thermal stability over their organic based counterparts, these results show that all‐inorganic perovskites can represent a promising next step for photovoltaic materials.
Calibrating the Cryogenian Macdonald, Francis A; Schmitz, Mark D; Crowley, James L ...
Science (American Association for the Advancement of Science),
03/2010, Letnik:
327, Številka:
5970
Journal Article
Recenzirano
The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of ...these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation. A volcanic tuff interbedded with Sturtian glacial deposits, dated at 716.5 million years ago, is synchronous with the age of the Franklin large igneous province and paleomagnetic poles that pin Laurentia to an equatorial position. Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent.
Perovskite-based photovoltaics have, in recent years, become poised to revolutionise the solar industry. While there have been many approaches taken to the deposition of this material, one-step ...spin-coating remains the simplest and most widely used method in research laboratories. Although spin-coating is not recognised as the ideal manufacturing methodology, it represents a starting point from which more scalable deposition methods, such as slot-dye coating or ink-jet printing can be developed. Here, we introduce a new, low-boiling point, low viscosity solvent system that enables rapid, room temperature crystallisation of methylammonium lead triiodide perovskite films, without the use of strongly coordinating aprotic solvents. Through the use of this solvent, we produce dense, pinhole free films with uniform coverage, high specularity, and enhanced optoelectronic properties. We fabricate devices and achieve stabilised power conversion efficiencies of over 18% for films which have been annealed at 100 °C, and over 17% for films which have been dried under vacuum and have undergone no thermal processing. This deposition technique allows uniform coating on substrate areas of up to 125 cm 2 , showing tremendous promise for the fabrication of large area, high efficiency, solution processed devices, and represents a critical step towards industrial upscaling and large area printing of perovskite solar cells.
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