Antarctic Intermediate Water influence on Mediterranean Sea Water outflow     

Essyllt Louarn  Pascal Morin 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(9):932-942

This study of the mixing of Mediterranean Sea Water (MW) with the surrounding waters was made possible by the Semane 2002 cruise (Sortie des Eaux Meditérranéennes dans l'Atlantique Nord-Est) that took place in the Gulf of Cadiz in July 2002. Potential temperature, salinity, oxygen, nutrients and CFC data are used to describe the water masses present in the Gulf. In the southern part of the basin, a water mass characterised by low oxygen, high nutrient and low CFC concentrations occurs along the African continental slope. This water has been identified as the modified Antarctic Intermediate Water (AAIW). It has been previously observed south of this section, at the latitude of the Canary Islands, as a northward flow between the African shelf and the islands. The modified AAIW found in the Gulf of Cadiz is situated at a density of 27.5 kg m⁻³. Above, at 27.3 kg m⁻³, the lower limb of the North Atlantic Central Water is observed as a salinity minimum. The modified AAIW enters the Gulf of Cadiz along the south-western part of the continental shelf. It flows cyclonically and exits north-westward. In the northern part of the gulf, due to the presence of the Mediterranean Undercurrent (MU), the AAIW flows off the coast. An optimum multiparameter analysis was conducted to evaluate the influence of the AAIW on the MW northwest of the basin. We show that the AAIW is present in the lower core of the MU at a proportion of 12.9±8.2% and is absent in the upper core.  相似文献   

Spectroscopic investigation and theoretical modeling of kaolinite-group minerals and other low-temperature phases     

Etienne Balan  Emmanuel Fritsch  Thierry Allard  Guillaume Morin  Maxime Guillaumet  Simon Delattre  Marc Blanchard  Georges Calas 《Comptes Rendus Geoscience》2011,343(2-3):177-187

This article summarizes some recent results obtained on the physical properties of environmental minerals, mostly kaolinite-group minerals and Fe- and Al-(hydr)oxides occurring in lateritic soils. The defective structure of these minerals, including impurities, stacking faults and radiation-induced defects, is probed using infrared spectroscopy and electron paramagnetic resonance. Resulting information bears on models of soil formation and transformation mechanisms of minerals in low-temperature environments. We underline the increasing impact of quantum chemical modeling in this field, providing straightforward interpretations of spectroscopic signals and overcoming the limits of fingerprint approaches. Importantly, the first-principles modeling of isotopic fractionation factors provides new links between mineralogical and geochemical investigations of secondary minerals.  相似文献   

UVMag: stellar formation,evolution, structure and environment with space UV and visible spectropolarimetry     

C. Neiner  D. Baade  A. Fullerton  C. Gry  G. Hussain  A. Lèbre  J. Morin  P. Petit  J. O. Sundqvist  A. ud-Doula  A. A. Vidotto  G. A. Wade  The UVMag consortium 《Astrophysics and Space Science》2014,354(1):215-227

Important insights into the formation, structure, evolution and environment of all types of stars can be obtained through the measurement of their winds and possible magnetospheres. However, this has hardly been done up to now mainly because of the lack of UV instrumentation available for long periods of time. To reach this aim, we have designed UVMag, an M-size space mission equipped with a high-resolution spectropolarimeter working in the UV and visible spectral range. The UV domain is crucial in stellar physics as it is very rich in atomic and molecular lines and contains most of the flux of hot stars. Moreover, covering the UV and visible spectral domains at the same time will allow us to study the star and its environment simultaneously. Adding polarimetric power to the spectrograph will multiply tenfold the capabilities of extracting information on stellar magnetospheres, winds, disks, and magnetic fields. Examples of science objectives that can be reached with UVMag are presented for pre-main sequence, main sequence and evolved stars. They will cast new light onto stellar physics by addressing many exciting and important questions. UVMag is currently undergoing a Research & Technology study and will be proposed at the forthcoming ESA call for M-size missions. This spectropolarimeter could also be installed on a large UV and visible observatory (e.g. NASA’s LUVOIR project) within a suite of instruments.  相似文献   

Infrared spectroscopic properties of goethite: anharmonic broadening,long-range electrostatic effects and Al substitution     

Marc Blanchard  Etienne Balan  Paola Giura  Keevin Béneut  Haohao Yi  Guillaume Morin  Carlos Pinilla  Michele Lazzeri  Andrea Floris 《Physics and Chemistry of Minerals》2014,41(4):289-302

