Architecture of the deep critical zone in the Río Icacos watershed (Luquillo Critical Zone Observatory,Puerto Rico) inferred from drilling and ground penetrating radar (GPR)          下载免费PDF全文

Joe Orlando  Xavier Comas  Scott A. Hynek  Heather L. Buss  Susan L. Brantley 《地球表面变化过程与地形》2016,41(13):1826-1840

In the critical zone, surficial bedrock interactions result in the formation of a mantle of chemically‐ and physically‐altered material defined here as regolith. In the watershed of the Río Icacos, an upland river draining the Luquillo Mountains in tropical Puerto Rico, we explored the influence of lithology (quartz diorite versus hornfels‐facies volcaniclastic rock) on weathering. Regolith profiles were studied by drilling boreholes and imaging the subsurface using ground penetrating radar (GPR). Overall, the regolith structure is not laterally continuous but rather is punctuated by zones of deep fractures that host in situ weathering, corestones, and colluvial material. GPR images of these vertical zones show reflectors at 15–20 m depth. Thus, the architecture of the critical zone in the upper Luquillo Mountains is highly dependent on lithology and its influence on fracture development. At the highest elevations where hornfels overlies quartz diorite, positive feedbacks occur when the water table drops so that oxidative weathering of biotite in the more felsic rock creates microfractures and allows deeper infiltration of meteoric waters. Such exposure results in some of the fastest weathering rocks in the world and may contribute to formation of the knickpoint in the Río Icacos watershed. This work represents the first study combining GPR and drilling to look at the structure of the deep critical zone and demonstrates: (1) the importance of combining direct methods (such as drilling) with indirect methods (such as GPR) to understand the architecture of the critical zone in tropical systems; (2) the interplay of the surficial stress regime, lithology and climate in dictating the architecture of weathering. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

北祁连东部两类Ⅰ型花岗岩定年及其地质意义     

吴才来  杨经绥  杨宏仪  郑秋光  史仁灯  陈松永  Joe Wooden  Trevor lreland 《地质学报》2005,79(2):286

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Radiocarbon deficiencies of US Gulf Coast lakes compromise paleo-hurricane records     

Paul Aharon  W. Joe Lambert 《Quaternary Research》2009,71(3):266-270

Radiocarbon assays of sediments from Lake Shelby, US Gulf Coast, exhibit substantial ¹⁴C deficiencies of 9.3% and 4.7% for the limnic sapropel and associated fresh-water clams Rangia cuneata, respectively. Measured radiocarbon dates from the sapropel and clams require corrections of 785 ± 80 and 365 ± 90 ¹⁴C yr (1σ), respectively, in order to achieve consistency with the radiocarbon time scale. Lake sediments of the US Gulf Coast serve as unique repositories of pre-historic hurricane strikes. Previously unrecognized radiocarbon deficiencies likely render compromised chronologies of the paleo-hurricane records, and erroneous estimates of return period and landfall probability that are derived from the storm chronologies. The recalculated severe hurricane chronologies suggest that the annual landfall probabilities of the last millennium on the US Gulf Coast are equal to, or higher than, the preceding three millennia.  相似文献   

Exploring how alternative mapping approaches influence fireshed assessment and human community exposure to wildfire     

Joe H. Scott  Matthew P. Thompson  Julie W. Gilbertson-Day 《GeoJournal》2017,82(1):201-215

Attaining fire-adapted human communities has become a key focus of collaborative planning on landscapes across the western United States and elsewhere. The coupling of fire simulation with GIS has expanded the analytical base to support such planning efforts, particularly through the “fireshed” concept that identifies areas where wildfires could ignite and reach a human community. Previous research has identified mismatches in scale between localized community wildfire planning and the broader fireshed considering patterns of wildfire activity across landscapes. Here we expand upon this work by investigating the degree to which alternative geospatial characterizations of human communities could influence assessment of community exposure and characterization of the fireshed. We use three methods of mapping human communities (point, raster, and polygon) and develop three fireshed metrics (size, number of fires reaching houses, and number of houses exposed), and apply this analytical framework on a 2.3 million ha case study landscape encompassing the Sierra National Forest in California, USA. We simulated fire occurrence and growth using FSim for 10,000 iterations (fire seasons) at 180-m resolution. The simulation resulted in 3.9 large fires per million ha per year, with a mean size of 3432 ha. Results exhibit similarities and differences in how exposure is quantified, specifically indicating that polygons representing recognized community boundaries led to the lowest exposure levels. These results highlight how choice of the mapping approach could lead to misestimating the scope of the problem or targeting mitigation efforts in the wrong areas, and underscore the importance of clarity and spatial fidelity in geospatial data representing communities at risk.  相似文献   

Innovative applications of laser scanning and rapid prototype printing to rock breakdown experiments     

Mary Bourke  Heather Viles  Joe Nicoli  Parris Lyew‐Ayee  Rebecca Ghent  James Holmlund 《地球表面变化过程与地形》2008,33(10):1614-1621

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Mapping distortion of detectors in UVIT onboard AstroSat observatory     

V Girish  Shyam N. Tandon  S. Sriram  Amit Kumar  Joe Postma 《Experimental Astronomy》2017,43(1):59-74

Ultraviolet Imaging Telescope (UVIT) is one of the payloads onboard AstroSat, India’s first multi-wavelength Astronomy mission. UVIT is primarily designed to make high resolution images in wide field, in three wavelength channels simultaneously: FUV (130–180 nm), NUV (200–300 nm) and VIS (320–550 nm). The intensified imagers used in UVIT suffer from distortions, and a correction is necessary for these to achieve good astrometry. In this article we describe the methodology and calculations used to estimate the distortions in ground calibrations.  相似文献   

