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63.
Jacques Mathieu Fabrice Jeannerod Frédéric Hervant Thomas C. Kane 《Aquatic Sciences - Research Across Boundaries》1997,59(1):39-47
Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus. 相似文献
64.
Wallace S. Broecker Rik Wanninkhof Guy Mathieu Tsung-Hung Peng Scott Stine Steve Robinson Andy Herczeg Minze Stuiver 《Earth and Planetary Science Letters》1988,88(1-2)
Since 1957 the 14C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced14C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO2 exchange rate, and (4) biological enhancement of the CO2 exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity. 相似文献
65.
Mathieu Schuster Philippe Duringer Jean‐Francois Ghienne Patrick Vignaud Alain Beauvilain Hassan Taisso Mackaye Michel Brunet 《地球表面变化过程与地形》2003,28(10):1059-1069
This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega‐Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross‐section, their pro?le reveals a well de?ned cliff–platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave‐worked for the longest time are the best rounded. The cliff–platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega‐Chad events. Asymmetrical erosion pro?les moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff–platform junction is an indication of the highest water level of Lake Mega‐Chad at 320–325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon‐related winds were prevalent during Lake Mega‐Chad events, suggesting the Inter‐Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
Vania Rosolen Mathieu Lamotte René Boulet Jean Trichet Olivier Rouer Adolpho José Melfi 《Comptes Rendus Geoscience》2002,334(3):187-195
A mottled horizon in a laterite cover (without any duricrust) was studied by microscopy and quantitative chemical microanalysis. Apart from the voids, light red spots consisting of Fe-rich particles (≈2 μm) are set in clayey plasma. Dark red spots consisted of concentrations of Fe-rich particles. These patterns are inherited. On the border of structural or biological voids, where Fe-depletion features are systematic, gray or yellow spots result from dissolution of the Fe-rich particles and impregnation of the plasma by iron, respectively. The present Fe-depletion is the dominant process that explains the mottled differentiation and the absence of lateritic duricrust. To cite this article: V. Rosolen et al., C. R. Geoscience 334 (2002) 187–195. 相似文献
67.
This paper presents an overview of some of the most significant, recent to ancient, littoral morpho-sedimentary structures and deposits from the Lake Turkana Basin. We highlight the importance of wave-related sedimentary processes in lakes, and more specifically in rift lakes. In the published literature, references to wave-dominated shorelines are mainly in regards to coastal marine environments. However, numerous modern lakes exhibit typical wave-dominated littoral landforms, and related sedimentary deposits are known from several paleolake successions in the geological record. Wave-related processes are often of relatively minor importance in depositional models for lacustrine environments. Classical models emphasize clastics transported by rivers, which are then distributed by fan-deltas and/or deltas into a water body of fluctuating depth, where reworking of clastics is limited in the littoral domain, and episodic in deep waters. Modern processes in Lake Turkana and the exposed paleolake deposits of the Turkana Basin demonstrate that this view is incomplete. Wave-dominated shorelines are evident (1) for modern Lake Turkana based on prominent and active littoral landforms (e.g., beach ridges, sand spits, washover fans, and arcuate-cuspate deltas); (2) for the Holocene (African Humid Period) climate-driven highstand of Megalake Turkana and its subsequent forced regression based on conspicuous raised beach ridges and spits; and (3) for the Pliocene–Pleistocene (Omo Group, Nachukui Formation) from typical nearshore sedimentary facies and stratigraphic architectures associated with paleolake Turkana. These examples from the Turkana Basin coupled with examples from other lacustrine settings, suggest that wave-dominated clastic shorelines represent significant portions of existing and ancient lake-shores. As this view contrasts with classic depositional models for lakes, notably for those found in rift setting, we also present examples of wave-influenced littoral landforms from other lakes of the East African Rift System. Identifying lacustrine paleoshorelines from typical clastic landforms and deposits is the key to the spatial reconstruction of lakes over time, and to determine transgressive–regressive cycles. Waves action is an important agent in lakes for the erosion, transport, and deposition of clastics at the basin-scale, an aspect that needs to be integrated in sedimentary models. 相似文献
68.
We have acquired resolved images of Titan with the adaptive optics systems PUEO/KIR at the CFHT (Hawaii) and NAOS/CONICA at the VLT (Chile). We report here on images and maps (when data at several orbital phases are available) of Titan's surface from observations taken during the last 4 years (2001-2004) in all the methane windows between 1 and 2.5 μm (namely, at 1.08, 1.28, 1.6, and 2 μm). We present the only complete maps of Titan currently available at 1.3 μm, a spectral window where Titan appears particularly bright in spectroscopy, with a resolution of about 200 km at best on the ground. Our surface maps show the bright and dark regions sharing Titan's landscape with as much detail as possible from the ground and with high contrast in most cases. From the information gathered by comparing the maps at different wavelengths we derive constraints on the ground's composition. Our results could complete/optimize the return of the Cassini-Huygens mission. 相似文献
69.
Small hydrocarbon grains in the vicinity of a supernova could be annealed by the absorption of several far-ultraviolet photons to produce the tiny diamonds found in meteorites. These freshly-synthesized diamond grains would be bombarded by the heavy ions and neutrals in the supernovae outflow and would thereby acquire the distinctive noble-gas isotopic signature by which they were first isolated. Only diamonds formed relatively close to supernovae would acquire such a signature, since grains formed farther out would be subjected to a much diluted and less energetic plasma environment. 相似文献
70.
Minghelli-Roman A. Polidori L. Mathieu S. Loubersac L. Cauneau F. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(2):274-277
Bathymetric estimation using remote sensing images has previously been applied to high spatial resolution imagery such as CASI, Ikonos, or SPOT but not on medium spatial resolution images (i.e., MERIS). This choice can be justified when there is a need to map the bathymetry on large areas. In this letter, we present the results of the bathymetry estimation over a large known area, the Gulf of Lion (France), expanding over 270times180 km 相似文献