Seismic and Petrophysical Relationships from UK Continental Shelf Rocks at Elevated Pressures

There are few published seismic (P- and S-waves) properties for seafloor bedrocks. At low pressures (1 to 10 MPa), velocities and attenuations are determined mainly by open microcracks. At higher pressures, the microcracks close, and the velocities and attenuations depend primarily on the matrix porosity. We have investigated both the relationships between the acoustic, petrophysical, and geological properties of the rocks at 40 MPa pressure and the effect of microcracks on the acoustic properties at 10 MPa pressure. In this paper we discuss the former; the latter will be discussed separately. P- and S-wave velocity and attenuation measurements were carried out on a suite of seabed sedimentary and igneous rocks at effective pressures from 10 to 40 MPa at ultrasonic frequencies. The porosities and permeabilities of the rocks ranged from 0% to 32% and 0 to 110 mDarcy, respectively. Characterization of the rocks revealed that most of the sandstones have a substantial clay content (kaolinite, illite, and chlorite) and fractures. Most of the igneous rocks are chloritized. The seismic properties of the rocks are markedly lower than those of similar continental rocks because of the microporosity formed by the alteration of feldspars, micas, and mafic minerals to clays (e.g., chloritization of pyroxenes) and the corresponding reduction of the elastic moduli. The results of this study suggest that the values of velocities and quality factors used for ocean acoustic propagation models are lower than normally assumed.     

A new scenario framework for climate change research: background,process, and future directions

The scientific community is developing new global, regional, and sectoral scenarios to facilitate interdisciplinary research and assessment to explore the range of possible future climates and related physical changes that could pose risks to human and natural systems; how these changes could interact with social, economic, and environmental development pathways; the degree to which mitigation and adaptation policies can avoid and reduce risks; the costs and benefits of various policy mixes; and the relationship of future climate change adaptation and mitigation policy responses with sustainable development. This paper provides the background to and process of developing the conceptual framework for these scenarios, as described in the three subsequent papers in this Special Issue (Van Vuuren et al., 2013; O’Neill et al., 2013; Kriegler et al., Submitted for publication in this special issue). The paper also discusses research needs to further develop, apply, and revise this framework in an iterative and open-ended process. A key goal of the framework design and its future development is to facilitate the collaboration of climate change researchers from a broad range of perspectives and disciplines to develop policy- and decision-relevant scenarios and explore the challenges and opportunities human and natural systems could face with additional climate change.     

The role of technology for achieving climate policy objectives: overview of the EMF 27 study on global technology and climate policy strategies

This article presents the synthesis of results from the Stanford Energy Modeling Forum Study 27, an inter-comparison of 18 energy-economy and integrated assessment models. The study investigated the importance of individual mitigation options such as energy intensity improvements, carbon capture and storage (CCS), nuclear power, solar and wind power and bioenergy for climate mitigation. Limiting the atmospheric greenhouse gas concentration to 450 or 550 ppm CO₂ equivalent by 2100 would require a decarbonization of the global energy system in the 21^st century. Robust characteristics of the energy transformation are increased energy intensity improvements and the electrification of energy end use coupled with a fast decarbonization of the electricity sector. Non-electric energy end use is hardest to decarbonize, particularly in the transport sector. Technology is a key element of climate mitigation. Versatile technologies such as CCS and bioenergy are found to be most important, due in part to their combined ability to produce negative emissions. The importance of individual low-carbon electricity technologies is more limited due to the many alternatives in the sector. The scale of the energy transformation is larger for the 450 ppm than for the 550 ppm CO₂e target. As a result, the achievability and the costs of the 450 ppm target are more sensitive to variations in technology availability.     

Anisotropy and depth‐related heterogeneity of hydraulic conductivity in a bog peat. II: modelling the effects on groundwater flow

Anisotropy and heterogeneity of hydraulic conductivity (K) are seldom considered in models of mire hydrology. We investigated the effect of anisotropy and heterogeneity on groundwater flow in bog peat using a steady‐state groundwater model. In five model simulations, four sets of K data were used. The first set comprised measured K values from an anisotropic and heterogeneous bog peat. These data were aggregated to produce the following simplified data sets: an isotropic and heterogeneous distribution of K; an isotropic and homogeneous distribution; and an anisotropic and homogeneous distribution. We demonstrate that, where anisotropy and heterogeneity exist, groundwater flow in bog peat is complex. Fine‐scale variations in K have the potential to influence patterns and rates of groundwater flow. However, for our data at least, it is heterogeneity and not anisotropy that has the greater influence on producing complex patterns of groundwater flow. We also demonstrate that patterns and rates of groundwater flow are simplified and reduced when measured K values are aggregated to create a more uniform distribution of K. For example, when measured K values are aggregated to produce isotropy and homogeneity, the rate of modelled seepage is reduced by 28%. We also show that when measured K values are used, the presence of a drainage ditch can increase seepage through a modelled cross‐section. Our work has implications for the accurate interpretation of hydraulic head data obtained from peat soils, and also the understanding of the effect of drainage ditches on patterns and rates of groundwater flow. Copyright © 2002 John Wiley & Sons, Ltd.     

A Chandra X-ray observation of the globular cluster Terzan 1

We present a ∼19-ks Chandra Advanced CCD Imaging Spectrometer (ACIS)-S observation of the globular cluster Terzan 1. 14 sources are detected within 1.4 arcmin of the cluster centre with two of these sources predicted to be not associated with the cluster (background active galactic nuclei or foreground objects). The neutron star X-ray transient, X1732−304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12 yr. Here, we find four sources that are consistent with the ROSAT position for this transient, but none of the sources are fully consistent with the position of a radio source detected with the Very Large Array that is likely associated with the transient. The most likely candidate for the quiescent counterpart of the transient has a relatively soft spectrum and an unabsorbed 0.5–10 keV luminosity of  2.6 × 10³² erg s⁻¹  , quite typical of other quiescent neutron stars. Assuming standard core cooling, from the quiescent flux of this source we predict long (>400 yr) quiescent episodes to allow the neutron star to cool. Alternatively, enhanced core cooling processes are needed to cool down the core. However, if we do not detect the quiescent counterpart of the transient this gives an unabsorbed 0.5–10 keV luminosity upper limit of  8 × 10³¹ erg s⁻¹  . We also discuss other X-ray sources within the globular cluster. From the estimated stellar encounter rate of this cluster we find that the number of sources we detect is significantly higher than expected by the relationship of Pooley et al.