Synchrotron X-ray microscopy of marine calcifiers: How plankton record past climate change

© Published under licence by IOP Publishing Ltd. We have used STXM and PEEM to reveal the underpinning chemistry and nanoscale structure behind palaeo-climate geochemical signatures, such as trace Mg in shells- proposed proxies for palaeo-ocean temperature. This has allowed us to test the chemical assumptions and mechanisms underpinning the use of such empirical proxies. We have determined the control on driving chemical variations in biogenic carbonates using STXM at the absorption edge of Mg, B, and Na in the shells of modern plankton. The power of these observations lies in their ability to link changes in chemistry, microstructure, and growth process in biogenic carbonate to environmental influences. We have seen that such changes occur at length scales of tens of nanometres and demonstrated that STXM provides an invaluable route to understanding chemical environment and key heterogeneity at the appropriate length scale. This new understanding provides new routes for future measurements of past climate variation in the sea floor fossil record

Synchrotron X-ray microscopy of marine calcifiers: how plankton record past climate change

We have used STXM and PEEM to reveal the underpinning chemistry and nanoscale structure behind palaeo-climate geochemical signatures, such as trace Mg in shells- proposed proxies for palaeo-ocean temperature. This has allowed us to test the chemical assumptions and mechanisms underpinning the use of such empirical proxies. We have determined the control on driving chemical variations in biogenic carbonates using STXM at the absorption edge of Mg, B, and Na in the shells of modern plankton. The power of these observations lies in their ability to link changes in chemistry, microstructure, and growth process in biogenic carbonate to environmental influences. We have seen that such changes occur at length scales of tens of nanometres and demonstrated that STXM provides an invaluable route to understanding chemical environment and key heterogeneity at the appropriate length scale. This new understanding provides new routes for future measurements of past climate variation in the sea floor fossil record

The coordination and distribution of B in foraminiferal calcite

The isotopic ratio and concentration of B in foraminiferal calcite appear to reflect the pH and bicarbonate concentration of seawater. The use of B as a chemical proxy tracer has the potential to transform our understanding of the global carbon cycle, and ocean acidification processes. However, discrepancies between the theory underpinning the B proxies, and mineralogical observations of B coordination in biomineral carbonates call the basis of these proxies into question. Here, we use synchrotron X-ray spectromicroscopy to show that B is hosted solely as trigonal BO3 in the calcite test of Amphistegina lessonii, and that B concentration exhibits banding at the micron length scale. In contrast to previous results, our observation of trigonal B agrees with the predictions of the theoretical mechanism behind B palaeoproxies. These data strengthen the use of B for producing palaeo-pH records. The observation of systematic B heterogeneity, however, highlights the complexity of foraminiferal biomineralisation, implying that B incorporation is modulated by biological or crystal growth processes.We would like to acknowledge David Nicol, Iris Buisman and Martin Walker for invaluable technical assistance, and James Bryson for his help with synchrotron data collection. Wewould like to thank Jean DeMouthe (California Academy of Sciences) and Mike Rumsey (Natural History Museum, London) for provision of B-containing minerals for use as reference materials. This work was funded by ERC (grant 2010-ADG-267931 to HE), NERC, Jesus College (Cambridge)and the US Department of Energy (via ALS).This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0012821X15000849

Predicting in-hospital mortality and unanticipated admissions to the intensive care unit using routinely collected blood tests and vital signs: development and validation of a multivariable model.

AIM: The National Early Warning System (NEWS) is based on vital signs; the Laboratory Decision Tree Early Warning Score (LDT-EWS) on laboratory test results. We aimed to develop and validate a new EWS (the LDTEWS:NEWS risk index) by combining the two and evaluating the discrimination of the primary outcome of unanticipated intensive care unit (ICU) admission or in-hospital mortality, within 24 hours. METHODS: We studied emergency medical admissions, aged 16 years or over, admitted to Oxford University Hospitals (OUH) and Portsmouth Hospitals (PH). Each admission had vital signs and laboratory tests measured within their hospital stay. We combined LDT-EWS and NEWS values using a linear time-decay weighting function imposed on the most recent blood tests. The LDTEWS:NEWS risk index was developed using data from 5 years of admissions to PH, and validated on a year of data from both PH and OUH. We tested the risk index's ability to discriminate the primary outcome using the c-statistic. RESULTS: The development cohort contained 97,933 admissions (median age = 73 years) of which 4,723 (4.8%) resulted in in-hospital death and 1,078 (1.1%) in unanticipated ICU admission. We validated the risk index using data from PH (n = 21,028) and OUH (n = 16,383). The risk index showed a higher discrimination in the validation sets (c-statistic value (95% CI)) (PH, 0.901 (0.898-0.905); OUH, 0.916 (0.911-0.921)), than NEWS alone (PH, 0.877 (0.873-0.882); OUH, 0.898 (0.893-0.904)). CONCLUSIONS: The LDTEWS:NEWS risk index increases the ability to identify patients at risk of deterioration, compared to NEWS alone

