Evidence for Holocene environmental change from C/N ratios, and δ13C and δ15N values in Swan Lake sediments, western Sand Hills, Nebraska     

Kamaleldin M. Hassan  James B. Swinehart  Roy F. Spalding 《Journal of Paleolimnology》1997,18(2):121-130

Profiles of percent carbon and nitrogen, carbon/nitrogen (C/N) ratios and stable carbon (¹³C), and nitrogen (¹⁵N) isotopic ratios in organic matter from an 11.6 m core were used to reconstruct environments of deposition in the Swan Lake basin during the past 5300 YBP. The upper 6.5 m consisted of gyttja containing variable amounts of reddish brown-colored fine organic matter and calcium carbonate. It was followed by a 0.5 m sandy silt, which was followed by a 3.6 m reduced layer characterized by large quantities of black organic plant remains, sapropel, and then by another sapropel layer consisting mainly of well-sorted sapropelic sand with relatively low organic matter content. The C- and N-contents in the organic matter in the sediment profile ranged from 0.5 to 23% and from 0.02 to 2%, respectively. Carbon content were positively correlated to both N and clay content while carbon content was negatively correlated to sand content. Two major environmental phases in Swan Lake were apparent from large differences in the C and N data of the sediment organic matter. These include the sapropel (marsh) stage that stretched from approximately 5330 to 3930 YBP, and the following gyttja (open water stage). During the sapropel marsh plants identified in a previous pollen study as cattails and sedges proliferated and produced copious amounts of well-preserved organic matter. C/N ratios, ¹³C values, and ¹⁵N values in the sapropel were significantly different from those that characterized organic matter in the gyttja. During the gyttja ¹³C values indicated that deep primary producers have dominated lake biomass. By utilizing bicarbonate as their C-source, the accumulating biomass became relatively enriched ¹³C values. The presence of high sediment CaCO₃ contents indicated more alkaline and deeper water conditions prevailed during the gyttja. Further refinement of the data suggested that each major phase initially contained an identifiable transition stage. During the sapropelic (initial marsh stage) which occurred before 5330 YBP, sand content gradually decreased as organic matter increased. As reflected by high C/N ratios and slightly enriched ¹³C values, these sands appear to have contained sufficient permeability to promote partial mineralization of accumulated organic-N containing compounds. A short initial gyttja transition period from about 3930–3830 YBP occurred in which the sediment silt content was anomalously high relative that measured in the surrounding layers. The silt content suggests that this turbid transition layer can not be completely explained by sediment mixing via bioturbation. The silts appeared to have been associated with the sharp climate change that resulted in higher water-table conditions during the gyttja stage.  相似文献   

Experimental introduction of excess Ar40 into a granitic melt     

D. M. Roy  S. P. Faile 《Contributions to Mineralogy and Petrology》1970,27(3):258-258

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Mössbauer studies of marine and fresh water manganese nodules     

Roy Carpenter  Stuart Wakeham 《Chemical Geology》1973,11(2):109-116

Practically identical Mössbauer spectra have been obtained for 40 ferromanganese nodules from a wide variety of marine and fresh-water locations. None of the nodules examined contains more than one weight percent Fe²⁺, so no more than a few percent of the total iron in these nodules can be Fe²⁺. Most of the iron is present as Fe³⁺ in paramagnetic or superparamagnetic oxide phases, although hysteresis loops show the presence of small amounts of ferromagnetic phases not detected by the Mössbauer technique.  相似文献   

Ten Years of Science Based on the Canadian Precipitation Analysis: A CaPA System Overview and Literature Review†     

