Till‐forming processes beneath parts of the Cordilleran Ice Sheet,British Columbia,Canada: macroscale and microscale evidence and a new statistical technique for analysing microstructure data     

Christina M. Neudorf  Tracy A. Brennand  Olav B. Lian 《Boreas: An International Journal of Quaternary Research》2013,42(4):848-875

This paper presents the first integrated macroscale and microscale examination of subglacial till associated with the last‐glacial (Fraser Glaciation) Cordilleran Ice Sheet (CIS). A new statistical approach to quantifying till micromorphology (multivariate hierarchical cluster analysis for compositional data) is also described and implemented. Till macrostructures, macrofabrics and microstructures support previous assertions that primary till in this region formed through a combination of lodgement and deformation processes in a temperate subglacial environment. Macroscale observations suggest that subglacial environments below the CIS were probably influenced by topography, whereby poor drainage of the substrate in topographically constricted areas, or on slopes adverse to the ice‐flow direction at glacial maximum, facilitated ductile deformation of the glacier bed. Microscale observations suggest that subglacial till below the CIS experienced both ductile and brittle deformation, including grain rotation and squeeze flow of sediment between grains under moist conditions, and microshearing, grain stacking and grain fracturing under well‐drained conditions. Macroscale observations suggest that ductile deformation events were probably followed by brittle deformation events as the substrate subsequently drained. The prevalence of ductile‐type microstructures in most till exposures investigated in this study suggests that ductile deformation signatures can be preserved at the microscale after brittle deformation events that result in larger‐scale fractures and shear structures. It is likely that microscale ductile deformation can also occur within distributed shear zones during lodgement processes. Cluster analysis of microstructure data and qualitative observations made from thin sections suggest that the relative frequency of countable microstructures in this till is influenced by topography in relation to ice‐flow direction (bed drainage conditions) as well as by the frequency and distribution of voids in the till matrix and skeletal grain shapes.  相似文献   

Swedish coastal fisheries—From conflict mitigation to participatory management     

Karl Bruckmeier  Christina Höj Larsen 《Marine Policy》2008

Several research projects have studied Swedish coastal fishery to investigate the conflict between seals and fishery. In recent years, a strategy of participation by means of co-management has been unfolding. Realising that maintaining the coastal fishery requires societal support and knowledge integration, attempts have been made to introduce the principle of participatory management into the centralised Swedish fisheries management system. However, this co-management approach, presently implemented in six pilot projects, will take a long time to develop through a sustained process of experimentation and improvement.  相似文献   

PM2.5 co-benefits of climate change legislation part 2: California governor’s executive order S-3-05 applied to the transportation sector     

Michael J. Kleeman  Christina Zapata  John Stilley  Mark Hixson 《Climatic change》2013,117(1-2):399-414

California Governor’s Executive Order (CGEO) S-3-05 requires that California greenhouse gas (GHG) emissions be reduced to 80 % below 1990 levels by the year 2050. Meeting this target will require drastic changes in transportation technology, fuel, and behavior which will reduce criteria pollutant emissions as well as GHG emissions. The improvement to local air quality caused by the reduced criteria pollutant emissions must be calculated to fully evaluate the overall benefits and costs of CGEO S-3-05. In the present study, seven different transportation scenarios that move towards the goals of CGEO S-3-05 in the transportation sector were examined to determine how they would affect future airborne particulate matter (PM_2.5) concentrations in California: (1) hydrogen fuel cells, (2) electric vehicles, (3) high efficiency vehicles, (4) public mass transit, (5) biofuels, (6) biofuels + hybrid electric vehicles, and (7) hydrogen fuel cells + electric vehicles. The air quality implications of each scenario were evaluated using a chemical transport model applied during a wintertime stagnation episode representing future climate in California. Scenarios (6) and (7) reduced population-weighted PM_2.5 mass concentrations by ~9 % and PM_2.5 elemental carbon (EC) concentrations by ~30 % relative to base-case predictions.  相似文献   

Hydrogeologic controls on summer stream temperatures in the McKenzie River basin,Oregon     

Christina Tague  Michael Farrell  Gordon Grant  Sarah Lewis  Serge Rey 《水文研究》2007,21(24):3288-3300

Stream temperature is a complex function of energy inputs including solar radiation and latent and sensible heat transfer. In streams where groundwater inputs are significant, energy input through advection can also be an important control on stream temperature. For an individual stream reach, models of stream temperature can take advantage of direct measurement or estimation of these energy inputs for a given river channel environment. Understanding spatial patterns of stream temperature at a landscape scale requires predicting how this environment varies through space, and under different atmospheric conditions. At the landscape scale, air temperature is often used as a surrogate for the dominant controls on stream temperature. In this study we show that, in regions where groundwater inputs are key controls and the degree of groundwater input varies in space, air temperature alone is unlikely to explain within-landscape stream temperature patterns. We illustrate how a geologic template can offer insight into landscape-scale patterns of stream temperature and its predictability from air temperature relationships. We focus on variation in stream temperature within headwater streams within the McKenzie River basin in western Oregon. In this region, as in other areas of the Pacific Northwest, fish sensitivity to summer stream temperatures continues to be a pressing environmental issue. We show that, within the McKenzie, streams which are sourced from deeper groundwater reservoirs versus shallow subsurface flow systems have distinct summer temperature regimes. Groundwater streams are colder, less variable and less sensitive to air temperature variation. We use these results from the western Oregon Cascade hydroclimatic regime to illustrate a conceptual framework for developing regional-scale indicators of stream temperature variation that considers the underlying geologic controls on spatial variation, and the relative roles played by energy and water inputs. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Delgada Fan: Preliminary interpretation of channel development     

