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1.
Evolution of sand waves in the Messina Strait, Italy 总被引:1,自引:0,他引:1
In the present paper the morphodynamics of sand waves in the Messina Strait, Italy, is analysed by comparing data gathered during two different surveys carried out in 1991 and 2001, respectively. In particular, a morphometric analysis on the most recent data and a qualitative analysis of the differences between bottom bedform patterns, are carried out. At locations characterised by greater depths, only minor changes to the planimetric configuration of the field, i.e. crest orientation (which is seen to be orthogonal to the direction of net gross sand transport) and wave length are observed, while differences in wave length and crest direction are more evident in more shallow areas. On the other hand, wave height has significantly increased in the whole field. A possible explanation of such a change, based on the previsions of a theory which relates sand-wave growth and migration to the main components of the tidal ellipse, is provided.Responsible Editor: Jens Kappenberg 相似文献
2.
Alyson E. Santoro 《Hydrogeology Journal》2010,18(1):187-202
Microbial communities inhabiting “subterranean estuaries” along the subsurface freshwater–saltwater continuum determine the fate of nitrogen discharged to coastal waters. Little is known about the microbes that comprise these communities, or what their ecological and biogeochemical responses will be to increased salinity resulting from saltwater intrusion and aquifer salinization. This review covers basic aspects of the nitrogen cycle relevant to the coastal subsurface and provides a framework for predicting the types of microbes and nitrogen transformations that exist in different subterranean estuary systems. Literature concerning the freshwater–saltwater mixing zones of surficial estuaries, where microbial communities are better characterized, is also reviewed to explore what is known about the impact of increasing salinity on both the community composition and biogeochemical function of the microbial assemblage. Collectively, these studies suggest that salinization will alter microbial community composition for all functional groups involved in nitrogen cycling, and may lead to decreases in nitrification and coupled nitrification-denitrification, and increases in dissimilatory nitrate reduction to ammonium (DNRA). Future collaboration between hydrogeologists and microbial ecologists is needed to fully predict the impact of saltwater intrusion on subsurface microbial communities. 相似文献
3.
A semi-numeric method was used to study the evolution of a general-relativistic radiating shell in its Post-Newtonian and
Newtonian approximations. The solutions, where the main parameters are given reasonable values, show that a relativistic effect
can be found in X-ray-burster-like objects.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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5.
The SE Pacific stock of Patagonian grenadier (Macruronus magellanicus) showed evidence of an abrupt reduction in recruitment after 2000. This drop exceeded expectations from changes in the spawning stock biomass (SSB), indicating a change in the stock-recruitment relationship (S-R). We evaluated whether variability in recruitment could be explained by concurrent changes in three environmental indices: sea-surface temperature anomaly (SSTA); southern oscillation index (SOI); and latitudinal position of the west wind drift bifurcation (WWDL). Continuous and discrete effects of these indices were tested as covariates in linear log-log and non-linear Ricker's S-R models. Discrete effects represented regime shifts detected in SSTA (1998), SOI (1998) and WWDL (1995). While SSTA was the only continuous variable found to be significant, the discrete 1998 regime shift supported the most informative model. The best Ricker's model considered a discrete intercept change in the same year: 1998. Although a spurious correlation between SSTA and S-R changes is possible, SSTA may be reflecting major physical or biological changes relevant to M. magellanicus juveniles in the SE Pacific. 相似文献
6.
西藏羊八井热田地热流体成因及演化的惰性气体制约 总被引:4,自引:5,他引:4
地热流体中惰性气体的相对丰度和同位素组成,不仅可以揭露热田的热源性质,而且还能够揭示深,浅层地热流体的内在联系和演化过程等。在西藏羊八井热田的地热气体中,已检测出大量的^4He组分,3He/^4He值是大气的0.087-0.259倍,表明深部地壳物质的局部熔融为热田提供能量,浅层地热流体的3He/4He 值自西北向东南呈降低趋势,与热储温度的变化相一致,反映出侧向运移时补充了更多的壳源氦,热田北区深层地热流体具有稍高的3He/4He值,是浅层地热流体的母源,气体中氪和氙的相对丰度具有大气降水成因的特征,结合现有的实际资料,建立了热田地热流体的概念模型。 相似文献
7.
The limited period of observational data and the long orbital period have limited the accuracy of the Pluto ephemerides. This condition will continue for some time. Ephemerides of Pluto are compared with the observational data. 相似文献
8.
Pablo Santoro Mónica Fossati Pablo Tassi Nicolas Huybrechts Damien Pham Van Bang Ismael Piedra-Cueva 《国际泥沙研究》2019,34(5):444-454
The effect of the consolidation process on the morphodynamics and fine sediment dynamics of the Río de la Plata estuary is explored through a circulation-wave-sediment transport model. The consolidation model is calibrated based on settling column experimental data. Different simulations are done in order to initialize the mud layer distribution and to investigate the impact of different erosion parameter assumptions on the modeled sediment dynamics. Finally a two-year simulation is done with and without the consolidation process and realistic hydrodynamic forcings. Considering the consolidation process, the model correctly reproduces measured vertical density profiles in the Montevideo Bay access channel. The simulated suspended sediment dynamics behavior in Montevideo Bay with the consolidation process provides a more realistic deposition pattern in regard to the dredging activities. 相似文献
9.
Environmental factors influence the accuracy in stem volume retrieval using European Remote Sensing Satellite (ERS) tandem synthetic aperture radar (SAR) interferometry. Some forest stands are more sensitive than others to heterogeneity of environmental properties, forest properties, and noise. It is shown that the consistency of coherence observations between different image pairs or the consistency of the estimated stem volume can be used to sort forest stands according to increasing errors in stem volume estimates associated with varying forest properties. Fifteen ERS tandem pairs were used to determine the relative root mean square error (RMSE) of stem volume estimated from C-band SAR interferometry. The test site, Tuusula in Finland, contains 210 forest stands with stem volumes up to 539 m3/ha. RMSE varies between 17% and 63% depending on number and type of stands included in the retrieval accuracy analysis. The more homogeneous forest stands with larger area and higher stem volumes of spruce and pine are those with highest retrieval accuracy 相似文献
10.
Paula C. Ugalde Calogero M. Santoro Eugenia M. Gayo Claudio Latorre Sebastin Maldonado Ricardo De Pol‐Holz Donald Jackson 《Geoarchaeology》2015,30(4):352-368
Archaeological sites composed only of surficial lithics are widespread in arid environments. Numerical dating of such sites is challenging, however, and even establishing a relative chronology can be daunting. One potentially helpful method for assigning relative chronologies is to use lithic weathering, on the assumption that the most weathered artifacts are also the oldest. Yet, few studies have systematically assessed how local environmental processes affect weathering of surficial lithics. Using macroscopic analyses, we compared the weathering of surficial lithic assemblages from seven mid‐to‐late Holocene archaeological sites sampled from four different microenvironments in the Atacama Desert of northern Chile. Changes in polish, texture, shine, and color were used to establish significant differences in weathering between two kinds of locations: interfluves and canyon sites. Lithics from interfluve sites were moderately to highly weathered by wind and possessed a dark coating, whereas canyon lithics were mildly weathered despite greater exposure to moisture, often lacked indications of eolian abrasion, and lacked dark coatings. Our results show that lithic weathering can be used as a proxy for relative age, but only after considering local environmental factors. The power of such chronologies can be improved by combining archaeological, paleoenvironmental, geomorphological, and taphonomic data. 相似文献