A 2-D synthetic study of global traveltime tomography     

Olafur Gudmundsson  Robert W. Clayton 《Geophysical Journal International》1991,106(1):53-65

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The 2000 April multiwavelength campaign of GRS 1915+105     

Y. Ueda  K. Yamaoka  J.E. Grove  M. McCollough  P. Durouchoux  J. Rodriguez  F. Mirabel  J. Swank  M. Feroci  P. Casella  A.J. Castro-Tirado  C. Sánchez-Fernández  S. Chaty  H. Castaneda  K. Kohno  V. Dhawan  S.A. Trushkin  K. Ebisawa  T. Kotani  H. Inoue 《Astrophysics and Space Science》2001,276(1):25-28

We report results from multiwavelength observations of the microquasarGRS 1915+105 performed during the 2000 April campaign. This is one ofthe biggest campaigns ever made for this source covering the broadband from radio to γ-rays. Multiwavelength light curves compiledfrom all the data reduced up to date and broad band spectra obtainedwith ASCA and RXTE are presented.  相似文献   

The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes,Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction     

E. Martin  I. Bindeman  T. L. Grove 《Contributions to Mineralogy and Petrology》2011,162(5):945-960

We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ¹⁸O (δ¹⁸O_Ol) values of 5.9–6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast, HAOT lavas from Medicine Lake have δ¹⁸O_Ol values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived magmas. Other magma types from both volcanoes show intermediate δ¹⁸O_Ol values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ¹⁸O_Ol signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ¹⁸O_Ol reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ¹⁸O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting process in the mantle wedge above the modern subduction zone and require a mantle source enriched in ¹⁸O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades.  相似文献   

Radon as an indicator of limited cross-shelf mixing of submarine groundwater discharge along an open ocean beach in the South Atlantic Bight during observed hypoxia     

Clayton McCoy  Richard Viso 《Continental Shelf Research》2011,31(12):1306-1317

Hypoxic conditions (dissolved oxygen (DO)<2 mg l⁻¹) have been documented in the nearshore coastal waters of Long Bay, South Carolina, United States of America, during summer months over the past several years. Hypoxia was documented in August 2009 in the nearshore (<500 m offshore) for ten consecutive days and four days in September 2009 corresponding with spring tides. This study measured radon activities of shallow beachface groundwater and nearshore bottom waters to estimate mixing rates and submarine groundwater discharge (SGD) in the nearshore waters of central Long Bay. Statistical analyses demonstrate significant correlations between high bottom water radon activities, low DO, and cooler bottom water temperatures during hypoxic conditions. Elevated radon activities during hypoxia were significantly influenced by upwelling favorable conditions which severely limited cross-shelf mixing. Model results indicate mixing of nearshore and offshore waters was limited by up to 93% (range: 43-100%) relative to non-hypoxic conditions. Data suggests previously overlooked natural phenomena including limited cross-shelf mixing and SGD can significantly influence nearshore water quality.  相似文献   

Northwest Africa 773: Lunar origin and iron‐enrichment trend     

T. J. Fagan  G. J. Taylor  K. Keil  T. L. Hicks  M. Killgore  T. E. Bunch  J. H. Wittke  D. W. Mittlefehldt  R. N. Clayton  T. K. Mayeda  O. Eugster  S. Lorenzetti  M. D. Norman 《Meteoritics & planetary science》2003,38(4):529-554

Abstract— The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole‐rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP‐like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Carich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized. The meteorite is composed of two distinct lithologies: a two‐pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO‐rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe‐enrichment trend that culminated in crystallization of fayalite + silica + hedenbergite‐bearing symplectites. The Fe‐enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow‐level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE‐enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE‐depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heatproducing elements.  相似文献   

RECENT HISTORICAL FLUCTUATIONS OF THE GLACIER DU TAILLON,PYRÉNÉES     

Anne F. Gellatly  Jean M. Grove  Alain Bücher  Richard Latham  Brian W. Whalley 《自然地理学》2013,34(5):399-413

The Taillon Glacier in the French Pyrénées offers one of the most detailed records of recent glacier fluctuations in the region. A comprehensive collection of early maps, paintings, and photographs, together with short-term measurements relating to the ice margins and glacier behavior, have made possible a full reconstruction of the glacier's history since the end of the 19th century. The general pattern of ice-front retreat has been punctuated by a series of significant local readvances, dated 1886–1890, 1906–1911, 1926–1928, 1945, and 1964. The record is compared with the more detailed histories of glaciers from the Alps, and signals a surprising degree of sensitivity for the Taillon Glacier, given its overall size and state of survival. [Key words: Taillon Glacier, Pyrénées, Little Ice Age, glaciology.]  相似文献   

IMPACTS OF URBANIZATION ON SURFACE HYDROLOGY,LITTLE EAGLE CREEK,INDIANA, AND ANALYSIS OF LTHIA MODEL SENSITIVITY TO DATA RESOLUTION     

Matt Grove  Jon Harbor  Bernie Engel  Suresh Muthukrishnan 《自然地理学》2013,34(2):135-153