V. Fortin  G. Roy  T. Stadnyk  K. Koenig  N. Gasset  A. Mahidjiba 《大气与海洋》2018,56(3):178-196

Near real-time quantitative precipitation estimates are required for many applications including weather forecasting, flood forecasting, crop management, forest fire prevention, hydropower production, and dam safety. Since April 2011, such a product has been available from Environment and Climate Change Canada for a domain covering all North America. This product, known as the Regional Deterministic Precipitation Analysis, is generated using the Canadian Precipitation Analysis (CaPA) system. Although it was designed for near real-time use, an archive of pre-operational and operational products going back to 2002 is now available and has been used in numerous studies. This paper presents a review of the various scientific publications that have reported either using or evaluating CaPA products. We find that the product is used with success both for scientific studies and operational applications and compares well with other precipitation datasets. We summarize the strengths and weaknesses of the system as reported in the literature. We also provide users with information on how the system works, how it has changed over time, and how the archived and near real-time analyses can be accessed and used. We finally briefly report on recent and upcoming improvements to the product based, in part, on the results of this literature review.  相似文献   

Enhanced geochemical gradients in a marine shallow-water hydrothermal system: Unusual arsenic speciation in horizontal and vertical pore water profiles     

Roy E. Price  Jan P. Amend  Thomas Pichler 《Applied Geochemistry》2007,22(12):2595

The shallow marine hydrothermal vents near Ambitle Island in eastern Papua New Guinea discharge hot, slightly acidic, As-rich, chemically reduced fluid into cool, slightly alkaline, oxygenated seawater. Gradients in temperature, pH, and total As (As^T), among others, are established as the two aqueous phases mix. The hydrothermal fluid contained 900 μg/L As^T, almost exclusively present as the reduced As^III, while local seawater measured between 1.2 and 2.4 μg/L As, with approximately equal levels of As^III and As^V. Of particular interest in this study was As speciation and abundance in pore waters as a function of sediment depth and as a function of distance from the area of focused venting. With increasing distance, As^T concentration in the pore water decreased rapidly, but remained elevated up to 300 m from the area of focused venting when compared to a non-hydrothermal control site. As a function of depth (to 100 cm) As^T concentration in the pore water profiles was elevated and generally increased with depth. Surprisingly, aqueous As^V far exceeded aqueous As^III at almost all distances and depths investigated, while at the control site the As^III concentration exceeded that of As^V. In the Tutum Bay hydrothermal system, chemical disequilibria among As species provide potential metabolic energy for arsenite oxidizing microorganisms where hydrothermal fluid mixes with seawater near the vent orifice, and for arsenate reducing microorganisms with increasing distance and depth from the hydrothermal point source.  相似文献   

Habitat analysis for sambar in corbett national park using remote sensing and gis     

Anjana Pant  S. G. Chavan  P. S. Roy  K. K. Das 《Journal of the Indian Society of Remote Sensing》1999,27(3):133-139

Habitat analysis for sambar in terms of food, cover, water, space and extent of edge in Corbett National Park using remote sensing and GIS has been attempted. Other physical parameters include climate, topography, fire history, disturbance regimes, weeds etc. IRS-IB LISS II data (FCC, hardcopy) on 1:50.000 scale was interpreted to generate vegetation cover and density map. Other maps showing drainage, water bodies, roads, human habitations and contours were prepared using Survey of India topographical maps. During evaluation of sambar habitat information regarding habitat parameters and their tolerance was collected from existing literature as well as during field observations. Twenty-two transects of one km. length were laid down in all the strata randomly to collect information regarding the structure and composition of the forest and also habitat use (direct and indirect evidences) by sambar. This was then integrated using condition-based equations in the GIS domain to generate suitability maps. Actual sightings on the ground to a large extent supported the results.  相似文献   

Chemistry of rainwater in the Massif Central (France): a strontium isotope and major element study   总被引：3，自引：0，他引：3  