Sedimentary environments of the east-central Bering Sea continental shelf     

Harley J. Knebel  Joe S. Creager 《Marine Geology》1973,15(1):25-47

A factor analysis of 180 bottom sediment samples from the east-central Bering Sea continental shelf identifies five factors that account for 95% of the variation in the 17 whole ø size classes that were used as variables. Factor I represents coarse sediments that have been bypassed in areas of active water circulation. Factors II and III represent fine and very fine sands that have been hydraulically sorted, reworked, and mixed. Factor IV represents coarse to medium silt that has been segregated from areas of relatively high energy. Factor V represents both the production of sediments finer than medium silt and deposition within the lowest-energy environment in this area.Modern and palimpsest sediments are areally prevalent over this section of the shelf. Relict sediments occur in only a few small areas. The dispersal of sediments is affected by surface and tidal currents as well as wave action. Ice rafting is not an important geological agent. Data from the eastcentral Bering Sea shelf indicate that sediments on subarctic continental shelves are not necessarily characterized by an abundance of rocky sediments or gravel.  相似文献   

Marine ecosystem management: Fish abundance and size under exploitation     

Joe Horwood 《Marine Policy》2010

This study is targeted on policy makers and environmental scientists to illustrate the typical historical scale of depletion of our fish stocks, and what current and emerging legislation might mean for fisheries management and the metrics of fish stocks. The population demography of the Bristol Channel sole is described since 1820. Their decline in abundance, and change in length compositions, are modelled. By 2000, the mature stock had been depleted to less than 5% of its original size, and larger sole were rarely caught. The implications of maximum sustainable yield targets, and of good environmental status, are examined.  相似文献   

Instrumentation needs for ocean biology     

Colwell  R. Tabor  P. 《Oceanic Engineering, IEEE Journal of》1978,3(4):128-134

Research and development in ocean engineering, particularly in the areas of deep ocean drilling and platform construction, have progressed remarkably in the past few decades. By and large, instrumentation for biological ocean research, in comparison, remains simplistic. A brief review of marine biological sampling devices is provided, indicating the relative inadequacies of marine bio-instrumentation. Equipment for plankton, benthos, and nekton sampling has been improved in recent years compared to that available for nannoplankton. Nevertheless, there are limitations even in the best of these devices, and improvements in sampling gear would benefit ocean biology significantly. Precise sample collection of surface slicks, water column, and ocean sediment is mandatory for biological assessment of environmental impact. The necessary sampling gear is either not available or under development and, in cases where the instrumentation is available, it is, in general, either limited in application or not entirely reliable. As an example, increasingly, the ocean serves as the receptor of discharge from sewage outfalls, deep water disposal, and ocean dumping. Thus assessment of biological impact is required, particularly in light of the increasing frequency of reports of survival of bacteria and viruses pathogenic for man in those regions of the world oceans significantly affected by these activities. Improved instrumentation for aseptic sample collection and retrieval of water, sediment, and biota for quantitative, as well as qualitative, microbiological analyses are needed. Developments in baromicrobiology have been rapid, but improved instrumentation is needed. Even though aseptic collection of deep ocean water samples is possible, sediment sample collection for microbiology is still accomplished by coring or grab devices, with no instrument yet available for quantitative undisturbed sample collection without contamination from water column microorganisms.  相似文献   

Hydrochemical variations during flood pulses in the south‐west China peak cluster karst: impacts of CaCO3–H2O–CO2 interactions     

Zaihua Liu  Chris Groves  Daoxian Yuan  Joe Meiman  Guanghui Jiang  Shiyi He  Qiang Li 《水文研究》2004,18(13):2423-2437

High‐resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the Guilin Karst Experimental Site in Guangxi Province, China, were made with different types of multiparameter sonde. The data were stored using data loggers recording with 2 min or 15 min resolution. Waters from a large, perennial spring represent the exit for the aquifer's conduit flow, and a nearby well measures water in the conduit‐adjacent, fractured media. During flood pulses, the pH of the conduit flow water rises as the conductivity falls. In contrast, and at the same time, the pH of groundwater in the fractures drops, as conductivity rises. As Ca²⁺ and HCO₃^? were the dominant (>90%) ions, we developed linear relationships (both r² > 0·91) between conductivity and those ions, respectively, and in turn calculated variations in the calcite saturation index (SI_C) and CO₂ partial pressure (P) of water during flood pulses. Results indicate that the P of fracture water during flood periods is higher than that at lower flows, and its SI_C is lower. Simultaneously, P of conduit water during the flood period is lower than that at lower flows, and its SI_C also is lower. From these results we conclude that at least two key processes are controlling hydrochemical variations during flood periods: (i) dilution by precipitation and (ii) water–rock–gas interactions. To explain hydrochemical variations in the fracture water, the water–rock–gas interactions may be more important. For example, during flood periods, soil gas with high CO₂ concentrations dissolves in water and enters the fracture system, the water, which in turn has become more highly undersaturated, dissolves more limestone, and the conductivity increases. Dilution of rainfall is more important in controlling hydrochemical variations of conduit water, because rainfall with higher pH (in this area apparently owing to interaction with limestone dust in the lower atmosphere) and low conductivity travels through the conduit system rapidly. These results illustrate that to understand the hydrochemical variations in karst systems, considering only water–rock interactions is not sufficient, and the variable effects of CO₂ on the system should be evaluated. Consideration of water–rock–gas interactions is thus a must in understanding variations in karst hydrochemistry. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献