The infrared spectrum and its temperature dependence (20–320 K) were collected on a synthetic goethite sample (α-FeOOH). In addition, the infrared powder absorption spectrum of goethite and aluminum-substituted goethite was computed using ab initio quantum mechanical calculations based on density functional theory. This combined experimental and theoretical approach allows (1) the unequivocal assignment of absorption bands to the corresponding vibrational modes, (2) separate identification of the effects of the particle shape and of the aluminum substitution on the infrared spectrum, and (3) a discussion of the anharmonic properties and the origin of the line broadening in goethite. In particular, the two well-resolved OH bending absorption bands show different temperature evolution. Their detailed analysis suggests that the broadening of the band at ~800 cm^?1 cannot be described solely by a usual three-phonon process. The strong anharmonic behavior of this mode implies the addition of a four-phonon process, such as a pure dephasing process. In our calculations, the effect of the Hubbard U correction is also investigated and found to be most visible on the OH stretching and bending modes, in relation to the associated structural relaxation. The OH stretching frequencies decrease, leading to a better agreement with experimental frequencies, while the OH bending frequencies increase.  相似文献   

Analysis of different methods for monitoring the urbanization process     

L. Charbonneau  D. Morin  A. Royer 《国际地球制图》2013,28(1):17-25

The monitoring of urban sprawl in agricultural and natural areas requires the frequent acquisition of information relative to land cover changes. The loss of high capability agricultural lands is a major problem. The sound management of resources requires the knowledge of the nature and orientation of the urban dynamics.

Remote sensing is a useful tool for highlighting areas where changes have occured,for determining the type of change and for quantifying these changes. A spatial‐temporal analysis of the urban processes is carried out for the urban area of Montreal, Canada. Different sources of information are used: three Landsat MSS satellite images acquired in 1972, 1979 and 1982, planimetric data from the Department of Municipal Affairs of Quebec and statistics compiled by Environment Canada.

The satellite data shows a sharp increase, in the order of 65%, in urban areas during the period under consideration. These results are compared with governmental data derived from classical photo‐interpretation techniques.

On one hand, we observe that the results obtained by automatic classification of the satellite data are superior in the order of between 5% to 30%, depending on the year and the different governmental sources. On the other hand, we discuss problems of homogeneity in the use of terms related to land cover between the various governmental organizations.  相似文献   

From straight to deeply incised meandering channels: Slope impact on sinuosity of confined streams     

Elad Dente  Nadav G. Lensky  Efrat Morin  Yehouda Enzel 《地球表面变化过程与地形》2021,46(5):1041-1054

Meandering channels and valleys are dominant landscape features on Earth. Their morphology and remnants potentially indicate past base-level fluctuations and changing regional slopes. The prevailing presence of meandering segments in low-slope areas somewhat confuses the physically based relationships between slope and channel meandering. This relationship underlies a fundamental debate: do incised sinuous channels actively develop during steepening of a regional slope, or do they inherit the planform of a preexisting sinuous channel through vertical incision? This question was previously explored through reconstructed evolution of meandering rivers, numerical simulations, and controlled, scaled-down laboratory experiments. Here, we study a rare, field-scale set of a dozen adjacent perennial channels, evolving in recent decades in a homogeneous erodible substrate in response to the Dead Sea level fall (> 30 m over 40 years). These channels are fed by perennial springs and have no drainage basin or previous fluvial history; they initiated straight and transformed into incising meandering channels following the emergence of the preexisting lake bathymetry, which resulted in increased channel lengths and regional slopes at different rates for each channel. This field setting allows testing the impact of changing regional slope on the sinuosity of a stream in the following cases: (a) relatively long and low-gradient shelf-like margins, (b) a sharp increase in the basinward gradient at the shelf-slope transition, and (c) gradually steepening slopes. Under a stable and low valley slope, the channels mainly incise vertically, inheriting a preexisting sinuous pattern. When the regional slope steepens, the channels start to meander, accompanying the vertical incision. The highest sinuosity evolved in the steepest channel, which also developed the deepest and widest valley. These results emphasize the amplifying impact of steepening regional slope on sinuosity. This holds when the flow is confined and chute cutoffs are scarce.  相似文献   

Effects of crustal stresses on fluid transport in fractured rock: case studies from northeastern and southwestern USA     

Roger?H.?Morin  William?Z.?SavageEmail author 《Hydrogeology Journal》2003,11(1):100-112

The link between stress and hydrologic properties was examined at two sites that are distinguished by different rock types and different stress states. This investigation is based upon the analysis and interpretation of geophysical logs obtained in water wells at the two locations. At the northeast site (Newark Basin), the hydrologic characteristics of sedimentary rocks are dependent upon the relationship to the current regional stress field of two primary types of orthogonal features that serve as preferential pathways for fluid flow. Subhorizontal bedding-plane partings are highly transmissive near the surface and delineate transversely isotropic fluid flow at shallow depths. With increasing depth, the subhorizontal planes become less dominant and steeply dipping fractures become more influential hydrologically. These high-angle features define anisotropic flow pathways that are preferentially oriented along strike. At the southwest site (west Texas), extrusive rocks are subjected to topographically modified tectonic and gravitational stresses that vary spatially within a valley setting. The attendant changes in stress invariants cause fracture connectivity within the rock mass to systematically increase with depth along the valley flanks, but to remain relatively low in the central valley. The degree of fracture connectivity predicted within this valley configuration is consistent with variations in transmissivity determined at several well locations. In each of these cases, the idealized understanding of the hydrologic system is enhanced by considering the effects of regional and local stresses that act upon the fractured-rock aquifer. Electronic Publication  相似文献   

