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Brent B. Wolfe Matthew D. Falcone Ken P. Clogg-Wright Cherie L. Mongeon Yi Yi Bronwyn E. Brock Natalie A. St. Amour William A. Mark Thomas W. D. Edwards 《Journal of Paleolimnology》2007,37(2):221-231
Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis
of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments
have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy
studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring
a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake
water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced
by studies conducted over the past 15 years that span Holocene and pre-historical timescales. 相似文献
75.
Plinian plumes erupt with a bulk density greater than that of air, and depend upon air entrainment during their gas-thrust phase to become buoyant; if entrainment is insufficient, the column collapses into a potentially deadly pyroclastic flow. This study shows that strombolian ash plumes can be erupted in an initially buoyant state due to their extremely high initial gas content, and in such cases are thus impervious to column collapse. The high gas content is a consequence of decoupled gas rise in the conduit, in which particles are ultimately incidental. The relations between conduit gas flow, eruption style and plume density are explored here for strombolian scenarios and contrasted with conventional wisdom derived from plinian eruptions. Considering the inherent relation between gas content and initial plume density together with detailed measurements of plume velocities can help unravel ambiguities surrounding conduit processes, eruption styles and hazards at poorly understood volcanoes. Analysis of plume dynamics at Santiaguito volcano, Guatemala adds further support for a model involving decoupled gas rise in the conduit. 相似文献
76.
Conservative tracers are necessary to obtain groundwater transport velocities at the field scale. Deuterated water is an
effective tracer for this purpose due to its similarity to water, chemical stability, non-reactivity, ease of handling and
sampling, relatively neutral buoyancy, and reasonable price. Reliable detection limits of 0.1 mg deuterium/L may be obtained
in field tests. A field example is presented in which deuterated water, bromide, and pentafluorobenzoic acid are used as groundwater
tracers. Deuterated water appeared to be transported conservatively, producing almost identical breakthrough curves as that
of other soluble tracers.
Electronic Publication 相似文献
77.
Wang Zonghao Mao Jianping Huang Jihong Arnold Gruber Albert Thomasell Tan Sun Chen 《Acta Meteorologica Sinica》1992,6(4):421-432
This paper is to examine the impact of satellite data on the systematic error of operational B-model in China.Em-phasis is put on the study of the impact of satellite sounding data on forecasts of the sea level pressure field and 500 hPaheight.The major findings are as follows.(1)The B-model usually underforecasts the strength of features in the sea level pressure(SLP)field,i.e.pressuresare too low near high pressure systems and too high near low pressure systems.(2)The nature of the systematic errors found in the 500 hPa height forecasts is not as clear cut as that of the SLPforecasts,but most often the same type of pattern is seen,i.e.,the heights in troughs are not low enough and those inridges are not high enough.(3)The use of satellite data in the B-model analysis/forecast system is found to have an impact upon the model'sforecast of SLP and 500 hPa height.Systematic errors in the vicinity of surface lows/500 hPa troughs over the oceansare usually found to be significantly reduced.A less conclusive mix of positive and negative impacts was found for allother types of features. 相似文献
78.
