The Dodo: from extinction to the fossil record

The dodo, Raphus cucullatus (Aves, Columbidae), has become one of the most famous birds in the world, a true icon of extinction. Known from a few contemporary illustrations and accounts, probably more has been written about it than any other species, yet we know practically nothing about the bird in life. Recent excavations on Mauritius are now revealing the ecology and habitat of this iconic bird, and providing new information as to why it was so vulnerable to human interference.     

A self‐limiting bank erosion mechanism? inferring temporal variations in bank form and skin drag from high resolution topographic data

Fluvial bank erosion rates are often quantified by assuming that the erosion rate is a function of the excess (above a critical threshold) boundary shear stress applied by the flow. Research has shown that the form roughness induced by natural topographic bank features, such as slumps, spurs and embayments, is the dominant component of the spatially‐averaged total shear stress, meaning that form roughness provides an important control on bank erosion rates. However, measuring the relative components of the total shear stress for a natural system is not straightforward. In this work we use the method of Kean and Smith to partition the form and skin drag components of river bank roughness using a time series (2005–2011) of high‐resolution topographic surveys of an eroding bank of the Cecina River in central Italy. This method approximates the form drag component of the roughness along a longitudinal bank profile as a series of user‐defined Gaussian curves. The extracted metrics are used in conjunction with an estimate of the outer region flow velocity to partition the form and skin drag components of the total boundary shear stress according to the Kean and Smith analytical solution. The relative magnitude of the form and skin shear stress at each survey date is analysed alongside DEMs of difference to reveal that intense episodes of erosion are followed by periods of quiescence. We show that this is due to the protection offered by increased form drag roughness following erosion. We conceptualise the dynamic feedbacks that exist between river discharge, bank erosion processes and bank form roughness, into a simple model of the self‐limiting nature of river bank erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic Source Characteristics of Nuclear and Chemical Explosions in Granite from Hydrodynamic Simulations

Seismic source characteristics of low-yield (0.5–5 kt) underground explosions are inferred from hydrodynamic simulations using a granite material model on high-performance (parallel) computers. We use a non-linear rheological model for granite calibrated to historical near-field nuclear test data. Equivalent elastic P-wave source spectra are derived from the simulated hydrodynamic response using reduced velocity potentials. Source spectra and parameters are compared with the models of Mueller and Murphy (Bull Seism Soc Am 61:1675–1692, 1971, hereafter MM71) and Denny and Johnson (Explosion source phenomenology, pp 1–24, 1991, hereafter DJ91). The source spectra inferred from the simulations of different yields at normal scaled depth-of-burial (SDOB) match the MM71 spectra reasonably well. For normally buried nuclear explosions, seismic moments are larger for the hydrodynamic simulations than MM71 (by 25 %) and for DJ91 (by over a factor of 2), however, the scaling of moment with yield across this low-yield range is consistent for our calculations and the two models. Spectra from our simulations show higher corner frequencies at the lower end of the 0.5–5.0 kt yield range and stronger variation with yield than the MM71 and DJ91 models predict. The spectra from our simulations have additional energy above the corner frequency, probably related to non-linear near-source effects, but at high frequencies the spectral slopes agree with the f ^?2 predictions of MM71. Simulations of nuclear explosions for a range of SDOB from 0.5 to 3.9 show stronger variations in the seismic moment than predicted by the MM71 and DJ91 models. Chemical explosions are found to generate higher moments by a factor of about two compared to nuclear explosions of the same yield in granite and at normal depth-of-burial, broadly consistent with comparisons of nuclear and chemical shots at the US Nevada Test Site (Denny, Proceeding of symposium on the non-proliferation experiment, Rockville, Maryland, 1994). For all buried explosions, the region of permanent deformation and material damage is not spherical but extends along the free surface above and away from the source. The effect of damage induced by a normally buried nuclear explosion on seismic radiation is explored by comparing the motions from hydrodynamic simulations with those for point-source elastic Green’s functions. Results show that radiation emerging at downward takeoff angles appears to be dominated by the expected isotropic source contribution, while at shallower angles the motions are complicated by near-surface damage and cannot be represented with the addition of a simple secondary compensated linear vector dipole point source above the shot point. The agreement and differences of simulated source spectra with the MM71 and DJ91 models motivates the use of numerical simulations to understand observed motions and investigate seismic source features for underground explosions in various emplacement media and conditions, including non-linear rheological effects such as material strength and porosity.     

Hydrogen isotopes in palmitic and stearic acids in suspended particles from the Changjiang River Estuary

Hydrogen isotopes in lipid biomarkers can trace past changes in the hydrologic cycle. Recent studies have revealed the potential of hydrogen isotopes in microalgal lipids for quantitatively reconstructing water δ~2H(δD) values and salinity. In this study we collected suspended particles along a salinity gradient from the Changjiang River Estuary(CRE), and measured δD values in fatty acids in these particles. The results indicated that δD values of water were correlated highly with salinity from the CRE, in agreement with the results from other estuaries. δD values in palmitic acid and stearic acid had a positive correlation with δD values of water from the CRE. Nevertheless, in the CRE, hydrogen isotope fractionation in fatty acids relative to water increased as salinity increased, opposite the trend in hydrogen isotope fractionation with salinity found in microalgal culture and field studies. We attribute the increase in hydrogen isotope fractionation as salinity increased to light availability, which was likely lower in the particle rich mixing zone at the end of the estuary, and potentially as well to multiple sources of fatty acids in the CRE.     

