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491.
Germain Bayon Dominique Birot Claire Bollinger Jean Alix Barrat 《Geostandards and Geoanalytical Research》2011,35(1):145-153
We report on an improved method for determining trace element abundances in seawater and other natural waters. The analytical procedure involves co‐precipitation on iron hydroxides after addition of a Tm spike, and measurement by inductively coupled plasma‐sector field mass spectrometry (ICP‐SFMS). The validity of the method was assessed through a series of co‐precipitation experiments, using ultra‐diluted solutions of a certified rock reference material (BIR‐1). Results obtained for four natural water reference materials (NASS‐5, CASS‐4, SLEW‐3, SLRS‐4) are in agreement with published working values for rare earth elements, yttrium, vanadium and, when available, for hafnium, zirconium, thorium and scandium. A set of proposed values with uncertainties typically better than 8% RSD is proposed for Hf, Zr and Th. 相似文献
492.
Catherine Jeandel Celia Venchiarutti Michael Bourquin Catherine Pradoux François Lacan Pieter van Beek Jean Riotte 《Geostandards and Geoanalytical Research》2011,35(4):449-459
A new procedure allowing the sequential extraction of Ra, Nd, Th, Pa and U from the same initial natural sample (sea or river waters, particles, sediments, rocks) is proposed. Extraction recoveries were better than 90%. Procedural blanks ranged from 80 pg (for Nd) to below 1 fg, the detection limit of the MC‐ICP‐MS used (for Pa); all were negligible compared with the amounts of elements currently determined. Based on classical anionic resins attached to a peristaltic pump allowing precise flow rate control, this procedure allowed a consequent reduction of the sample size, which improved the sampling resolution and reduced the sampling cost. It also ensured a better consistency of the samples for the five tracers. 相似文献
493.
Volcanic islands, being characterized by highly porous basaltic/andesitic lava flows and pyroclastic deposits, are subject
to important chemical weathering by subsurface waters. Moreover, such subsurface weathering is impacted by hydrothermal springs
in both active and non-active volcanic areas, thus increasing dissolved load concentrations. Here, we focus on the subsurface
water chemistry in the volcanic islands of the Lesser Antilles and Réunion and on the origin of these subsurface flows. We
are able, through the use of various isotopic tools (C, Sr, U–Th), to identify hydrothermal influences in river water. For
example, Li concentrations show a positive correlation with temperature of hot and cold springs and also a relationship with
δ13C; from this, we can show that several sources of hydrothermal activity influence the rivers of the Lesser Antilles and that
some rivers also reveal an important organic influence. As much as 20% of the subsurface hydrothermal springs go to feed the
rivers. The increasing temperatures result in more dissolved elements being mobilized and an increase in chemical weathering
rates. In addition, using the (230Th/238U) isochron for the well and river dissolved loads in Martinique, Guadeloupe and Réunion, we can evaluate residence times
in the river water, i.e. the average residence time in the water along the circulation path to the sampling point. Alteration
takes longer when the water circulates through thick soil, for example, 400–5,000 years when circulating under an ash profile
and 1,200–15,000 years when circulating through a collapse zone. It would appear that waters circulation is globally three
times longer for subsurface water than for surficial water. The weathering regime in tropical volcanic environments seems
to be controlled mainly by such subsurface circulation with high chemical concentration from hydrothermal inputs. The origin
of these compositions is varied and not controlled by a single hydrothermal spring. Consequently, it is subsurface circulation
that determines the weathering regime in tropical volcanic islands with the main controlling parameters being temperature
and residence time. 相似文献
494.
A. H. M. Selim Reza Jiin-Shuh Jean Ming-Kuo Lee Shang-De Luo Jochen Bundschuh Hong-Chun Li Huai-Jen Yang Chia-Chuan Liu 《Environmental Earth Sciences》2011,63(5):955-967
Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and
groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3
−, SO4
2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was
performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major
chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher
amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic
substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood
plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the
Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges
from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R
2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier
transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic
carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly
support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin. 相似文献
495.
Abstract The optical parameters of Arctic haze, such as the scattering and the absorption coefficients and the asymmetry factor, have been estimated using a theoretical haze model. The Aden and Kerker solution for spherical nuclei coated with a spherical shell was employed to account for the observed sulphuric acid coating on Arctic aerosols. Six original aerosol materials are considered; four are natural and two are anthropogenic in origin (sulphuric acid and soot). The relative humidity is varied between 0 and 99% and the effects of anthropogenic substances are examined. Carbonaceous material can increase the absorption coefficient by up to a factor 5 in the visible range, while sulphuric acid significantly increases the growth of particles and affects all of the optical parameters. The haze model is found to be consistent with available measurements of aerosol characteristics and optical parameters. The haze model is then used to convert a vertical profile of the extinction coefficient to a profile of particle concentration. 相似文献
496.
