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Tracing Bioavailability of ZnO Nanoparticles Using Stable Isotope Labeling
No full textZinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their environmental fate is a priority for ecological protection. Here we synthesized model ZnO NPs that were made from and thus labeled with the stable isotope Zn-68 and this enables highly sensitive and selective detection of labeled components against high natural Zn background levels. We combine high precision stable isotope measurements and novel bioimaging techniques to characterize parallel water borne exposures of the common mudshrimp Corophium volutator to (ZnO)-Zn-68 NPs, bulk (ZnO)-Zn-68, and soluble (ZnCl2)-Zn-68 in the presence of sediment. C. volutator is an important component of coastal ecosystems where river-borne NPs will accumulate and is used on a routine basis for toxicity assessments Our results demonstrate that ionic Zn from ZnO NPs is bioavailable to C volutator and that Zn uptake is active. Bioavailability appears to be governed primarily by the dissolved Zn content of the water, whereby Zn uptake occurs via the aqueous phase and/or the ingestion of sediment particles with adsorbed Zn from dissolution of ZnO particles. The high sorption capacity of sediments for Zn thus enhances the potential for trophic transfer of Zn derived from readily soluble ZnO NPs. The uncertainties of our isotopic data are too large, however, to conclusively rule out any additional direct uptake route of ZnO NPs by C. volutator
Boron isotopic signatures of melt inclusions from North Iceland reveal recycled material in the Icelandic mantle source
Get PDFTrace element and volatile heterogeneity in the Earth’s mantle is influenced by the recycling of oceanic lithosphere through subduction. Oceanic island basalts commonly have high concentrations of volatiles compared to mid-ocean ridge basalts, but the extent to which this enrichment is linked to recycled mantle domains remains unclear. Boron is an ideal tracer of recycled subducted material, since only a small percentage of a recycled component is required to modify the bulk δ11B of the source mantle. Boron isotopic compositions of primary melts thus have potential to trace the fate of recycled subducted material in the deep mantle, and to constrain the lengthscales of lithologic and compositional heterogeneities in diverse tectonic settings.
We present new measurements of volatiles, light elements and boron isotopic ratios in basaltic glasses and melt inclusions that sample the mantle at two endmember spatial scales. Submarine glasses from the Reykjanes Ridge sample long-wavelength mantle heterogeneity on the broad scale of the Iceland plume. Crystal-hosted melt inclusions from the Askja and Bárarbunga volcanic systems in North Iceland sample short-wavelength mantle heterogeneity close to the plume centre. The Reykjanes Ridge glasses record only very weak along-ridge enrichment in B content approaching Iceland, and there is no systematic variability in δ11B along the entire ridge segment. These observations constrain ambient Reykjanes Ridge mantle to have a δ11B of -6.1% (2SD=1.5%, 2SE=0.3%). The North Iceland melt inclusions have widely variable δ11B between -20.7 and +0.6%. We screen melt inclusions against influence from crustal contamination, identifying high [B] and low δ18O as fingerprints of assimilation processes. Only the most primitive melt inclusions with MgO⩾8 wt.% reliably record mantle-derived δ11B. In North Iceland, incompatible trace element (ITE)-depleted primitive melt inclusions from Holuhraun record a δ11B of -10.6%, a signal that has also been seen in melt inclusions from southwest Iceland. In contrast, primitive ITE-enriched melt inclusions from nearby Askja volcano record a δ11B of -5.7%, overlapping with our new constraint on the δ11B of Reykjanes Ridge mantle. Coupled [B], δ11B and δ18O signatures of more evolved melt inclusions from North Iceland are consistent with primary melts assimilating <5-20% of hydrothermally altered basaltic hyaloclastite as they ascend through the upper crust.
