Distributions of branched GDGTs in soils and lake sediments from western Uganda: Implications for a lacustrine paleothermometer     

Shannon E. Loomis  James M. RussellJaap S. Sinninghe Damsté 《Organic Geochemistry》2011,42(7):739-751

Bacterially produced branched glycerol dialkyl glycerol tetraethers (GDGTs) are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures. In lakes, however, it is still unclear if these compounds are derived from eroded soils or if they are produced in situ. To better understand environmental controls on the distributions of these compounds and the sources of branched GDGTs to lake sediments, we compare branched GDGT distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western Uganda. Reconstructed mean annual air temperature (MAAT), determined from the degree of methylation (MBT) and cyclisation (CBT) of branched GDGTs in soils, decreases with increasing altitude, as is expected from the air temperature gradient in our transect. However, we observe significant offsets between observed and reconstructed temperatures in soils from wet, high elevation soils but not in most dry, low elevation soils. Branched GDGT distributions differ significantly between lake sediments and soils at all elevations, with greater differences at low elevations than at high elevations. These data support previous hypotheses that branched GDGTs are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched GDGTs. While branched GDGTs in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes, we urge caution in utilizing this proxy in lacustrine systems with high soil loadings, especially if there is evidence of changing clastic fluxes through time.  相似文献   

Interactions of Salinity,Marsh Fragmentation and Submerged Aquatic Vegetation on Resident Nekton Assemblages of Coastal Marsh Ponds     

Alan T. Hitch  Kevin M. Purcell  Shannon B. Martin  Paul L. Klerks  Paul L. Leberg 《Estuaries and Coasts》2011,34(3):653-662

Increases in relative sea level are fragmenting the emergent vegetation of Louisiana’s coastal marshes. Nekton abundance is likely impacted by salinity and whether emergent vegetation is replaced by submerged aquatic vegetation (SAV) or open water. To assess these effects, we sampled nekton densities along a salinity gradient (categorized as freshwater, intermediate, and brackish marsh) in fragmented and non-fragmented areas. Total nekton density increased strongly with SAV in brackish marsh but only weakly in freshwater marsh (F _2,238 = 10.03, p < 0.0001). Freshwater and intermediate marshes had higher nekton densities when fragmented than when non-fragmented; this relationship was reversed in brackish marsh (F _2,238 = 8.89, p = 0.0002). Fragmentation, SAV, and salinity interacted to affect the densities of Gambusia affinis, Poecilia latipinna, Cyprinodon variegates, and Lucania parva. Our results suggest that the presence of both emergent vegetation and SAV was necessary for maintaining high nekton densities, with this combination being especially important in brackish marshes.  相似文献   

Geological Applications of Laser‐Induced Breakdown Spectroscopy     

Nancy J. McMillan  Shannon Rees  Kristen Kochelek  Catherine McManus 《Geostandards and Geoanalytical Research》2014,38(3):329-343

Laser‐induced breakdown spectroscopy (LIBS) records light emitted from the decay of electrons to lower‐energy orbitals during cooling of laser‐induced ablation plasmas; the resultant spectra can be used in a variety of geoanalytical applications. Four aspects of LIBS analysis distinguish LIBS from traditional laboratory‐based analytical techniques: (i) the lack of necessary sample preparation, allowing rapid analysis of many samples, (ii) the ability to analyse both 20 to 100 μm‐diameter spots and whole rocks, (iii) the detailed chemical signature contained in a LIBS spectrum and (iv) the ability to take LIBS into the field in backpack portable instrumentation. Three case studies illustrate potential applications of LIBS in the geosciences. First, analysis of the Carrizozo basalt flow in New Mexico, USA, illustrated that LIBS spectra could discriminate between samples of similar composition within uncertainties typical of whole‐rock analysis by X‐ray fluorescence spectrometry. Second, spectra from four sets of rubies from Madagascar and Tanzania illustrate the use of LIBS and multivariate analysis to determine provenance with success rates of > 95%. This technique can also be applied to correlation of units. Finally, a chemical map of a copper ore from Butte, MT, USA, illustrates the use of spatially defined LIBS spectra to understand chemical variations within textural context.  相似文献   

Dimensions of territorial conflict and resolution: tangible and intangible values of territory     

Shannon O’Lear  Paul F. Diehl  Derrick V. Frazier  Todd L. Allee 《GeoJournal》2005,64(4):259-261

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Changes in the frequency of extreme temperature records for Toronto,Ontario, Canada     

Shannon M. J. Allen  William A. Gough  Tanzina Mohsin 《Theoretical and Applied Climatology》2015,119(3-4):481-491

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花岗质岩浆和矿化之间的关系:重要概念和关键特征   总被引：1，自引：0，他引：1  

ZUREVINSKI Shannon  HOLLINGS Pete  周涛发  王世伟 《岩石学报》2017,33(5):1541-1553

最近对与花岗岩相关的锂、稀土金属和贱金属(例如Cu和Mo)矿产需求重新激发了人们对其成矿作用研究的兴趣。本文综述了不同类型花岗质岩石及与其相关的矿床:1)与高分异花岗岩有关的浸染状稀有金属矿化;2)热液型锡和钨矿化(如:矽卡岩型矿床);3)伟晶岩型稀有元素矿化;4)斑岩型矿化。虽然花岗岩和相关矿化作用之间(特别是斑岩系统相对于稀有金属)的联系还没有明确,但最近这些成矿系统的相关研究进展为探讨两者之间的关系提供了条件。本文重点回顾了与花岗岩相关成矿作用的主要特征,以及与不同类型矿化有关的花岗质岩浆的多样性,并论述了不同类型矿床的成矿模式。尽管长英质侵入岩浆系统复杂多样,但近来与这些矿化系统有关的研究进展可望能够作为找矿勘探的指示。地球化学特征可以揭示岩浆系统的氧化还原状态,进而可以判断斑岩系统的成矿潜力,它还可以与其他找矿勘探指标如矿物的同位素和微量元素分析联合使用。本文还讨论了通过熔融包裹体分析,研究微量元素在硅酸盐岩浆与挥发分体系中的行为。  相似文献   

