排序方式： 共有14条查询结果，搜索用时 15 毫秒
1.
B. Wilhelm F. Arnaud P. Sabatier O. Magand E. Chapron T. Courp K. Tachikawa B. Fanget E. Malet C. Pignol E. Bard J. J. Delannoy 《第四纪科学杂志》2013,28(2):189-199
A high‐resolution sedimentological and geochemical study of a high‐altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352 m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800–1300) and the current period of global warming. On a multi‐decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi‐centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi‐decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
Concentrations of rare earth elements (REE) and Nd isotopic ratios were analyzed for seawater, filtered suspension and sediment trap samples collected in the tropical Atlantic Ocean (EUMELI program, EUtrophic, MEsotrophic and oLIgotrophic sites, 20°N, 18°–21°W). This is the first REE/Nd dataset on solution and different-sized particles collected at the same site. We present direct evidence of the Nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer. This exchange is probably one of the main factors that simultaneously constrains the Nd concentration and isotopic ratio budget. We propose a new approach to estimate the residence time of Nd in the ocean (τNd) based on isotopic exchange: 200 yr < τNd< 1000 yr. The exchange requires a partial dissolution of lithogenic Nd. We estimate that the fraction of soluble Nd proportion in atmospheric dust is of the order of 20% based on the isotopic ratios. We suggest that the partial dissolution of atmospheric fallout is probably one of the main REE sources of the ocean. 相似文献
3.
Kazuyo Tachikawa Laurence Vidal Corinne Sonzogni Edouard Bard 《Quaternary Science Reviews》2009,28(13-14):1160-1170
The phase relationship between climate parameters during terminations gives insight into deglaciation mechanisms. By combining foraminiferal Mg/Ca and alkenone thermometers with planktonic and benthic foraminiferal δ18O, we determined the phase relationship between local sea surface temperature (SST) and global seawater δ18O changes in the Coral Sea in the Southwestern Pacific over the last 360 ka. The onset of the SST warming preceded the seawater δ18O change by several ka for Termination I, II and III. During Termination I, the SST warming started at 20 ka BP, earlier than atmospheric CO2 rise suggesting that the greenhouse effect was not the main trigger of this early warming. Compilation of 14C-dated SST records from the whole Pacific during Termination I reveals that the onset of the warming is generally earlier in the Southern and the tropical Pacific than in the North Pacific. This spatio-temporal warming pattern suggests linkage between the southern ocean and tropical Pacific. The early tropical warming could provide heat and moisture to the northern high latitudes, modifying radiative balance and precipitation over ice sheets at the onset of deglaciation. 相似文献
4.
Spatial Variability of Living Coccolithophore Distribution in the Western Subarctic Pacific and Western Bering Sea 总被引：1，自引：0，他引：1
Hiroshi Hattori Makoto Koike Kenichi Tachikawa Hiroaki Saito Kazuya Nagasawa 《Journal of Oceanography》2004,60(2):505-515
Vertical distributions of coccolithophores were observed in the depth range 0–50 m in the western subarctic Pacific and western
Bering Sea in summer, 1997. Thirty-five species of coccolithophores were collected. Overall, Emiliania huxleyi var. huxleyi was the most abundant taxon, accounting for 82.8% of all coccolithophores, although it was less abundant in the western Bering
Sea. Maximum abundance of this species was found in an area south of 41°N and east of 175°E (Transition Zone) reaching >10,000
cells L−1 in the water column. In addition to this species, Coccolithus pelagicus f. pelagicus, which accounted for 4.2% of the assemblage, was representative of the coccolithophore standing crop in the western part
of the subarctic Pacific. Coccolithus pelagicus f. hyalinus was relatively abundant in the Bering Sea, accounting for 2.6% of the assemblage. Coccolithophore standing crops in the top
50 m were high south of 41°N (>241 × 106 cells m−2) and east of 170°E (542 × 106 cells m−2) where temperatures were higher than 12°C and salinities were greater than 34.2. The lowest standing crop was observed in
the Bering Sea and Oyashio areas where temperatures were lower than 6–10°C and salinities were less than 33.0. From the coccolithophore
volumes, the calcite stocks in the Transition, Subarctic, and the Bering Sea regions were estimated to be 73.0, 9.7, and 6.9
mg m−2, respectively, corresponding to calcite fluxes of 3.6, 0.5, and 0.3 mg m−2d−1 using Stoke's Law.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
6.
Dehydration behavior of muscovite flake was investigated at 760–860°C by using in situ high-temperature IR microspectroscopy
for the OH absorption band around 3,620 cm−1. Isothermal kinetic heating experiments at each temperature gave detailed decrease curves of the OH band area with time.
These curves have been simulated by the first and second order reactions or mono- and two-dimensional diffusion processes.
The mono-dimensional diffusion was found to give the best fit to the experimental data and apparent diffusion coefficients
D were determined at 760–860°C with the activation energy of 290 ± 20 kJ/mol. The apparent diffusion coefficients D varied with the sample thickness L. This variation can be explained by an m layers model with a unit length of L′ with a constant diffusion coefficient D′. Therefore, the dehydration process might be rate-limited by mono-dimensional diffusion through tetrahedral silicate sheet
perpendicular to (001) planes of muscovite with a unit length of L′. 相似文献
7.
