On the feasibility of characterizing jovian auroral electrons via H3+ infrared line-emission analysis     

Chihiro Tao  Sarah V. Badman  Takeru Uno  Masaki Fujimoto 《Icarus》2012,221(1):236-247

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The orbital distribution of Near-Earth Objects inside Earth’s orbit     

Sarah Greenstreet  Henry Ngo  Brett Gladman 《Icarus》2012,217(1):355-366

Canada’s Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with a < 1.0 AU. In order to construct an optimal pointing strategy for NEOSSat, we needed more detailed information in the a < 1.0 AU region than the best current model (Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H.F., Michel, P., Metcalfe, T.S. [2002]. Icarus 156, 399–433) provides. We present here the NEOSSat-1.0 NEO orbital distribution model with larger statistics that permit finer resolution and less uncertainty, especially in the a < 1.0 AU region. We find that Amors = 30.1 ± 0.8%, Apollos = 63.3 ± 0.4%, Atens = 5.0 ± 0.3%, Atiras (0.718 < Q < 0.983 AU) = 1.38 ± 0.04%, and Vatiras (0.307 < Q < 0.718 AU) = 0.22 ± 0.03% of the steady-state NEO population. Vatiras are a previously undiscussed NEO population clearly defined in our integrations, whose orbits lie completely interior to that of Venus. Our integrations also uncovered the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ?0.1% of the steady-state NEO population. The relative NEO impact rate onto Mercury, Venus, and Earth, as well as the normalized distribution of impact speeds, was calculated from the NEOSSat-1.0 orbital model under the assumption of a steady-state. The new model predicts a slightly higher Mercury impact flux.  相似文献   

A benchmark study on problems related to CO2 storage in geologic formations   总被引：1，自引：0，他引：1  

Holger Class  Anozie Ebigbo  Rainer Helmig  Helge K. Dahle  Jan M. Nordbotten  Michael A. Celia  Pascal Audigane  Melanie Darcis  Jonathan Ennis-King  Yaqing Fan  Bernd Flemisch  Sarah E. Gasda  Min Jin  Stefanie Krug  Diane Labregere  Ali Naderi Beni  Rajesh J. Pawar  Adil Sbai  Sunil G. Thomas  Laurent Trenty  Lingli Wei 《Computational Geosciences》2009,13(4):409-434

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Geochemical and isotopic constraints on the interaction between saline lakes and groundwater in southeast Australia     

Ian Cartwright  Sharon Hall  Sarah Tweed  Marc Leblanc 《Hydrogeology Journal》2009,17(8):1991-2004

Major ion and stable isotope geochemistry allow groundwater/surface-water interaction associated with saline to hypersaline lakes from the Willaura region of Australia to be understood. Ephemeral lakes lie above the water table and locally contain saline water (total dissolved solids, TDS, contents up to 119,000 mg/L). Saline lakes that lack halite crusts and which have Cl/Br ratios similar to local surface water and groundwater are throughflow lakes with high relative rates of groundwater outflows. Permanent hypersaline lakes contain brines with TDS contents of up to 280,000 mg/L and low Cl/Br ratios due to the formation of halite in evaporite crusts. These lakes are throughflow lakes with relatively low throughflow rates relative to evaporation or terminal discharge lakes. Variations in stable isotope and major ion geochemistry show that the hypersaline lakes undergo seasonal cycles of mineral dissolution and precipitation driven by the influx of surface water and evaporation. Despite the generation of highly saline brines in these lakes, leakage from the adjacent ephemeral lakes or saline throughflow lakes that lack evaporite crusts is mainly responsible for the high salinity of shallow groundwater in this region.  相似文献   

Climate and environmental change at the end of the Holocene Humid Period: A pollen record off Pakistan     

Sarah J. Ivory  Anne-Marie Lézine 《Comptes Rendus Geoscience》2009,341(8-9):760-769

