Produced fluids and shallow groundwater in coalbed methane (CBM) producing regions of Alberta, Canada: Trace element and rare earth element geochemistry     

Katrina Cheung  Hamed Sanei  Patrick Klassen  Bernhard Mayer  Fariborz Goodarzi 《International Journal of Coal Geology》2009,77(3-4):338-349

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Holocene environments and climate in the Mongolian Altai reconstructed from the Hoton-Nur pollen and diatom records: a step towards better understanding climate dynamics in Central Asia   总被引：1，自引：0，他引：1  

Natalia Rudaya  Pavel Tarasov  Nadezhda Dorofeyuk  Nadia Solovieva  Ivan Kalugin  Andrei Andreev  Andrei Daryin  Bernhard Diekmann  Frank Riedel  Narantsetseg Tserendash  Mayke Wagner 《Quaternary Science Reviews》2009,28(5-6):540-554

This study presents the results of the palynological and diatom analyses of the sediment core recovered in Hoton-Nur Lake (48°37′18″N, 88°20′45″E, 2083 m) in 2004. Quantitative reconstruction of the Holocene vegetation and climate dynamics in the semiarid Mongolian Altai suggests that boreal woodland replaced the primarily open landscape of northwestern Mongolia at about 10 kyr BP (1 kyr = 1000 cal yr) in response to a noticeable increase in precipitation from 200–250 mm/yr to 450–550 mm/yr. A decline of the forest vegetation and a return to a predominance of open vegetation types occurred after 5 kyr BP when precipitation sums decreased to 250–300 mm/yr. Prior to 11.5 kyr BP diatom concentrations are relatively low and the lake is dominated by planktonic Cyclotella and small Fragilariaceae, suggesting the existence of a relatively deep and oligotrophic/mesotrophic lake. The great abundance of Staurosirella pinnata from the beginning of the record until 10.7 kyr BP might imply intensified erosion processes in the catchment and this is fully consistent with the presence of scarce and dry vegetation and the generally arid climate during this period. From about 10.7 kyr BP, more planktonic diatom taxa appeared and increased in abundance, indicating that the lake became more productive as diatom concentration increased. This change correlates well with the development of boreal woodland in the catchment. Decrease in precipitation and changes in the vegetation towards steppe are reflected by the rapid increase in Aulacoseira distans from about 5 kyr BP. The Holocene pollen and diatom records do not indicate soil and vegetation cover disturbances by the anthropogenic activities, implying that the main transformations of the regional vegetation occurred as a result of the natural climate change. Our reconstruction is in agreement with the paleomonsoon records from China, demonstrating an abrupt strengthening of the summer monsoon at 12 kyr BP and an associated increase in precipitation and in lake levels between 11 and 8 kyr BP, followed by the stepwise attenuation of the monsoon circulation and climate aridization towards the modern level. The records from the neighboring areas of Kazakhstan and Russia, situated west and north of Hoton-Nur, demonstrate spatially and temporally different Holocene vegetation and climate histories, indicating that the Altai Mountains as a climate boundary are of pivotal importance for the Holocene environmental and, possibly, habitation history of Central Asia.  相似文献   

A longer-term perspective on soil moisture,groundwater and stream flow response to the 2018 drought in an experimental catchment in the Scottish Highlands     

Chris Soulsby  Bernhard Scheliga  Aaron Neill  Jean-Christophe Comte  Doerthe Tetzlaff 《水文研究》2021,35(6):e14206