William R. Normark  Christina E. Gutmacher 《Geo-Marine Letters》1984,3(2-4):79-83

The Delgada Fan, an irregularly shaped turbidite deposit extending more than 350 km offshore from northern California, consists of two large leveed-valley units each fed by a separate complex of coalescing submarine canyons and slope gullies. Although the leveed-valley units head within 25 km of each other, both appear to have developed independently during fan growth. The larger southern leveed-valley system has not developed middle-fan distributary channels and appears to illustrate a period of progressive valley abandonment. Although the lower-fan area is underlain by sandy sediments, little sand has been recovered in piston cores from the leveed-valley unit. Margin setting represents fan and/or source area  相似文献   

Volcanic risk ranking for Auckland, New Zealand. I: Methodology and hazard investigation     

Christina Magill  Russell Blong 《Bulletin of Volcanology》2005,67(4):331-339

Volcanic eruptions typically produce a number of hazards, and many regions are at risk from more than one volcano or volcanic field. So that detailed risk assessments can be carried out, it is necessary to rank potential volcanic hazards and events in terms of risk. As it is often difficult to make accurate predictions regarding the characteristics of future eruptions, a method for ranking hazards and events has been developed that does not rely on precise values. Risk is calculated individually for each hazard from each source as the product of likelihood, extent and effect, based on the parameters order of magnitude. So that multiple events and outcomes can be considered, risk is further multiplied by the relative probability of the event occurring (probability_e) and the relative importance of the outcome (importance_o). By adding the values obtained, total risk is calculated and a ranking can be carried out.This method was used to rank volcanic hazards and events that may impact the Auckland Region, New Zealand. Auckland is at risk from the Auckland volcanic field, Okataina volcanic centre, Taupo volcano, Tuhua volcano, Tongariro volcanic centre, and Mt. Taranaki volcano. Relative probabilities were determined for each event, with the highest given to Mt. Taranaki. Hazards considered were, for local events: tephra fall, scoria fall and ballistic impacts, lava flow, base surge and associated shock waves, tsunami, volcanic gases and acid rain, earthquakes and ground deformation, mudflows and mudfills, lightning and flooding; and for distal events: tephra fall, pyroclastic flows, poisonous gases and acid rain, mudflows and mudfills, climate variations and earthquakes. Hazards from each source were assigned values for likelihood, with the largest for tephra fall from all sources, earthquakes and ground deformation, lava flows, scoria fall and base surge for an Auckland eruption on land, and earthquakes and ground deformation from an Auckland eruption in the ocean. The largest values for extent were for tephra fall and climate variation from each of the distal centres. However, these parameters do not give a true indication of risk. In a companion paper the effect of each hazard is fully investigated and the risk ranking completed.  相似文献   

Tectonic evolution of the Brian?onnais units along a transect (ECORS-CROP) through the Italian-French Western Alps     

Stefan Bucher  Christina Ulardic  Romain Bousquet  Stefano Ceriani  Bernhard Fügenschuh  Yves Gouffon  Stefan M. Schmid 《Eclogae Geologicae Helvetiae》2004,97(3):321-345

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Ideal width of transects for monitoring source-related categories of plastics on beaches     

de Araújo MC  Santos PJ  Costa MF 《Marine pollution bulletin》2006,52(8):957-961

Although there is a consensus on the necessity of monitoring solid wastes pollution on beaches, the methods applied vary widely. Therefore, creating, testing and recommending a method that not only allows comparisons of places and periods, but also the detection of source signals, will be important to reach the objectives of the source-prevention principle. This will also allow the optimisation of time, resources, and processing of samples and data. A classification of the items found into specific categories was made according to their most probable source/use (fisheries, food packaging, hazardous, sewage/personal hygiene, beach user, general home). This study tested different widths of sampling transects to be used in the detection of plastics contamination on beaches, until all the categories were significantly represented. Each transect had its total width (50m) sub-divided into eight intervals of 0-2.5m; 2.5-5m; 5-10m; 10-15m; 15-20m; 20-30m; 30-40m; and 40-50m. The accumulated number of categories in the 50m (up to 2.5m; up to 5m and so on) was used to determine the minimal width necessary to qualitatively characterize the area regarding plastics contamination. The diversity of the categories was directly related to the area of the sampling transect. These results indicate that a significant increase in the number of categories in the first intervals tend to stabilize from 15-20m onwards.  相似文献   

Personality type differences between Ph.D. climate researchers and the general public: implications for effective communication     

