Rapid Holocene hydrologic change along boreal treeline revealed by δ13C and δ18O in organic lake sediments, Northwest Territories, Canada     

Brent B. Wolfe  Thomas W. D. Edwards  Ramon Aravena  Glen M. MacDonald 《Journal of Paleolimnology》1996,15(2):171-181

Analysis of ¹⁸O_cellulose, ¹³C_{organic matter}, and ¹³C_cellulose at about 100 year intervals from organic matter deposited in Toronto Lake, Northwest Territories, Canada, revealed an 8000-year history of rapid, post-glacial hydrologic change at the treeline zone. Several mid-Holocene phases of enriched ¹³C_org and ¹³C_cell, caused by elevated lake productivity, declining [CO_2(aq)], and closed basin conditions, were abruptly terminated by intervals of open hydrology recorded by sharply depleted ¹⁸O_cell. Two of these events, at 5000 and 4500 BP, are correlated with increased total organic content and Picea mariana pollen concentration, which indicate that high levels of productivity were also accompanied by northern treeline advances. A third treeline advance at about 2500 BP is also marked by an apparent outflow event from Toronto Lake, but this was not associated with ¹³C_org/cell enrichment in the sediment record because rapid and substantial lake water renewal probably prevented productivity-driven enrichment of the dissolved inorganic carbon and replenished the CO_2(aq) supply to thriving phytoplankton. However, high sediment organic content during this period suggests increased productivity. Increases in the inflow:evaporation ratio at about 6500 and 3500 BP were also sufficient to cause Toronto Lake to overflow but the prevailing climate during these periods apparently did not favour appreciable northward treeline migration or changes in lake productivity.This is the 14th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers  相似文献   

Error bounds in cascading regressions     

Michael R. Karlinger  Brent M. Troutman 《Mathematical Geology》1985,17(3):287-295

Cascading regressions is a technique for predicting a value of a dependent variable when no paired measurements exist to perform a standard regression analysis. Biases in coefficients of a cascaded-regression line as well as error variance of points about the line are functions of the correlation coefficient between dependent and independent variables. Although this correlation cannot be computed because of the lack of paired data, bounds can be placed on errors through the required properties of the correlation coefficient. The potential meansquared error of a cascaded-regression prediction can be large, as illustrated through an example using geomorphologic data.  相似文献   

Software tools for accessing the GPS Seamless Archive     

Michael Scharber  Yehuda Bock  Brent Gilmore 《GPS Solutions》2004,7(4):271-276

The Scripps Orbit and Permanent Array Center (SOPAC) has completed development for the UNAVCO community of first-generation GPS Seamless Archive (GSAC) software. The GSAC is a virtual archive composed of an assembly of agencies and investigators exchanging information about their respective GPS-related data holdings in a well defined, cohesive manner. The superset of this published information is collected and ingested into centralized databases administered currently by two data brokers (Retailers), who make the data available to the public in a seamless manner. There are three user interfaces available: the interactive GSAC Wizard, a command-line Unix-style executable called gsac-client, and a front door HTTP service called the GSAC Retailer Service Interface. Each user interface provides access to the data collections of 6 different GPS archives (GSAC Wholesalers) in North America. Together these archives have published more than 2 million GPS data files pertaining to over 10,000 different geodetic monuments. These datasets are composed in large part of data collected by US scientists and their collaborators over the period 1986 to the present in Western North America and other tectonically active regions around the globe, as well as the holdings of two IGS global data centers. In this article, we describe how the three GSAC user interfaces provide the community a powerful set of tools for seamlessly mining information and collecting data files from a distributed network of GPS archives.The GPS Toolbox is a column dedicated to highlighting algorithms and source code utilized by GPS Engineers and scientists. If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to download source code, visit our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada.  相似文献   

SOPAC Web site (http://sopac.ucsd.edu)   总被引：1，自引：0，他引：1  

Paul?Jamason  Yehuda?BockEmail author  Peng?Fang  Brent?Gilmore  David?Malveaux  Linette?Prawirodirdjo  Michael?Scharber 《GPS Solutions》2004,8(4):272-277

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Sources and sinks of methylgermanium in natural waters     

Brent L. Lewis  Meinrat O. Andreae  Philip N. Froelich 《Marine Chemistry》1989,27(3-4)

