Exploring the Effects of Residence Time on the Utility of Stable Isotopes and S/C Ratios as Proxies for Ocean Connectivity

Various geochemical proxies have been developed to determine if ancient sedimentary strata were deposited in marine or nonmarine environments. A critical parameter for proxy reliability is the residence time of aqueous species in seawater, which is rarely considered for proxies relying on stable isotopes and elemental abundance ratios. Differences in residence time may affect our ability to track geologically short-lived alternations between marine and nonmarine conditions. To test this effect for sulfur and nitrogen isotopes and sulfur/carbon ratios, we investigated a stratigraphic section in the Miocene Oberpullendorf Basin in Austria. Here, previous work revealed typical seawater-like rare earth element and yttrium (REY) systematics transitioning to nonmarine-like systematics. This shift was interpreted as a brief transition from an open marine depositional setting to a restricted embayment with a reduced level of exchange with the open ocean and possibly freshwater influence. Our isotopic results show no discernible response in carbonate-associated sulfate sulfur isotopes and carbon/sulfur abundance ratios during the interval of marine restriction inferred from the REY data, but nitrogen isotopes show a decrease by several permil. This observation is consistent with the much longer residence time of sulfate in seawater compared with REY and nitrate. Hence, this case study illustrates that the residence time is a key factor for the utility of seawater proxies. In some cases, it may make geochemical parameters more sensitive to marine water influx than paleontological observations, as in the Oberpullendorf Basin. Particular care is warranted in deep time, when marine residence times likely differ markedly from the modern

The origin of rare alkali metals in geothermal fluids of southern Tibet, China: A silicon isotope perspective

Geothermal waters from the Semi, Dagejia and Kawu hot springs in the Shiquanhe-Yarlung Zangbo geothermal field of southern Tibet (China) are highly enriched in rare alkali metals (RAM). However, the enrichment mechanism is still hotly debated. Here, we report the first silicon isotope data of these geothermal waters to unravel the origin of the extreme RAM enrichments. Sinter precipitation in the spring vents and water-rock interaction in the deep reservoir controlled both the silicon budget and silicon isotope fractionation. The rates of water-rock interaction and sinter precipitation in three spring sites decrease in the sequences Semi > Kawu > Dagejia, and Dagejia > Kawu > Semi respectively. Silicon isotope fractionation during sinter precipitation (i.e. Δ30Siprecipitate-solution < -0.1‰) is less than that due to water-rock interaction (i.e. Δ30Sisolution-rocks at least as high as -0.47‰), which makes it possible to use the δ30Si signatures of springs to evaluate the intensity of water-rock interaction. Based on the available evidence, a conceptual model of RAM enrichment is proposed: (i) persistent magmatic activity in southern Tibet provided the initial enrichment of the RAM in host rocks and a heat sources for the deep reservoirs of geothermal systems; (ii) the high Cl- content and long residence time (thousands of years) promote the leaching of RAM from the silicate host rocks.National Key R&D Program of China [2017YFC0602405]; National Natural Science Foundation of China [41673001, 41872074, 41422302]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Impact of Aspergillus fumigatus in allergic airway diseases

For decades, fungi have been recognized as associated with asthma and other reactive airway diseases. In contrast to type I-mediated allergies caused by pollen, fungi cause a large number of allergic diseases such as allergic bronchopulmonary mycoses, rhinitis, allergic sinusitis and hypersensitivity pneumonitis. Amongst the fungi, Aspergillus fumigatus is the most prevalent cause of severe pulmonary allergic disease, including allergic bronchopulmonary aspergillosis (ABPA), known to be associated with chronic lung injury and deterioration in pulmonary function in people with chronic asthma and cystic fibrosis (CF). The goal of this review is to discuss new understandings of host-pathogen interactions in the genesis of allergic airway diseases caused by A. fumigatus. Host and pathogen related factors that participate in triggering the inflammatory cycle leading to pulmonary exacerbations in ABPA are discussed

Multielement-Analyse von Flach- und Tiefwasserkarbonaten des Ediakariums auf der Yangtze Platform, Südchina

