Fundamental parameters of the LMC clusters NGC 1836, NGC 1860, NGC 1865, SL 444, LW 224 and SL 548     

Andrés E. Piatti  Eduardo Bica  Doug Geisler  Juan J. Clariá 《Monthly notices of the Royal Astronomical Society》2003,344(3):965-977

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The composition and crystallinity of the near-surface regions of weathered alkali feldspars     

Martin R. Lee  Mark E. Hodson  Maureen MacKenzie  Caroline L. Smith 《Geochimica et cosmochimica acta》2008,72(20):4962-4975

Our ability to identify thin non-stoichiometric and amorphous layers beneath mineral surfaces has been tested by undertaking X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) work on alkali feldspars from pH 1 dissolution experiments. The outcomes of this work were used to help interpret XPS and TEM results from alkali feldspars weathered for <10,000 years in soils overlying the Shap Granite (north-west England). The chemistry of effluent solutions indicates that silica-rich layers a few nanometers in thickness formed during the pH 1 experiments. These layers can be successfully identified by XPS and have lower Al/Si, Na/Si, K/Si and Ca/Si values than the outermost ∼9 nm of unweathered controls. Development of Al-Si non-stoichiometry is coupled with loss of crystal structure to produce amorphous layers that are identifiable by TEM where >∼2.5 nm thick, whereas the crystallinity of albite is retained despite leaching of Na to depths of tens to hundreds on nanometers. Integration of XPS data over the outermost 6-9 nm of naturally weathered Shap feldspars shows that they have stoichiometric Al/Si and K/Si ratios, which is consistent with findings of previous TEM work on the same material that they lack amorphous layers. There is some XPS evidence for loss of K from the outermost couple of nanometers of Shap orthoclase, and the possibility of leaching of Na from albite to greater depths cannot be excluded using the XPS or TEM results. This study demonstrates that the leached layer model, as formulated from laboratory experiments, is inapplicable to the weathering of alkali feldspars within acidic soils, which is an essentially stoichiometric reaction.  相似文献   

Sustainable management of mixed demersal fisheries in the North Sea through fleet-based management a proposal from a biological perspective     

Ratz  Hans-Joachim; Bethke  Eckhard; Dorner  Hendrik; Beare  Doug; Groger  Joachim 《ICES Journal of Marine Science》2007,64(4):652-660

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The Southern Antarctic Circumpolar Current Front: physical and biological coupling at South Georgia     

Peter Ward  Mick Whitehouse  Mike Meredith  Eugene Murphy  Rachael Shreeve  Rebecca Korb  Jon Watkins  Sally Thorpe  Rachel Woodd-Walker  Andrew Brierley  Nathan Cunningham  Sharon Grant  Doug Bone 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12):139

The coupling of physics and biology was examined along a 160 km long transect running out from the north coast of South Georgia Island and crossing the Southern Antarctic Circumpolar Current Front (SACCF) during late December 2000. Surface and near surface potential TS properties indicated the presence of three water types: a near-shore group of stations characterised by water which became progressively warmer and fresher closer to South Georgia, an offshore grouping in which sea surface temperatures and those at the winter water level were relatively warm (1.8°C and 0.5°C, respectively), and a third in which surface and winter water temperatures were cooler and reflected the presence of the SACCF. The transect bisected the SACCF twice, revealing that it was flowing in opposite directions, north-westward closest to South Georgia and south-eastwards at its furthest point from the island. The innermost limb was a narrow intense feature located just off the shelf break in 2000–3500 m of water and in which rapid surface baroclinic velocities (up to 35 cm s⁻¹) were encountered. Offshore in the outermost limb, shown subsequently to be a mesoscale eddy that had meandered south from the retroflected limb of the SACCF, flow was broader and slower with peak velocities around 20 cm s⁻¹. Chlorophyll a biomass was generally low (<1 mg m⁻³) over much of the transect but increased dramatically in the region of the innermost limb of the SACCF, where a deepening of the surface mixed layer was coincident with a subsurface chlorophyll maximum (7.4 mg m⁻³) and elevated concentrations down to 100 m. The bloom was coincident with depleted nutrient concentrations, particularly silicate, nitrate and phosphate, and although ammonium concentrations were locally depleted the bloom lay within an elevated band (up to 1.5 mmol m⁻³) associated with the frontal jet. Increased zooplankton abundance, higher copepod body carbon mass and egg production rates all showed a strong spatial integrity with the front. The population structure of the copepods Calanoides acutus and Rhincalanus gigas at stations within the front suggested that rather than simply resulting from entrainment and concentration within the jet, increased copepod abundance was the result of development in situ. Estimates of bloom duration, based on silicate and carbon budget calculations, set the likely duration between 82 and 122 d, a figure supported by the development schedule of the two copepod species. Given this timescale, model outputs from FRAM and OCCAM indicated that particles that occurred on the north side of South Georgia in December would have been in the central-southern Scotia Sea 2–3 months earlier, probably in sea ice affected regions.  相似文献   

