Microstructures of structure I and II gas hydrates from the Gulf of Mexico     

Stephan A. Klapp  Gerhard Bohrmann  Werner F. Kuhs  M. Mangir Murshed  Thomas Pape  Helmut Klein  Kirsten S. Techmer  Katja U. Heeschen  Friedrich Abegg 《Marine and Petroleum Geology》2010

Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities.  相似文献   

An assessment of monitoring requirements and costs of 'Reduced Emissions from Deforestation and Degradation'     

Hannes Böttcher  Katja Eisbrenner  Steffen Fritz  Georg Kindermann  Florian Kraxner  Ian McCallum  Michael Obersteiner 《Carbon balance and management》2009,4(1):7-14

Background  

Negotiations on a future climate policy framework addressing Reduced Emissions from Deforestation and Degradation (REDD) are ongoing. Regardless of how such a framework will be designed, many technical solutions of estimating forest cover and forest carbon stock change exist to support policy in monitoring and accounting. These technologies typically combine remotely sensed data with ground-based inventories. In this article we assess the costs of monitoring REDD based on available technologies and requirements associated with key elements of REDD policy.  相似文献   

The liver of wrasse - morphology and function as a mirror of point source chemical impact.     

Katja Broeg  Wiebke Kaiser  Sieglinde Bahns  Angela Koehler 《Marine environmental research》2008,66(1):191-192

Corkwing wrasse (Symphodus melops L.), a protogynous, non-migratory lipfish species, living close to rocky shores was chosen as an indicator species for the monitoring of biological effects of contaminants. Fish were caught by local fisherman at the Norwegian west coast in fjord sites within the framework of the EU BEEP project. The sites represented different point source impacts of (I) copper (a former copper mine), (II) polycyclic aromatic hydrocarbons (PAHs, aluminium smelter discharge), (III) formaldehyde plus PAHs (kelp-factory and influence of the aluminium smelter). Livers of wrasse were studied for histopathological alterations and compared to healthy livers of fish from a reference location. Besides liver morphology, different functional and metabolic parameters were measured to link pathological alterations to functional disorders. The integrity of the lysosomal compartment was tested by the assessment of lysosomal membrane stability (lys), and the accumulation of neutral lipids and lipofuscin. Activity and intracellular localisation of the NADPH-producing enzymes in the liver were assessed histochemically and measured by computer-assisted image analysis. Histopathological alterations were most severe at the site impacted by formaldehyde and PAHs. These findings were associated with highest tumor prevalence, lowest membrane stabilities in hepatocytes and highest accumulation rates of lipofuscin in the liver. The activities of the NADPH-producing enzymes phosphogluconate dehydrogenase (PGDH) and glucose-6-phosphate dehydrogenase (G6PDH) were significantly lower compared to unimpacted reference fish. Histopathological alterations showed clear differences dependent on the input source. Potential links between specific contaminant impact and functional and morphological disorders are discussed.  相似文献   

Observation of Conditions Preceding Peak Indoor Air Volatile Organic Compound Concentrations in Vapor Intrusion Studies     

Chris Lutes  Chase Holton  Brian Schumacher  John Zimmerman  Andrew Kondash  Robert Truesdale MS  AB. 《Ground Water Monitoring & Remediation》2021,41(2):99-111

Temporal and spatial variability of indoor air volatile organic compound (VOC) concentrations can complicate vapor intrusion (VI) assessment and decision-making. Indicators and tracers (I&T) of VI, such as differential temperature, differential pressure, and indoor radon concentration, are low-cost lines of evidence to support sampling scheduling and interpretation of indoor air VOC sampling results. This study compares peak indoor air chlorinated VOC concentrations and I&T conditions before and during those peak events at five VI sites. The sites differ geographically and in their VI conceptual site models (CSM). Relative to site-specific baseline values, the results show that cold or falling outdoor temperatures, rising cross slab differential pressures, and increasing indoor radon concentrations can predict peak VOC concentrations. However, cold outdoor air temperature was not useful at one site where elevated shallow soil temperature was a better predictor. Correlations of peak VOC concentrations to elevated or rising barometric pressure and low wind speed were also observed with some exceptions. This study shows how the independent variables that control or predict peak indoor air VOC concentrations are specific to building types, climates, and VI CSMs. More I&T measurements at VI sites are needed to identify scenario-specific baseline and peak related I&T conditions to improve decision-making.  相似文献   

Oxygen stable isotope ratios from British oak tree-rings provide a strong and consistent record of past changes in summer rainfall     

Giles H. F. Young  Neil J. Loader  Danny McCarroll  Roderick J. Bale  Joanne C. Demmler  Daniel Miles  Nigel T. Nayling  Katja T. Rinne  Iain Robertson  Camilla Watts  Matthew Whitney 《Climate Dynamics》2015,45(11-12):3609-3622

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Significance of trace elements in syntaxial quartz cement,Haushi Group sandstones,Sultanate of Oman     

Katja Lehmann  Thomas Pettke  Karl Ramseyer 《Chemical Geology》2011,280(1-2):47-57

