G.S. Henderson and D.R. Baker (eds): Synchrotron Radiation: Earth,Environmental and Material Sciences Applications. (Short Course Series Volume 30)     

Ian M. Steele 《Mineralium Deposita》2003,38(4):516-516

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Atmospheric deposition of Be and Be in New Zealand rain (1996-98)     

Ian Graham  Robert Ditchburn 《Geochimica et cosmochimica acta》2003,67(3):361-373

Beryllium isotope concentrations were determined in monthly rainfall collections at three sites across New Zealand (36 to 45° S), from October 1996 to November 1998. At the northern sites of Leigh (near Auckland) and Gracefield (near Wellington), ⁷Be and ¹⁰Be concentrations are relatively constant at 1.2 to 1.4 × 10⁷ atoms kg⁻¹ rain and 2.1 to 2.6 × 10⁷ atoms kg⁻¹ rain, respectively. These concentrations correspond to annual flux rates of ∼15 and ∼27 × 10⁹ atoms m⁻² y⁻¹, respectively. At the southern site of Dunedin, concentrations are similar to those at the northern sites, but flux rates are significantly lower at ∼ 9 and ∼19 × 10⁹ atoms m⁻² y⁻¹, respectively, because of lower average rainfall east of the Southern Alps mountain range. These results are broadly similar to those reported by Brown et al. (1989) and Knies et al. (1994) for rain from midlatitude sites in the USA sampled from 1986 to 1994. Mean ⁷Be/¹⁰Be ratios for New Zealand (0.47 to 0.61) are, however, significantly lower than for the USA (0.69 to 0.78), due in part to the addition of ¹⁰Be from re-suspended dust. Subtraction of the dust component increases the New Zealand ⁷Be/¹⁰Be ratios to 0.70 (Leigh), 0.65 (Gracefield) and 0.50 (Dunedin). The adjusted results provide evidence for transfer of older stratospheric air to the troposphere in late-spring-summer, an effect which is strongest in the north. The overall reduction of ⁷Be/¹⁰Be from north to south implies an increase in residence time from ∼ 80 to ∼100 d for Be isotopes in the atmosphere above New Zealand.  相似文献   

UV Laser Ablation ICP-MS: Some Applications in the Earth Sciences   总被引：4，自引：0，他引：4  

Robert W. Nesbitt  Takafumi Hirata  Ian B. Butler  James A. Milton 《Geostandards and Geoanalytical Research》1997,21(2):231-243

This study reports a series of applications of UV laser ablation ICP-MS in the geological sciences. The advantages and disadvantages of the PQ "S" option and the use of nitrogen in the carrier gas are discussed. A general problem common to all ablation techniques is the calibration technique and experiments involving synthetic calibration samples are covered. Zircon geochemistry and geochronology by LA-ICP-MS are discussed and data are presented for REE, Hf and U for a standard zircon (91500) as well as a series of zircons from Zimbabwe. The potential of using Ce and Eu anomalies in petrologic studies is illustrated by zircons from a fractionated gabbroic-granite in the Urals. The potential of the LA-ICP-MS method to utilise standard X-ray fluorescence glass discs is demonstrated as a useful semi-quantitative tool in determining REE patterns. LA-ICP-MS is a powerful tool in the analysis of the platinum group elements (and Re) and some examples are given in the successful application of the technique to partitioning in iron meteorites.  相似文献   

Unusual biomarker maturation ratio changes through the oil window, a consequence of varied thermal history     

Christopher P. N. Davies   《Organic Geochemistry》1997,27(7-8)

Saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas-condensate window to high vitrinite reflectances (R_o = 1.16%) in mature marine and lacustrine Mesozoic clastic samples from a South African basin. Two of the ratios reverse above R_o = 0.9%. These unusual maturation effects result from isolated periods of high rates of maturation increase. The basin cooled regionally after the break-up of Gondwana but high heating rates prevailed during the late Cretaceous-early Tertiary, as Africa moved across a hotspot, and again in the late Tertiary as a result of a possible hotspot and hydrothermal event.  相似文献   

Shear-wave anisotropy: spatial and temporal variations in time delays at Parkfield, Central California   总被引：4，自引：0，他引：4  

Yun Liu  Stuart Crampin  Ian Main 《Geophysical Journal International》1997,130(3):771-785

Shear-wave splitting is analysed on data recorded by the High Resolution Seismic Network (HRSN) at Parkfield on the San Andreas fault, Central California, during the three-year period 1988-1990. Shear-wave polarizations either side of the fault are generally aligned in directions consistent with the regional horizontal maximum compressive stress, at some 70° to the fault strike, whereas at station MM in the immediate fault zone, shear-wave polarizations are aligned approximately parallel to the fault. Normalized time delays at this station are found to be about twice as large as those in the rock mass either side. This suggests that fluid-filled cracks and fractures within the fault zone are elastically or seismically different from those in the surrounding rocks, and that the alignment of fault-parallel shear-wave polarizations are associated with some fault-specific phenomenon.
Temporal variations in time delays between the two split shear-waves before and after a M_L = 4 earthquake can be identified at two stations with sufficient data: MM within the fault zone and VC outside the immediate fault zone. Time delays between faster and slower split shear waves increase before the M_L = 4 earthquake and decrease near the time of the event. The temporal variations are statistically significant at 68 per cent confidence levels. Earthquake doublets and multiplets also show similar temporal variations, consistent with those predicted by anisotropic poroelasticity theory for stress modifications to the microcrack geometry pervading the rock mass. This study is broadly consistent with the behaviour observed before three other earthquakes, suggesting that the build-up of stress before earthquakes may be monitored and interpreted by the analysis of shear-wave splitting.  相似文献   

