Modeling IR spectral energy distributions: a?pilot study of?starburst parameters and silicate absorption curves for some GOALS galaxies

This paper describes a pilot study into the spectral energy distribution (SED) fitting and the derivation of physical parameters for 19 galaxies observed as part of the Great Observatories All-sky LIRG Survey (GOALS) survey as observed with the Spitzer Space Telescope. For this we have used the pan-spectral fitting tools developed in a series of papers by Dopita and his co-workers. We show that the standard Lee and Draine ??astronomical silicate?? model cannot provide a good fit to the silicate absorption features as observed in the heavily dust-extinguished (A _V??50 mag.) starbursts. We have derived an empirical fit to the ??starburst silicate?? absorption in these objects. This absorption curve is consistent with the silicate grains being systematically larger in starburst environments than in the local Galactic interstellar medium. We demonstrate the sensitivity of the SED fitting to each of the fitted parameters, and derive these parameters for those galaxies which do not have an embedded AGN. This technique is simple and provides reasonably robust and uniform parameters for the starburst, especially as far as the star formation rate, population of old stars, compactness of the starburst region and total foreground extinction are concerned. However, the chemical abundances and the optical extinction cannot be reliably determined by this analysis, and optical SEDs will also be required to provide a complete characterization of the starburst region and of the surrounding galaxy.     

Mapping sub‐pixel fluvial grain sizes with hyperspatial imagery

This study presents an investigation of image texture approaches for mapping sub‐pixel fluvial grain‐size features from airborne imagery, allowing for the rapid acquisition of surface sand and coarse fraction (>1·41 mm) grain‐size information. Imagery at 30 mm resolution was acquired over four gravel bars from the Fraser River (British Columbia, Canada). Combined first‐order and second‐order image texture approaches (windowed standard deviation filter and the grey level co‐occurrence matrix) were used. First‐order image texture, through the application of a standard deviation filter and subsequent thresholding was used to detect the presence of surface sand, with optimal accuracy achieved at 91 ± 1·9%. A wide‐ranging parameter space investigation was used to derive optimum parameters for the grey‐level co‐occurrence matrix. Subsequently first‐order and second‐order image textures were used in multiple linear regression to achieve good calibrations with several sub‐pixel grain‐size percentiles; relative error at 1·44%, 3·18%, 6·80% and 10·6% for D₅, D₁₆, D₃₅ and D₅₀, respectively. The larger percentiles of D₈₄ and D₉₅ had relative errors of 24·7% and 29·7%, respectively. The breakdown of calibration precision for larger percentiles is attributed to a ‘pixel averaging effect’. It is concluded that multispectral imagery is not required, because sufficient image texture information can be derived from standard colour imagery. Recommendations are suggested for the application of this method to other localities and data sets, thus reducing exhaustive parameter searches in future studies.     

A multi-isotope (δD, δO,Sr/Sr,and δB) approach for identifying saltwater intrusion and resolving groundwater evolution along the Western Caprock Escarpment of the Southern High Plains,New Mexico

Declining water levels in arid and semi-arid regions increase an aquifer’s vulnerability to natural and anthropogenic influences. A multi-isotope (δD, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr, and δ¹¹B) approach was used to resolve the geochemical evolution of groundwater in a declining aquifer in a semi-arid region of the southwestern USA as groundwater composition reacts to source-water mixing, cross-formational flow including saltwater intrusion, water–rock interaction, and likely agricultural recharge. Sub-aquifers or local flow systems are present in the Southern High Plains aquifer along the Western Caprock Escarpment in New Mexico, and the study site’s local flow system contains a Na–Cl, high dissolved-solids groundwater that flows from the escarpment until it mixes with a high quality regional aquifer or regional flow system. The local flow system contains water that is similar in composition to the underlying, upper Dockum Group aquifer. Saltwater found in the upper Dockum Group aquifer likely originates in the adjacent Pecos River Basin and crosses beneath or possibly through the hydrologic divide of the Western Caprock Escarpment. Strontium concentrations of 0.9–31 mg/L and a ⁸⁷Sr/⁸⁶Sr range of 0.70845–0.70906 were sufficient to estimate source-water fractions, mixing patterns, and contributions from chemical weathering through mass balance inverse calculations. Boron concentrations (59–1740 mg/L) and δ¹¹B values (+6.0–+46.0‰) were used to confirm source-water mixing, further evaluate water–rock interaction, and examine the influence of possible agricultural recharge. Alteration of B concentrations and δ¹¹B values in an area of likely agricultural recharge indicated the loss of B and decrease in δ¹¹B values likely from plant uptake, adsorption, and weathering contributions in the soil/vadose zone prior to recharge. The effectiveness of ⁸⁷Sr/⁸⁶Sr and δ¹¹B for resolving the geochemical influences in groundwater in the Southern High Plains along the Western Caprock Escarpment allowed for the reinterpretation of the isotopic composition of water that has been shown to be highly variable in the Southern High Plains. This study shows the utility of a multi-isotope approach for resolving the geochemical evolution of groundwater in an aquifer that has a complex relationship with underlying aquifers and the applicability of these isotopes as indicators of the alteration of source waters from natural or anthropogenic influences.     

