Revisiting stepwise ocean oxygenation with authigenic barium enrichments in marine mudrocks

There are current debates around the extent of global ocean oxygenation, particularly from the late Neoproterozoic to the early Paleozoic, based on analyses of various geochemical indices. We present a temporal trend in excess barium (Ba_{excess}) contents in marine organic-rich mudrocks (ORMs) to provide an independent constraint on global ocean redox evolution. The absence of remarkable Ba_{excess} enrichments in Precambrian (>ca. 541 Ma) ORMs suggests limited authigenic Ba formation in oxygen- and sulfate-deficient oceans. By contrast, in the Paleozoic, particularly the early Cambrian, ORMs are marked by significant Ba_{excess} enrichments, corresponding to substantial increases in the marine sulfate reservoir and oxygenation level. Analogous to modern sediments, the Mesozoic and Cenozoic ORMs exhibit no prominent Ba_{excess} enrichments. We suggest that variations in Ba_{excess} concentrations of ORMs through time are linked to secular changes in the marine dissolved Ba reservoir associated with elevated marine sulfate levels and global ocean oxygenation. Further, unlike Mo, U, and Re abundances, significant Ba_{excess} enrichments in ORMs indicate that the overall ocean oxygenation level in the early Paleozoic was substantially lower than at present

Seawater carbon and strontium isotope variations through the late Ediacaran to late Cambrian in the Tarim Basin

The radiation of early animals during the Cambrian explosion was accompanied by widespread perturbations in oceanic and atmospheric conditions. However, the cause-effect relationships between evolutionary innovations, carbon (C) cycling, and continental weathering are still a matter of debate. Further paleoenvironmental reconstructions of poorly studied paleo-continents covering the Precambrian/Cambrian (PC/C) transition may improve the correlation of the events and their impact on the Earth system on a global scale. The Tarim Basin was presumably located proximal to the well-studied South China craton during the Ediacaran-Cambrian boundary and is expected to contribute equally to our paleoenvironmental reconstructions. Here we apply carbon and strontium (Sr) isotope records (δ13C and 87Sr/86Sr) obtained from well-preserved marine carbonates spanning the late Ediacaran to the late Cambrian from the Keping region in the northwestern Tarim Basin, NW China. By comparison to other carbonate successions from various paleo-continents, our obtained seawater 87Sr/86Sr curve in this study shows a stepwise first-order increase to more radiogenic values superimposed by second-order presumably regional variations. Our obtained δ13C variations exhibit four prominent negative and three positive excursions identical to the global δ13C record. Based on existing paleontological evidence and our new Tarim δ13C and 87Sr/86Sr curves, we propose a stratigraphic correlation from the late Ediacaran to the late Cambrian between the Tarim Basin and other paleo-continents. Besides, our paleoenvironmental reconstruction reveals both regional and global sea-level changes that may have controlled the influx of radiogenic Sr and presumably the influx of nutrients controlling primary production and the rate of organic carbon burial in the Tarim Basin at the time of deposition. These feedbacks may have ultimately influenced the rapid diversification of metazoans and the oxygenation of the Cambrian ocean and atmosphere approaching-present pO2 levels

Characterisation of Innate Fungal Recognition in the Lung

The innate recognition of fungi by leukocytes is mediated by pattern recognition receptors (PRR), such as Dectin-1, and is thought to occur at the cell surface triggering intracellular signalling cascades which lead to the induction of protective host responses. In the lung, this recognition is aided by surfactant which also serves to maintain the balance between inflammation and pulmonary function, although the underlying mechanisms are unknown. Here we have explored pulmonary innate recognition of a variety of fungal particles, including zymosan, Candida albicans and Aspergillus fumigatus, and demonstrate that opsonisation with surfactant components can limit inflammation by reducing host-cell fungal interactions. However, we found that this opsonisation does not contribute directly to innate fungal recognition and that this process is mediated through non-opsonic PRRs, including Dectin-1. Moreover, we found that pulmonary inflammatory responses to resting Aspergillus conidia were initiated by these PRRs in acidified phagolysosomes, following the uptake of fungal particles by leukocytes. Our data therefore provides crucial new insights into the mechanisms by which surfactant can maintain pulmonary function in the face of microbial challenge, and defines the phagolysosome as a novel intracellular compartment involved in the innate sensing of extracellular pathogens in the lung

