High-resolution Secondary Ion Mass Spectrometry Research Articles

Zinc and cadmium mapping by NanoSIMS within the root apex after short-term exposure to metal contamination

Zinc as a micronutrient and cadmium as a nonessential toxic element share similar pathways for entering plant tissues and thus may be antagonistic. In nutrient solution culture, 17-day-old radish (Raphanus sativus L) plants were exposed to short-term (24 h) equimolar metal contamination (2.2 µM of each 70Zn and total Cd) to investigate the in situ Zn/Cd distribution in the apical root tissues using high-resolution secondary ion mass spectrometry (NanoSIMS) imaging. Inductively-coupled plasma mass spectrometry analysis of bulk root tissue confirmed large root uptake of both metal elements. After 24-h exposure the total root concentration (in µg/g DW) of 70Zn was 180 ± 24 (mean±SE) and of total Cd 352 ± 11. NanoSIMS mapping was performed on the cross sections of the radish root apex as a crucial component in root growth and uptake of water and nutrients from soil. Elemental maps of 70Zn and 114Cd isotopes revealed greater enrichment of both metals in the outer epidermal root layer than in cortical tissues and especially stele, confirming the epidermal root cells as preferential sites of metal uptake, and indicating relatively slow and less-intensive metal transport into other parts (edible hypocotyl, shoot) of metal-sensitive radish. NanoSIMS has been confirmed as a powerful tool for spatial detection and visualisation of some ultra-trace metal isotopes (e.g. 70Zn) in the fast-growing root tips. However, precise (sub)cellular mapping of diffusible metallic ions (Cd, Zn) remains a technically-challenging task in plant specimens given an unavoidable compromise between optimising methodology for structural preservation vs. authentic in vivo ion localisation.

(Invited) Polarization-Induced Doping in Graded AlGaN Epilayers Grown on AlN Single Crystal Substrates

Wide-bandgap nitride semiconductor-based lateral and vertical power switching devices are reaching a mature state and gaining increasing commercial acceptance. This is due to the nitrides’ outstanding properties, including high critical electric fields, mobilities, and saturation velocities, and to progress made in the understanding of key issues, such as controllable doping and polarization engineering. Since many of the figures of merit for power device performance scale with the critical electric field, itself a strong function of the bandgap, the ultrawide-bandgap (UWBG) materials, with bandgaps beyond the 3.4 eV of GaN, have the potential for improved power device performance [1]. However, research and development into these emerging materials is still at a relatively immature stage. Significant challenges remain in the growth of high Al composition AlGaN, including efficient n-type doping at very high Al compositions, and, even more so, p-type doping in general. In spite of these challenges, high-quality, controllably-doped AlGaN epilayers grown on AlN single crystal substrates have been demonstrated in devices, including UV emitters [2] and Schottky diodes [3]. Improved approaches to doping the high Al composition AlGaN layers required for operation of these devices will lead to increased device performance. AlGaN epilayers are commonly doped with substitutional impurities, typically Si for n-type and Mg for p-type, which require thermal activation to generate free carriers. As the Al composition, x, in AlxGa1-xN increases, the Mg impurity activation energy increases, while the Si impurity undergoes a DX transition beyond x~ 0.84, leading to rapidly decreasing free carrier concentrations in high Al content layers. In contrast to this approach, doping in compositionally graded AlGaN epilayers by taking advantage of the distributed polarization charge has been demonstrated for both n-type [4] and p-type [5] doping. The polarization-doped layers thus formed exhibit high sheet carrier densities and are resistant to carrier freeze-out at low temperatures, since they do not depend on thermal activation. We have investigated graded AlGaN epilayers grown on Al-polar AlN single crystal substrates by metal-organic chemical vapor deposition (MOCVD), and measured n-type or p-type doping in increasing or decreasing Al composition layers, respectively. The structural quality and compositional grading were assessed by high-resolution x-ray diffraction (HRXRD) and secondary ion mass spectrometry (SIMS). The space charge profile in an n-type layer graded from x= 0.66 to x= 1.0 was calculated from capacitance-voltage (CV) measurements of a Schottky diode structure. Furthermore, the temperature-dependent resistivity, carrier concentration, and mobility in p-type layers was determined by Hall effect measurements using the Van der Pauw method, and a room-temperature resistivity of 1 Ωcm was obtained for a p-type layer graded from x= 1.0 to x= 0.36. This talk will review MOCVD growth and characterization of both n-type and p-type doped, compositionally graded AlGaN epilayers by HRXRD, SIMS, CV, and Hall effect measurements. Results of integrating these layers into UWBG device structures will also be discussed. [1] R. J. Kaplar, A. A. Allerman, A. M. Armstrong, M. H. Crawford, J. R. Dickerson, A. J. Fischer, A. G. Baca, and E. A. Douglas, ECS J. Solid State Sci. and Technol., 6(2), Q3061 (2017). [2] T. Kinoshita, K. Hironaka, T. Obata, T. Nagashima, R. Dalmau, R. Schlesser, B. Moody, J. Xie, S. Inoue, Y. Kumagai, A. Koukitu, and Z. Sitar, Appl. Phys. Express, 5, 122101 (2012). [3] R. Dalmau, H. S. Craft, R. Schlesser, S. Mita, J. Smart, C. Hitchcock, G. Pandaey, T. P. Chow, and B. Moody, ECS Trans., 80(7), 217 (2017). [4] D. Jena, S. Heikman, D. Green, D. Buttari, R. Coffie, H. Xing, S. Keller, S. DenBaars, J. S. Speck, U. K. Mishra, Appl. Phys. Lett., 81, 4395 (2002). [5] J. Simon, V. Prosatenko, C. Lian, H. Xing, and D. Jena, Science, 327, 60 (2010).

