Pearce, Nicholas, Denton, J.S., Perkins, W.T., Westgate, J.A., (2007) 'Correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation ICP-MS analyses: current status and future potential', Journal of Quaternary Science 22(7) pp.721-736 RAE2008Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a high spatial resolution analytical method which has been applied to the analysis of silicic tephras. With current instrumentation, around 30 trace elements can be determined from single glass shards as small as 40 ?m, separated from tephra deposits. As a result of element fractionation during the ablation process using a 266 nm laser, a relatively complex calibration strategy is required. Nonetheless, such a strategy gives analyses which are accurate (typically within ?5%) and have an analytical precision which varies from ?2% at 100 ppm, to ?15% at 1 ppm. Detection limits for elements used in correlation and discrimination studies are well below 1 ppm. Examples of the application of trace element analysis by LA-ICP-MS in tephra studies are presented from the USA, New Zealand and the Mediterranean. Improvements in instrumental sensitivity in recent years have the potential to lower detection limits and improve analytical precision, thus allowing the analysis of smaller glass shards from more distal tephras. Laser systems operating at shorter wavelengths (e.g. 193 nm) are now more widely available, and produce a much more controllable ablation in glasses than 266 nm lasers. Crater sizes ofPeer reviewe

Knowledge of the plasma fluxes at geosynchronous orbit is important to both scientific and operational investigations. We present a new empirical model of the ion flux and the electron flux at geosynchronous orbit (GEO) in the energy range~1 eV to~40 keV. The model is based on a total of 82 satellite years of observations from the magnetospheric plasma analyzer instruments on Los Alamos National Laboratory satellites at GEO. These data are assigned to a fixed grid of 24 local times and 40 energies, at all possible values of Kp. Bilinear interpolation is used between grid points to provide the ion flux and the electron flux values at any energy and local time, and for given values of geomagnetic activity (proxied by the 3 h Kp index), and also for given values of solar activity (proxied by the daily F 10.7 index). Initial comparison of the electron flux from the model with data from a Compact Environmental Anomaly Sensor II, also located at geosynchronous orbit, indicates a good match during both quiet and disturbed periods. The model is available for distribution as a FORTRAN code that can be modified to suit user requirements.

The degassing of magmatic volatiles during eruptions beneath ice sheets and glaciers, as recorded by the dissolved volatile content quenched in volcanic rocks, could provide powerful new constraints on former ice thicknesses in volcanic areas. As volcanic rocks are readily dateable using radiometric methods, subglacial volcanoes may therefore provide crucial information on the timing of palaeo-environmental fluctuations in the Quaternary. Volatile degassing is also likely to control the mechanisms of subglacial eruptions and their associated hazards. In this paper we lay out a number of criteria that must be satisfied for degassing to potentially record palaeo-ice thicknesses, using a variety of new datasets and calculations to highlight existing problems with the technique. These include uncertainties about volatile solubilities, non-equilibrium degassing, sample heterogeneity, hydration, post-quenching movement and whether subglacial pressures deviated significantly from glaciostatic. We propose new strategies for improvement of the technique and discuss how magmatic volatiles may control the style of subglacial eruptions.

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