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排序方式: 共有107条查询结果,搜索用时 15 毫秒
1.
2.
Corinne Sonzogni Edouard Bard Frauke Rostek Denis Dollfus Antoni Rosell-Melé Geoffrey Eglinton 《Quaternary Research》1997,47(3):344-355
We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20°N–45°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index (U37K′) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. TheU37K′versus SST relationship for Indian Ocean sediments (U37K′= 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops givesU37K′= 0.031 T + 0.084 (R= 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24° and 29°C, however, the slope seems to decrease to about 0.02U37K′unit/°C. For Indian Ocean core tops, the ratios of total C37alkenones/total C38alkenones and the slope of theU37K′-SST relationship are similar to those previously observed for cultures ofEmiliania huxleyibut different from those previously published forGephyrocapsa oceanica.EitherE. huxleyiis a major producer of alkenones in the Indian Ocean or strains ofG. oceanicaliving in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C37alkenones to total C38alkenones lack clear geographic pattern in the Indian Ocean. 相似文献
3.
Summary Mid-grade low P/high T Paleozoic amphibolites from Acebuches (S. W. Spain) represent a mostly isochemically metamorphosed basaltic suite which is partly cumulative and partly differentiated. They have chemical compositions and element variations similar to ocean-floor tholeiites. The amphibolites may be related to the early stages of rapid rifting during the formation of the Variscan belt.
With 1 Figure 相似文献
Geochemie der Spurenelemente in Paläozoischen Amphiboliten aus Südwest-Spanien
Zusammenfassung Amphibolite mittleren Metamorphose-Grades (niedrige Drucke, hohe Temperaturen) von Acebuches, Südwest-Spanien, repräsentieren eine weithin isochemisch metamorphosierte Abfolge von Basalten, die teils differenzierte und teils Cumulus-Gesteine waren. Chemismus und Element-Variationen entsprechen den Tholeiiten von Ozeanböden. Diese Amphibolite können den Frühstadien intensiver Grabenbildung im Zuge der Entstehung des Varistischen Gürtels zugeordnet werden.
With 1 Figure 相似文献
4.
Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence 下载免费PDF全文
A. Svay V. Perron A. Imtiaz I. Zentner R. Cottereau D. Clouteau P.‐Y. Bard F. Hollender F. Lopez‐Caballero 《地震工程与结构动力学》2017,46(12):1895-1917
The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100 m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
5.
6.
Edouard L. Davin Reto St?ckli Eric B. Jaeger Samuel Levis Sonia I. Seneviratne 《Climate Dynamics》2011,37(9-10):1889-1907
This study presents an evaluation of a new biosphere-atmosphere Regional Climate Model. COSMO-CLM2 results from the coupling between the non-hydrostatic atmospheric model COSMO-CLM version 4.0 and the Community Land Model version 3.5 (CLM3.5). In this coupling, CLM3.5 replaces a simpler land surface parameterization (TERRA_ML) used in the standard COSMO-CLM. Compared to TERRA_ML, CLM3.5 comprises a more complete representation of land surface processes including hydrology, biogeophysics, biogeochemistry and vegetation dynamics. Historical climate simulations over Europe with COSMO-CLM and with the new COSMO-CLM2 are evaluated against various data products. The simulated climate is found to be substantially affected by the coupling with CLM3.5, particularly in summer. Radiation fluxes as well as turbulent fluxes at the surface are found to be more realistically represented in COSMO-CLM2. This subsequently leads to improvements of several aspects of the simulated climate (cloud cover, surface temperature and precipitation). We show that a better partitioning of turbulent fluxes is the central factor allowing for the better performances of COSMO-CLM2 over COSMO-CLM. Despite these improvements, some model deficiencies still remain, most notably a substantial underestimation of surface net shortwave radiation. Overall, these results highlight the importance of land surface processes in shaping the European climate and the benefit of using an advanced land surface model for regional climate simulations. 相似文献
7.