The stage of seed development influences iron bioavailability in pea (Pisum sativum L.)

Pea seeds are widely consumed in their immature form, known as garden peas and petit pois, mostly after preservation by freezing or canning. Mature dry peas are rich in iron in the form of ferritin, but little is known about the content, form or bioavailability of iron in immature stages of seed development. Using specific antibodies and in-gel iron staining, we show that ferritin loaded with iron accumulated gradually during seed development. Immunolocalization and high-resolution secondary ion mass spectrometry (NanoSIMS) revealed that iron-loaded ferritin was located at the surface of starch-containing plastids. Standard cooking procedures destabilized monomeric ferritin and the iron-loaded form. Iron uptake studies using Caco-2 cells showed that the iron in microwaved immature peas was more bioavailable than in boiled mature peas, despite similar levels of soluble iron in the digestates. By manipulating the levels of phytic acid in the digestates we demonstrate that phytic acid is the main inhibitor of iron uptake from mature peas in vitro. Taken together, our data show that immature peas and mature dry peas contain similar levels of ferritin-iron, which is destabilized during cooking. However, iron from immature peas is more bioavailable because of lower phytic acid levels compared to mature peas.

Cholesterol is enriched in the sphingolipid patches on the substrate near nonpolarized MDCK cells, but not in the sphingolipid domains in their plasma membranes

Information about the distributions of cholesterol and sphingolipids within the plasma membranes of mammalian cells provides insight into the roles of these molecules in membrane function. In this report, high-resolution secondary ion mass spectrometry was used to image the distributions of metabolically incorporated rare isotope-labeled sphingolipids and cholesterol on the surfaces of nonpolarized epithelial cells. Sphingolipid domains that were not enriched with cholesterol were detected in the plasma membranes of subconfluent Madin-Darby canine kidney cells. Surprisingly, cholesterol-enriched sphingolipid patches were observed on the substrate adjacent to these cells. Based on the shapes of these cholesterol-enriched sphingolipid patches on the substrate and their proximity to cellular projections, we hypothesize that they are deposits of membranous particles released by the cell.