C. Susan Weiler  Jason K. Keller  Christina Olex 《Climatic change》2012,112(2):233-242

Effectively communicating the complexity of climate change to the public is an important goal for the climate change research community, particularly for those of us who receive public funds. The challenge of communicating the science of climate change will be reduced if climate change researchers consider the links between personality types, communication tendencies and learning preferences. Jungian personality type is one of many factors related to an individual’s preferred style of taking in and processing information, i.e., preferred communication style. In this paper, we demonstrate that the Jungian personality type profile of interdisciplinary, early career climate researchers is significantly different from that of the general population in the United States. In particular, Ph.D. climate researchers tend towards Intuition and focus on theories and the “big picture”, while the U.S. general population tends towards Sensing and focuses on concrete examples and experience. There are other differences as well in the way the general public as a group prefers to take in information, make decisions, and deal with the outer world, compared with the average interdisciplinary climate scientist. These differences have important implications for communication between these two groups. We suggest that climate researchers will be more effective in conveying their messages if they are aware of their own personality type and potential differences in preferred learning and communication styles between themselves and the general public (and other specific audiences), and use this knowledge to more effectively target their audience.  相似文献   

Rate of growth of the preserved North American continental crust: Evidence from Hf and O isotopes in Mississippi detrital zircons   总被引：2，自引：0，他引：2  

Christina Yan Wang  Ian H. Campbell  Charlotte M. Allen  Ian S. Williams  Stephen M. Eggins 《Geochimica et cosmochimica acta》2009,73(3):712-728

Detrital zircons from the Mississippi River have been analyzed for U-Th-Pb, Lu-Hf and O isotopes to constrain the rate of growth of the preserved North American continental crust. One hundred and forty two concordant zircon U/Pb dates on grains mounted in epoxy, obtained by Excimer laser ablation ICP-MS method, resolved six major periods of zircon crystallization: 0-0.25, 0.3-0.6, 0.95-1.25, 1.3-1.5, 1.65-1.95 and 2.5-3.0 Ga. These age ranges match the ages of the recognized lithotectonic units of the North American continent in the hinterland of the Mississippi River. Ninety-six zircons mounted on tape, which show no age zonation and were within 7.5% of concordance, were selected to represent the six U/Pb age time intervals and analyzed for Lu-Hf and O isotope by laser ablation MC-ICP-MS and SHRIMP II, respectively. The δ¹⁸O values of the zircons show a small step increase in the maximum δ¹⁸O values at the Archean-Proterozoic boundary from 7.5‰ in the Archean to 9.5‰, and rarely 13‰, in the Proterozoic and Phanerozoic. However, the average value of δ¹⁸O in zircons changes little with time, showing that the increase in the maximum δ¹⁸O values between 2.5 and 2.0 Ga, which can be attributed to an increase in the sediment content of the source regions of younger granitoids, is largely balanced by an increase in zircons with anomalously low δ¹⁸O, which can be attributed to hydrothermally altered crust in the granitoid source region.εHf_i values for the zircons range from 13.1 to −26.9. Zircons derived from juvenile crust, which we define as having mantle δ¹⁸O (4.5-6.5‰) and lying within error of the Hf depleted mantle growth curve, are rare or absent in the Mississippi basin. The overwhelming majority of zircons crystallized from melted pre-existing continental crust, or mantle-derived magmas that were contaminated by continental crust. The average time difference between primitive crust formation and remelting for each of the recognized lithotectonic time intervals, which is defined as crustal incubation time in this study, is 890 ± 460 Myr. There is also a suggestion that the crustal incubation time increases with decreasing age in the Mississippi basin, which is consistent with the declining role of radioactive heat production in the lower crust with time.The average Hf model age (1.94 Ga), weighted by fraction of zircons in the river load is in reasonable agreement with the Nd model age (1.7 Ga) for the Mississippi River. However, if the zircons are weighted by the area of North America covered by the six recognized periods of zircon crystallization the average model age is 2.35 Ga, which compares favorably with an area weighted Nd model age of 2.36 Ga. Our preferred approach is to use the measured O isotope values to constrain variations in the ¹⁷⁶Lu/¹⁷⁷Hf ratio of the granitic source region from which the zircons crystallized, making the assumption that zircons with mantle-like O isotopic ratios have higher ¹⁷⁶Lu/¹⁷⁷Hf than zircons with higher O isotope values. This method gives an average Hf model age of 2.53 Ga, which is 180 Myr older than the constant ¹⁷⁶Lu/¹⁷⁷Hf calculation.The area weighted zircon Hf model ages show two distinct periods of crust formation for the North American continent, 1.6-2.2 and 2.9-3.4 Ga. At least 50% of the preserved North American continental crust was extracted from the mantle by 2.9 Ga and 90% by 1.6 Ga. Two similar periods of crustal growth are also recognized in Gondwana (Hawkesworth C. J. and Kemp A. I. S. (2006) Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution. Chem. Geol.226, 144-162.), suggesting that these may be periods of global continental crustal growth. However, we stress that more data from other continents are required before the hypothesis of episodic global continental growth can be accepted with confidence.  相似文献