The Ediacaran era (635 to 542 Ma) has seen some of the largest geochemical fluctuations and biological innovations in Earth history. The change from icehouse to greenhouse climate resulted in melting of low latitude Marinoan ice sheets and presumably triggered the radiation of early animals at the Precambrian/Cambrian boundary. Contemporaneous oxygenation of the Earth’s atmosphere and presumably the deeper oceanic realms further led to evolution of metazoans, predation and, as a result, extended bio-mineralisation. The Doushantuo Formation on the Yangtze Platform, South China, is an ideal archive of temporal and spatial geochemical changes in the late Neoproterozoic oceans, as it spans 90 % of the Ediacaran (635 ± 0.6 to 551 ± 0.7 Ma) and was deposited under shallow- to deep water marine environmental conditions. The major scope of this thesis is to understand the geochemical variations in Ediacaran marine carbonates and link them to environmental changes. Therefore carbonate rock leachates of the Doushantuo (and overlying Dengying) lithologies from the shallow water Xiaofenghe (Hubei Province) and deep water Yanwutan section (Hunan Province) have been sampled. These samples were investigated for their major- and trace element concentrations as well as for their 87Sr/86Sr, δ18Ocarb and δ13Ccarb isotopic compositions. Radiogenic Sr and stable C and O isotopes were used to distinguish between pristine marine precipitates and those whose isotopic compositions have been modified by post depositional fluid flow. Paleo-seawater conditions, such as oxygenation of the water body and seawater-freshwater mixing were inferred from shale normalised REE+Y patterns of pristine carbonates. Redox-sensitive elements were used to assess pore-water redox conditions in the sediments. Furthermore, the Nd isotopic composition of shallow water carbonates was analysed to deduce the provenance of the lanthanide source of the Yangtze Platform sediments. Finally this thesis aims to test whether Cd isotopes may be used to pinpoint the onset of bio-diversification and the appearance of early animals before the Cambrian explosion. Therefore Cd isotopes were analysed together with δ13Corg, δ15N, TOC and N concentrations in carbonates and mudstones from the extreme shallow water section Xiaofenghe, Hubei Province. This thesis provides deeper insight into carbonate diagenesis and focuses on the recognition of pristine, open marine seawater geochemical signatures from signatures modified by either mixing with freshwater or diagenetic overprint. Deep water carbonates at Yanwutan section show a distinct overprint by continental basin fluids, strongly modifying the isotope composition of the sediments. Despite this, marine REE+Y patterns are commonly still preserved in these lithologies. Shallow water carbonates at Xiaofenghe section reveal minor diagenetic overprint. However, the influence of terrestrial lanthanide input, presumably brought in by freshwater influx via estuarine mixing processes, strongly modified REE+Y patterns in the very shallow to lagoonal Xiaofenghe section. N and Cd isotopic compositions of mudstones and carbonates in the same stratigraphic units reveal distinct fluctuations that cannot be explained by biological fractionation alone. Hence, δ15N variations might be the result of isotope fractionation during diagenetic N-loss. The variation in ε112/110Cd may be caused by isotope fractionation during Cd incorporation in sulphides and likely modified by salinity-dependent fractionation during carbonate precipitation. The work suggests that the Cd isotope composition of Neoproterozoic carbonates, unlike modern marine precipitates, may not be used as proxy for biological Cd utilisation. It is likely that the modern enzyme responsible for the isotopically selective Cd utilisation in phytoplankton may not have been active in Precambrian organisms yet.Das Ediakarium (635 bis 542 Ma) war eine Periode gewaltiger geochemischer Umwälzungen und biologischer Innovationen. Der Wechsel von der marinoischen Eiszeit zum Treibhausklima ging einher mit massivem Abschmelzen der Eispanzer und mag durch den damit verbunden Eintrag