Guillaume Leduc Laurence Vidal Kazuyo Tachikawa Edouard Bard 《Quaternary Research》2009,72(1):123-126
Latitudinal movements of the Intertropical Convergence Zone (ITCZ), analogous to its present-day seasonal shifts, and El Niño Southern Oscillation (ENSO)-type variability both potentially impacted rainfall changes at the millennial timescale during the last glacial period. In this study we compare tropical Pacific sedimentary records of paleoprecipitation to decipher which climate mechanism was responsible for the past rainfall changes. We find that latitudinal movements of the ITCZ are consistent with the observed rainfall patterns, challenging the ENSO hypothesis for explaining the rapid rainfall changes at low latitudes. The ITCZ-related mechanism appears to reflect large-scale atmospheric rearrangements over the tropical belt, with a pronounced Heinrich-Dansgaard/Oeschger signature. This observation is coherent with the simulated tropical rainfall anomalies induced by a weakening of the Atlantic thermohaline circulation in modeling experiments. 相似文献
8.
T. Kosugi K. Matsuzaki T. Sakao T. Shimizu Y. Sone S. Tachikawa T. Hashimoto K. Minesugi A. Ohnishi T. Yamada S. Tsuneta H. Hara K. Ichimoto Y. Suematsu M. Shimojo T. Watanabe S. Shimada J. M. Davis L. D. Hill J. K. Owens A. M. Title J. L. Culhane L. K. Harra G. A. Doschek L. Golub 《Solar physics》2007,243(1):3-17
The Hinode satellite (formerly Solar-B) of the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science (ISAS/JAXA) was successfully launched
in September 2006. As the successor to the Yohkoh mission, it aims to understand how magnetic energy gets transferred from the photosphere to the upper atmosphere and results
in explosive energy releases. Hinode is an observatory style mission, with all the instruments being designed and built to work together to address the science
aims. There are three instruments onboard: the Solar Optical Telescope (SOT), the EUV Imaging Spectrometer (EIS), and the
X-Ray Telescope (XRT). This paper provides an overview of the mission, detailing the satellite, the scientific payload, and
operations. It will conclude with discussions on how the international science community can participate in the analysis of
the mission data.
T. Kosugi deceased 26 November 2006. 相似文献
9.
M. E. Zolensky K. Nakamura M. Gounelle T. Mikouchi T. Kasama O. Tachikawa E. Tonui 《Meteoritics & planetary science》2002,37(5):737-761
Abstract— In this paper we describe the recovery, handling and preliminary mineralogical investigation of the Tagish Lake meteorite. Tagish Lake is a type 2 carbonaceous chondrite which bears similarities to CI1 and CM chondrite groups, but is distinct from both. Abundant phyllosilicates as well as chondrules (however sparse) and common olivine grains in the matrix preclude any other classification. The bulk density of Tagish Lake (1.67 g/cc) is far lower than CI or CM chondrites (2.2‐2.3 and 2.6‐2.9 g/cc, respectively), or any other meteorite for that matter. We have identified two lithologies: a dominant carbonate‐poor lithology and a less‐abundant carbonate‐rich lithology. The meteorite is a breccia at all scales. We have noted similarities between Tagish Lake and some clasts within the enigmatic meteorite Kaidun; possibly there are genetic relationships here worth exploring. In the paper we describe a clast of CM1 material within Tagish Lake which is very similar to a major lithology in Kaidun. 相似文献
10.
K. Tachikawa M. Roy-Barman D. Thouron C. Jeandel 《Geochimica et cosmochimica acta》2004,68(14):3095-3106
Nine depth-profiles of dissolved Nd concentrations and isotopic ratios (εNd) were obtained in the Levantine Basin, the Ionian, the Aegean, the Alboran Seas and the Strait of Gibraltar. Thirteen core-top sediments and Nile River particle samples were also analyzed (leached with 1 N HCl, acetic acid or hydroxylamine hydrochloride). The seawater εNd values become more radiogenic during the eastward circulation in the Mediterranean Sea. The relationship between salinity and the seawater εNd shows that the Nd isotopic signature is more conservative than salinity in the Mediterranean Sea. The water mass with the highest εNd (−4.8) is found at about 200 m in the easternmost Levantine basin. The average εNd value for deep waters is −7.0 in the eastern basin, 2.5 ε-units higher than in the western basin. By examining the sensitivity of seawater εNd to Nd inputs from the Nile, we conclude that the most significant radiogenic Nd source is partially dissolved Nile River particles. The Nd flux from the Nile River water has a minor influence on the Mediterranean seawater εNd. Except for the easternmost Levantine Basin, the leachate εNd values are consistent with the seawater values. In the easternmost Levantine Basin, the leachate εNd values obtained with HCl leaching are systematically higher than the seawater values. The relationship between leachate and residual εNd values indicates that the HCl leaching partially dissolves lithogenic Nd, so the dissolution of Nile River particles is the cause of the observed shift. Some εNd values obtained with hydroxylamine hydrochloride leaching are higher than those obtained with HCl leaching. Although the reason for this shift is not clear, 87Sr/86Sr successfully detects the presence of a nonmarine component in the leachate. Our results suggest that leaching performance may vary with the mineralogy of marine sediments, at least in the case of the Mediterranean Sea. 相似文献