The drought of summer 2018, which affected much of Northern Europe, resulted in low river flows, biodiversity loss and threats to water supplies. In some regions, like the Scottish Highlands, the summer drought followed two consecutive, anomalously dry, winter periods. Here, we examine how the drought, and its antecedent conditions, affected soil moisture, groundwater storage, and low flows in the Bruntland Burn; a sub-catchment of the Girnock Burn long-term observatory in the Scottish Cairngorm Mountains. Fifty years of rainfall-runoff observations and long-term modelling studies in the Girnock provided unique contextualisation of this extreme event in relation to more usual summer storage dynamics. Whilst summer precipitation in 2018 was only 63% of the long-term mean, soil moisture storage across much of the catchment were less than half of their summer average and seasonal groundwater levels were 0.5 m lower than normal. Hydrometric and isotopic observations showed that ~100 mm of river flows during the summer (May-Sept) were sustained almost entirely by groundwater drainage, representing ~30% of evapotranspiration that occurred over the same period. A key reason that the summer drought was so severe was because the preceding two winters were also dry and failed to adequately replenish catchment soil moisture and groundwater stores. As a result, the drought had the biggest catchment storage deficits for over a decade, and likely since 1975–1976. Despite this, recovery was rapid in autumn/winter 2018, with soil and groundwater stores returning to normal winter values, along with stream flows. The study emphasizes how long-term data from experimental sites are key to understanding the non-linear flux-storage interactions in catchments and the “memory effects” that govern the evolution of, and recovery from, droughts. This is invaluable both in terms of (a) giving insights into hydrological behaviours that will become more common water resource management problems in the future under climate change and (b) providing extreme data to challenge hydrological models.  相似文献   

Physical properties of near-Earth Asteroid (33342) 1998 WT24     

Michael W. Busch  Lance A.M. Benner  Jon D. Giorgini  Randy Rose  Christopher Magri  Michael C. Nolan 《Icarus》2008,195(2):614-621

During its close Earth approach in 2001, the E-class near-Earth Asteroid (33342) 1998 WT24 was the focus of extensive radar, optical, and thermal infrared observations. We present a physical model of this object, estimated from Arecibo and Goldstone radar images that cover multiple rotations and span over 100° of sky motion. The asteroid has an equivalent diameter of 415±40 m and a diffuse radar scattering law that is identical in both senses of circular polarization, implying a surface that is extremely rough on centimeter-to-decimeter scales. The shape is dominated by three large basins, which may be impact craters or a relic of past dynamical disruption of the object. Analysis of YORP perturbations on WT24's spin state predicts that the asteroid's spin rate is decreasing at a rate of . Simply extrapolating this rate suggests that the asteroid will despin over the next 150 kyr and was spinning at its surface disruption rate 75 kyr ago, but the rotational evolution of WT24 depends on the surface's thermal properties and probably is more complex than a simple spin-down.  相似文献   

Holocene hydrological variability of Lake Ladoga,northwest Russia,as inferred from diatom oxygen isotopes     

Svetlana S. Kostrova  Hanno Meyer  Hannah L. Bailey  Anna V. Ludikova  Raphael Gromig  Gerhard Kuhn  Yuri A. Shibaev  Anna V. Kozachek  Alexey A. Ekaykin  Bernhard Chapligin 《Boreas: An International Journal of Quaternary Research》2019,48(2):361-376

This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ¹⁸O_diatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ¹⁸O_diatom values range from +29.8 to +35.0‰, and relatively higher δ¹⁸O_diatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ¹⁸O_diatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ¹⁸O_diatom values, whereas lower lake levels cause higher δ¹⁸O_diatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ¹⁸O_diatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ¹⁸O_diatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely.  相似文献   

Foundations of cable car towers upon alpine glaciers     

Wolfgang Fellin  Bernhard Lackinger 《Acta Geotechnica》2007,2(4):291-300

This paper presents a design approach for strip footings upon glacier ice. Safety against ultimate limit state is proved by the geotechnical slip-line field solution by Prandtl. Glacier ice at 0°C can be modelled as purely cohesive material. Statistical evaluation of uniaxial compression tests with high strain rate revealed a mean value of the cohesion of 600 kPa and a characteristic value c _k = 355 kPa (5% fractile). With a coefficient of variation V _c = 0.3, the partial safety factor turns out to be γ _c = 1.9. An approximate solution for estimating the creep settlement rate is presented to check the serviceability limit state: with the width b of the strip foundation, p the foundation pressure and for ice at 0°C. Experiences on Stubai glacier with grate shaped footings showed that creep settlements occurring per year due to maximum foundation pressures 250 kPa did not influence the operation and the maintenance of the cable cars.  相似文献   

