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161.
Florence Bigot-Cormier Christophe Basile Gérard Poupeau Jean-Pierre Bouillin Erika Labrin 《地学学报》2005,17(2):189-195
Apatite fission track analysis of samples from the shoulder (marginal ridge) of the Côte d'Ivoire-Ghana transform continental margin reveal a cooling of the margin between 85 and 65 Ma for the central and eastern parts of the ridge. All samples were heated in situ during sedimentary burial with a temperature >120 °C, except for two samples located in the eastern part which were heated between 105 and 120 °C. For the first time, age/depth diagram along a transform margin shows a shape involving erosion starting at the bottom of the continental slope, then stepping backwards towards the edge of the slope. This retrogressive erosion can result from the deepening of the lithospheric plate sliding along the transform margin, from thick continental crust to thin continental crust, and finally to oceanic crust. This process could be at the origin of the shoulder uplift by flexural response to the important crustal discharge (>2 km). 相似文献
162.
David L. Jauncey Helen M. Johnston Hayley E. Bignall J.E.J. Lovell Lucyna Kedziora-Chudczer A.K. Tzioumis Jean-Pierre Macquart 《Astrophysics and Space Science》2003,288(1-2):63-68
We have measured annual cycles in the time scales of the rapid, intra-day variability of the total and circularly polarized flux density, of the unusual BL Lac source PKS 1519–273 at 4.8 and 8.6 GHz. This data was collected at the ATCA over the last seven years, and establishes unequivocally interstellar scintillation as the principal mechanism responsible for this cm-wavelength intra-day variability. 相似文献
163.
Markus J. Aschwanden Jean-Pierre Wülser Nariaki V. Nitta James R. Lemen Sam Freeland William T. Thompson 《Solar physics》2014,289(3):919-938
We generated an event catalog with an automated detection algorithm based on the entire EUVI image database observed with the two Solar Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over the first six years of the mission (2006?–?2012). The event catalog includes the heliographic positions of some 20?000 EUV events, transformed from spacecraft coordinates to Earth-based coordinates, and information on associated GOES flare events (down to the level of GOES A5-class flares). The 304 Å wavelength turns out to be the most efficient channel for flare detection (79?% of all EUVI event detections), while the 171 Å (4?%), 195 Å (10?%), and the 284 Å channel (7?%) retrieve substantially fewer flare events, partially due to the suppressing effect of EUV dimming, and partially due to the lower cadence in the later years of the mission. Due to the Sun-circling orbits of STEREO-A and -B, a large number of flares have been detected on the farside of the Sun, invisible from Earth, or seen as partially occulted events. The statistical size distributions of EUV peak fluxes (with a power-law slope of α P =2.5±0.2) and event durations (with a power-law slope of α T =2.4±0.3) are found to be consistent with the fractal-diffusive self-organized criticality model. The EUVI event catalog is available on-line at secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve as a comprehensive tool to identify stereoscopically observed flare events for 3D reconstruction and to study occulted flare events. 相似文献
164.
The paired chemical reactions, Ca2+ + 2HCO3 ? ? CaCO3 + CO2 + H2O, overestimate the ratio of CO2 flux to CaCO3 flux during the precipitation or dissolution of CaCO3 in seawater. This ratio, which has been termed ??, is about 0.6 in surface seawater at 25°C and at equilibrium with contemporary atmospheric CO2 and increases towards 1.0 as seawater cools and pCO2 increases. These conclusions are based on field observations, laboratory experiments, and equilibrium calculations for the seawater carbonate system. Yet global geochemical modeling indicates that small departures of ?? from 1.0 would cause dramatic, rapid, and unrealistic change in atmospheric CO2. ?? can be meaningfully calculated for a water sample whether or not it is in equilibrium with the atmosphere. The analysis presented here demonstrates that the atmospheric CO2 balance can be maintained constant with respect to seawater CaCO3 reactions if one considers the difference between CaCO3 precipitation and burial and differing values for ?? (both <1.0) in regions of precipitation and dissolution within the ocean. 相似文献
165.
Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain 总被引:2,自引:2,他引:0
Thomas Philippe Vandorpe David Van Rooij Dorrik A. V. Stow Jean-Pierre Henriet 《Geo-Marine Letters》2011,31(5-6):391-403
This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275?m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north?Csouth current is deflected into an east?Cwest flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2?Ma), the upper Pliocene revolution (2.4?Ma) and the mid-Pleistocene revolution (0.9?Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150?m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time. 相似文献
166.
167.
168.
For three agricultural crop types, winter wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and canola (Brassica napus L.), we estimated biophysical parameters including fresh and dry biomass, leaf area index (LAI), and vegetation water content, for which we found the equivalent water thickness (EWT), fuel moisture content per fresh weight (FMCFW), and fuel moisture content per dry weight (FMCDW). We performed these estimations using data from the newly launched Landsat 8 Operational Land Imager (OLI) sensor, as well as its predecessor the Landsat 7 Enhanced Thematic Mapper Plus (ETM+). Progress in the design of the new sensor (i.e., Landsat 8), including narrower near-infrared (NIR) wavebands, higher signal-to-noise ratio (SNR), and greater radiometric resolution highlights the necessity to investigate the biophysical parameters of agricultural crops, especially compared to data from its predecessor. This study aims to evaluate vegetation indices (VIs) derived from the Landsat 8 OLI and the Landsat 7 ETM+. Both the Landsat 8 OLI and Landsat 7 ETM+ VIs agreed well with in-situ data measurements. However, the Landsat 8 OLI-derived VIs were generally more consistent with in situ data than the Landsat 7 ETM+ VIs. We also note that the Landsat 8 OLI is better able to capture the small variability of the VIs because of its higher SNR and wider radiometric range; in addition, the saturation phenomenon occurred earlier for the Landsat 7 ETM+ than for the Landsat 8 OLI. This indicates that the new sensor is better able to estimate the biophysical parameters of crops. 相似文献
169.
Claire Rollion-Bard Dominique Blamart Grégory Tricot Jean-Pierre Cuif 《Geochimica et cosmochimica acta》2011,75(4):1003-1012
Dissolved boron in modern seawater occurs in the form of two species, trigonal boric acid B(OH)3 and tetrahedral borate ion . One of the key assumption in the use of boron isotopic compositions of carbonates as pH proxy is that only borate ions, , are incorporated into the carbonate. Here, we investigate the speciation of boron in deep-sea coral microstructures (Lophelia pertusa specimen) by using high field magic angle spinning nuclear magnetic resonance (11B MAS NMR) and electron energy-loss spectroscopy (EELS). We observe both boron coordination species, but in different proportions depending on the coral microstructure, i.e. centres of calcification versus fibres. These results suggest that careful sampling is necessary before performing boron isotopic measurements in deep-sea corals. By combining the proportions of B(OH)3 and determined by NMR and our previous ion microprobe boron isotope measurements, we propose a new equation for the relation between seawater pH and boron isotopic composition in deep-sea corals. 相似文献
170.
In Provence and Languedoc, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age. Their recognition is based on sedimentological and stratigraphical evidence, and their timing, referred to ammonite zones or subzones, is as follows:
(1)
Late Barremian, at the G. sartousiana–Imerites giraudi transition, or merely the lowermost part of the I. giraudi zone, (2)
Middle Bedoulian, at the Deshayesitesweissi–Deshayesites deshayesi transition, (3)
Mid late Bedoulian in correspondence with the “Roloboceras hambrovi subzone”, (4)
Late Bedoulian at the Deshayesites grandis–Deshayesites furcata transition.