A Comparison of In Situ Analytical Methods for Trace Element Measurement in Gold Samples from Various South African Gold Deposits

Trace element concentrations in gold grains from various geological units in South Africa were measured in situ by field emission‐electron probe microanalysis (FE‐EPMA), laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and synchrotron micro X‐ray fluorescence spectroscopy (SR‐μ‐XRF). This study assesses the accuracy, precision and detection limits of these mostly non‐destructive analytical methods using certified reference materials and discusses their application in natural sample measurement. FE‐EPMA point analyses yielded reproducible and discernible concentrations for Au and trace concentrations of S, Cu, Ti, Hg, Fe and Ni, with detection limits well below the actual concentrations in the gold. LA‐ICP‐MS analyses required larger gold particles (> 60 μm) to avoid contamination during measurement. Elements that measured above detection limits included Ag, Cu, Ti, Fe, Pt, Pd, Mn, Cr, Ni, Sn, Hg, Pb, As and Te, which can be used for geochemical characterisation and gold fingerprinting. Although LA‐ICP‐MS measurements had lower detection limits, precision was lower than FE‐EPMA and SR‐μ‐XRF. The higher variability in absolute values measured by LA‐ICP‐MS, possibly due to micro‐inclusions, had to be critically assessed. Non‐destructive point analyses of gold alloys by SR‐μ‐XRF revealed Ag, Fe, Cu, Ni, Pb, Ti, Sb, U, Cr, Co, As, Y and Zr in the various gold samples. Detection limits were mostly lower than those for elements measured by FE‐EPMA, but higher than those for elements measured by LA‐ICP‐MS.     

Recovering physical parameters from galaxy spectra using MOPED

We derive physical parameters of galaxies from their observed spectra using MOPED, the optimized data compression algorithm of Heavens, Jimenez & Lahav. Here we concentrate on parametrizing galaxy properties, and apply the method to the NGC galaxies in Kennicutt's spectral atlas. We focus on deriving the star formation history, metallicity and dust content of galaxies. The method is very fast, taking a few seconds of CPU time to estimate ∼17 parameters, and is therefore specially suited to studying large data sets, such as the Anglo-Australian two-degree-field (2dF) galaxy survey and the Sloan Digital Sky Survey (SDSS). Without the power of MOPED, the recovery of star formation histories in these surveys would be impractical. In Kennicutt's atlas, we find that for the spheroidals a small recent burst of star formation is required to provide the best fit to the spectrum. There is clearly a need for theoretical stellar atmospheric models with spectral resolution better than 1 Å if we are to extract all the rich information that large redshift surveys contain in their galaxy spectra.     

Wave Propagation in Pulsating Stars

Lissajous diagrams are used to detect phase lags between radial velocity curves associated with different ions. Present in many kind of variable stars, this effect provides an important tool to study the atmosphere dynamics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Including the Urban Canopy Layer in a Lagrangian Particle Dispersion Model

Boundary-Layer Meteorology - When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 m) are generated, rapidly reaching an equilibrium with the overlying turbulence (at...     

Comment on: “Corrections to the Mathematical Formulation of a Backwards Lagrangian Particle Dispersion Model” by Gibson and Sailor (2012: Boundary-Layer Meteorology 145, 399–406)

We discuss the results of Gibson and Sailor (Boundary-Layer Meteorol 145:399–406, 2012) who suggest several corrections to the mathematical formulation of the Lagrangian particle dispersion model of Rotach et al. (Q J R Meteorol Soc 122:367–389, 1996). While most of the suggested corrections had already been implemented in the 1990s, one suggested correction raises a valid point, but results in a violation of the well-mixed criterion. Here we improve their idea and test the impact on model results using a well-mixed test and a comparison with wind-tunnel experimental data. The new approach results in similar dispersion patterns as the original approach, while the approach suggested by Gibson and Sailor leads to erroneously reduced concentrations near the ground in convective and especially forced convective conditions.     

Landslide deposits as stratigraphical markers for a sequence‐based glacial stratigraphy: a case study of a Younger Dryas system in the Eastern Alps

Detailed ¹⁰Be and ¹⁴C dating and supporting pollen analysis of Alpine Lateglacial glacial and landslide deposits in the Hohen Tauern Mountains (Austria) constrain a sequence‐based stratigraphy comprising a major landslide (13.0±1.1 ka) overlain by till and termino‐lateral moraines of an advancing (12.6±1.0 ka) and retreating (11.3±0.8 ka) glacier in turn overlain by a minor landslide (10.8±1.1 ka). These results define glacier activity during the Younger Dryas age Egesen stadial bracketed by landslide activities during the Bølling‐Allerød interstadial and the Preboreal. In contrast to recent studies on Holocene glaciation in the Alps, no traces of any Holocene glacier advance bigger than during the Little Ice Age are documented. Furthermore, this study demonstrates the advantages of using an allostratigraphical approach based on unconformity‐bounded sedimentary units as a tool for glacial stratigraphy in formerly glaciated mountain regions, rather than a stratigraphy based on either isolated morphological features or lithostratigraphical characteristics.     

Submicromolar Oxygen Profiles at the Oxic–Anoxic Boundary of Temperate Lakes

Elements involved in biogeochemical cycles undergo rapid turnover at the oxic–anoxic interface of stratified lakes. Here, the presence or absence of oxygen governs abiotic and biotic processes and rates. However, achieving a detailed sampling resolution to precisely locate the oxic–anoxic interface is difficult due to a lack of fast, drift-free sensors in the working range of 10 to a few 1,000 nmol O₂ L^?1. Here, we demonstrate that conventional amperometric and optical microsensors can be used to resolve submicromolar oxygen concentrations in a continuous profiling mode. The amperometric drift was drastically reduced by anoxic preconditioning. In situ offset correction in the anoxic layer and a high amplification scheme allowed for an excellent detection limit of < 10 nmol L^?1. The optical microsensors also showed a similar performance with a detection limit of < 20 nmol L^?1. Their drift stability allowed for a laboratory calibration in combination with a minor in situ anoxic offset correction. The two different sensor systems showed virtually identical profiles during parallel use in stratified lakes. Both sensors were able to resolve the fine-scale structure at the oxic–anoxic interface and revealed hitherto unnoticed extended zones of submicromolar oxygen concentrations even below a steep oxycline. The zones extended up to several meters and showed substantial vertical variability. These results underline the need of a precise localization of the oxic–anoxic interface on a submicromolar scale in order to constrain the relevant aerobic and anaerobic redox processes.