Changes in the spectral and chemical properties of a water mass passing through extensive macrophyte beds in a large fluvial lake (Lake Saint-Pierre, Québec, Canada)     

Carl Martin  Jean-Jacques Frenette  Jean Morin 《Aquatic Sciences - Research Across Boundaries》2005,67(2):196-209

Large fluvial lakes, as part of river corridors, are recognized as spatially heterogeneous ecosystems. Due to their shallowness, the littoral zone of these lakes occupies a large proportion of their surface and is extensively covered by macrophytes that are known to affect their physical, chemical and biological environments in various ways. This study documents the small-scale (5 km) bio-optical variations associated with the longitudinal passage of a water mass through macrophyte beds during their maximal growth season. The utilization of a 2D hydrodynamic model allowed us to establish hydrological connectivity between stations within the beds, and thus to identify longitudinal heterogeneity along the macrophyte beds. Significant changes in the inherent properties of the water were observed along the upstream-downstream gradient. Due to their effects on hydrodynamics, macrophytes were responsible for a decrease in particles and dissolved organic carbon (DOC) resulting in an increasing penetration depth of ultraviolet (UV) and photosynthetically active radiation (PAR). Along the transect, chromophoric dissolved organic matter (CDOM) decreased more rapidly than DOC resulting in a decrease of the CDOM to DOC ratio. The observed changes in the DOC pool may be explained by the constant input of non-chromophoric DOC from macrophyte leachates and exudation within the bed and/or the photochemical and microbial degradation of CDOM. The implication of such small-scale heterogeneity on Lake Saint-Pierre productivity is discussed.  相似文献   

High-pressure/ultrahigh-pressure eclogites from the Hong’an Block,East-Central China: geochemical characterization,isotope disequilibrium and geochronological controversy   总被引：3，自引：0，他引：3  

Bor-ming?JahnEmail author  Xiaochun?Liu  Tzen-Fu?Yui  N.?Morin  M.?Bouhnik-Le?Coz 《Contributions to Mineralogy and Petrology》2005,149(5):499-526

The Hongan Block (western Dabieshan) exposes a series of HP/UHP metamorphic rocks, with a S-to-N distribution from blueschist–greenschist, kyanite-free, to kyanite- and coesite-bearing eclogites. The available age data are inconclusive that hinder our understanding of the tectonic evolution of the Block. The metamorphic temperatures in the Hongan Block (T_meta 700 to 500°C) are lower by 50–150°C than that of the Dabie and Sulu terranes. In this work, we undertook new trace element and Sr–Nd–O isotopic analyses on minerals in order to gain more insight into the geochronological problems. The results are as follows: (1) Trace element distribution patterns suggest that garnet and omphacite in many cases are out of chemical equilibrium; and the presence of high-temperature LREE-rich mineral inclusions (e.g., epidote) in garnet and omphacite has contributed to isotope disequilibrium. (2) Sm–Nd isotope analyses yielded no isochron ages for the Hongan eclogites. (3) Rb–Sr isotope analyses gave mixed results; in some cases, coexisting minerals are completely out of isotope equilibrium, and in others, isochron relationship is established, yielding ages from 210 Ma to 225 Ma. The pattern of Rb–Sr isotope disequilibrium appears to be independent of the petrological and O-isotope temperatures. (4) In contrast to the unequilibrated Sm–Nd isotopic systems, oxygen isotopes of the eclogite minerals seem to have attained isotope equilibrium or near-equilibrium. Oxygen isotope temperatures are comparable with petrological temperatures. However, this is an apparent feature due to mass balance constraints. (5) Whole-rock ¹⁸O values show a large variation from +10 to –8, suggesting that their protoliths have undergone very different processes of water–rock interaction. In view of the overall geochronological information, we conclude that the HP/UHP metamorphism in the Hongan Block took place in the Triassic at about 220–230 Ma, as observed in the Dabie and Sulu terranes. The significance of published Paleozoic dates (450–300 Ma) for the Xiongdian eclogite is not clear. However, any hypotheses advocating two periods of UHP metamorphic events for the same tectonic unit or in the same locality are not constrained by the geochronological data.Electronic Supplementary Material Supplementary material is available for this article at  相似文献   

Electrical conductivity of olivine and the lunar temperature profile     

R. M. Housley  F. J. Morin 《Earth, Moon, and Planets》1972,4(1-2):35-38

The measured electrical conductivity of olivine has been shown to depend strongly on thePo₂ in which the sample has been equilibrated. At the present time, no definite limits can be placed on temperatures in the lunar interior assuming a model composition of olivine. It is certain that such limits will be at least several hundred degrees above the original estimates.  相似文献