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In this paper, we present 50 surface water samples collected during the IMAGES III cruise (June–July 1997) along a transect from New Zealand to the China Sea (42°S–178°E, 21°N–120°E) covering a temperature range from 13.3 to 30.4 °C. A very worthwhile aspect of this study is a coupling of both biomarker (alkenone) and coccolithophorid counting. We show that the U37k′–temperature relationship is very similar to the Prahl et al. [Geochim. Cosmochim. Acta 52 (1988) 2203] culture calibration and to the global core top calibration of Müller et al. [Geochim. Cosmochim. Acta 62 (1998) 1757]. However, in the warmest surface waters of the Western Pacific ocean (>26.4 °C) where Gephyrocapsa oceanica is likely the most widespread species, the associated U37k′ has a constant value of 1.0. The consequence is that above this temperature threshold, U37k′ cannot be used as an accurate paleothermometer. 相似文献
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本文利用沉积物捕获器回收的连续时间序列沉降颗粒物样品,研究了南海西北部海南岸外陆坡外缘海域颗石藻的通量和属种组成变化及其环境意义。研究发现,东亚夏季风引起的海南岸外上升流以及冬季风导致的混合层深度增加都会刺激该区域颗石藻的生长,其中夏季上升流的影响尤为显著。从颗石粒属种组成来看,Florisphaera profunda是南海西北部中深层(1 000m)水体中主要的颗石粒优势种,此外Emiliania huxleyi,Gephyrocapsa oceanica和Gephyrocaps ericsonii等属种含量也颇高。然而在将颗石粒折算成颗石球数量后,Emiliania huxleyi则成为主要优势种。沉积物捕获器中F.profunda的相对百分含量与颗石粒总通量呈显著的负相关,表明F.profunda的相对含量与总的颗石藻生产力有着密切联系。本结果对于利用沉积物中的颗石藻记录,尤其是F.profunda相对含量变化,恢复和重建古海洋环境尤其是古海洋生产力的研究提供了直接的理论证据。 相似文献
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Élisa Morichon Thierry Allard Daniel Beaufort David Quirt 《Physics and Chemistry of Minerals》2010,37(3):145-152
Natural radiation-induced defects were identified in specimens of sudoite (Al–Mg di-trioctahedral chlorite) related to unconformity-type
uranium deposits at the base of the Athabasca Group (Saskatchewan, Canada), using electron paramagnetic resonance (EPR) spectroscopy
at X- and Q-band frequencies. X-band spectra indicate the presence of a main native defect, named the As-center, whose EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g
// = 2,051 and g
⊥ = 2,005, and a secondary defect with apparent component g = 2,025. The study of oriented specimens shows that the main defect has its g
// component perpendicular to the (ab) plane of sudoite. The As-center corresponds to an electron hole located on oxygen atoms of the structure and is likely associated with Si, according
to the lack of hyperfine structure. The As-center in sudoite has EPR parameters similar to the A-center in kaolinite and dickite, and the Ai-center in illite. The saturation behavior of EPR spectra as a function of power demonstrates that native defects of sudoite
are different from those known in other clays, such as kaolinite, dickite or smectite, but are similar to those of illite.
