The geochemistry and petrogenesis of the Lower Paleozoic granitoids of the Lleyn Peninsula,North Wales

The Lleyn Peninsula of North Wales is penetrated by at least twenty stocks varying from microtonalite through to microgranite and these are closely associated with Caradocian volcanic rocks which include andesitic lavas.Major and trace element analyses show that the sample population may be separated into a peralkaline group and a sub-alkaline group. This latter group may be sub-divided into three compositional series which range from andesite to granite. The andesites are represented by the Caradocian lavas of the Moel y Penmaen district and these plot at one end of major and trace element variation diagrams. Their coherent relationships to the granitoids demonstrate the latter to be Ordovician and therefore ends a longstanding controversy concerning their age. The distinctive geochemistry of the andesites indicates the strong probability that they have evolved from transitional tholeiitic magma by low-pressure crystal fractionation. Apatite fractionation has strongly controlled the rare earth element abundances in the granitoids and for most compositions from andesite through granite their bulk distribution coefficient is greater than unity.The association of peralkaline granites, transitional tholeiites and other geological and geophysical evidence suggests that the area was a region of ensialic crustal tension during the mid-Ordovician.     

Seismic risk of circum-pacific earthquakes I. Strain energy release

Commonly used earthquake “whole process” frequency - magnitude and strain energy - magnitude laws are merged to obtain an analytic expression for an upper bound magnitude to regional earthquake occurrenceM ₃, which is expressed primarily in terms of the annual maximum magnitudeM ₁ and the magnitude equivalent of the annual average total strain energy releaseM ₂. Values ofM ₃ are also estimated graphically from cumulative strain energy release diagrams. Both methods are illustrated by application to the high seismicity of the circum-Pacific belt, using Duda’s (1965) data and regionalisation. Values ofM ₃ obtained analytically, with their uncertainties, are in agreement with those obtained graphically. Empirical relations are then obtained betweenM ₁,M ₂, andM ₃, which could be of general assistance in regional seismic risk considerations if they are found to be of a universal nature. For instance.M ₃ andM ₂ differ by one magnitude unit in subregions of the circum-Pacific.     

Chironomid-based paleosalinity records in southern British Columbia, Canada: a comparison of transfer functions

Chironomid remains from Big Lake, British Columbia were analysed and paleosalinities were estimated using a pre-existing transfer function and several developed using new regression methods. A two component partial-least-squares model (PLS-2) had the highest coefficient of determination (R² _(Jackknifed) = 0.75) and lowest root-mean-squared error-of-prediction (RMSEP). As compared to the pre-existing model, it was also less sensitive to the influence of rare taxa. Nevertheless, the marginally larger R² _(Jackknifed) and lower RMSEP do not clearly identify a single best model. The models were applied to Big, Mahoney and Kilpoola lakes, revealing the sensitivity of paleosalinity inferences to model selection. A synopsis of chironomid-based paleosalinities in British Columbia and their correspondence with other paleoclimatic data are presented and discussed.     

Inverse groundwater modelling in the Willunga Basin,South Australia

A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved groundwater resource management. Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478.     

International Year of Astronomy 2009

IYA2009 will be a great opportunity for all of us working in astronomy (and space) to make an impact; certainly locally and nationally and, we hope, globally. So what is going on and how can you participate? Ian Robson has the answers.     

Space exploration and the RAS

Mike Hapgood and Ian Crawford assess the relevance of the BNSC UKSEWG Report for the Royal Astronomical Society.     

Large-scale impacts of bottom trawling on shelf primary productivity

Disturbance of the seabed resulting from bottom trawling affects ecosystem processes, such as the rate and magnitude of nutrient regeneration. The potential responses of the plankton community arising from such effects can be modelled, provided that reliable data on the effects on nutrient fluxes are available. In a north Cretan outer continental shelf and upper slope fishing ground (Heraklion Bay, Crete, Eastern Mediterranean) we applied a new field instrument which can simulate the passage of trawl groundropes across the sea floor and made direct seasonal measurements of the rate of dissolved and particulate nutrient releases resulting from seabed disturbance. These observational data were then integrated in a 3D ecosystem model. Results revealed that bottom trawling may trigger off considerable productivity pulses, in addition to pulses from the natural seasonal cycle.     

Use of high spectral resolution remote sensing to determine leaf palatability of eucalypt trees for folivorous marsupials

In this study we assess the feasibility of remotely measuring canopy biochemistry, and thus the potential for conducting large-scale mapping of habitat quality. A number of studies have found nutrient composition of eucalypt foliage to be a major determinant of the distribution of folivorous marsupials. More recently it has been demonstrated that a specific group of secondary plant chemicals, the diformylphloroglucinols (DFPs), are the most important feeding deterrents, and are thus vital determinants of habitat quality. We report on the use of laboratory spectroscopy to attempt to identify one such DFP, sideroxylonal-A, in the foliage of Eucalyptus melliodora, one of the few eucalypt species browsed by folivorous marsupials. Reflectance spectra were obtained for freeze-dried, ground leaves using near infrared spectroscopy (NIRS) and for both oven-dried and fresh whole leaves using a laboratory-based (FieldSpec) spectroradiometer. Modified partial least squares (MPLS) regression was used to develop calibration equations for sideroxylonal-A concentration based on the reflectance spectra transformed as both the first and second difference of absorbance (Log 1/R). The predictive ability of the calibration equations was assessed using the standard error of calibration statistic (SECV). Coefficients of determination (r²) were highest for the ground leaf spectra (0.98), followed by the fresh leaf and dry leaf spectra (0.94 and 0.87, respectively). When applied to independent validation sub-sets, sideroxylonal-A was most accurately predicted from the ground leaf spectra (r² = 0.94), followed by the dry leaf and fresh leaf spectra (0.72 and 0.53, respectively). Two spectral regions, centred on 674 nm and 1394 nm, were found to be highly correlated with sideroxylonal-A concentration for each of the three spectral data sets studied. Results from this study suggest that calibration equations derived from modified partial least squares regression may be used to predict sideroxylonal-A concentration, and hence leaf palatability, of Eucalyptus melliodora trees, thereby indicating that the remote estimation of habitat quality of eucalypt forests for marsupial folivores is feasible.     

Vortex shedding behind tapered obstacles in neutral & stratified flow

Results of laboratory and numerical experiments on both homogeneous and density-stratified flow over single, bluff obstacles of various shapes are presented. The obstacle height is in most cases of the same order as the base diameter and the major controlling (flow) parameter is the Froude number, defined here as F_h=U/Nh, where U is the (uniform) upstream velocity, h the obstacle height and N is the buoyancy frequency. Attention is concentrated, firstly, on the case of homogeneous flows over rather weakly tapered obstacles and, secondly, for bodies whose height is similar to their base width, on the case F_h=0.1, representing stratification sufficiently strong that lee-wave motions do not play a significant role in the flow dynamics. For right-circular cones it is shown that the sectional contributions to the total fluctuating side force (lift) show significant phase variations up the height of the obstacle, which are not always reflected in the developed vortex street further downstream. For some obstacle shapes, the vortex lines linking the von Karman eddies at different heights can be significantly tilted, particularly in the upper part of the wake. Vortex convection speeds do not appear generally to vary greatly with height and, as found in previous work, the shedding frequency remains constant with height, despite the strong variation of cross-stream obstacle width. By comparison with the homogeneous results, it is suggested that the stratification enhances the shedding instability, which would otherwise be very weak for squat obstacles, but does not annihilate the ability of the flow at one level to influence that at another.