New data have extended our understanding of the distribution and behavior of methylgermanium in the environment. Laboratory attempts to induce aerobic methylation with known biological and abiotic methylating agents were unsuccessful; this confirmed previous field observations of methylgermanium's unreactive behavior. However, biomethylation of inorganic germanium was observed in the anaerobic digestor of a sewage treatment plant, which suggested a terrestrial methanogenic source. Attempts to locate such a source in methanogenic swamps and their drainages reveal very low methylgermanium concentrations typical of other remote, pristine rivers. Polluted rivers have monomethylgermanium (MMGe) and dimethylgermanium (DMGe) concentrations 3–100 times higher than those of pristine rivers, which suggests an anthropogenic source of methylgermanium as a result of the synergistic effects of sewage treatment and coal-ash derived inorganic germanium contamination. A new high-precision profile of MMGe and DMGe in the Sargasso Sea shows conservative behavior with no vertical gradients. However, marine anoxic basins have both inorganic germanium enrichment and methylgermanium depletion, which suggests that of marine anaerobic processes are responsible for demethylating marine organogermanium. These results all suggest that methylgermanium is produced on the continents, is unreactive in the open ocean, and is destroyed in marine anoxic environments. The residence time of organogermanium in the sea, based on a continental source (pristine rivers), is at least 1 Ma, consistent with its unreactive nature, its observed distribution in the ocean, and rates of destruction in anoxic basins.  相似文献   

Negotiating through nature: The resistant materiality and materiality of resistance in Bolivia’s natural gas sector     

Brent Z. Kaup   《Geoforum》2008,39(5):1734-1742

Over the past two decades, the natural gas of Bolivia has been a point of international interest and internal contention. Materially and discursively using Bolivia’s natural gas to express their demands, transnational energy firms, the Bolivian state, and Bolivia’s social movements have made the country’s natural gas into an object of profit and protest. In this paper, I examine how these actors have used the country’s natural gas to both secure and disrupt processes of capital accumulation. Extending regulation approaches that take into account the materiality of nature, I argue that the differential abilities of transnational energy firms, the Bolivian state, and the country’s social movements to materially and discursively use Bolivia’s natural gas have provided each of these actors with differential mediums through which to express their often times contradictory interests, and thus to the challenge or stabilize existing regulatory frameworks. Within this context, the Bolivian state has been forced to continually balance the tensions surrounding its natural gas in an attempt to secure a stable regime of accumulation.  相似文献   

Evidence of temperature depression and hydrological variations in the eastern Sierra Nevada during the Younger Dryas stade     

Glen M. MacDonald  Katrina A. Moser  David F. Porinchu  Brent B. Wolfe  Amanda Petel  Amalie Jo Orme 《Quaternary Research》2008,70(2):131-140

Sediment records from two lakes in the east-central Sierra Nevada, California, provide evidence of cooling and hydrological shifts during the Younger Dryas stade (YD; ~ 12,900-11,500 cal yr BP). A chironomid transfer function suggests that lake-water temperatures were depressed by 2°C to 4°C relative to maximum temperatures during the preceding Bølling-Allerød interstade (BA; ~ 14,500-12,900 cal yr BP). Diatom and stable isotope records suggest dry conditions during the latter part of the BA interstade and development of relatively moist conditions during the initiation of the YD stade, with a reversion to drier conditions later in the YD. These paleohydrological inferences correlate with similar timed changes detected in the adjacent Great Basin. Vegetation response during the YD stade includes the development of more open and xeric vegetation toward the end of the YD. The new records support linkages between the North Atlantic, the North Pacific, and widespread YD cooling in western North America, but they also suggest complex hydrological influences. Shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the YD stade in the Sierra Nevada and the discordance in some paleohydrological and glacial records of the YD stade from the western United States.  相似文献   

The evolving perceptual model of streamflow generation at the Panola Mountain Research Watershed     

Brent T. Aulenbach  Richard P. Hooper  H. J. van Meerveld  Douglas A. Burns  James E. Freer  James B. Shanley  Thomas G. Huntington  Jeffrey J. McDonnell  Norman E. Peters 《水文研究》2021,35(4):e14127