The isochronal annealing data suggest that the main defect in sudoite is stable to more than 300°C. The corresponding defects
characterized in sudoite may have the potential for tracing past radionuclide migration around unconformity-type uranium deposits. 相似文献
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G. N. Baturin I. O. Murdmaa L. Beaufort G. N. Alekhina 《Lithology and Mineral Resources》2016,51(2):93-106
The geochemistry of Upper Quaternary organic-rich (Corg 3.7–10.0%) sediments recovered by the 40-m-long Core MD02-2508 from the upper continental slope of Baja California is compared to the chemical composition of sedimentary rocks from the Miocene Monterey Formation, California. It is ascertained that concentrations of most macroelements (Al, Ti, Mg, K, Fe, M, S, Corg) and many microelements, including chalcophiles Ag, As, Mo, Sb, Se, Zn, along with some others (U, Co, Ni, Y, and REE) are nearly equal in both types of sediments. In addition, concentrations of most microelements in both types of sediments are close, to the average values common for the worldwide carbonaceous black shales irrespective of their lithology and age, indicating a stable influence of organic matter on their concentration during sedimentation and early digenesis. 相似文献
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T‐NET,a dynamic model for simulating daily stream temperature at the regional scale based on a network topology 
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下载免费PDF全文 Currently, the distribution areas of aquatic species are studied by using air temperature as a proxy of water temperature, which is not available at a regional scale. To simulate water temperature at a regional scale, a physically based model using the equilibrium temperature concept and including upstream‐downstream propagation of the thermal signal is proposed. This model, called Temperature‐NETwork (T‐NET), is based on a hydrographical network topology and was tested at the Loire basin scale (105 km2). The T‐NET model obtained a mean root mean square error of 1.6 °C at a daily time step on the basis of 128 water temperature stations (2008–2012). The model obtained excellent performance at stations located on small and medium rivers (distance from headwater <100 km) that are strongly influenced by headwater conditions (median root mean square error of 1.8 °C). The shading factor and the headwater temperature were the most important variables on the mean simulated temperature, while the river discharge influenced the daily temperature variation and diurnal amplitude. The T‐NET model simulates specific events, such as temperature of the Loire during the floods of June 1992 and the thermal regime response of streams during the heatwave of August 2003, much more efficiently than a simple point‐scale heat balance model. The T‐NET model is very consistent at a regional scale and could easily be transposed to changing forcing conditions and to other catchments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Emmanuel Laverret Norbert Clauer Anthony Fallick Julien Mercadier Patricia Patrier Daniel Beaufort Patrice Bruneton 《Applied Geochemistry》2010
Isotope analyses (K–Ar, δ18O and δD) were performed on illite from both the sandstone cover and the underlying basement, close to and distant from Shea Creek, an unconformity-type U deposit (Athabasca Basin, Canada); the illite had previously been characterized crystallographically. In the barren areas away from deposit, illite is mainly of the cis-vacant 1M polytype occurring as relatively coarse-grained lath-shaped particles, while it occurs as fine-grained particles of the trans-vacant 1M type next to and in the U mineralized strata. The tectonic-induced hydrothermal system that favored illite crystallization was multi-episodic 1453 ± 2, 1330 ± 20 and probably about 1235 Ma ago. These illite-forming episodes appear to have occurred contemporaneously to those favoring the concentration of the associated U oxides, which were dated independently by the U–Pb method in the Shea Creek deposits and elsewhere in the Athabasca Basin. 相似文献
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Ccile L. Blanchet Nicolas Thouveny Laurence Vidal Guillaume Leduc Kazuyo Tachikawa Edouard Bard Luc Beaufort 《Quaternary Science Reviews》2007,26(25-28):3118-3133
The sediments deposited off south-western Baja California have recorded millennial-scale fluctuations in biogenic compounds and trace metals accumulation during the last glacial period [Ortiz, J.D., O’Connell, S.B., DelViscio, J., Dean, W.E., Carriquiry, J.D., Marchitto, T., Zheng, Y., van Geen, A., 2004. Enhanced marine productivity off western North America during warm climate intervals of the past 52 ky. Geology 32, 521–524; Dean, W.E., Zheng, Y., Ortiz, J.D., van Geen, A., 2006. Sediment Cd and Mo accumulation in the oxygen-minimum zone off western Baja California linked to global climate over the past 52 ka. Paleoceanography 21, PA4209]. Since the variations in trace metals concentration appear to result from dilution with nonbiogenic matter, the variability of the terrigenous sedimentation needs to be addressed. Therefore, we performed rock magnetic and geochemical analysis on a 38 m-long sediment core collected from the slope off Baja California. The temporal framework provided by 14C dating and identification of palaeoclimatic transitions allows assigning the sequence to the last glacial–interglacial cycle (last 120 ka). The comparison of magnetic and geochemical properties led to retain the hypothesis of a primary modulation of iron oxides quantity and quality by terrigenous input variations, with a secondary diagenetic amplification. Two magnetic mineral input regimes are distinguished: (i) magnetic susceptibility variations reveal changes in titano-magnetite concentration related to fluvial transport of the terrigenous fraction; (ii) coercivity changes allow detecting variations of hematite or goethite concentrations, minerals generally issued from aeolian deflation of weathered rock surfaces. These two regimes are paced by two distinct climatic forcing: the millennial-scale changes in titano-magnetite input are related to the northern hemisphere climatic variability whilst the record of wind-blown magnetic mineral input contains its major power in the precessional frequency band, with higher input during low insolation periods (and conversely). This record highlights the great sensibility of this region to high and low latitudes climatic regimes. 相似文献