von Nährstoffen von den Kontinenten mit als Auslöser für die folgende Evolution von Metazoen gedient haben. Des Weiteren trug die zeitgleiche Sauerstoffanreicherung der Atmosphäre und der tieferen Schichten der Ozeane zur Evolution der Mehrzeller, sowie der Entwicklung von Jagdverhalten und daraus resultierend zur Entwicklung von Biomineralisation als Abwehrmechanismus bei. Die Doushantuo Formation auf der Yangtse Plattform in Südchina gilt als perfekte Lokalität zur Erfoschung von zeitlichen wie auch räumlichen geochemischen Veränderungen im ediakarischen Ozean. Die Formation wurde auf 635 ± 0.6 bis 551 ± 0.7 Millionen Jahre vor heute datiert und umfasst damit etwa 90 % des gesamten Ediakariums, des Weiteren finden sich in ihr unterschiedliche Ablagerungsräume vom Flach- bis hin zum Tiefwaser vereint. Das Hauptanliegen dieser Arbeit besteht darin, die geochemischen Variationen in ediakarischen Karbonaten besser zu verstehen und durch diese auf die sich verändernden Umweltbedingungen im Ediakarium zurück zu schließen. Dafür wurden Karbonatauszüge von Doushantuo (und darüber anstehnden Dengying) Lithologien des Flachwasserprofils bei Xiaofenghe (Hubei Provinz) und des Tiefwasserprofils bei Yanwutan (Hunan Provinz) untersucht. Von den Proben wurden Haupt- und Spurenelementkonzentrationen sowie 87Sr/86Sr, δ18Ocarb und δ13Ccarb Isotopenzusammensetzungen bestimmt. Radiogene Sr- und stabile O- und C-isotopenverhältnisse wurden als Indikator zur Abgrenzung von diagenetisch überprägten zu pristinen Karbonatproben genutzt. Paleo- Meerwasserbedingungen, wie die Sauerstoffsättigung oder der Einfluss von Frischwasser, wurden mittels PAAS normalisierter Seltener Erden Muster bestimmt. Die Analyse redox-sensitiver Elemente diente schließlich dazu Porenwasser Redoxbedingungen zu erfassen. Nd-Isotopenverhältnisse in den Flachwasserkarbonaten wurden zur Bestimmung der Herkunft der Lanthanidenquelle in den Karbonaten analysiert. Abschließend wurde mit der Arbeit versucht Cd Isotope als Indikator für das Einsetzen verstärkter Biodiversität und dem Aufkommen der ersten Tierstämme im späten Ediakarium zu etablieren. Daher wurden neben Cd in Karbonaten auch N Isotopenverhältnisse in organikreichen Lithologien zusammen mit TOC und N Konzentrationen sowie δ13Corg Werten im Xiaofenghe Flachwasserprofil bestimmt. Die Arbeit gibt weitergehende Einblicke in die Karbonatdiagenese und versucht die Unterschiede zwischen pristinen und offenmarinen geochemischen Signaturen von überprägten Signaturen in Karbonatgesteinen (letztere durch Diagenese oder Mischung von Wassermassen) zu charakterisieren. Daraus resultierend, haben die Tiefwasserproben des Yanwutan Profils eine stärkere diagenetische Überprägung der Isotopensignaturen als die Flachwasserkarbonate erfahren. Diese Überprägung läst sich vermutlich auf die Reaktion der Karbonate mit kontinentalen Beckenfluiden zurückführen. Diese Überprägung hat jedoch im allgmeinen die marinen seltenen Erden Muster der Karbonate nicht verändert. Dahingegen zeigen die Flachwasserkarbonate von Xiaofenghe eine Veränderung der seltenen Erden Muster durch verstärkten Eintrag der Lanthaniden in Flussmündungsnähe. N und Cd Isotopenzusammensetzungen in organikreichen Tonsteinen und Karbonaten der gleichen stratigraphischen Einheit zeigen starke Veränderungen durch das Ediakarium. Diese lassen sich nicht allein auf biologische Isotopenfraktionierung zurückführen. δ15N Variationen könnten auch auf Isotopenfraktionierung bei diagenetischer Stickstoffabfuhr im Sediment zurückzuführen sein. Die Variationen in ε112/110Cd werden möglicherweise durch Isotopenfraktionierung bei einem selektiven Einbau von Cd in Sulphide unter euxinischen Bedingungen, sowie salinitätsabhängiger Fraktionierung in Karbonate gesteuert. Als Resultat der Arbeit wird daher angenommen, dass die Cd Isotopenzusammensetzung von neoproterozoischen Karbonaten nicht von biologischer Fraktionierung gesteuert wurde. Anders als bei modernen marinen Sedimenten war damit das Enzym, das für die Cd Isotopenfraktionierung beim Einbau des Cd in phytoplanktonische Organismen verantwortlich ist, im Präkambrium vermutlich noch nicht aktiv