Trace element contents and distributions in authigenic quartz cement in deeply buried (2500–4000 m) Haushi Group sandstones from wells in Oman have been investigated in order to determine the factors that control trace element uptake during precipitation.Scanning electron microscope-cathodoluminescence images show well developed growth zones within the quartz cement, which correlate with chemical zonations observed in electron microprobe Al distribution maps. The most abundant trace elements are Al (50–3000 μg g^?1), Li (1–100 μg g^?1), Na (1–40 μg g^?1), and Ge (0.3–5 μg g^?1) with a strong linear correlation between Li and Al and a weaker one between Ge and Al. The molar concentration of Li (+ Na) accounts only for ~ 15% of the charge compensation for Al³⁺ substitution of Si⁴⁺. Though H was not measured in this study, these data indicate a major role of H in charge balancing Al³⁺. The samples belong to the same stratigraphic unit and have similar petrography, but show considerable variability in absolute trace element concentrations between different wells. This variability does not correlate with either sample depth or temperature and shows no regional pattern, but seems to reflect petrophysical and tectonic differences within the sedimentary basin.Petrographic observations of the cogenetic mineral assemblages and hydrochemical modelling indicate that a change from the equilibrium assemblage quartz–kaolinite (–dolomite) to quartz–illite (–dolomite) reflects a decrease in the CO₂ concentration and concurrent variations of the Al concentration. It is concluded that changes in the CO₂ concentrations are responsible for fluctuations in fluid Al concentrations and thus likely also in the investigated quartz cements.  相似文献   

Impact of resolution and downscaling technique in simulating recent Atlantic tropical cylone activity     

Louis-Philippe Caron  Colin G. Jones  Katja Winger 《Climate Dynamics》2011,37(5-6):869-892

Using the global environmental multiscale (GEM) model, we investigate the impact of increasing model resolution from 2° to 0.3° on Atlantic tropical cyclone activity. There is a clear improvement in the realism of Atlantic storms with increased resolution, in part, linked to a better representation of African easterly waves. The geographical distribution of a Genesis Potential Index, composed of large-scales fields known to impact cyclone formation, coincides closely in the model with areas of high cyclogenesis. The geographical distribution of this index also improves with resolution. We then compare two techniques for achieving local high resolution over the tropical Atlantic: a limited-area model driven at the boundaries by the global 2° GEM simulation and a global variable resolution model (GVAR). The limited-area domain and high-resolution part of the GVAR model coincide geographically, allowing a direct comparison between these two downscaling options. These integrations are further compared with a set of limited-area simulations employing the same domain and resolution, but driven at the boundaries by reanalysis. The limited-area model driven by reanalysis produces the most realistic Atlantic tropical cyclone variability. The GVAR simulation is clearly more accurate than the limited-area version driven by GEM-Global. Degradation in the simulated interannual variability is partly linked to the models failure to accurately reproduce the impact of atmospheric teleconnections from the equatorial Pacific and Sahel on Atlantic cyclogenesis. Through the use of a smaller limited-area grid, driven by GEM-Global 2°, we show that an accurate representation of African Easterly Waves is crucial for simulating Atlantic tropical cyclone variability.  相似文献   

On coastal flow in the northeast gulf of Alaska near yakutat 1     

R.K. Reed  J.D. Schumacher  Cathleen Wright 《大气与海洋》2013,51(1):47-53

Abstract

Seasonal maps of geopotential topography and salinity at 10 m were prepared for a region in the northeast Gulf of Alaska near Yakutat. Coastal waters in this region receive considerable runoff in late summer, but the dilution does not result in a greatly intensified coastal flow. Baroclinic coastal flow in the northeast Gulf appears to be weaker than the coastal flow (Kenai Current) to the west along the Kenai Peninsula and in Shelikof Strait.  相似文献   

The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton,Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana     

Mandy Hofmann  Ulf Linnemann  Karl-Heinz Hoffmann  Axel Gerdes  Katja Eckelmann  Andreas Gärtner 《International Journal of Earth Sciences》2014,103(5):1187-1202

This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203–2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323–354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0–1.4 Ga Namaqua Province, 1.7–2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu–Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. εHf(t) signatures range between ?24 and +14.8, which relate to T_DM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from magmas generated from Mesoproterozoic crustal material show more juvenile εHf(t) signatures of +14, +8 to +4 with T_DM model ages of 1.05–1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show εHf(t) signatures of ?3 to ?5.5 with T_DM model ages of 2.4–2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without any evidence for a passive margin. All of this can be explained by the erosion of rocks related to the Namaqua Belt, which represents one of the two major peaks of zircon U–Pb ages in all analysed samples. Therefore, the Namaqua Belt was well exposed during the Cryogenian, available to erosion and apart from the also well-exposed Palaeoproterozoic basement of the Kalahari Craton one potential source area for the sedimentary rocks in the investigated areas.  相似文献   

Highly parameterized model calibration with cloud computing: an example of regional flow model calibration in northeast Alberta,Canada     

Kevin Hayley  J. Schumacher  G. J. MacMillan  L. C. Boutin 《Hydrogeology Journal》2014,22(3):729-737

Expanding groundwater datasets collected by automated sensors, and improved groundwater databases, have caused a rapid increase in calibration data available for groundwater modeling projects. Improved methods of subsurface characterization have increased the need for model complexity to represent geological and hydrogeological interpretations. The larger calibration datasets and the need for meaningful predictive uncertainty analysis have both increased the degree of parameterization necessary during model calibration. Due to these competing demands, modern groundwater modeling efforts require a massive degree of parallelization in order to remain computationally tractable. A methodology for the calibration of highly parameterized, computationally expensive models using the Amazon EC2 cloud computing service is presented. The calibration of a regional-scale model of groundwater flow in Alberta, Canada, is provided as an example. The model covers a 30,865-km² domain and includes 28 hydrostratigraphic units. Aquifer properties were calibrated to more than 1,500 static hydraulic head measurements and 10 years of measurements during industrial groundwater use. Three regionally extensive aquifers were parameterized (with spatially variable hydraulic conductivity fields), as was the aerial recharge boundary condition, leading to 450 adjustable parameters in total. The PEST-based model calibration was parallelized on up to 250 computing nodes located on Amazon’s EC2 servers.  相似文献