Age discordance and mineralogy

Observations of discordant ages, meaning that an age given by one mineral geochronometer is different from the age given by another geochronometer from the same rock, began in the early days of geochronology. In the late 1950s and 1960s, discordant U-Pb zircon ages were unquestioningly attributed to Pb diffusion at high temperature. Later, the mineralogical properties and the petrogenesis of the zircon crystals being dated was recognized as a key factor in obtaining concordant U-Pb ages. Advances in analytical methods allowed the analysis of smaller and smaller zircon multigrain fractions, then the analysis of individual grains, and even pieces of grains, with higher degrees of concordancy. Further advances allowed a higher analytical precision, a clearer perception of accuracy, and a better statistical resolution of age discordance. As for understanding the cause(s) of discordance, belief revision followed the coupling of imaging, cathodoluminescence (CL) and back-scattered electrons (BSE), to in situ dating by secondary ion mass spectrometry (SIMS), or by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Discordant zircon and other accessory minerals (e.g., monazite, apatite, etc.) often consist of young rims accreted onto/into older cores. Age gradients are sharp, and no Pb diffusion gradients are observed. As U-Pb discordance in crystalline, non-radiation damaged grains is caused by diachronous, heterochemical mineral generations, interpretations of mineral ages, based on the exclusive role of diffusion, are superseded, and closure temperatures of zircon and monazite are irrelevant in geological reality. Other isotopic systems (Rb-Sr, K-Ar) were believed, since the 1960s, to be similarly controlled by the diffusivity of radiogenic daughters. When zircon and monazite discordance were recognized as zone accretion/reaction with sharp boundaries that showed little or no high-temperature diffusive re-equilibration, the other chronometric systems were left behind, and interpretations of mineral ages based on the exclusive role of diffusion survived. The evidence from textural-petrologic imaging (CL, BSE) and element mapping by electron probe microanalyzer (EPMA) or high spatial resolution SIMS or LA-ICPMS provides the decisive constraints. All microcline and mica geochronometers that have been characterized in detail document patchy textures and evidence for mineral replacement reactions. It is important not to confuse causes and effects; heterochemical microstructures are not the cause of Ar and Sr loss; rather, they follow it. Argon and Sr loss by dissolution of the older mineral generation occurs first, heterochemical textures form later, when the replacive assemblage recrystallizes. Heterochemical mineral generations are identified and dated by their Ca/Cl/K systematics in 39Ar-40Ar. Replacive reactions adding or removing Cl, such as, e.g., sericite overgrowths on K-feldspar, retrograde muscovite intergrowths with phengite, etc., are detected by Cl/K vs Ar/K isotope correlation diagrams. Calcium-poor reaction products, such as, e.g., young biotite intergrown with older amphibole, adularia replacing microcline, etc., can be easily identified by Ca/K vs Ar/K diagrams supported by EPMA analyses. Mixed mineral generations are observed to be the cause of discordant, staircase-shaped age spectra, while step-heating of crystals with age gradients produces concordant plateaus. Age gradients are therefore unrelated to staircase age spectra. There is a profound analogy between the U-Pb, Rb-Sr, and K-Ar systems. Lead and Ar diffusion rates are both much slower than mineral replacement rates for all T < 750 °C. Patchy retrogression textures are always associated with heterochemical signatures (U/Th ratios, REE patterns, Ca/Cl/K ratios). As a rule, single-generation minerals with low amounts of radiation damage give concordant ages, whereas discordance is caused by mixtures of heterochemical, resolvably diachronous, mineral generations in petrologic disequilibrium. This can also include (sub-)grains that have accumulated significant amounts of radiation damage. For accurate geochronology the petrologic characterization with the appropriate technique(s) of the minerals to be dated, and the petrologic context at large, are as essential as the mass spectrometric analyses.

A Nanoscale Study of Carbon and Nitrogen Fluxes in Mats of Purple Sulfur Bacteria: Implications for Carbon Cycling at the Surface of Coastal Sediments.

Mass blooms of purple sulfur bacteria growing seasonally on green stranded macroalgae have a major impact on the microbial composition and functionality of intertidal mats. To explore the active anoxygenic phototrophic community in purple bacterial mats from the Roscoff Aber Bay (Brittany, France), we conducted a combined approach including molecular and high-resolution secondary ion mass spectrometry (NanoSIMS) analyses. To investigate the dynamics of carbon and nitrogen assimilation activities, NanoSIMS was coupled with a stable isotope probing (SIP) experiment and a compound specific isotope analysis (CSIA) of fatty acid methyl ester (FAME). Sediment samples were incubated with 13C- and/or 15N-labeled acetate, pyruvate, bicarbonate and ammonium. NanoSIMS analysis of 13C - and 15N -incubated samples showed elevated incorporations of 13C - and 15N in the light and of 13C -acetate in the dark into dense populations of spherical cells that unambiguously dominated the mats. These results confirmed CSIA data that ranked vaccenic acid, an unambiguous marker of purple sulfur bacteria, as the most strongly enriched in the light after 13C -acetate amendment and indicated that acetate uptake, the most active in the mat, was not light-dependent. Analysis of DNA- and cDNA-derived pufM gene sequences revealed that Thiohalocapsa-related clones dominated both libraries and were the most photosynthetically active members of the mat samples. This study provides novel insights into the contribution of purple sulfur bacteria to the carbon cycle during their seasonal developments at the sediment surface in the intertidal zone.