Philippe Négrel  Stéphane Roy 《Applied Geochemistry》1998,13(8):941-952

Atmospheric aerosols (sea salt, crustal dust, and biogenic aerosols) are the primary source of dissolved species in rainwater as well as one of the sources of dissolved species in river water. Chemical weathering studies require quantification of this atmospheric input. The crustal component of atmospheric input can have various origins, both distant and local. The proportions of the various inputs (marine, distant or local) are determined in this study.Strontium isotope ratios and Ca, Na, K, Mg, Al, Cl, SO₄, NO₃ and Sr concentrations were measured in rainwater samples collected in the Massif Central (France) over a period of one year. Each sample, collected automatically, represents a monthly series of rain events. Chemical composition of the rainwater samples varied considerably and the ⁸⁷Sr/⁸⁶Sr ratios ranged between 0.709198 and 0.713143.Using Na as an indicator of marine origin, and Al for the crustal input in rain samples, the proportion of marine and crustal elements was estimated from elemental ratios. A marine origin of 4 to 100% of Cl, of 0.6 to 20% of the SO₄, of <1 to 10% of Ca, <1 to 40% of K, 4 to 100% of Mg and 1 to 44% of Sr was determined.Strontium isotopes were used to characterize the crustal sources. The ⁸⁷Sr/⁸⁶Sr ratios of the crustal sources varied considerably from 0.7092 to 0.71625 and indicate the occurrence of multiple sources for the crustal component in the analysed rainwaters.  相似文献   

Well tie for broadband seismic data          下载免费PDF全文

Ehsan Zabihi Naeini  James Gunning  Roy White 《Geophysical Prospecting》2017,65(2):503-522

The seismic industry is increasingly acquiring broadband data in order to reap the benefits of extra low‐ and high‐frequency contents. At the low end, as the sharp low‐cut decay gets closer to zero frequency, it becomes harder for a well tie to estimate the low‐frequency response correctly. The fundamental difficulty is that well logs are too short to allow accurate estimation of the long‐period content of the data. Three distinctive techniques, namely parametric constant phase, frequency‐domain least squares with multi‐tapering, and Bayesian time domain with broadband priors, are introduced in this paper to provide a robust solution to the wavelet estimation problem for broadband seismic data. Each of these techniques has a different mathematical foundation that would enable one to explore a wide range of solutions that could be used on a case‐by‐case basis depending on the problem at hand. A case study from the North West Shelf Australia is used to analyse the performance of the proposed techniques. Cross‐validation is proposed as a robust quality control measure for evaluating well‐tie applications. It is observed that when the seismic data are carefully processed, then the constant phase approach would likely offer a good solution. The frequency‐domain method does not assume a constant phase. This flexibility makes it prone to over‐fitting when the phase is approximately constant. Broadband priors for the time‐domain least‐squares method are found to perform well in defining low‐frequency side lobes to the wavelet.  相似文献   

Monitoring growth of built-up areas in indo-gangetic plain using multi-sensor remote sensing data   总被引：1，自引：0，他引：1  

P. K. Roy Chowdhury  S. Maithani 《Journal of the Indian Society of Remote Sensing》2010,38(2):291-300

This paper provides an approach for rapid and accurate estimation of built-up areas on a per pixel-basis using a integration of two coarse spatial resolution remote sensing data namely DMSP-OLS and MODIS NDVI. The DMSP-OLS data due to its free availability, high temporal resolution and wide swath was used for regional level mapping of built-up areas. However, due to its low radiometric resolution, the built-up areas cannot be estimated accurately from the DMSP-OLS data. In present study, the DMSP-OLS data was combined with MODIS NDVI data to develop an Human Settlement Index (HSI) image, which estimated the fraction of built-up area on a per pixel basis. The resultant HSI image conveys more information than both the individual datasets. These temporal HSI images were then used for monitoring urban growth in Indo-Gangetic plains during the 2001–2007 time period. Thus, the present research can be very useful for regional level monitoring of built-up areas from coarse resolution data within limited time and minimal cost.  相似文献   

Adjustability of exposed elements by updating their capacity for resistance after a damaging event: application to an earthquake–tsunami cascade scenario     

Negulescu  Caterina  Benaïchouche  Abed  Lemoine  Anne  Le Roy  Sylvestre  Pedreros  Rodrigo 《Natural Hazards》2020,104(1):753-793

Natural Hazards - The 2011 Great East Japan earthquake and tsunami remind us once again that these types of cascade event can occur and cause considerable damage. The scientific community realizes...  相似文献