Our data reveal the presence of a depleted, low-δ11B and an enriched, higher-δ11B mantle component, both intrinsic to the Icelandic mantle source and distinct from Reykjanes Ridge mantle. Non-modal melting calculations suggest that the enriched and depleted mantle components both contain ∼0.085 μg/g B, slightly lower than the 0.10-0.11 μg/g calculated for Reykjanes Ridge mantle. These data are consistent with the Icelandic mantle containing B-depleted dehydrated recycled oceanic lithosphere, in keeping with the low B/Pr of Icelandic melt inclusions in comparison to Reykjanes Ridge glasses or MORB. Our new data provide strong support for the role of recycled subducted lithosphere in melt generation at ocean islands, and highlight the need for careful screening of melt inclusion compositions in order to study global volatile recycling in ocean island basalts
Laser writing of electronic circuitry in thin film molybdenum disulfide: A transformative manufacturing approach
Get PDFElectronic circuits, the backbone of modern electronic devices, require precise integration of conducting, insulating, and semiconducting materials in two- and three-dimensional space to control the flow of electric current. Alternative strategies to pattern these materials outside of a cleanroom environment, such as additive manufacturing, have enabled rapid prototyping and eliminated design constraints imposed by traditional fabrication. In this work, a transformative manufacturing approach using laser processing is implemented to directly realize conducting, insulating, and semiconducting phases within an amorphous molybdenum disulfide thin film precursor. This is achieved by varying the incident visible (514 nm) laser intensity and raster-scanning the thin film a-MoS2 sample (900 nm thick) at different speeds for micro-scale control of the crystallization and reaction kinetics. The overall result is the transformation of select regions of the a-MoS2 film into MoO2, MoO3, and 2H-MoS2 phases, exhibiting conducting, insulating, and semiconducting properties, respectively. A mechanism for this precursor transformation based on crystallization and oxidation is developed using a thermal model paired with a description of the reaction kinetics. Finally, by engineering the architecture of the three crystalline phases, electrical devices such as a resistor, capacitor, and chemical sensor were laser-written directly within the precursor film, representing an entirely transformative manufacturing approach for the fabrication of electronic circuitry
Hydrogen Pentagraphenelike Structure Stabilized by Hafnium: A High-Temperature Conventional Superconductor
Get PDFThe recent discovery of H3S and LaH10 superconductors with record high superconducting transition temperatures Tc at high pressure has fueled the search for room-temperature superconductivity in the compressed superhydrides. Here we introduce a new class of high Tc hydrides with a novel structure and unusual properties. We predict the existence of an unprecedented hexagonal HfH10, with remarkably high value of Tc (around 213–234 K) at 250 GPa. As concerns the novel structure, the H ions in HfH10 are arranged in clusters to form a planar “pentagraphenelike” sublattice. The layered arrangement of these planar units is entirely different from the covalent sixfold cubic structure in H3S
and clathratelike structure in LaH10. The Hf atom acts as a precompressor and electron donor to the hydrogen sublattice. This pentagraphenelike H10 structure is also found in ZrH10, ScH10, and uH10 at high pressure, each material showing a high Tc ranging from 134 to 220 K. Our study of dense superhydrides with pentagraphenelike layered structures opens the door to the exploration of a new class of high Tc superconductors
Characterisation of immiscibility in calcium borosilicates used for the immobilisation of Mo 6+ under Au‐irradiation
Get PDFThe aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO3] and [B2O3] were synthesised and exposed to Au‐irradiation to examine compositional effects on the glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α‐decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO2−B2O3 and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy and diffraction. These glasses were then bombarded with 7 MeV Au3+ ions to a dose of 3×1014 ions/cm2 creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution and size of secondary phases were observed, indicative of significant structural reorganisation and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO3] < 2.5mol%, while segregation to form smaller more evenly distributed particles was seen for [B2O3] ≤ 15mol% and [MoO3] ≥ 2.5mol%. These microscopic changes were concurrent to surface‐bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B2O3] with a barrier identified at ~20mol%, as well as cross phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO4)2‐ units. Au‐irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO3] and [B2O3]/[SiO2], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses
Fine structures of acoustic emission spectra: How to separate dislocation movements and entanglements in 316L stainless steel