Success of chemolithoautotrophic SUP05 and Sulfurimonas GD17 cells in pelagic Baltic Sea redox zones is facilitated by their lifestyles as K- and r-strategists.

Chemolithoautotrophic sulfur-oxidizing and denitrifying Gamma- (particularly the SUP05 cluster) and Epsilonproteobacteria (predominantly Sulfurimonas subgroup GD17) are assumed to compete for substrates (electron donors and acceptors) in marine pelagic redox gradients. To elucidate their ecological niche separation we performed 34 S0 , 15 NO3- and H13 CO3- stable-isotope incubations with water samples from Baltic Sea suboxic, chemocline and sulfidic zones followed by combined phylogenetic staining and high-resolution secondary ion mass spectrometry of single cells. SUP05 cells were small-sized (0.06-0.09 µm3 ) and most abundant in low-sulfidic to suboxic zones, whereas Sulfurimonas GD17 cells were significantly larger (0.26-0.61 µm3 ) and most abundant at the chemocline and below. Together, SUP05 and GD17 cells accumulated up to 48% of the labelled substrates but calculation of cell volume-specific rates revealed that GD17 cells incorporated labelled substrates significantly faster throughout the redox zone, thereby potentially outcompeting SUP05 especially at high substrate concentrations. Thus, in synopsis with earlier described features of SUP05/GD17 we conclude that their spatially overlapping association in stratified sulfidic zones is facilitated by their different lifestyles: whereas SUP05 cells are streamlined, non-motile K-strategists adapted to low substrate concentrations, GD17 cells are motile r-strategists well adapted to fluctuating substrate and redox conditions.

Probing the lipid composition at the site of influenza virus assembly and budding with high‐resolution SIMS

The formation of infectious influenza virions is sensitive to the cholesterol levels in the host cell. The findings that the influenza viral envelope is enriched with cholesterol and sphingolipids and cholesterol depletion alters the clustering of influenza virus proteins in the plasma membrane, which is detrimental to virus assembly, suggests that the influenza virus assembles and bud from cholesterol‐ and sphingolipid‐enriched domains in the plasma membrane. Although this hypothesis has been around for decades, whether the region of the plasma membrane from which the influenza virus buds is enriched with cholesterol and sphingolipids is still unknown. To answer this question, we have used high‐resolution secondary ion mass spectrometry (SIMS) to image the distributions of stable isotope‐labeled cholesterol and immunolabeled influenza virus protein in the plasma membrane during virus budding with ~100 nm lateral resolution. This work involved metabolically incorporating distinct stable isotopes into the cholesterol and lipids of interest in living MDCK cells. After infecting these MDCK cells with influenza virus for 24 h, we immunolabeled the influenza envelope protein, hemagglutinin. Then we imaged the isotope‐labeled cholesterol, lipids, and immunolabeled influenza hemagglutinin on the surfaces of the virus infected cells with ~100 nm lateral resolution. The resulting images clearly show that the influenza virus does bud from cholesterol‐enriched domains in the membranes of MDCK cells.Support or Funding InformationThis research was supported by the U.S. National Science Foundation under CHE 15‐08662.

The 1.33–1.30 Ga Yanliao large igneous province in the North China Craton: Implications for reconstruction of the Nuna (Columbia) supercontinent, and specifically with the North Australian Craton

The Yanliao rift zone in the northern North China Craton (NCC) is the location of the standard section for late Paleoproterozoic–Mesoproterozoic stratigraphy in China and is associated with the emplacement of large volumes of diabase sills. Detailed field investigations show that the sills are distributed over a region that is >600 km long and >200 km wide, with areal extent >1.2×105 km2 and cumulative thickness of the sills in any one area ranging from 50 m to >1800 m. High-resolution secondary ion mass spectrometry (SIMS) baddeleyite dating shows that emplacement of these sills occurred between about 1330 and 1305 Ma with a peak age of 1323 Ma. Emplacement of these diabase sills was accompanied by pre-magmatic uplift that started at about 1.35–1.34 Ga as indicated by the disconformity between the Changlongshan and Xiamaling formations and absence of sedimentation after the Xiamaling Formation in some areas. All the diabase sills exhibit similar geochemical features of tholeiitic compositions with intraplate characteristics. Given a relatively short duration of emplacement at 1.33–1.30 Ga, along with the large areal extent and volume, as well as intraplate character, this magmatic province constitutes a large igneous province (LIP). This Yanliao LIP and the accompanying pre-magmatic uplift were related either to a mantle plume and/or continental rifting during breakup of the NCC from the Nuna (Columbia) supercontinent. Paleomagnetic, ash bed and LIP data and other geological constraints suggest that the NCC had a close connection with Siberia, Laurentia, Baltica, North Australia and India crustal blocks. In particular, the most direct age match between the 1.33–1.30 Ga Yanliao LIP and the 1.33–1.30 Ga Derim Derim–Galiwinku LIP of the North Australian Craton (NAC), as well as the similarities between the late Paleoproterozoic–Mesoproterozoic stratigraphic units of the Yanliao rift in the NCC with the southeastern McArthur Basin in the NAC, indicate that the Yanliao and Derim Derim–Galiwinku events are fragmented parts of the same LIP, supporting the paleomagnetically plausible idea that the NCC and NAC were connected (or at least near neighbors) during the early Mesoproterozoic period.