Detecting and quantifying sources of non-stationarity via experimental semivariogram modeling

Conventional geostatistics often relies on the assumption of second order stationarity of the random function (RF). Generally, local means and local variances of the random variables (RVs) are assumed to be constant throughout the domain. Large scale differences in the local means and local variances of the RVs are referred to as trends. Two problems of building geostatistical models in presence of mean trends are: (1) inflation of the conditional variances and (2) the spatial continuity is exaggerated. Variance trends on the other hand cause conditional variances to be over-estimated in certain regions of the domain and under-estimated in other areas. In both cases the uncertainty characterized by the geostatistical model is improperly assessed. This paper proposes a new approach to identify the presence and contribution of mean and variance trends in the domain via calculation of the experimental semivariogram. The traditional experimental semivariogram expression is decomposed into three components: (1) the mean trend, (2) the variance trend and (3) the stationary component. Under stationary conditions, both the mean and the variance trend components should be close to zero. This proposed approach is intended to be used in the early stages of data analysis when domains are being defined or to verify the impact of detrending techniques in the conditioning dataset for validating domains. This approach determines the source of a trend, thereby facilitating the choice of a suitable detrending method for effective resource modeling.     

Extending ground-motion prediction equations for spectral accelerations to higher response frequencies

Ground-motion prediction equations (GMPEs) for spectral accelerations have traditionally focused on the range of response periods most closely associated with the dynamic characteristics of buildings. Providing predictions only in this period range (from 0.1 to 2 or 3 s) has also accommodated the assumed limitations on the usable period range resulting from the processing of accelerograms. There are, however, engineering applications for which estimates of spectral ordinates are required at shorter response periods. Recent work has demonstrated that high-frequency spectral ordinates are relatively insensitive to record processing, contrary to previous assumptions. In the light of this finding, additional regressions are performed to extend a recent pan-European GMPE to higher response frequencies. This model and others that also include coefficients for spectral ordinates at several high response frequencies are used to explore options for interpolating coefficients for equations that do not provide good coverage in this range. The challenges and uncertainties associated with such interpolations are discussed. The paper concludes that a set of standard response frequencies could be usefully established for future GMPEs.     

In Situ Biotreatment of TBA with Recirculation/Oxygenation

The potential for in situ biodegradation of tert‐butyl alcohol (TBA) by creation of aerobic conditions in the subsurface with recirculating well pairs was investigated in two field studies conducted at Vandenberg Air Force Base. In the first experiment, a single recirculating well pair with bromide tracer and oxygen amendment successfully delivered oxygen to the subsurface for 42 d. TBA concentrations were reduced from approximately 500 μg/L to below the detection limit within the treatment zone and the treated water was detected in a monitoring transect several meters downgradient. In the second experiment, a site‐calibrated model was used to design a double recirculating well pair with oxygen amendment, which successfully delivered oxygen to the subsurface for 291 d and also decreased TBA concentrations to below the detection limit. Methylibium petroleiphilum strain PM1, a known TBA‐degrading bacterium, was detectable at the study site but addition of oxygen had little impact on the already low baseline population densities, suggesting that there was not enough carbon within the groundwater plume to support significant new growth in the PM1 population. Given favorable hydrogeologic and geochemical conditions, the use of recirculating well pairs to introduce dissolved oxygen into the subsurface is a viable method to stimulate in situ biodegradation of TBA or other aerobically degradable aquifer contaminants.     

An evaluation of the applicability of the NGA models to ground-motion prediction in the Euro-Mediterranean region

The first phase of the Next Generation Attenuation (NGA) project has now finished, resulting in the publication of five new sets of empirical ground-motion models for PGA, PGV and response spectral ordinates. These models mark a significant advancement in the state-of-the-art in empirical ground-motion modelling and include many effects that are not accounted for in existing European equations. Under the assumption that the Euro-Mediterranean database from which the European relationships are derived is unlikely to drastically change in the near future, a prudent question to ask is: can the NGA models be applied in Europe? In order to answer this question, the NGA model of Boore and Atkinson (PEER Report 2007/01, Pacific Earthquake Engineering Research Center, Berkeley, CA, 234 pp., 2007), which is shown to be representative of the NGA models as a suite, is compared with the dataset used for the development of the most recent European empirical ground-motion models for response spectral ordinates and peak ground velocity. The comparisons are made using analyses of model residuals and the likelihood approach of Scherbaum et al. (Bull Seism Soc Am 94(6):2164–2185, 2004). The analyses indicate that for most engineering applications, and particularly for displacement-based approaches to seismic design, the NGA models may confidently be applied within Europe. Furthermore, it is recommended that they be used in conjunction with existing European models to provide constraint on finite-fault effects and non-linear site response within logic-tree frameworks. The findings also point to the potential benefits of merging the NGA and European datasets.