Land-use change in urbanizing areas can significantly alter the hydrology of a watershed and can have serious impacts on wetland water balances, downstream flooding, and groundwater recharge. Most currently available models used in determining the hydrologic impacts of urbanization are not well suited to long-term hydrologic analysis or are too complex and data intensive for widespread practical application. The Long-Term Hydrologic Impact Assessment (LTHIA) model run on a Geographic Information System (GIS) is a relatively simple, user-friendly model that uses the Curve Number method to estimate changes in surface runoff between different stages of development. Application of the model to a large, rapidly urbanizing watershed near Indianapolis, Indiana, suggests that average annual runoff depths increased by more than 60% from 1973 to 1991, with even greater increases for some individual sub-basins. These results are consistent with runoff changes estimated from historical stream flow data in the watershed. A sensitivity analysis to determine minimum data requirements shows that a precipitation record length of 15 years or more is required to produce consistent results with LTHIA and that the highest possible resolution land-use and soils data should be used. The LTHIA model is now available on the Internet at http://www.ecn.purdue.edu/runoff. [Key words: hydrology, urbanization, modeling, GIS.]  相似文献   

An approximate method for joint sequential simulation of multiple spatial variables     

Olena Babak  David F. Machuca-Mory  Clayton V. Deutsch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):327-336

Multivariate simulation is an important longstanding problem in geostatistics. Fitting a model of coregionalization to many variables is intractable and often not permitted; however, the matrix of collocated correlation coefficients is often well informed. Performing a matrix simulation with LU decomposition of the correlation matrix at each step of sequential simulation is implemented in some software. The target correlation matrix is not reproduced because of conditioning to local data and the particular variable ordering in the sequential/LU decomposition. A correction procedure is developed to calculate a modified correlation matrix that leads to reproduction of the target correlation matrix. The theoretical and practical aspects of this correction are developed.  相似文献   

Using overlapping sonobuoy data from the Ross Sea to construct a 2D deep crustal velocity model     

M. M. Selvans  R. W. Clayton  J. M. Stock  R. Granot 《Marine Geophysical Researches》2012,33(1):17-32

Sonobuoys provide an alternative to using long streamers while conducting multi-channel seismic (MCS) studies, in order to provide deeper velocity control. We present analysis and modeling techniques for interpreting the sonobuoy data and illustrate the method with ten overlapping sonobuoys collected in the Ross Sea, offshore from Antarctica. We demonstrate the importance of using the MCS data to correct for ocean currents and changes in ship navigation, which is required before using standard methods for obtaining a 1D velocity profile from each sonobuoy. We verify our 1D velocity models using acoustic finite-difference (FD) modeling and by performing depth migration on the data, and demonstrate the usefulness of FD modeling for tying interval velocities to the shallow crust imaged using MCS data. Finally, we show how overlapping sonobuoys along an MCS line can be used to construct a 2D velocity model of the crust. The velocity model reveals a thin crust (5.5 ± 0.4 km) at the boundary between the Adare and Northern Basins, and implies that the crustal structure of the Northern Basin may be more similar to that of the oceanic crust in the Adare Basin than to the stretched continental crust further south in the Ross Sea.  相似文献   

Effects of land use on water column bacterial activity and enzyme stoichiometry in stream ecosystems     

Clayton J. Williams  Andrew B. Scott  Henry F. Wilson  Marguerite A. Xenopoulos 《Aquatic Sciences - Research Across Boundaries》2012,74(3):483-494

Fifty streams, located in southern Ontario, Canada, were visited in September 2008 to investigate the effect of varying land use, land cover, and associated resource inputs on water column bacterial abundance (BACT), production (BP), and extracellular enzyme activity and stoichiometry. Principle components analysis was used to summarize landscape data, producing three components (PCs), which explained 79.2% of the variability in the data. The PCs grouped into the following gradients: (PC1) urban land use and continuous annual cropping to wetland-like cover, (PC2) rotational cropping to forest-like cover, and (PC3) increasing rural and agricultural land uses with increasing watershed size. These landscape gradients created imbalanced resource availability. Nutrient resources were more abundant in streams with more intensive anthropogenic land uses, but carbon availability was primarily controlled by the abundance of natural land covers (wetland and wooded areas). BACT, BP, and enzyme activities were positively related primarily to nutrient availability and/or anthropogenic land use (Stepwise R ² range: 0.33?C0.73). The ratio of ??-glucosidase to alkaline phosphatase activity approached a 1:1 balance with increasing anthropogenic land use, decreased wetland and forest cover, and increased total dissolved nitrogen. The ratio of leucine-aminopeptidase to alkaline phosphatase activity approached 1:1 with both increased dissolved organic carbon and nitrogen. Moreover, enzyme C:N:P ratios moved closer to 1:1:1 with faster water column bacterial turnover times. These results suggest that water column microbial communities are better able to balance resource availability with growth in streams receiving nutrient subsidies from anthropogenic sources and under these conditions when carbon resources increase.  相似文献