Is the Site of Influenza Virus Assembly and Budding Enriched with Cholesterol and Sphingolipids?

The observation that the influenza viral envelope is enriched with cholesterol and sphingolipids contributed to the hypothesis that the influenza virus assembles and bud from cholesterol- and sphingolipid-enriched domains in the plasma membrane. The formation of infectious influenza virions and the clustering of influenza virus proteins in the plasma membrane during virus assembly are reportedly reduced by depletion of cellular cholesterol. Though this cholesterol sensitivity certainly suggests that cholesterol plays a role in influenza virus infection, whether the plasma membrane domain from which the influenza virus buds is enriched with cholesterol and sphingolipids has not been decisively determined. We have addressed this question by using high-resolution secondary ion mass spectrometry (SIMS) to image the distributions of stable isotope-labeled lipids and immunolabeled influenza virus proteins in the plasma membranes of virus-infected cells with ∼100 nm lateral resolution. In these experiments, we metabolically incorporated the distinct stable isotopes 15N and 18O into the sphingolipids and cholesterol, respectively, in living MDCK cells. We infected these MDCK cells with an H3N2 strain of the influenza virus for 24 h, and immunolabeled the influenza envelope protein, hemagglutinin, to permit the detection of budding virus. Finally, we imaged the metabolically incorporated 15N-sphingolipids and 18O-cholesterol and immunolabeled influenza hemagglutinin on the surfaces of the influenza-infected MDCK cells, and assessed co-localization between these components. The results of these experiments and there implications will be presented.

Sphingolipid Organization in the Plasma Membrane and the Mechanisms That Influence It.

Sphingolipids are structural components in the plasma membranes of eukaryotic cells. Their metabolism produces bioactive signaling molecules that modulate fundamental cellular processes. The segregation of sphingolipids into distinct membrane domains is likely essential for cellular function. This review presents the early studies of sphingolipid distribution in the plasma membranes of mammalian cells that shaped the most popular current model of plasma membrane organization. The results of traditional imaging studies of sphingolipid distribution in stimulated and resting cells are described. These data are compared with recent results obtained with advanced imaging techniques, including super-resolution fluorescence detection and high-resolution secondary ion mass spectrometry (SIMS). Emphasis is placed on the new insight into the sphingolipid organization within the plasma membrane that has resulted from the direct imaging of stable isotope-labeled lipids in actual cell membranes with high-resolution SIMS. Super-resolution fluorescence techniques have recently revealed the biophysical behaviors of sphingolipids and the unhindered diffusion of cholesterol analogs in the membranes of living cells are ultimately in contrast to the prevailing hypothetical model of plasma membrane organization. High-resolution SIMS studies also conflicted with the prevailing hypothesis, showing sphingolipids are concentrated in micrometer-scale membrane domains, but cholesterol is evenly distributed within the plasma membrane. Reductions in cellular cholesterol decreased the number of sphingolipid domains in the plasma membrane, whereas disruption of the cytoskeleton eliminated them. In addition, hemagglutinin, a transmembrane protein that is thought to be a putative raft marker, did not cluster within sphingolipid-enriched regions in the plasma membrane. Thus, sphingolipid distribution in the plasma membrane is dependent on the cytoskeleton, but not on favorable interactions with cholesterol or hemagglutinin. The alternate views of plasma membrane organization suggested by these findings are discussed.