A simultaneous maximum likelihood approach for galaxy--galaxy lensing and cluster lens reconstruction     

Bernhard Geiger  Peter Schneider 《Monthly notices of the Royal Astronomical Society》1999,302(1):118-130

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Himalayan inverted metamorphism constrained by oxygen isotope thermometry   总被引：3，自引：0，他引：3  

Jean-Claude Vannay  Zachary D. Sharp  Bernhard Grasemann 《Contributions to Mineralogy and Petrology》1999,137(1-2):90-101

Inverted metamorphic field gradients are preserved in two amphibolite facies metapelitic sequences forming the crystalline core zone of the Himalayan orogen in the Sutlej valley (NW India). In the High Himalayan Crystalline Sequence (HHCS), metamorphic conditions increase upwards from the staurolite zone at the base, through the kyanite-in and sillimanite-in isograds, finally to reach partial melting conditions at the top. The structurally lower Lesser Himalayan Crystalline Sequence (LHCS) shows a gradual superposition of garnet-in, staurolite-in and kyanite + sillimanite-in isograds. Although phase equilibria constraints imply inverted temperature field gradients in both units, garnet-biotite (GARB) rim thermometry indicates final equilibration at a nearly uniform temperature around T ≈ 600 °C across these sequences. The P-T path and garnet zoning data show that this apparent lack of thermal field gradient is mainly the consequence of a resetting of the GARB equilibria during cooling. In order to constrain peak temperature conditions, 20 samples along the studied section have been analysed for oxygen isotope thermometry. The isotopic fractionations recorded by quartz-garnet and quartz-aluminosilicate mineral pairs indicate temperatures consistent with phase equilibria and P-T path constraints for metamorphic peak conditions. Together with barometry results, based on net transfer continuous reactions, the oxygen isotope thermometry indicates peak conditions characterized by: (1) a temperature increase from T ≈ 570 to 750 °C at a nearly constant pressure around P ≈ 800 MPa, from the base to the top of the HHCS unit; (2) a temperature increase from T ≈ 610 to 700 °C and a pressure decrease from P ≈ 900 to 700 MPa, from the base to the top of the LHCS metapelites. Oxygen isotope thermometry thus provides the first quantitative data demonstrating that the Himalayan inverted metamorphism can be associated with a complete inversion of the thermal field gradient across the crystalline core zone of this orogen. Received: 1 April 1999 / Accepted: 12 July 1999  相似文献   

A geo-environmental map for the sustainable development of the Kathmandu Valley, Nepal     

Omkar M. Shrestha  Achyuta Koirala  Jörg Hanisch  Klaus Busch  Martin Kerntke  Stefan Jäger 《GeoJournal》1999,49(2):165-172

An engineering and environmental geological map of the Kathmandu Valley in Nepal has been elaborated within a project of German-Nepalese cooperation. In the Kathmandu Valley, the major geo-environmental problems arise from haphazard exploitation of geologic resources, local landslide zones, severe problems of garbage disposal, river flooding and a dramatic river pollution. The map was prepared by the use of GIS techniques. It contains all basic geological and environmental data, as geotechnical risk zones (landslide-prone areas or those of poor foundation conditions), areas for preferable extraction of construction material and those not to be allowed to be exploited, areas of immediate need of reforestation in order to prevent landslide or badland development, groundwater protection zones, and suitable garbage disposal sites. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Synonymy and circum‐tropical biogeography of the Devonian calcareous alga Zeapora Penecke, 1894 (Chlorophyta,Bryopsidales)          下载免费PDF全文

Bernhard Hubmann  Markus Reuter 《Island Arc》2017,26(3)

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