Pollen studies from core SO90-56KA recovered from the Arabian Sea off the Makran Coast (24° 509N, 65° 559E; 695 m depth) show that the end of the Holocene Humid Period, linked to the weakening of Indian monsoon fluxes, took place between 4700 and 4200 BP. Two periods of strong summer monsoon activity are identified between 5400–4200 BP and 2000–1000 BP during which the montane pollen taxa coming from the Himalayas reached the Makran coast due to increased fluvial activity of the Indus River. A contrasting period, dominated by the winter monsoon between 4200 and 2000 BP, is identified based on the presence of pollen taxa from the Baluchistan plateaus. The regional vegetation of the low- and midaltitudes, arid and semiarid, are remarkably stable from 4500 BP to the present.  相似文献   

Cl/Br ratios and stable chlorine isotope analysis of magmatic–hydrothermal fluid inclusions from Butte,Montana and Bingham Canyon,Utah     

Taras Nahnybida  Sarah A. Gleeson  Brian G. Rusk  Len I. Wassenaar 《Mineralium Deposita》2009,44(8):837-848

A bulk geochemical study has been carried out on fluid inclusion leachates extracted from quartz veins from porphyry Cu deposits in Butte, Montana, USA and Bingham Canyon, Utah, USA. The leachates mostly represent low-salinity magmatic–hydrothermal fluid inclusions. Their halogen ratios (Br/Cl) of fluid inclusion leachates were determined by ion chromatography, and δ³⁷Cl values of the leachates were measured by continuous-flow isotope ratio mass spectrometry. Br/Cl ratios from early pre-Main stage and later Main stage veins at Butte range from 0.60 to 1.88 × 10⁻³ M. Ratios are similar in pre-Main stage veins with sericite bearing selvages and Main stage samples ranging from 0.81 to 1.08 × 10⁻³ and from 0.92 to 1.88 × 10⁻³ M, respectively, clustering below seawater (1.54 × 10⁻³ M) and overlapping mantle values (~1–2 × 10⁻³ M). Two samples associated with early pre-Main stage potassic alteration yield distinctly lower Br/Cl ratios of 0.60 and 0.64 × 10⁻³ M. Butte δ³⁷Cl values range from −0.8‰ to −2.3‰ with no significant difference between pre-Main stage and Main stage samples. Br/Cl ratios for quartz veins from Bingham Canyon range from 0.18 to 3.68 × 10⁻³ M. Br/Cl ratios from Bingham range above and below previously reported for porphyry copper deposits. In contrast to Butte, δ³⁷Cl values for Bingham are lower, ranging from −0.9‰ to −4.1‰. In the absence of any processes which can significantly fractionate chlorine isotopes at high temperatures, we suggest that the porphyry system at Bingham, and to a lesser extent at Butte, have inherited negative chlorine isotopic signatures from the subducting slab generated at low temperatures.  相似文献   

Prediction of stresses and strains around model tunnels with adjacent embedded walls in overconsolidated clay   总被引：1，自引：0，他引：1  

Emilio Bilotta  Sarah E. Stallebrass 《Computers and Geotechnics》2009

This paper presents the results of finite element analyses carried out using different constitutive models for overconsolidated clay: the Modified Cam clay model and the Three-Surface Kinematic Hardening (3-SKH) model. These analyses are evaluated against data from an extensive series of physical model tests examining the influence of an embedded wall placed near a tunnel on ground movements and tunnel stability. It is shown that for heavily overconsolidated soils reasonable predictions of both deformations and failure can be obtained from kinematic hardening models such as the 3-SKH model, which allow plastic deformation inside a Modified Cam clay state boundary surface.  相似文献   

Tepexpan Palaeoindian site, Basin of Mexico: multi-proxy evidence for environmental change during the late Pleistocene–late Holocene     

Angela L. Lamb  Silvia Gonzalez  David Huddart  Sarah E. Metcalfe  Christopher H. Vane  Alistair W.G. Pike 《Quaternary Science Reviews》2009,28(19-20):2000-2016