P-T-t evolution of Neoarchaean to Paleoproterozoic pelitic granulites from the Jidong terrane, eastern North China Craton

Four metamorphic mineral assemblages, formed at different metamorphic stages, are identified in pelitic granulites exposed in the Jidong terrane, east Hebei Province, North China Craton (NCC). Prograde mineral assemblages (M1) are represented by biotite, plagioclase, quartz, and ilmenite, preserved as mineral inclusions within garnet porphyroblasts. Peak mineral assemblages (M2), which are represented by the garnet cores, rutile, pseudomorphs of sillimanite after kyanite, and some matrix minerals, formed at P–T conditions of ∼12–13kbar/820–850°C. Post-peak mineral assemblages (M3), which consist of the inner rims of garnets and some matrix minerals, formed at P–T conditions of ∼11kbar/850°C. The final retrograde mineral assemblages (M4) are mainly represented by matrix biotite without rutile exsolution, and minor matrix plagioclase with relatively high anorthite content. High-resolution secondary ion mass spectrometry (SIMS) U−Pb dating of metamorphic zircons demonstrates that the pelitic granulites possibly reached the peak metamorphic stage at ∼2.5Ga. Younger metamorphic ages (2.41–2.45Ga) possibly represent the cooling ages of the granulites. Accordingly, the pelitic granulites exposed in the Jidong terrane record clockwise P–T–t paths with sequential isothermal decompression (ITD) and isobaric cooling (IBC) segments, likely caused by a subduction–collision event during the late Neoarchean to early Palaeoproterozoic in the eastern NCC.

Metamorphic evolution and SIMS U-Pb geochronology of the Qingshigou area, Dunhuang block, NW China: Tectonic implications of the southernmost Central Asian orogenic belt

Garnet-bearing mafic granulite and amphibolite exposed as lenses, boudins, or interlayers within metasediments in the Qingshigou area, Dunhuang block, southernmost Central Asian orogenic belt, record important information for understanding the tectono-metamorphic evolution of subduction and collision zones in the southern Central Asian orogenic belt during the mid-Paleozoic. Three stages of metamorphic assemblages (M1, M2, M3) are recognized in the high- and medium-pressure mafic granulite and amphibolite. In the high-pressure mafic granulite, the prograde assemblage (M1) is represented by inclusion minerals (hornblende + plagioclase + quartz) preserved in garnet porphyroblasts; the metamorphic peak assemblage (M2) is characterized by garnet porphyroblasts and matrix minerals (garnet + clinopyroxene + plagioclase + quartz ± zircon ± titanite); and the retrograde assemblage (M3) is marked by coronitic symplectite (hornblende + plagioclase + quartz ± magnetite) rimming the garnet porphyroblasts. In the medium-pressure mafic granulite, the prograde assemblage (M1) of hornblende + plagioclase + quartz is included in the garnet porphyroblasts; the peak assemblage (M2) consists of garnet + orthopyroxene + clinopyroxene + plagioclase + quartz ± zircon ± titanite (M2) in the matrix; and the retrograde assemblage (M3) of hornblende + orthopyroxene + plagioclase + quartz (M3) surrounds the garnet porphyroblasts. In the amphibolite, the prograde assemblage (hornblende + plagioclase + quartz + ilmenite) is preserved as inclusions in garnet (M1); the peak assemblage (M2) is composed of garnet + hornblende + plagioclase + quartz ± zircon ± titanite; and the retrograde assemblage (M3), consisting of hornblende + biotite + plagioclase + quartz + epidote + magnetite, rings the garnet porphyroblasts. Geothermobarometric calculations suggest that the metamorphic pressure-temperature paths pass from 568 °C and 8.8 kbar through 607 °C and 10.6 kbar and 861 °C and 16.9 kbar and finally to 598 °C and 4.4 kbar for the high-pressure mafic granulite; from 756 °C and 9.0 kbar through 750–874 °C and 9.3–11.6 kbar to 675 °C and 4.7 kbar for the medium-pressure mafic granulite; and from 686 °C and 7.6 kbar through 715–766 °C and 10.6–11.2 kbar to 671 °C and 5.6 kbar for the amphibolite, and the paths show clockwise pressure-temperature loops typical of an orogenic process. The metamorphic peak of the high-pressure mafic granulite lies in the eclogite facies, which is indicative of a subduction zone environment. High-resolution secondary ion mass spectrometry (SIMS) U-Pb dating of metamorphic zircon indicates that the metamorphism occurred in the Early Silurian (ca. 430 Ma) and lasted for at least 65 m.y. This study reveals a possible southward subduction history of a branch of the Paleo–Asian Ocean, the Liuyuan Ocean, from the Silurian to Late Devonian, which may be an important event in the accretionary history of the Central Asian orogenic belt.