No full textIntermittent avalanches in a multitude of materials are characterized by acoustic emission, AE, where local events lead to strain relaxations and generate shock waves (so-called “jerks”), which are measured at the sample surface. The bane of this approach is that several avalanche mechanisms may contribute to the same AE spectrum so that a detailed analysis of each individual contribution becomes virtually impossible. It is, hence, essential to develop tools to separate signals from different dynamical processes, such as ferroic domain switching, collapse of porous inclusions, dislocation movements, entanglements, and so on. Particularly, difficult cases are dynamical microstructures in fcc alloys where the AE signal strength is weak. Nevertheless, using profile analysis of AE signals, we can distinguish between two mechanisms, namely, dislocation movements and dynamic entanglements in fcc 316L stainless steel. In this approach, we are able to measure the statistical AE durations of both subsets separately. The fingerprint for superposed avalanches with different durations is seen by the scaling between the energy E and the maximum amplitude A of each avalanche E ∼ Ax with x = 2. While the same exponent x applies for both mechanisms, the scaling relation shows two branches with different absolute energy values. The two mechanisms are then confirmed by separating the energy distributions P(E) ∼ E−ε for the two mechanisms with ε = 1.55 for dislocation movements and ε = 1.36 for entanglements
New insights from multi-proxy data from the West Antarctic continental rise: Implications for dating and interpreting Late Quaternary palaeoenvironmental records
Get PDFThe Antarctic Peninsula’s Pacific margin is one of the best studied sectors of the Antarctic continental margin. Since the 1990s, several research cruises have targeted the continental rise with geophysical surveys, conventional coring and deep-sea drilling. The previous studies highlighted the potential of large sediment drifts on the rise as high-resolution palaeoenvironmental archives. However, these studies also suffered from chronological difficulties arising from the lack of calcareous microfossils, with initial results from geomagnetic relative palaeointensity (RPI) dating promising a possible solution.
This paper presents data from new sediment cores recovered on cruise JR298 from seven continental rise sites west of the Antarctic Peninsula and in the Bellingshausen Sea with the objectives to (i) seek calcareous foraminifera, especially at shallow drift sites, to constrain RPI-based age models, and (ii) investigate the depositional history at these locations. We present the results of chronological and multi-proxy analyses on these cores and two cores previously collected from the study area. We establish new age models for the JR298 records and compare them with published RPI-based age models. In addition, we evaluate the reliability of different palaeoproductivity proxies and infer depositional processes.
Planktic foraminifera are present in various core intervals. Although their stable oxygen isotope (δ18O) ratios, tephrochronological constraints and glacial-interglacial changes in sediment composition provide age models largely consistent with the RPI chronologies, we also observe distinct differences, predominantly in the Bellingshausen Sea cores. Enrichments of solid-phase manganese together with evidence for “burn-down” of organic carbon in late glacial and peak interglacial sediments document non-steady-state diagenesis that may have altered magnetic mineralogy and, thus, RPI proxies. This process may explain discrepancies between RPI-based age models and those derived from δ18O data combined with tephrochronology. The data also indicate that organic carbon is a much less reliable productivity proxy than biogenic barium or organically-associated bromine in the investigated sediments.
In agreement with previous studies, sediment facies indicate a strong control of deposition on the rise by bottom currents that interacted with detritus supplied by meltwater plumes, gravitational down-slope transport processes and pelagic settling of iceberg-rafted debris (IRD) and planktic microfossils. Bottom-current velocities underwent only minor changes over glacial-interglacial cycles at the drift crests, with down-slope deposition only rarely affecting these shallow locations. Maximum concentrations of coarse IRD at the seafloor surfaces of the shallow sites result predominantly from upward pumping caused by extensive bioturbation. This process has to be taken into account when past changes in IRD deposition are inferred from quantifying clasts >1 mm in size
Antarctic Ice Sheet elevation impacts on water isotope records during the Last Interglacial
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The Last Interglacial period (LIG, 116,000 to 130,000 years ago) was globally ∼ 0.8 °C warmer than today at its peak, with substantially more warming at the poles. It is a valuable analogue for future global temperature rise, especially for understanding rates and sources of polar ice melt and subsequent global sea level rise. Records of water stable isotopes from Antarctic ice cores have been crucial for understanding past polar temperature during the LIG. However we currently lack a framework for estimating how changes in the ice sheet elevation, alongside sea‐ice feedbacks, affect these water stable isotopes. To address this, we examine the effect of the Antarctic Ice Sheet (AIS) elevation on water stable isotopes, using an ensemble of climate simulations where we vary the AIS elevation. We observe that (i) water stable isotope values lower with increasing AIS elevation following linear relationships, (ii) the effect of sea‐ice induced by AIS elevation is small so the effect of AIS elevation can be isolated. Finally, this study provides appropriate elevation‐water stable isotope gradients for the reconstruction of the AIS topography using ice cores.