Kathryn L. Linge L. Paul Bédard Roxana Bugoi Jacinta Enzweiler Klaus Peter Jochum Rüdiger Kilian Jingao Liu Johanna Marin‐Carbonne Silke Merchel Frans Munnik Luiz F.G. Morales Claire Rollion‐Bard A. Kate Souders Paul J. Sylvester Ulrike Weis 《Geostandards and Geoanalytical Research》2017,41(4):493-562
This GGR biennial critical review covers developments and innovations in key analytical methods published since January 2014, relevant to the chemical, isotopic and crystallographic characterisation of geological and environmental materials. In nine selected analytical fields, publications considered to be of wide significance are summarised, background information is provided and their importance evaluated. In addition to instrumental technologies, this review also presents a summary of new developments in the preparation and characterisation of rock, microanalytical and isotopic reference materials, including a précis of recent changes and revisions to ISO guidelines for reference material characterisation and reporting. Selected reports are provided of isotope ratio determinations by both solution nebulisation MC‐ICP‐MS and laser ablation‐ICP‐MS, as well as of radioactive isotope geochronology by LA‐ICP‐MS. Most of the analytical techniques elaborated continue to provide new applications for geochemical analysis; however, it is noted that instrumental neutron activation analysis has become less popular in recent years, mostly due to the reduced availability of nuclear reactors to act as a neutron source. Many of the newer applications reported here provide analysis at increasingly finer resolution. Examples include atom probe tomography, a very sensitive method providing atomic scale information, nanoscale SIMS, for isotopic imaging of geological and biological samples, and micro‐XRF, which has a spatial resolution many orders of magnitude smaller than conventional XRF. 相似文献
8.
Edouard Bard Maurice Arnold H. Gte
stlund Pierre Maurice Patrick Monfray Jean-Claude Duplessy 《Earth and Planetary Science Letters》1988,87(4)
Radiocarbon measurements performed on seawater samples by means of accelerator mass spectrometry (AMS) enable to reduce by a factor of 2000 the water sample size needed for the14C measurements. Therefore no chemical treatment on board the oceanographic vessel is required. Seventy-four AMS14C determinations on samples collected in the tropical-equatorial Indian Ocean during the second leg of the INDIGO program (1986) are presented and compared with the β-counting results obtained during the same campaign and the GEOSECS program (1978). A pronounced reduction of the equatorial14C deficit suggests that substantial amounts of bomb-14C are associated with the westward flowing Pacific water which enters the Indian Ocean via passages through the Indonesia archipelago and/or to meridional mixing with14C-rich water of the southern subtropical gyre. 相似文献
9.
Quality Assessment of Cartographic Generalisation 总被引:2,自引:1,他引:2
Sylvain Bard 《Transactions in GIS》2004,8(1):63-81
This paper proposes a methodology to assess the quality of cartographic generalisa‐tion, which consists of representing geographic space in a simplified way according to the scale and the objectives of the intended map. The automation of this process makes the derivation of data easier, but the quality of the results is often not evaluated. This paper proposes an assessment model based on: (1) characterisation of the data in their initial and final states at different levels of analysis; (2) a data quality assessment by comparison of the two characterisations; and (3) aggregation of the various assessment results to summarise data quality. The assessment algorithm has been implemented and the method has been tested to assess the generalisation of a small urban area. A visualisation tool for assessment of the results has been developed to validate the generalisation evaluation. The results of the research are presented and discussed at the end of the paper. 相似文献
10.
The formation and temporal variability of the oxygen minimum zone (OMZ) of the Arabian Sea is a subject of intense research. We contribute to the discussion by studying modern seawater profiles of the Indian Ocean (salinity, O2, pH, aragonite saturation, nitrate deficit, nutrients), which show that Subantarctic Mode and Antarctic Intermediate Waters (SAMW-AAIW) have a strong influence on the OMZ characteristics of the Arabian Sea. To obtain a better grasp of the range of possible OMZ variations, we studied a 50-kyr record in the NE Arabian Sea (core MD042876) from a site at 828 m water depth within the thermocline. In this core, aragonite is preserved during North Atlantic Heinrich events (HEs) and Dansgaard-Oeschger (DO) stadials, while it is absent during DO interstadials and most of the Holocene. Considering the excellent correlation between aragonite content and Sr/Ca ratio, as well as the presence of fine-grained aragonitic needles and the isotopic composition (δ13C) of carbonates in the fine fraction, we infer that essentially all aragonite originates as fine Sr-rich debris from shallow water. A comparison with other records from the NE Arabian Sea (Sr/Ca, δ15N) indicates that aragonite variability in the cores is rather controlled by OMZ intensity variations as forcing mechanism while changes in aragonite supply seem to play a minor role. The strong correlation of aragonite content with changes in millennial-scale ventilation of the Indian Ocean, as well as a comparison with modern oceanographic conditions, supports the theory that OMZ intensity variations are controlled by changes in the formation of SAMW-AAIW, and are not only due to monsoonal changes. Thus, during HEs and DO stadials, the thermocline Arabian Sea experienced a strengthened influx of O2-rich SAMW-AAIW. On the other hand, OMZ conditions during DO interstadials and the Holocene seem best explained by analogy with the present-day situation: low supply of O2 combined with elevated O2 demand controlled by monsoon-related productivity. 相似文献