Michael B. Underwood Matthew M. Laughland Tim Byrne J. P. Hibbard Lee DiTullio 《Island Arc》1992,1(1):116-132
Abstract The Shimanto accretionary complex on the Muroto Peninsula of Shikoku comprises two major units of Tertiary strata: the Murotohanto Sub-belt (Eocene-Oligocene) and the Nabae Sub-belt (Oligocene-Miocene). Both sub-belts have been affected by thermal overprints following the peak of accretion-related deformation. Palaeotemperatures for the entire Tertiary section range from ~ 140 to 315°C, based upon mean vitrinite reflectance values of 0.9–5.0%Rm. Values of illite crystallinity index are consistent with conditions of advanced diagenesis and anchimetamorphism. Illite/mica b0 lattice dimensions indicate that burial pressures were probably no greater than 2.5kbar. In general, levels of thermal maturity are higher for the Murotohanto Sub-belt than for the Nabae Sub-belt. The Eocene-Oligocene strata also display a spatial decrease in thermal maturity from south to north and this pattern probably was caused by regional-scale differential uplift following peak heating. Conversely, the palaeothermal structure within the Nabae Sub-belt is fairly uniform, except for the local effects of mafic intrusions at the tip of Cape Muroto. There is a paleotemperature difference of ~ 90°C across the boundary between the Murotohanto and Nabae Sub-belts (Shiina-Narashi fault), and this contrast is consistent with approximately 1200 m of post-metamorphic vertical offset. Subduction prior to Middle Miocene probably involved the Kula or fused Kula-Pacific plate and the background geothermal gradient during the Eocene-Oligocene phase of accretion was ~ 30–35°C/km. Rapid heating of the Shimanto Belt evidently occurred immediately after a Middle Miocene reorganization of the subduction boundary. Hot oceanic lithosphere from the Shikoku Basin first entered the subduction zone at ~ 15 Ma; this event also coincided with the opening of the Sea of Japan and the rapid clockwise rotation of southwest Japan. The background geothermal gradient at that time was ~ 70°C/km. Whether or not all portions of the inherited (Eocene-Oligocene) palaeothermal structure were overprinted during the Middle Miocene remains controversial. 相似文献
79.
Zusammenfassung Es wird gezeigt, daß durch Weglassung des Relais bzw. durch Wegnahme der Relaisspannung von der Kontaktbahn ihr Isolationszustand (Feuchtigkeit, Verunreinigungen) ohne Einfluß auf den Temperaturmeßkreis bleibt. Zur Feuchtigkeitsmessung wird das Feuchtigkeitselement dem Temperaturelement parallel geschaltet. Dadurch ergibt sich außerdem eine Erweiterung des Feuchtemeßbereichs. Die Temperatur-registrierung wird damit auch zur Ausgangslinie für die Registrierung mit weiteren Meßelementen.
Mit 4 Textabbildungen 相似文献
Summary It is shown that, by eliminating the relay and, therefore, the relay voltage from the commutator the state of the latter with respect to isolation (humidity, contamination) does no longer affect the temperature measuring circuit. In the modified radiosonde, the humidity element is connected in parallel to the temperature element. This results in an extension of the humidity measuring range down to about 15%. The temperature recording trace becomes the base-line for the humidity or other additional traces.
Résumé En supprimant le relais ou la tension de relais sur le cercle de contact, l'état d'isolation de la sonde (humidité, impuretés) est sans effet sur le circuit de mesure de la température. Pour mesurer l'humidité, l'élément sensible est connecté en parallèle sur l'élément thermique, ce qui accroît le domaine de mesure de l'humidité. L'enregistrement de température sert alors de ligne de base pour l'enregistrement avec d'autres éléments de mesure.
Mit 4 Textabbildungen 相似文献
80.
ABSTRACTIndia has been the subject of many recent groundwater studies due to the rapid depletion of groundwater in large parts of the country. However, few if any of these studies have examined groundwater storage conditions in all of India’s river basins individually. Herein we assess groundwater storage changes in all 22 of India’s major river basins using in situ data from 3420 observation locations for the period 2003–2014. One-month and 12-month standardized precipitation index measures (SPI-1 and SPI-12) indicate fluctuations in the long-term pattern. The Ganges and Brahmaputra basins experienced long-term decreasing trends in precipitation in both 1961–2014 and the study period, 2003–2014. Indeterminate or increasing precipitation trends occurred in other basins. Satellite-based and in situ groundwater storage time series exhibited similar patterns, with increases in most of the basins. However, diminishing groundwater storage (at rates of >0.4 km3/year) was revealed in the Ganges-Brahmaputra River Basin based on in situ observations, which is particularly important due to its agricultural productivity. 相似文献