Abstract
Changes of the topography of the Antarctic ice sheet (AIS) can complicate the interpretation of ice core water stable isotope measurements in terms of temperature. Here, we use a set of idealised AIS elevation change scenarios to investigate this for the warm Last Interglacial (LIG). We show that LIG δ 18 O against elevation relationships are not uniform across Antarctica, and that the LIG response to elevation is lower than the preindustrial response. The effect of LIG elevation‐induced sea ice changes on δ 18 O is small, allowing us to isolate the effect of elevation change alone. Our results help to define the effect of AIS changes on the LIG δ 18 O signals, and should be invaluable to those seeking to use AIS ice core measurements for these purposes. Especially, our simulations strengthen the conclusion that ice core measurements from the Talos Dome core exclude the loss of the Wilkes Basin at around 128 ky
Land-ocean changes on orbital and millennial time scales and the penultimate glaciation
No full textPast glacials can be thought of as natural experiments in which variations in boundary conditions influenced the character of climate change. However, beyond the last glacial, an integrated view of orbital- and millennial-scale changes and their relation to the record of glaciation has been lacking. Here, we present a detailed record of variations in the land-ocean system from the Portuguese margin during the penultimate glacial and place it within the framework of ice-volume changes, with particular reference to European ice-sheet dynamics. The interaction of orbital- and millennial-scale variability divides the glacial into an early part with warmer and wetter overall conditions and prominent climate oscillations, a transitional mid-part, and a late part with more subdued changes as the system entered a maximum glacial state. The most extreme event occurred in the mid-part and was associated with melting of the extensive European ice sheet and maximum discharge from the Fleuve Manche river. This led to disruption of the meridional overturning circulation, but not a major activation of the bipolar seesaw. In addition to stadial duration, magnitude of freshwater forcing, and background climate, the evidence also points to the influence of the location of freshwater discharges on the extent of interhemispheric heat transport
Cenozoic Epeirogeny of Arabian Peninsula from Drainage Modeling
No full textIt is generally accepted that the Arabian Peninsula has been uplifted by subcrustal processes. Positive residual depth anomalies from oceanic crust in the Red Sea and in the Gulf of Aden suggest that a region surrounding this peninsula is dynamically supported. Admittance calculations, surface wave tomography studies, and receiver function analyses all imply that regional topography is generated and maintained by some combination of mantle convective circulation and lithospheric thickness changes. Despite these significant advances, the spatial and temporal uplift rate history of the Arabian Peninsula is not well known. Here we show that a regional uplift rate history can be obtained by jointly inverting 225 longitudinal river profiles that drain this peninsula. Our strategy assumes that shapes of individual river profiles are controlled by uplift rate history and moderated by erosional processes. We used local measurements of incision rate to calibrate the relevant erosional parameters. In our inverse algorithm, uplift rate is permitted to vary smoothly as a function of space and time but upstream drainage area remains invariant. We also assume that knickzone migration is not lithologically controlled. Implications of these important assumptions have been investigated. Our results suggest that the Arabian Peninsula underwent two phases of asymmetric uplift during the last 20–30 Ma at rates of 0.05–0.1 mm a−1. The southwestern flank of the peninsula has been uplifted by 1.5–2.5 km. Regional stratigraphic constraints, the age and composition of volcanism, paleosol formation, incised peneplains, emergent marine terraces, and thermochronometric measurements corroborate our calculated patterns of uplift. Progressive development of three domal swells along the western margin of the peninsula is consistent with localized upwelling of hot asthenospheric mantle