Examining barriers and opportunities for sustainable adaptation to climate change in Interior Alaska     

Shannon M. McNeeley 《Climatic change》2012,111(3-4):835-857

Human adaptation to climate change is comprised of “adjustments” in response to (or anticipation of) climatic impacts. Adaptation does not necessarily imply favorable or equitable change, nor does it automatically imply sustainable use of ecosystems. “Sustainable adaptation” in this case implies strategic, collective action to respond to or anticipate harmful climate change to reduce disruption to key resource flows and adverse effects on general well-being. This research examined social-ecological system responses to recent warming trends in the remote northwest region of Interior Alaska using a unique vulnerability and adaptive capacity assessment (VA) approach that integrated indigenous observations and understanding of climate (IC) with western social and natural sciences. The study found that Alaska Native communities that were historically highly mobile and flexible across the landscape for subsistence hunting are increasingly restricted by the institutional rigidity of the regulatory system for wildlife and subsistence management. This has resulted in negative impacts to game harvest access and success threatening food security and community well-being. This suggests that policies limiting the ability of natural resource-dependent societies to be flexible, diversify, or innovate can threaten livelihoods and exacerbate vulnerability. Nevertheless, opportunities for sustainable adaptation exist where wildlife management is adaptive and includes an understanding of and response to climate variability and slow-onset climate change with the human dimensions of subsistence hunting for more effective “in-season” management.  相似文献   

Remagnetization and fluid flow in the Old Red Sandstone along the Great Glen Fault, Scotland     

R. Douglas Elmore  Shannon Dulin  Michael H. Engel  John Parnell 《Journal of Geochemical Exploration》2006,89(1-3):96

The Devonian Old Red Sandstone in the vicinity of the Great Glen Fault (GGF) in Scotland contains two different components residing in hematite: a postfolding Carboniferous CRM1 in the Loch Ness area and a Cretaceous or perhaps Triassic CRM2 near Hilton. The CRM1 could be related to major fluid flow events in the Late Paleozoic which caused hematite authigenesis and remagnetization along other faults in Scotland. The CRM2 near Hilton was also related to a fluid event in the Cretaceous or Triassic which caused hematite authigenesis. The presence of different CRMs residing in hematite along different segments of the GGF is similar to what has been reported for other major faults in Scotland.  相似文献   

Surficial Geologic Surveys of Gale Crater and Melas Chasma, Mars: Integration of Remote-Sensing Data     

Shannon M. Pelkey  Bruce M. Jakosky 《Icarus》2002,160(2):228-257

Remote-sensing observations of Gale Crater and Melas Chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions. Data sets analyzed include geologic maps, Mars Orbiter Laser Altimeter (MOLA) elevation, Thermal Emission Spectrometer (TES) albedo, TES thermal inertia, MOLA residual pulse width, TES rock abundance, and Viking and Mars Orbiter Camera images. Using these data sets, we constrain the properties of and processes acting on the present surface and create self-consistent models for the surface layer. Surface properties within Gale Crater are variable and complex, and interpreting the surface layer is not straightforward. Observations indicate that aeolian processes have shaped some of the intracrater surface, but other areas do not comply with this model and have counterintuitive surface characteristics. In contrast, aeolian activity appears to have played a large role in shaping the present-day physical structure of all surfaces in Melas Chasma and is reflected in the remote-sensing data sets. Here we summarize our analysis and discuss the surface attributes as determined from these data sets.  相似文献   

Biophysical properties and biomass production of elephant grass under saline conditions     

D. Wang  J. A. Poss  T. J. Donovan  M. C. Shannon  S. M. Lesch 《Journal of Arid Environments》2002,52(4):447

Elephant grass (Pennisetum purpureum Schum.) is a new fast-growing alternative forage crop. However, salinity is a major concern for its production in the arid south-western United States. This study was conducted in the arid Imperial Valley of Southern California to evaluate salt tolerance of elephant grass. Salinity treatments were created in field plots irrigated with water possessing an electrical conductivity (EC_iw) of 1·5, 5, 10, 15, 20, and 25 dS m⁻¹, respectively. Canopy spectral reflectance, temperature, plant height, leaf area index (LAI), chlorophyll-SPAD meter readings, and dry weights were measured over time. Results indicated that canopy reflectance in the near-infrared spectral region was reduced incrementally with increasing levels of salt stress. Canopy temperature increased with increasing salinity, especially at longer times after salinity treatment. Plant height and LAI were reduced with increasing salinity. Biomass accumulation was reduced incrementally with increasing salinity. About 50% yield reduction was found when EC_iw increased from 5 to 25 dS m⁻¹. The study shows that elephant grass is sensitive to salt stress, and relatively low salinity must be maintained to achieve a high rate of growth and biomass production.  相似文献