The Tepexpan Palaeoindian skeleton was discovered in 1947 close to the former Lake Texcoco margin, in the Basin of Mexico. The find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation. Here we report new AMS radiocarbon dates associated with the sedimentary succession at Tepexpan with ages between 19,110 ± 90 and 612 ± 22 ¹⁴C years BP and a new uranium-series date for the skeleton with an age of 4700 ± 200 years BP that indicates a mid Holocene age. The sedimentary succession was studied in detail using: stable isotopes, diatoms, organic geochemistry and tephrochronology. The multi-proxy evidence suggests large changes around the margins of Lake Texcoco in terms of the balance between aquatic and terrestrial plants, C₃ and C₄ plants, saline, alkaline and freshwater conditions, volcanic activity, marginal reworking of lake sediments and input from the drainage basin through the late Pleistocene–late Holocene. These changes had large impacts on the prehistoric human populations living by the lake shores since the late Pleistocene in the Basin of Mexico.  相似文献   

Visual methodologies through a feminist lens: South African soap operas and the post-apartheid nation     

Sarah F. Ives 《GeoJournal》2009,74(3):245-255

Using a discussion of South African soap operas, I will place the idea of visuality in a discourse analysis that incorporates a feminist epistemological lens, or an epistemology that integrates reflexivity and an acknowledgment of the dialogic nature of visual media. Through this discussion, I will examine the possibilities that dialogism provides for unpacking and exploring the politics of imperfect translation between the visual and the textual. These methodological interventions, I argue, will help enrich discussions of the visual’s role in the contested realm of geographic imaginations and move beyond the distanced position of the masculine gaze.

Sarah F. IvesEmail:

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Iron isotope fractionation in a buoyant hydrothermal plume, 5°S Mid-Atlantic Ridge     

Sarah A. Bennett  Olivier Rouxel  Katja Schmidt  Dieter Garbe-Schnberg  Peter J. Statham  Christopher R. German 《Geochimica et cosmochimica acta》2009,73(19):5619-5634

Fe isotopes are a potential tool for tracing the biogeochemical redox cycle of Fe in the ocean. Specifically, it is hypothesized that Fe isotopes could enable estimation of the contributions from multiple Fe sources to the dissolved Fe budget, an issue that has received much attention in recent years. The first priority however, is to understand any Fe isotope fractionation processes that may occur as Fe enters the ocean, resulting in modification of original source compositions. In this study, we have investigated the Fe inputs from a basalt-hosted, deep-sea hydrothermal system and the fractionation processes that occur as the hot, chemically reduced and acidic vent fluids mix with cold, oxygen-rich seawater.The samples collected were both end-member vent fluids taken from hydrothermal chimneys, and rising buoyant plume samples collected directly above the same vents at 5°S, Mid-Atlantic Ridge. Our analyzes of these samples reveal that, for the particulate Fe species within the buoyant plume, 25% of the Fe is precipitated as Fe-sulfides. The isotope fractionation caused by the formation of these Fe-sulfides is δ_Fe(II)–FeS = +0.60 ± 0.12‰.The source isotope composition for the buoyant plume samples collected above the Red Lion vents is calculated to be −0.29 ± 0.05‰. This is identical to the value measured in end-member vent fluids collected from the underlying “Tannenbaum” chimney. The resulting isotope compositions of the Fe-sulfide and Fe-oxyhydroxide species in this buoyant plume are −0.89 ± 0.11‰ and −0.19 ± 0.09‰, respectively. From mass balance calculations, we have been able to calculate the isotope composition of the dissolved Fe fraction, and hypothesize that the isotope composition of any stabilised dissolved Fe species exported to the surrounding ocean may be heavier than the original vent fluid. Such species would be expected to travel some distance from areas of hydrothermal venting and, hence, contribute to not only the dissolved Fe budget of the deep-ocean but also it’s dissolved Fe isotope signature.  相似文献