Emmanuel Masini Gianreto Manatschal Geoffroy Mohn Jean‐François Ghienne François Lafont 《Basin Research》2011,23(6):652-677
We describe the tectono‐sedimentary evolution of a Middle Jurassic, rift‐related supra‐detachment basin of the ancient Alpine Tethys margin exposed in the Central Alps (SE Switzerland). Based on pre‐Alpine restoration, we demonstrate that the rift basin developed over a detachment system that is traced over more than 40 km from thinned continental crust to exhumed mantle. The detachment faults are overlain by extensional allochthons consisting of upper crustal rocks and pre‐rift sediments up to several kilometres long and several hundreds of metres thick, compartmentalizing the distal margin into sub‐basins. We mapped and restored one of these sub‐basins, the Samedan Basin. It consists of a V‐shape geometry in map view, which is confined by extensional allochthons and floored by a detachment fault. It can be restored over a minimum distance of 11 km along and about 4 km perpendicular to the basin axis. Its sedimentary infill can be subdivided into basal (initial), intermediate (widening) and top (post‐tectonic) facies tracts. These tracts document (1) formation of the basin initially bounded by high‐angle faults and developing into low‐angle detachment faults, (2) widening of the basin and (3) migration of deformation further outboard. The basal facies tract is made of locally derived, poorly sorted gravity flow deposits that show a progressive change from hangingwall to footwall‐derived lithologies. Upsection the sediments develop into turbidity current deposits that show retrogradation (intermediate facies tract) and starvation of the sedimentary system (post‐tectonic facies tract). On the scale of the distal margin, the syn‐tectonic record documents a thinning‐ and fining‐upward sequence related to the back stepping of the tectonically derived sediment source, progressive starvation of the sedimentary system and migration of deformation resulting in exhumation and progressive delamination of the thinned crust during final rifting. This study provides valuable insights into the tectono‐sedimentary evolution and stratigraphic architecture of a supra‐detachment basin formed over hyper‐extended crust. 相似文献
497.
MUPENZI Jean de la Paix 《山地科学学报》2011,8(5):704-710
The main goal of this study was to assess the long-term impacts of global warming perturbation on water resources of the Kaidu River Basin in Northwest China. Temperature, precipitation and hydrology data during the past 29 years from 1979 to 2007 were collected and analyzed using parametric and non-parametric methods, the connection between temperature and precipitation by the combination of grey correlation analysis method and the hypothesis testing for trend of climate change. The results show a high inc... 相似文献
498.
An attempt to detect the finest white-light coronal features observed with a large optical telescope was made at the July 11, 1991 Solar Total Eclipse. A few selected results taken from the video-CCD high speed observations obtained at the prime focus of the Canada-France-Hawaï-Telescope (CFHT) with a red coronal interference filter are presented. The smallest (sub-arsec) detected and/or resolved coronal features are shown. The methods that were used to extract them from the noisy and seeing-limited images taken from video frames are described. 相似文献
499.
High sedimentation rates in Pleistocene active margin basins can provide a very detailed record of tectonic and climatic controls on sediment preservation. A 500 m thick, Pleistocene rock section exposed in northeastern North Island of New Zealand (Kidnappers Group), provides the opportunity to discuss these controls. The section is composed of conglomerate, sandstones, siltstones and minor shales, interbedded with tephra layers. The sediments were deposited in alluvial to shallow marine environments and preserved in stacks of depositional units decimetres to hundreds of metres thick as a result of base‐level changes through time. The correlation of base‐level changes in the section with the deep sea oxygen isotope stratigraphy shows that the sequences at 10 m and 80 m scales can correlate, respectively, to the 20 and 100 kyr changes in eustatic sea‐level, but that the 80‐m‐thick sequences correlate also to changes in tectonic uplift rates. A major change in the stratigraphical architecture occurs at the Mid‐Pleistocene Transition (MPT) when the 40 kyr ice volume variations shifted to a dominant 100 kyr variation. This change includes an increase in the amplitude of the shifts in depositional environments and an overall simplification of the stacking pattern of the depositional units through the MPT. This study illustrates that active margin basins can record orbitally forced sedimentary cycles and points to a possible leading influence of eustasy on the pattern of sediment preservation in tectonically active areas. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
500.