Proterozoic to Phanerozoic case studies of laser ablation microanalysis for microbial carbonate U–Pb geochronology

Some of the earliest bio-sedimentary records of life on Earth are represented by microbial carbonates, which are also critical geochemical archives of ancient seawater chemistry and the environmental circumstances in which they precipitated. Reconstructing paleo-microbial environments on Earth and potentially other planets requires precise determination of the depositional ages of these materials. The (abiogenic) carbonate geochemistry communities can now use developments in in-situ laser ablation U-Pb dating using inductively coupled plasma mass spectrometry (LA-ICP-MS). Due to the effects of impurity mixing and diagenesis, microbial carbonates have received little geochronological study despite their broad relevance for understanding ancient seawater's environmental conditions and geochemical compositions. This study demonstrates using time-of-flight mass spectrometry (TOF-MS) to perform quick, quantitative elemental mapping before U-Pb spot dating to improve experiment success rates and data reliability and offers four practical application examples

Disentangling Combined Effects of Sediment Sorting, Provenance, and Chemical Weathering From a Pliocene‐Pleistocene Sedimentary Core (CSDP‐1) in the South Yellow Sea

Abstract The South Yellow Sea is an important sink for sediments delivered by the Yellow and Yangtze rivers in East Asia. We conducted a high‐resolution geochemical analysis on the bulk sediments retrieved from a marine drill core (CSDP‐1) using the method of X‐ray fluorescence (XRF). Our results show large geochemical variations along the core. As demonstrated by linear correlations along with the Al‐Si link in a compositional principal component analysis (PCA), the variations in elemental ratios among Al, K, Zr, Ba, and Si are primarily controlled by sediment sorting effects. A closer examination indicates a gradual shift of sediment provenance from the Yangtze to the Yellow River catchment in the core. With the help of a fuzzy c‐means cluster analysis on elemental ratios of Al/Si, Al/Ti, K/Si as well as the chemical index of alteration (CIA), the timing of a major provenance change in the core is narrowed down to 1.5–1.7 Ma. This timing corresponds to a major seismic and sedimentary boundary (T2) in the Yellow Sea Basin and coincides with the onset of fluvial terrace deposition and incision in the middle and upper reaches of the Yellow River. As a result, we argue that the major provenance change derived from geochemical variations in the Yellow Sea sedimentary basin can be linked with the integration of the modern Yellow River. The provenance change is likely caused by a coupling between regional tectonic deformation and the Asian summer monsoon enhancement in the early Pleistocene

Geochemical and Sr‐Nd‐Pb‐Fe Isotopic Constraints on the Formation of Fe‐Si Oxyhydroxide Deposits at the Ultraslow‐Spreading Southwest Indian Ridge

Abstract Modern Fe‐Si oxyhydroxide deposits occur in global marine hydrothermal vent sites. Despite their role as biogenic substrates and potential ore resources, much remains unknown about their formation processes. Here, we apply analyses of major and trace elements as well as Sr‐Nd‐Pb‐Fe isotopes combined with 238U‐230Th dating to Fe‐Si oxyhydroxides obtained from several hydrothermal fields along the Southwest Indian Ridge. These mineralized oxyhydroxides primarily consist of poorly crystalline two‐line ferrihydrite and amorphous opal‐A, with lesser amounts of nontronite and birnessite. The ubiquitous and characteristic Fe‐rich ultrastructures in the oxyhydroxides directly indicate microbial activity. The 238U‐230Th dating constrains their crystallization ages from ca. 11,873 to 384 years old. The seawater‐like 87Sr/86Sr and varying 143Nd/144Nd ratios underline a high proportion of seawater mixed with hydrothermal fluids. The radiogenic Pb isotopic patterns suggest a primary derivation of Pb leached from substrate basalts and to a lesser extent Pb from seawater. Stable iron isotopic compositions for different oxyhydroxides display a remarkable range between −1.47 and 0.82‰, which were interpreted as reflecting the fractionation processes during the formation of the deposits under evolving depositional redox conditions. The partial oxidation of Fe(II) and the subsurface removal of isotopically heavy Fe oxyhydroxides are suggested to play a vital role in shifting the Fe isotopic signature toward more negative values. Given that these Fe‐Si oxyhydroxide deposits exhibit features similar to certain ancient iron formations (IFs), Fe isotope systematics of these deposits may hold significant potential for fingerprinting the biological Fe oxidation processes that drove IF deposition on early Earth