Phase Transitions in Zeolitic Imidazolate Framework 7: The Importance of Framework Flexibility and Guest-Induced Instability

A study of the phase transitions in ZIF-7 (zeolitic imidazolate frameworks- (Zn(PhIm)2, PhIm = benzimidazolate)) as a function of guest occupancy and temperature was reported. Raman spectra of an as-synthesized sample were collected in air between 297 and 421 K. The major contributions of the spectra come from the vibrational modes of the benzimidazolate ligand. Upon heating, most of the Raman bands remain similar and keep the same frequencies until 357 K, indicating that the structure of ZIF-7 seems to be stable in this temperature range. Above 357 K, strong modifications are observed in the regions corresponding to the lattice modes. The formation of ZIF-7-II is attributed to the loss of dimethylformamide (DMF) solvent molecules from the ZIF-7-I framework. This can be confirmed by the differential scanning calorimetry and thermogravimetric analysis traces of ZIF-7-I. The highly-distorted and locally-strained nature of ZIF-7-II leads to its poor crystallinity, reflected by X-ray powder diffraction and scanning electron microscope

The distribution and coordination of trace elements in Krithe ostracods and their implications for paleothermometry

The Mg and Sr content of ostracod valves have been used to reconstruct past temperature and salinity, and their stable isotopes have been used to reveal aspects of marine, lake and estuary hydrology. However, significant uncertainties surround the ostracod calcification processes, the incorporation mechanisms of trace elements, and the sensitivity of proxy tracers to complex confounding factors. The valves of most ostracods are composed of micron-scale crystal grains embedded in an organic matrix. The fine-scale geochemistry of these structures, and the nature of the influence of biological mineralisation processes on valve chemistry remain poorly constrained. We have performed sub-micron resolution X-ray microscopy of a marine Krithe ostracod valve, and determined the chemical coordination of Mg, and the distribution of Mg, Na and S throughout the crystal-organic valve structure. These trace elements display systematic sub-micron-scale compositional variations within the mineral grains and iner-granular matrix of the valve ultrastructure. These patterns imply that Krithe biomineralisation processes significantly modulate trace element incorporation at the sub-micron scale. Thus Krithe chemical composition is likely to be decoupled to some extent from the water in which they calcified. Most importantly, Mg K-edge Near- Edge X-Ray Absorption Fine Structure (NEXAFS) spectra, and the coincidence of high-Mg regions with S-rich organic layers reveal that Mg is not primarily hosted in the calcite structure in the valve. Our results highlight the need to understand the processes that drive this fine-scale chemical heterogeneity and their influence on connections between the external environment and valve geochemistry, if ostracods are to be used as sources of paleoenvironmental proxies

Pressure-Induced Amorphization of Small Pore Zeolites-the Role of Cation-H2O Topology and Anti-glass Formation

Systematic studies of pressure-induced amorphization of natrolites (PIA) containing monovalent extra-framework cations (EFC) Li+, Na+, K+, Rb+, Cs+ allow us to assess the role of two different EFC-H2O configurations within the pores of a zeolite: one arrangement has H2O molecules (NATI) and the other the EFC (NAT(II)) in closer proximity to the aluminosilicate framework. We show that NAT(I) materials have a lower onset pressure of PIA than the NAT(II) materials containing Rb and Cs as EFC. The onset pressure of amorphization (P-A) of NAT(II) materials increases linearly with the size of the EFC, whereas their initial bulk moduli (P-1 phase) decrease linearly. Only Cs- and Rb-NAT reveal a phase separation into a dense form (P-2 phase) under pressure. High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) imaging shows that after recovery from pressures near 25 and 20 GPa long-range ordered Rb-Rb and Cs-Cs correlations continue to be present over length scales up to 100 nm while short-range ordering of the aluminosilicate framework is significantly reduced-this opens a new way to form anti-glass structuresopen