Baltic cod recruitment - the impact of climate variability on key processes   总被引：3，自引：0，他引：3  

Koster  Friedrich W.; Mollmann  Christian; Hinrichsen  Hans-Harald; Wieland  Kai; Tomkiewicz  Jonna; Kraus  Gerd; Voss  Rudiger; Makarchouk  Andrei; MacKenzie  Brian R.; St. John  Michael A.; Schnack  Dietrich; Rohlf  Norbert; Linkowski  Tomasz; Beyer  Jan E. 《ICES Journal of Marine Science》2005,62(7):1408-1425

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Structural controls on Tertiary orogenic gold mineralization during initiation of a mountain belt, New Zealand   总被引：3，自引：2，他引：3  

D. Craw  M. Begbie  D. MacKenzie 《Mineralium Deposita》2006,41(7):645-659

Two types of structurally controlled hydrothermal mineralization have occurred during folding of fissile schist in southern New Zealand: fold-related mineralization and normal fault-related mineralization. Both types have the same mineralogy and textures, and are dominated by quartz–ankerite veins and silicified breccias with ankeritic alteration. Most mineralized zones are thin (centimetre scale), although host schist is commonly impregnated with ankerite up to 20 m away. Thick (up to 5 m wide) mineralized zones are generally gold-bearing and contain pyrite and arsenopyrite with stibnite pods locally. Some of these auriferous zones have been extensively mined historically despite rugged topography and difficult access. Mineralization occurred during regional tectonic compression in the initial stages of development of the Southern Alps mountain belt at the Pacific–Australian plate boundary in the Miocene. Most of the gold-bearing deposits occur in east to south-east, striking normal faults that cut across mesoscopic folds in a belt that coincides with the southern termination of a regional-scale north trending antiform. Mineralized zones have similar structural control and relative timing to a nearby swarm of Miocene lamprophyre dykes and carbonatites. Limited stable isotopic data (C and O) and trace element geochemistry suggest that there was probably no genetic link between the igneous activity and gold mineralization. However, these two types of fluid flow have been controlled by the same tectonically created crustal plumbing system. This Miocene hydrothermal activity and gold deposition demonstrates that orogenic (mesothermal) mineralization can occur during the inception of an orogenic belt, not just in the latter stages as is commonly believed. These Miocene structures have been preserved in the orogen because the locus of uplift has moved northwards, so the early-formed gold deposits have not yet been structurally overprinted or eroded.  相似文献   

Drainage, sediment transport, and denudation rates on the Nanga Parbat Himalaya, Pakistan     

Kevin Cornwell  Doug Norsby  Richard Marston 《Geomorphology》2003,55(1-4):25

The Nanga Parbat Himalaya presents some of the greatest relief on Earth, yet sediment production and denudation rates have only been sporadically addressed. We utilized field measurements and computer models to estimate bank full discharge, sediment transport, and denudation rates for the Raikot and Buldar drainage basins (north slope of Nanga Parbat) and the upper reach of the Rupal drainage basin (south slope).The overall tasks of determining stream flow conditions in such a dynamic geomorphic setting is challenging. No gage data exist for these drainage basins, and the overall character of the drainage basins (high relief, steep flow gradients, and turbulent flow conditions) does not lend itself to either ready access or complete profiling.Cross-sectional profiles were surveyed through selected reaches of these drainage basins. These data were then incorporated into software (WinXSPRO) that aids in the characterization (stage, discharge, velocity, and shear stress) of high altitude, steep mountain stream conditions.Complete field measurements of channel depths were rarely possible (except at several bridges where the middle of the channel could actually be straddled and probed) and, when coupled with velocity measurements, provided discrete points of field-measured discharge calculations. These points were then used to calibrate WinXSPRO results for the same reach and provided a confidence level for computer-generated results.Flow calculations suggest that under near bank full conditions, the upper Raikot drainage basin produces discharges of 61 cm and moves about 11,000 tons day⁻¹ (9980 tons day⁻¹) of sediment through its channel. Bank full conditions on the upper portion of the Rupal drainage basin generate discharges of 84 cm and moves only about 3800 tons day⁻¹ (3450 tons day⁻¹) of sediment. Although the upper Rupal drainage basin moves more water, the lower slope of the drainage basin (0.03) generates a much smaller shear stress (461 Pa) than does the higher slope (0.12) of the upper Raikot drainage basin (1925 Pa).Dissolved and suspended sediment loads were measured from water/sediment samples collected throughout the day and night over a period of 10 days at the height of the summer melt season but proved to be a minor variable in transport flux. Channel bed loads were measured using a pebble count method of bank material and then used to generate ratings curves of bed loads relative to discharge volumes. When coupled with discharge data and basin area, mean annual sediment yield and denudation rates for Nanga Parbat are produced. Denudation rates calculated in this fashion range from 0.2 mm year⁻¹ in the slower, more sluggish Rupal drainage basin to almost 6 mm year⁻¹ in the steeper, faster flowing Raikot and Buldar drainage basins.  相似文献   