Contrasting hydrological processes of meteoric water incursion during magmatic–hydrothermal ore deposition: An oxygen isotope study by ion microprobe

Meteoric water convection has long been recognized as an efficient means to cool magmatic intrusions in the Earth's upper crust. This interplay between magmatic and hydrothermal activity thus exerts a primary control on the structure and evolution of volcanic, geothermal and ore-forming systems. Incursion of meteoric water into magmatic–hydrothermal systems has been linked to tin ore deposition in granitic plutons. In contrast, evidence from porphyry copper ore deposits suggests that crystallizing subvolcanic magma bodies are only affected by meteoric water incursion in peripheral zones and during late post-ore stages. We apply high-resolution secondary ion mass spectrometry (SIMS) to analyze oxygen isotope ratios of individual growth zones in vein quartz crystals, imaged by cathodo-luminescence microscopy (SEM-CL). Existing microthermometric information from fluid inclusions enables calculation of the oxygen isotope composition of the fluid from which the quartz precipitated, constraining the relative timing of meteoric water input into these two different settings. Our results confirm that incursion of meteoric water directly contributes to cooling of shallow granitic plutons and plays a key role in concurrent tin mineralization. By contrast, data from two porphyry copper deposits suggest that downward circulating meteoric water is counteracted by up-flowing hot magmatic fluids. Our data show that porphyry copper ore deposition occurs close to a magmatic–meteoric water interface, rather than in a purely magmatic fluid plume, confirming recent hydrological modeling. On a larger scale, the expulsion of magmatic fluids against the meteoric water interface can shield plutons from rapid convective cooling, which may aid the build-up of large magma chambers required for porphyry copper ore formation.

Diazotroph derived nitrogen supports diatom growth in the South West Pacific: A quantitative study using nanoSIMS

Nitrogen is essential for life but is often a major limiting nutrient for growth in the ocean. Biological dinitrogen fixation is a major source of new nitrogen to surface waters and promotes marine productivity. Yet the fate of diazotroph-derived nitrogen (DDN) in marine ecosystems has been poorly studied, and its transfer to auto- and heterotrophic plankton has not been measured. Here, we use high-resolution nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with N-15(2) isotopic labelling and flow cytometry cell sorting to examine the DDN transfer to specific groups of natural phytoplankton and bacteria during three diazotroph blooms dominated by the cyanobacterium Trichodesmium spp. in the South West Pacific. During these experiments, 13%+/- 2% to 48%+/- 5% of the fixed N-15(2) was released into the dissolved pool and 6%+/- 1% to 8%+/- 2% of this DDN was transferred to non-diazotrophic plankton after 48 h. The primary beneficiaries of this DDN were diatoms (45%+/- 4% to 61%+/- 38%) and bacteria (22%+/- 27% to 38%+/- 12%), followed by pico-phytoplankton (3%+/- 1% to 21%+/- 14%). The DDN was quickly converted to non-diazotrophic plankton biomass, in particular that of diatoms, which increased in abundance by a factor of 1.4-15 over the course of the three experiments. The single-cell approach we used enabled quantification of the actual transfer of DDN to specific groups of autotrophic and heterotrophic plankton in the surface ocean, revealing a previously unseen level of complexity in the pathways that occur between N-2 fixation and the eventual export of DDN from the photic zone.

Oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 Merapi eruption (Central Java, Indonesia)

Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800–1700μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6‰ to 7.9‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6–6.6‰) are found in anorthite-rich cores (An82–97), whereas higher δ18O values (5.7–7.9‰) are found in anorthite-poorer zones (An33–86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 and 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82–92), available experimental data, and the results of thermodynamic modeling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200–600MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100–200MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13–20km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5–9km). Thermodynamic modeling is consistent with ∼18wt.% assimilation of crustal calc-silicate material at 925–950°C and 100–200MPa by the 2010 Merapi basaltic andesite magma prior to eruption. Timescales for plagioclase phenocryst growth and residence in the magmatic plumbing system are ⩽34years. The combined data thus reveal efficient magma recharge and crustal assimilation processes that characterize the open-system magma storage and transport systems associated with the 2010 Merapi eruption.