Dectin-1: a role in antifungal defense and consequences of genetic polymorphisms in humans

The clinical relevance of fungal infections has increased dramatically in recent decades as a consequence of the rise of immunocompromised populations, and efforts to understand the underlying mechanisms of protective immunity have attracted renewed interest. Here we review Dectin-1, a pattern recognition receptor involved in antifungal immunity, and discuss recent discoveries of polymorphisms in the gene encoding this receptor which result in human disease

Widespread clay authigenesis and highly congruent silicate weathering in the Marinoan aftermath

The termination of the Cryogenian period marks a transition from an extreme ice- to a greenhouse climate, likely initiated by increased atmospheric CO2, however uncertainties persist on continental weathering regarding this climate transition. Here we present paired lithium isotope data from carbonate (δ7Licarb) and carbonate-hosted silicate (δ7Lisili) components of the Marinoan cap carbonates to constrain C and Si cycles in the deglacial period. We find that the silicate component of cap carbonates is dominated by marine authigenic clays with minor contributions from terrestrially detrital materials and oxides. Built from δ7Lisili data, large variations of seawater δ7Li suggest a heterogeneous marine Li reservoir due to a stratified ocean in the deglacial period. Overall, widespread clay authigenesis and low seawater δ7Li values indicate active carbon-silicon cycling and congruent silicate weathering due to warm climate and exposure of fresh rock surface in the Marinoan aftermath, which promotes the deposition of cap carbonates and stabilization of Earth's surface environment

Thermal reactions in mixtures of micron-sized silicon monoxide and titanium monoxide: redox paths overcoming passivation shells

Směsné oxidy a kompozity oxidu TiO2/SiO2 byly intenzivně studovány, zatímco kekich protějšky oxidu titanatého (TiO) a oxidu křemnatého (SiO) stále zůstávají neprozkoumány. Tato studie odhaluje strukturální změny ve zahřátých směsích SiO-TiO. Změny složení ve smísených mikro-částicích TiO a SiO zahřívaných při 1000 ° C byly zkoumány pomocí FTIR, UV-Vis a Ramanovy spektroskopie, rentgenové difrakce a elektronové mikroskopie (SEM a TEM). Ukazuje se, že dochází k úbytku krystalického TiO a tvorbě suboxidů titanu (Ti2.5O3, Ti2O3), rutilu, elementárního křemíku, silicidu titanu Ti5Si3 a amorfních binárních SiOx, TiOx a ternárních nanostruktur SixTiyOz. Tvorba tohoto Si/Ti/O kompozitu je vysvětlena disproprciací SiO, redukcí TiO křemíkem, přenosem kyslíku (redoxní reakce) mezi TiOx a SiOx a kombinací Ti a Si k získání silicidu titanu. Vytvořený Si/Ti/O kompozit absorbuje viditelné světlo a jeho fotokatalytická aktivita ve slunečním záření byla testována na odbarvování methylenové modři (bBlue) a porovnávána s práškem nezahřátého SiO, TiO a Ti5Si3.Silica–titania mixed oxides and composites have been extensively studied, whereas the titanium monoxide (TiO)–silicon monoxide (SiO) counterparts still remain to be explored. Here, we report on structural changes in heated SiO–TiO mixtures. The changes in composition in intimately mixed μm-sized particles of TiO and SiO heated at 1000 °C were examined by FTIR, UV–Vis and Raman spectroscopy, X-ray diffraction and electron (SEM and TEM) microscopy. They are shown to involve depletion of crystalline TiO and formation of titanium suboxides (Ti2.5O3, Ti2O3), rutile, elemental silicon, titanium silicide Ti5Si3 and amorphous binary SiOx, TiOx and ternary SixTiyOz nano-structures. These constituents of the developed Si/Ti/O composite are explained by SiO disproportionation, reduction of TiO by silicon, oxygen transfer (redox) reactions between TiOx and SiOx species and the combination of Ti and Si to obtain titanium silicide. The produced Si/Ti/O composite absorbs visible light and its solar-light photocatalytic activity in decolorization of methylene bBlue is compared to that of the unheated SiO, TiO and Ti5Si3 powders