Determination of the high-pressure properties of fayalite from first-principles calculations     

Stephen Stackhouse  Lars Stixrude  Bijaya B. Karki 《Earth and Planetary Science Letters》2010,289(3-4):449-456

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Volcanic lightning: global observations and constraints on source mechanisms     

Stephen R. McNutt  Earle R. Williams 《Bulletin of Volcanology》2010,72(10):1153-1167

Lightning and electrification at volcanoes are important because they represent a hazard in their own right, they are a component of the global electrical circuit, and because they contribute to ash particle aggregation and modification within ash plumes. The role of water substance (water in all forms) in particular has not been well studied. Here data are presented from a comprehensive global database of volcanic lightning. Lightning has been documented at 80 volcanoes in association with 212 eruptions. The Volcanic Explosivity Index (VEI) could be determined for 177 eruptions. Eight percent of VEI = 3–5 eruptions have reported lightning, and 10% of VEI = 6, but less than 2% of those with VEI = 1–2. These findings suggest consistent reporting for larger eruptions but either less lightning or possible under-reporting for small eruptions. Ash plume heights (142 observations) show a bimodal distribution with main peaks at 7–12 km and 1–4 km. The former are similar to heights of typical thunderstorms and suggest involvement of water substance, whereas the latter suggest other factors contributing to electrical behavior closer to the vent. Reporting of lightning is more common at night (56%) and less common in daylight (44%). Reporting also varied substantially from year to year, suggesting that a more systematic observational strategy is needed. Several weak trends in lightning occurrence based on magma composition were found. The bimodal ash plume heights are obvious only for andesite to dacite; basalt and basaltic-andesite evenly span the range of heights; and rhyolites are poorly represented. The distributions of the latitudes of volcanoes with lightning and eruptions with lightning roughly mimic the distribution of all volcanoes, which is generally flat with latitude. Meteorological lightning, on the other hand, is common in the tropics and decreases markedly with increasing latitude as the ability of the atmosphere to hold water decreases poleward. This finding supports the idea that if lightning in large (deep) eruptions depends on water substance, then the origin of the water is primarily magma and not entrainment from the surrounding atmosphere. Seasonal effects show that more eruptions with lightning were reported in winter (bounded by the respective autumnal and vernal equinoxes) than in summer. This result also runs counter to the expectations based on entrainment of local water vapor.  相似文献   

Distribution of petroleum hydrocarbons and organochlorinated contaminants in marine biota and coastal sediments from the ROPME Sea Area during 2005   总被引：3，自引：0，他引：3  

de Mora S  Tolosa I  Fowler SW  Villeneuve JP  Cassi R  Cattini C 《Marine pollution bulletin》2010,60(12):2323-2349

The composition and spatial distribution of various petroleum hydrocarbons (PHs), comprising both aliphatic and polycyclic aromatic hydrocarbons (PAHs), and selected chlorinated pesticides and PCBs were measured in biota and coastal sediments from seven countries in the Persian Gulf and the Gulf of Oman (Bahrain, Iran, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates). Evidence of extensive marine contamination with respect to organochlorinated compounds and PHs was not observed. Only one site, namely the BAPCO oil refinery in Bahrain, was considered to be chronically contaminated. Comparison of the results from this survey for Σ DDTs and Σ PCBs in rock oysters from the Gulf of Oman with similar measurements made at the same locations over the past two decades indicates a temporal trend of overall decreasing Σ PCB concentrations in oysters, whereas Σ DDTs levels have little changed during that period.  相似文献   

An isotope dilution method to measure nitrification rates in the northern Gulf of Mexico and other eutrophic waters     

Stephen A. Carini  Mark J. McCarthy  Wayne S. Gardner 《Continental Shelf Research》2010

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Extreme daily loads: role in annual phosphorus input to a north temperate lake     

Stephen R. Carpenter  Eric G. Booth  Christopher J. Kucharik  Richard C. Lathrop 《Aquatic Sciences - Research Across Boundaries》2015,77(1):71-79

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Landscapes on the edge: examining the role of climatic interactions in shaping coastal watersheds using a coastal–terrestrial landscape evolution model          下载免费PDF全文

Christopher Hackney  Stephen E. Darby  Julian Leyland 《地球表面变化过程与地形》2015,40(3):313-325

Incised coastal gullies (ICGs) are dynamic features found at the terrestrial‐coastal interface. Their geomorphic evolution is driven by the interactions between processes of fluvial knickpoint migration and coastal cliff erosion. Under scenarios of future climate change the frequency and magnitude of the climatological drivers of both terrestrial (fluvial and hillslope) and coastal (cliff erosion) processes are likely to change, with an adjunct impact on these types of coastal features. Here we explore the response of an incised coastal gully to changes in both terrestrial and coastal climate in order to elucidate the key process interactions which drive ICG evolution. We modify an extant landscape evolution model, CHILD, to incorporate processes of soft‐cliff erosion. This modified version, termed the Coastal‐Terrestrial‐CHILD (CT‐CHILD) model, is then employed to explore the interactions between changing terrestrial and coastal driving forces on the future evolution of an ICG found on the south‐west Isle of Wight, UK. It was found that the magnitude and frequency of storm events will play a key role in determining the future trajectory of ICGs, highlighting a need to understand the role of event sequencing in future projections of landscape evolution. Furthermore, synergistic (positive) and antagonistic (negative) interactions were identified between coastal and terrestrial parameters, such as wave height intensity and precipitation duration, which act to modulate the impact of changes in any one parameter. Of note was the role played by wave height intensity in driving coastal erosion, which was found to play a more important role than sea‐level rise in determining rates of coastal erosion. This highlights the need for a greater focus on wave height in studies of soft‐cliff erosion. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Hydrothermal Alteration, Fluid Inclusion and Stable Isotope Studies of the North Roby Zone, Lac des Iles PGE Mine, Ontario, Canada     