Genome Evolution and Nitrogen Fixation in Bacterial Ectosymbionts of a Protist Inhabiting Wood-Feeding Cockroaches

By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protist Barbulanympha from the hindguts of the wood-eating cockroach Cryptocercus punctulatus In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesis of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis of C. punctulatus hindgut symbionts exposed in vivo to (15)N2 supports the hypothesis that Barbulanympha ectosymbionts are capable of nitrogen fixation. This genomic and in vivo functional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. In this study, we investigated the evolution and nitrogen fixation capabilities of ectosymbionts attached to the protist Barbulanympha from the hindgut of the wood-eating cockroach Cryptocercus punctulatus In addressing genome evolution of protist ectosymbionts, our data suggest that the ecological pressures influencing the evolution of extracellular symbionts clearly differ from intracellular symbionts and organelles. Using NanoSIMS analysis, we also obtained direct imaging evidence of a specific hindgut microbe playing a role in nitrogen fixation. These results demonstrate the power of combining NanoSIMS and genomics tools for investigating the biology of uncultivable microbes. This investigation paves the way for a more precise understanding of microbial interactions in the hindguts of wood-eating insects and further exploration of the diversity and ecological significance of symbiosis between microbes.

Dynamics of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Abstract. N2 fixation rates were measured daily in large (∼ 50 m3) mesocosms deployed in the tropical southwest Pacific coastal ocean (New Caledonia) to investigate the temporal variability in N2 fixation rates in relation with environmental parameters and study the fate of diazotroph-derived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. The mesocosms were fertilized with ∼ 0.8 µM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L−1 d−1 over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L−1 d−1. These later rates measured after the DIP fertilization are higher than the upper range reported for the global ocean. During the 23 days of the experiment, N2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), and alkaline phosphatase activity, and negatively correlated with DIP concentrations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during a bloom of the unicellular diazotroph UCYN-C that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that ∼ 10 % of UCYN-C from the water column was exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 ± 0.8 µm) UCYN-C cells into large (100–500 µm) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometer-scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labeling revealed that 16 ± 6 % of the DDN was released to the dissolved pool and 21 ± 4 % was transferred to non-diazotrophic plankton, mainly picoplankton (18 ± 4 %) followed by diatoms (3 ± 2 %). This is consistent with the observed dramatic increase in picoplankton and diatom abundances, primary production, bacterial production, and standing stocks of POC, PON, and POP in the mesocosms during the second half of the experiment. These results offer insights into the fate of DDN during a bloom of UCYN-C in low-nutrient, low-chlorophyll ecosystems.

Investigation of oxygen diffusion behavior in terbium using 18O2 isotopic tracking by high resolution SIMS

High resolution secondary ion mass spectrometry (SIMS) analysis has been used to study the oxidation mechanisms when high purity terbium (Tb) metal is exposed to corroding environments containing 18O2 isotope. The diffusion coefficients for 18O in Tb at a natural atmosphere can be calculated, which plays an important role in subsequent purification and application in industry. Clear evidence has been shown for the characteristic distributions of 18O after the kinetic transitions. The migration behavior is correlated with the existence of defects in the metal which allow the corrosions occur as localized nucleation. A set of ionization model has been developed to describe the oxidation process.

Establishment of stable synthetic mutualism without co-evolution between microalgae and bacteria demonstrated by mutual transfer of metabolites (NanoSIMS isotopic imaging) and persistent physical association (Fluorescent in situ hybridization)

The demonstration of a mutualistic interaction requires evidence of benefits for both partners as well as stability of the association over multiple generations. A synthetic mutualism between the freshwater microalga Chlorella sorokiniana and the soil-derived plant growth-promoting bacterium (PGPB) Azospirillum brasilense was created when both microorganisms were co-immobilized in alginate beads. Using stable isotope enrichment experiments followed by high-resolution secondary ion mass spectrometry (SIMS) imaging of single cells, we demonstrated transfer of carbon and nitrogen compounds between the two partners. Further, using fluorescent in situ hybridization (FISH), mechanical disruption and scanning electron microscopy, we demonstrated the stability of their physical association for a period of 10days after the aggregated cells were released from the beads. The bacteria significantly enhanced the growth of the microalgae while the microalgae supported growth of the bacteria in a medium where it could not otherwise grow. We propose that this microalga-bacterium association is a true synthetic mutualism independent of co-evolution.