Influence of tectonic structures on the Hope Slide, British Columbia, Canada     

Marc-Andr  Brideau  Doug Stead  Derek Kinakin  Karin Fecova 《Engineering Geology》2005,80(3-4):242-259

The Hope Slide, which occurred on January 9, 1965, involved an estimated 47-Mm³ of meta-volcanics and intrusive rocks. Previous workers reported the presence of tectonic structures (faults and shear zones) along the failure surface at the Hope Slide. These tectonic features were investigated in detail to assess their effects on rock-mass quality and the related implications for slope stability. This paper integrates basic field and laboratory concepts from structural and engineering geology. Subdividing the failure area into structural domains allowed distinct discontinuity sets to be associated with specific tectonic structures. The Geological Strength Index (GSI) was used to estimate the rock-mass damage related to the tectonic structures. Low GSI values were seen to outline tectonic damage zones. Point-load tests were used to characterise the compressive strength of rocks adjacent to the tectonic structures. Strength anisotropy, tentatively attributed to damage caused by a large shear zone, was observed in greenstone samples. Seepage zones along the failure surface were observed preferentially along shallow discontinuities that dipped downslope and in rock masses of good quality (GSI > 40). An alternative morphology of the slope failure is proposed by distinguishing between the extent of the surficial damage due to the rock-slope failure and the zone of failed material (depletion zone). For the first time, a kinematic mechanism for the Hope Slide is proposed, based on a preliminary 3-dimensional block model. A pre-1965 DEM was produced from estimates of material lost and gained as reported by previous workers. The pre-1965 DEM revealed that the tectonic structures recognised during fieldwork bounded the material that failed in the 1965 event.  相似文献   

The Relationship between Narratives,Wildlife Value Orientations,Attitudes, and Policy Preferences     

Eric Knackmuhs  James Farmer  Doug Knapp 《社会与自然资源》2019,32(3):303-321

Overabundance of white-tailed deer is a pervasive problem across the United States. Deer are blamed for increased risk of auto accidents, tick-borne diseases, and overbrowsing of native species. Lethal management techniques, cited as cost-effective and humane, are commonly employed for herd management. However, the approach frequently sparks outrage among various stakeholders who feel killing of animals is unjustified and prefer nonlethal measures. Wildlife managers then face the challenge of communicating with the public to build policy support for lethal management. The Narrative Policy Framework was used to test the effects of differing narratives on public opinion for lethal deer management. Results indicated narratives were influential in shifting attitudes toward and support for a proposed sharpshooting policy even in some cases where respondents were already familiar with the issue and held a previous opinion. This study also supported the utility of the Narrative Policy Framework for examining human dimensions of wildlife issues.  相似文献   

Engineering geomorphological characterisation of the Vajont Slide,Italy, and a new interpretation of the chronology and evolution of the landslide   总被引：1，自引：0，他引：1  

Andrea Wolter  Doug Stead  Brent C. Ward  John J. Clague  Monica Ghirotti 《Landslides》2016,13(5):1067-1081

Although the 1963 Vajont Slide in Italy has been extensively studied for over 50 years, its regional geological and geomorphological context has been neglected. In this paper, we use field observations and remote sensing data to elucidate the interaction between endogenic and exogenic processes that brought the north slope of Monte Toc to failure. We present the first detailed pre- and post-failure engineering geomorphology maps of the slide area. The maps delineate two main landslide blocks, several sub-blocks, compressional and extensional zones, and secondary failures in the deposit. The maps provide new insights into the kinematics, dynamics and evolution of the slide. Finally, we discuss the origin of Vajont Gorge and a prehistoric failure that occurred at the same location as the 1963 slide. We propose, as part of a newly developed multi-stage landscape evolution sequence, that the prehistoric failure was a deep-seated gravitational slope deformation (sackung) that initiated during deglaciation and continued to slowly move until the catastrophic failure in 1963. We argue that the gorge was created by these deep-seated slow movements.  相似文献