The Panola Mountain Research Watershed (PMRW) is a 41-hectare forested catchment within the Piedmont Province of the Southeastern United States. Observations, experimentation, and numerical modelling have been conducted at Panola over the past 35 years. But to date, these studies have not been fully incorporated into a more comprehensive synthesis. Here we describe the evolving perceptual understanding of streamflow generation mechanisms at the PMRW. We show how the long-term study has enabled insights that were initially unforeseen but are also unachievable in short-term studies. In particular, we discuss how the accumulation of field evidence, detailed site characterization, and modelling enabled a priori hypotheses to be formed, later rejected, and then further refined through repeated field campaigns. The extensive characterization of the soil and bedrock provided robust process insights not otherwise achievable from hydrometric measurements and numerical modelling alone. We focus on two major aspects of streamflow generation: the role of hillslopes (and their connection to the riparian zone) and the role of catchment storage in controlling fluxes and transit times of water in the catchment. Finally, we present location-independent hypotheses based on our findings at PMRW and suggest ways to assess the representativeness of PMRW in the broader context of headwater watersheds.  相似文献   

Dating of raised marine and lacustrine deposits in east Greenland using beryllium‐10 depth profiles and implications for estimates of subglacial erosion     

Brent M. Goehring  Meredith A. Kelly  Joerg M. Schaefer  Robert C. Finkel  Thomas V. Lowell 《第四纪科学杂志》2010,25(6):865-874

Here we combine ¹⁰Be depth profile techniques applied to late glacial ice‐contact marine and lacustrine deltas, as well as boulder exposure dating of associated features in the Scoresby Sound region, east Greenland, to determine both the surface age and the magnitude of cosmogenic nuclide inheritance. Boulder ages from an ice‐contact delta in northern Scoresby Sund show scatter typical of polar regions and yield an average age of 12.8 ± 0.5 ka – about 2 ka older than both our average profile surface age of 10.9 ± 0.7 ka from three depth profiles and a radiocarbon‐based estimate. On the other hand, boulder exposure ages from a set of moraines in southern Scoresby Sund show excellent internal consistency for polar regions and yield an average age of 11.6 ± 0.2 ka. The profile surface age from a corresponding ice‐contact delta is 8.1 ± 0.9 ka, while a second delta yields an age of 10.0 ± 0.4 ka. Measured ¹⁰Be inheritance concentrations from all depth profiles are internally consistent and are between 10% and 20% of the surface concentrations, suggesting a regional cosmogenic inheritance signal for the Scoresby Sound landscape. Based on the profile inheritance concentrations, we explore the first‐order catchment‐averaged bedrock erosion under the Greenland ice sheet, yielding estimates of total erosion during the last glacial cycle of the order of 2–30 m. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Boundary depletion rate and drawdown in leaky wedge‐shaped aquifers     

Mohammad Mahdi Sedghi  Nozar Samani  Brent Sleep 《水文研究》2012,26(20):3101-3113

This study presents analytical solutions of the three‐dimensional groundwater flow to a well in leaky confined and leaky water table wedge‐shaped aquifers. Leaky wedge‐shaped aquifers with and without storage in the aquitard are considered, and both transient and steady‐state drawdown solutions are derived. Unlike the previous solutions of the wedge‐shaped aquifers, the leakages from aquitard are considered in these solutions and unlike similar previous work for leaky aquifers, leakage from aquitards and from the water table are treated as the lower and upper boundary conditions. A special form of finite Fourier transforms is used to transform the z‐coordinate in deriving the solutions. The leakage induced by a partially penetrating pumping well in a wedge‐shaped aquifer depends on aquitard hydraulic parameters, the wedge‐shaped aquifer parameters, as well as the pumping well parameters. We calculate lateral boundary dimensionless flux at a representative line and investigate its sensitivity to the aquitard hydraulic parameters. We also investigate the effects of wedge angle, partial penetration, screen location and piezometer location on the steady‐state dimensionless drawdown for different leakage parameters. Results of our study are presented in the form of dimensionless flux‐dimensionless time and dimensionless drawdown‐leakage parameter type curves. The results are useful for evaluating the relative role of lateral wedge boundaries and leakage source on flow in wedge‐shaped aquifers. This is very useful for water management problems and for assessing groundwater pollution. The presented analytical solutions can also be used in parameter identification and in calculating stream depletion rate and volume. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献