Geohydrological models and earthquake effects at Yucca Mountain, Nevada     

J. B. Davies  Charles B. Archambeau 《Environmental Geology》1997,32(1):23-35

 Yucca Mountain, the proposed site for the high-level nuclear waste repository, is located just south of where the present water table begins a sharp rise in elevation. This large hydraulic gradient is a regional feature that extends for over 100 km. Yucca Mountain and its vicinity are underlain by faulted and fractured tuffs with hydraulic conductivities controlled by flow through the fractures. Close to and parallel with the region of large hydraulic gradient, and surrounding the core of the Timber Mountain Caldera, there is a 10- to 20-km-wide zone containing few faults and thus, most likely, few open fractures. Consequently, this zone should have a relatively low hydraulic conductivity, and this inference is supported by the available conductivity measurements in wells near the large hydraulic gradient. Also, slug injection tests indicate significantly higher pressures for fracture opening in wells located near the large hydraulic gradient compared to the opening pressures in wells further to the south, hence implying that lower extensional stresses prevail to the north with consequently fewer open fractures there. Analytical and numerical modeling shows that such a boundary between media of high and low conductivity can produce the observed, large hydraulic gradient, with the high conductivity medium having a lower elevation than the water table. Further, as fractures can close due to tectonic activity, the conductivity of the Yucca Mountain tuffs can be reduced to a value near that for the hydraulic barrier due to strain release by a moderate earthquake. Under these conditions, simulations show that the elevation of the steady-state water table could rise between 150 and 250 m at the repository site. This elevation rise is due to the projected shift in the location of the large hydraulic gradient to the south in response to a moderate earthquake, near magnitude 6, along one of the major normal faults adjacent to Yucca Mountain. As the proposed repository would only be 200–400 m above the present water table, this predicted rise in the water table indicates a potential hazard involving water intrusion. Received: 7 June 1996 / Accepted: 19 November 1996  相似文献   

High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater   总被引：1，自引：0，他引：1  

T. K. Yeoman  D. M. Wright  T. R. Robinson  J. A. Davies  M. Rietveld 《Annales Geophysicae》1997,15(6):634-644

The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.  相似文献   

Objective cyclone climatologies of the North Atlantic – a comparison between the ECMWF and NCEP Reanalyses     

C. E. Hanson  J. P. Palutikof  T. D. Davies 《Climate Dynamics》2004,22(6-7):757-769

Simple and easily reproducible techniques have been used to construct two objective cyclone climatologies of the North Atlantic-European sector. The goal of this study is to increase understanding of cyclones with the potential to cause damage, in particular, those reaching Beaufort category 7 and above. The two climatologies constructed here span the period 1979–2000 and have been developed from reanalysis mean sea level pressure data from the ECMWF (European Centre for Medium Range Weather Forecasts) and NCEP (National Centres for Environmental Prediction). The ECMWF reanalysis data are only available for 15 years, and have been extended from 1994 using operational analyses. The major temporal and spatial characteristics of North Atlantic cyclones are examined and a comparison between the climatologies developed from the two data sets is carried out. The well-known cyclogenesis regions along the east coast of the United States and to the southeast of Greenland are replicated by both reanalyses, as is the characteristic southwest/northeast orientation of the dominant cyclone track across the Atlantic basin. However, only weak correlations are found between the time series of cyclone frequency produced from the two reanalyses, and this is particularly true for the lower intensity Beaufort Scale category 0–6 cyclones. This result, together with the large differences in the spatial distribution of cyclones over Greenland for Beaufort Scale 0–6 cyclones, indicates the NCEP reanalyses generates fewer systems than the ECMWF reanalyses. The overall conclusion is that the ECMWF mean sea level pressure data produce a more comprehensive climatology of North Atlantic cyclones at all scales.  相似文献   

Radiative Exchange in an Urban Street Canyon   总被引：1，自引：4，他引：1  

Ian N. Harman  Martin J. Best  Stephen E. Belcher 《Boundary-Layer Meteorology》2004,110(2):301-316

The influence of building geometry on the radiation terms ofthe surface energy balance is a principal reason for surfacetemperature differences between rural and urban areas.Methods exist to calculate the radiation balance in an urban area,but their validity across the range of urban geometries andmaterials has not been carefully considered.Here the exchange of diffuse radiation in an urban street canyon isinvestigated using a method incorporating all reflections of radiation.This exact solution is compared to two commonly used approximationsthat retain either no reflections, or just one reflection of radiation.The area-averaged net radiative flux density from the facets of the canyondecreases in magnitude monotonically as the canyon aspect ratio increases.The two approximate solutions possess unphysical differences from thismonotonic decrease for high canyon aspect ratios or low materialemissivities/high material albedos.The errors of the two approximate solutions are small for near blackbodymaterials and small canyon aspect ratios but can be an order ofmagnitude for intermediate material properties and deep street canyons.Urban street canyon models need to consider at least one reflectionof radiation and multiple reflections are desirable for full applicability.  相似文献   

International and National Aspects of a Legislative Framework to Manage Soil Carbon Sequestration   总被引：1，自引：0，他引：1  

Ian Hannam 《Climatic change》2004,65(3):365-387

This article discusses the international and national environmental law framework for the management of soil carbon sequestration. Aspects of the legislative framework important to this process include its ability to recognise carbon sinks, expand existing sinks, and the procedures available to return and store carbon in soil reservoirs. International law provides global standards and guidelines and national legislative systems provide the substantive and procedural legal mechanisms to manage soil carbon. The United Nations Framework Convention on Climate Change and the Kyoto Protocol are the primary international legislative instruments but other international instruments and strategies have a significant synergistic role. Various approaches are presented for framing new legislation or to reform existing legislative frameworks to improve the procedures to manage soil carbon.  相似文献