Alireza Karimzadeh Somarin  Stephen A. Kissin    Donald D. Heerema    Daniel J. Bihari 《Resource Geology》2009,59(2):107-120

The Archean mafic–ultramafic complex of Lac des Iles, Ontario, Canada, hosts economic platinum group elements (PGE)-Au-Cu-Ni mineralization in the Roby Zone. All lithologies in the North Roby Zone have been affected by hydrothermal alteration. The alteration products include talc (the most dominant mineral), anthophyllite, serpentine, actinolite, tremolite, chlorite, hornblende, zoisite, clinozoisite, epidote and sericite. In the altered rocks, light rare earth elements (La, Ce, Nd, Sm), Pb, Rb, Ba, Cs, S and possibly Y have been added by hydrothermal solution whereas Eu and heavy rare earth elements (Yb, Gd, Dy, Er) remained immobile. There are five types of fluid inclusions in the pegmatitic plagioclase with homogenization temperature and salinity ranging from 240°C to 445°C and 15.37 to 48.52 wt% equivalent NaCl, respectively. The δ¹⁸O and δD of talc range form 6.2‰ to 6.9‰ and −28‰ to −48‰, respectively. δ¹⁸O and δD water in equilibrium with talc during the hydrothermal alteration suggest a modified source for the hydrothermal solution. Microthermometry and stable isotope studies suggest that high temperature–high salinity fluid was diluted by, and mixed with, low temperature–low salinity meteoric solution. This mechanism precipitated the hydrothermal assemblage and redistributed trace elements during and after pegmatite formation in the North Ruby Zone.  相似文献   

Thermal Variability in a Tidal River     

Stephen G. Monismith  James L. Hench  Derek A. Fong  Nicholas J. Nidzieko  William E. Fleenor  Laura P. Doyle  S. Geoffrey Schladow 《Estuaries and Coasts》2009,32(1):100-110

In this paper, we discuss observations of temperature variability in the tidal portion of the San Joaquin River in California. The San Joaquin River makes up the southern portion of the Sacramento San Joaquin Delta, the eastern end of San Francisco Bay. Observations made in August 2004 and August 2005 show significant diurnal variations in temperature in response to surface heat exchange. However, to account for observed changes in heat content a sizeable downstream heat flux (approximately 100 W m⁻²) must be added to the surface heat flux. To account for this flux via Fickian dispersion, a flow-dependent dispersion coefficient varying from 500 to 4,000 m² s⁻¹ is needed. These values are much larger than would be predicted for a river of this size, suggesting that the complex topology of the Delta greatly enhances longitudinal dispersion. Building on these observations, we present a simple theory that explores how the subtidal temperature field varies in response to changes in flow rate, dispersion, and heat exchange.  相似文献   

Estuarine and Coastal Habitat Use of Gulf Sturgeon (<Emphasis Type="Italic">Acipenser oxyrinchus desotoi</Emphasis>) in the North-Central Gulf of Mexico     

Stephen T. Ross  W. Todd Slack  Ryan J. Heise  Mark A. Dugo  Howard Rogillio  Bryant R. Bowen  Paul Mickle  Richard W. Heard 《Estuaries and Coasts》2009,32(2):360-374

Gulf sturgeon are anadromous, spawning in freshwater and returning to the marine environment to feed. Herein, we document the marine distribution and timing of movement in and out of the marine environment of Gulf sturgeon natal to the Pascagoula and Pearl rivers (MS and LA). From 1999 to 2004, we attached sonic transmitters to 194 fish averaging 151 (MS) to 160 (LA) cm in fork length. We located 56 different Gulf sturgeon in the estuarine or marine environments, some multiple times. Fish were distributed nonrandomly, being found primarily in shallow water (mean = 3.9 m) in barrier island passes. Benthic samples taken at Gulf sturgeon telemetry location sites were dominated by Florida lancelets, sand dollars, annelids, haustoriid amphipods, and mollusks—all documented prey of Gulf sturgeon. Movement into salt water consistently occurred in October and November; movement back into rivers or low salinity estuaries was complete by the end of March.  相似文献   

Identification and occurrence of 25-norbenzohopanes in biodegraded bitumen from Palaeozoic carbonates in northern Alberta     

Barry Bennett  Chunqing Jiang  Stephen R. Larter 《Organic Geochemistry》2009,40(6):667-670

In addition to the previously reported 25-norhopanes and 25-norhopanoic acids, for the first time we report the identification of 25-norbenzohopanes. The hydrocarbon composition of the bitumen from Palaeozoic carbonates in northern Alberta displays molecular evidence for severe levels of biodegradation characterised by the removal of C₃₀–C₃₅ hopanes. Biodegradation is also indicated by the removal of C₃₂ and C₃₃ benzohopanes. The appearance of C₃₁ and C₃₂ 25-norbenzohopanes corresponds to the decrease in C₃₂ and C₃₃ benzohopanes, suggesting that 25-norbenzohopanes originate by demethylation of benzohopane counterparts. Demethylation at C-10 in the hopanoids affects a broader class of compounds that so far includes the hopanes and hopanoic acids, as well as the benzylated hopanoid species.  相似文献