Sediment quality of the lower St. Johns River, Florida: an integrative assessment of benthic fauna, sediment-associated stressors, and general habitat characteristics

Sediment quality of the lower St. Johns River (LSJR) estuary, Florida was evaluated using synoptic data on benthic community structure, levels of potential stressors (chemical contaminants, ammonia and sulfide), and other basic habitat characteristics (depth, dissolved oxygen, salinity, temperature) collected at seven stations, three times a year from July 2000-July 2002. Un-ionized ammonia and hydrogen sulfide were detected at toxic levels on at least one sampling occasion at four stations. Chemical contamination of sediment at probable bioeffect levels also was observed at four stations. Concentrations of pesticides or other chemical substances typically associated with human activities (e.g., PCBs) were detectable at all stations, though not always present at concentrations likely of causing significant bioeffects. A total of 251 taxa and 9783 individuals were identified and enumerated from the benthic infaunal samples. Polychaete worms and molluscs dominated the benthic fauna at all seven stations. The opportunistic and pollution-tolerant polychaete Streblospio benedicti was the most abundant species overall (from all samples combined), appearing as a dominant at five of the seven stations. Overall, the sites sampled as part of this study indicate a highly stressed benthos resulting from multiple anthropogenic impacts.     

Stepwise inversion of a groundwater flow model with multi-scale observation data

Based on the regional hydrogeology and the stratigraphy beneath the Los Alamos National Laboratory (LANL) site, New Mexico (USA), a site-scale groundwater model has been built with more than 20 stratified hydrofacies. A stepwise inverse method was developed to estimate permeabilities for these hydrofacies by coupling observation data from different sources and at various spatial scales including single-well test, multiple-well pumping test and regional aquifer monitoring data. Statistical analyses of outcrop permeability measurements and single-well test results were used to define the prior distributions of the parameters. These distributions were used to define the parameter initial values and the lower and upper bounds for inverse modeling. A number of inverse modeling steps were performed including the use of drawdown data from the pump tests at two wells (PM-2 and PM-4) separately, and a joint inversion coupling PM-2 and PM-4 pump test data and head data from regional aquifer monitoring. Parameter sensitivity coefficients for different data sets were computed to analyze if the model parameters can be estimated accurately with the data provided at different steps. The joint inversion offers a reasonable fit to all data sets. The uncertainty of estimated parameters for the hydrofacies is addressed with the parameter confidence intervals.     

FDE index for goodness‐of‐fit between measured and calculated response signals

A method is presented for determining the goodness‐of‐fit between measured and calculated structural response signals. The method is termed as the frequency domain error (FDE) index, which is a value between 0 and 1 where zero indicates a perfect correlation. The FDE is calculated from the Fourier spectra of the measured and calculated waveforms, using a relatively simple calculation procedure, readily implemented using standard fast Fourier transform (FFT) libraries. The FDE is demonstrated herein using three different types of problems: simple harmonic waves, a large number of earthquake response simulations, and a set of limited simulations. Along with the FDE concept, effective methods for displaying the results are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Identifying uncertainties in Arctic climate change projections

Wide ranging climate changes are expected in the Arctic by the end of the 21st century, but projections of the size of these changes vary widely across current global climate models. This variation represents a large source of uncertainty in our understanding of the evolution of Arctic climate. Here we systematically quantify and assess the model uncertainty in Arctic climate changes in two CO₂ doubling experiments: a multimodel ensemble (CMIP3) and an ensemble constructed using a single model (HadCM3) with multiple parameter perturbations (THC-QUMP). These two ensembles allow us to assess the contribution that both structural and parameter variations across models make to the total uncertainty and to begin to attribute sources of uncertainty in projected changes. We find that parameter uncertainty is an major source of uncertainty in certain aspects of Arctic climate. But also that uncertainties in the mean climate state in the 20th century, most notably in the northward Atlantic ocean heat transport and Arctic sea ice volume, are a significant source of uncertainty for projections of future Arctic change. We suggest that better observational constraints on these quantities will lead to significant improvements in the precision of projections of future Arctic climate change.     

A case study of a modelled episode of low Arctic sea ice

Simulations of the Arctic sea ice cover over the last 32 years generated by the HadGEM1 coupled climate model are able to capture the observed long term decline in mean September ice extent. HadGEM1 is also capable of producing an episode of low September ice extent of similar magnitude to the anomalously low extent observed in 2007. Using a heat budget analysis, together with diagnostics partitioning the changes in ice and snow mass into thermodynamic and dynamic components, we analyse the factors driving the long term decline in the ice mass and extent as well as those causing the modelled low ice event. The long term decline in the mass of ice and snow in HadGEM1 is largely due to extra melting during the summer, partly at the top surface of the ice, and partly via extra heating from the ocean as it warms due to the ice retreat. The episode of low summer ice extent is largely driven by the synoptic conditions over the summer moving the ice across and out of the Arctic basin, and also due to pre-conditioning of the snow and ice which is thinner than usual in the Eastern Arctic at the start of the melt season. This case study demonstrates that although HadGEM1 does not capture the persistent dipole pressure anomaly observed during the summer of 2007, it represents broadly similar mechanisms of generating a low ice extent.     

New Zealand's abandonment of the Carbon Neutral Public Service programme

In 2009, New Zealand's new National-led government abandoned the Carbon Neutral Public Service (CNPS) programme, a Labour-led government initiative intended to help Government achieve carbon neutrality within its core agencies. This short analysis article provides an overview and brief assessment of the CNPS initiative by drawing on the relevant scholarly literature and public documents relating to New Zealand's climate change agenda. It is argued that although the CNPS programme faced a range of challenges it was successful in some respects. Although the Labour-led government was keen to act on climate change mitigation, New Zealand no longer intends to take a lead on carbon neutrality under the National-led government.