Structural basis for triacylglyceride extraction from mycobacterial inner membrane by MFS transporter Rv1410

Mycobacterium tuberculosis is protected from antibiotic therapy by a multi-layered hydrophobic cell envelope. Major facilitator superfamily (MFS) transporter Rv1410 and the periplasmic lipoprotein LprG are involved in transport of triacylglycerides (TAGs) that seal the mycomembrane. Here, we report a 2.7 Å structure of a mycobacterial Rv1410 homologue, which adopts an outward-facing conformation and exhibits unusual transmembrane helix 11 and 12 extensions that protrude ~20 Å into the periplasm. A small, very hydrophobic cavity suitable for lipid transport is constricted by a functionally important ion-lock likely involved in proton coupling. Combining mutational analyses and MD simulations, we propose that TAGs are extracted from the core of the inner membrane into the central cavity via lateral clefts present in the inward-facing conformation. The functional role of the periplasmic helix extensions is to channel the extracted TAG into the lipid binding pocket of LprG

Geochemical evolution of the Rabaul volcanic complex, Papua New Guinea - Insights from HFSE, Sr-Nd-Hf, and Fe isotopes

The Rabaul volcanic complex, Papua New Guinea, is among the few calderas worldwide with ongoing volcanic activity. Its volcanic lithologies vary from mafic lavas from outer caldera cones to differentiated lavas within. In this study, representative lavas have been analysed for their major and trace element concentrations and radiogenic Sr-Nd-Hf isotope compositions to study the geochemical evolution of the magmatic system. Stable Fe isotopes and concentrations of high field strength elements (HFSE) complement the analyses as novel tools to assess the effect of high-temperature fractional crystallisation during ongoing differentiation. Major element systematics reveal a typical fractional crystallisation sequence of olivine, pyroxene, and plagioclase as the critical process controlling the magmatic evolution. A distinct increase of Zr/Hf from the basaltic (older) outer caldera lavas (similar to 39) to the dacitic (younger) inner caldera lavas (similar to 41-44) can be explained by fractionation of clinopyroxene and amphibole. Ratios of Nb/Ta tend to decrease with an increasing degree of differentiation, consistent with fractional crystallisation of amphibole but not clinopyroxene. Additional fractionation of Ti-magnetite and rather oxidising conditions are further supported by the Fe isotope compositions in the inner caldera lavas (delta Fe-57 from +0.03 to +0.22 parts per thousand, +/- 0.04 parts per thousand, 2 SD). The high Nb/Ta in more primitive outer caldera samples are coupled with increasing rare earth elements (REE) abundances, and slab melt-like subduction components can explain high Sr/Y and Gd-N/Yb-N in the magma sources. Complementary enrichments in fluid-mobile trace elements indicate that slab dehydration controlled the sub-arc enrichment of the inner caldera volcanism. Coupled Hf-Nd isotope compositions reveal the presence of the Indian-Australian mantle domain beneath Rabaul and a temporal trend towards sediment melt components overprinting inner caldera lavas. In conclusion, geochemical features show a temporal evolution controlled by (i) variable influence of partial slab melts vs slab fluids and (ii) a change in fractional crystallisation patterns from solely olivine and pyroxene-controlled to increasingly titano-magnetite and amphibole-controlled fractionation