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Spectra taken by Cassini’s Composite Infrared Spectrometer (CIRS) between 10 and 600 cm−1 (17-1000 μm) of surface thermal emission of Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus have been used to derive the thermal inertia and bolometric Bond albedo values. Only an upper limit for the bolometric Bond albedo of Iapetus’ dark leading side could be determined due to the insensitivity of the thermal model to albedo when albedos are very low. The thermal inertia in this region however is better constrained. The CIRS coverage of Enceladus is extensive enough that the latitudinal variation in these values from 60°S to 70°N has been determined in 10° wide bins. The bolometric Bond albedos determined here are consistent with literature values which show the surface of the saturnian icy moons to be covered in ice contaminated to varying degrees. The thermal inertia of the moons is shown to be in the range 9-, approximately 2-6 times lower than that of the Galilean satellites, implying a less well consolidated and more porous surface. The thermal inertias of Iapetus and Phoebe are somewhat higher, suggesting that the very low thermal inertias of satellites from Rhea inwards may be related to their probable coating of E-ring material. Latitudinal variations on the surface of Enceladus show that the bolometric Bond albedo and thermal inertia increase towards the active plume source at the south pole. 相似文献
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F. Barroso-Barcenilla O. Cambra-Moo F. Escaso F. Ortega A. Pascual A. Pérez-García J. Rodríguez-Lázaro J.L. Sanz M. Segura A. Torices 《Cretaceous Research》2009,30(5):1268-1278
The palaeontological site of “Lo Hueco” was discovered in Cuenca, Spain, in 2007. It includes a stratigraphic interval in “Garumn” facies belonging to the upper part of the Villalba de la Sierra Formation. A succession of versicolor marly mudstone levels (V, G1, R1, G2, R2 and M) can be observed at the site studied. This succession is partially modified by a sandy channel structure (C) and by a sulphated interval (S). The C structure and the G1, G2 and R2 (lower part) levels have an extremely rich and varied fossil concentration and have provided to date more than 8500 macroremains. These are mainly from vertebrates, but also from plants and invertebrates. In general, vertebrates are represented by mineralized bones with an early infilling of gypsum, a ferruginous crust, and a secondary precipitation of gypsum; invertebrates by internal moulds; and plants by carbonized remains. Among the vertebrates, titanosaur dinosaurs (some of them with partially articulated skeletons) are by far the most common representatives, although lepisosteid fishes, bothremydid turtles, squamate lizards, eusuchian crocodiles, and ornithischian and theropod dinosaurs are also well represented. The relative stratigraphic position and the palaeontological content of this site allow to attribute it to the upper Campanian-lower Maastrichtian. Interpretation of its materials suggests a near coast muddy flood plain crossed by distributary sandy channels environment, exposed to brackish to fresh water aquatic influence. 相似文献
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Stream water temperature (ts) is a critical water quality parameter for aquatic ecosystems. However, ts records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict ts at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (ta) and ts. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the ta–ts linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict ts resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict ts at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the ta–ts relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean ts in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean ts in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on ts across the USA. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Donald R. Cahoon Brian C. Perez Bradley D. Segura James C. Lynch 《Estuarine, Coastal and Shelf Science》2011,91(4):463-474
Given the potential for a projected acceleration in sea-level rise to impact wetland sustainability over the next century, a better understanding is needed of climate-related drivers that influence the processes controlling wetland elevation. Changes in local hydrology and groundwater conditions can cause short-term perturbations to marsh elevation trends through shrink–swell of marsh soils. To better understand the magnitude of these perturbations and their impacts on marsh elevation trends, we measured vertical accretion and elevation dynamics in microtidal marshes in Texas and Louisiana during and after the extreme drought conditions that existed there from 1998 to 2000. In a Louisiana marsh, elevation was controlled by subsurface hydrologic fluxes occurring below the root zone but above the 4 m depth (i.e., the base of the surface elevation table benchmark) that were related to regional drought and local meteorological conditions, with marsh elevation tracking water level variations closely. In Texas, a rapid decline in marsh elevation was related to severe drought conditions, which lowered local groundwater levels. Unfragmented marshes experienced smaller water level drawdowns and more rapid marsh elevation recovery than fragmented marshes. It appears that extended drawdowns lead to increased substrate consolidation making it less resilient to respond to future favorable conditions. Overall, changes in water storage lead to rapid and large short-term impacts on marsh elevation that are as much as five times greater than the long-term elevation trend, indicating the importance of long-term, high-resolution elevation data sets to understand the prolonged effects of water deficits on marsh elevation change. 相似文献
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Santa Mar&#;a Hern&#;n Hube Mat&#;as A. Rivera Felipe Yepes-Estrada Catalina Valc&#;rcel Jairo A. 《Natural Hazards》2016,81(1):55-69
Large-scale impacts from natural disasters suffered by society encourage researchers and public agencies to develop methods to evaluate, mitigate, respond, and recover from these events. A key aspect for the calculation of the potential earthquake losses is to properly describe the characteristics and value of assets exposed to seismic hazard. This article describes a methodology to develop an exposure model at a census-block resolution for residential structures in Chile using statistical data. The methodology is based on three steps: (1) obtaining dwelling count, construction material and location from census data, (2) defining classification rules for dwellings associated with houses and apartment buildings, and (3) assigning structural typologies and replacement cost. The resulting exposure model consists of a database with the number of residential structures classified into 18 structural typologies at each census block and the associated replacement cost. A total of 4,259,804 residential structures were identified in the national exposure model. Overall, clay brick and concrete block masonry account for 53.5 % of the structures of the country followed by timber (33.7 %), reinforced concrete (8.1 %), and adobe (4.6 %). Also, a methodology using remote digital survey techniques is proposed and used to obtain local exposure models for the cities of Iquique, Rancagua, and Osorno. The results of the national exposure model are compared with the local exposure models. An important feature of the proposed methodologies is that the building stock is classified into structural typologies, which is a key aspect for conducting seismic risk assessment. The methodologies used to construct the national and local exposure models may be extrapolated to other countries by adjusting the classification rules. The exposure models that were constructed represent an important input for risk calculations, by improving the technical capabilities for seismic risk management of the country.
相似文献47.
Habitat use patterns of the invasive red lionfish Pterois volitans: a comparison between mangrove and reef systems in San Salvador,Bahamas 
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下载免费PDF全文 Catalina Pimiento James C. Nifong Margaret E. Hunter Eric Monaco Brian R. Silliman 《Marine Ecology》2015,36(1):28-37
The Indo‐Pacific red lionfish Pterois volitans is widespread both in its native and its non‐native habitats. The rapid invasion of this top predator has had a marked negative effect on fish populations in the Western Atlantic and the Caribbean. It is now well documented that lionfish are invading many tropical and sub‐tropical habitats. However, there are fewer data available on the change in lionfish abundance over time and the variation of body size and diet across habitats. A recent study in San Salvador, Bahamas, found body size differences between individuals from mangrove and reef systems. That study further suggested that ontogenetic investigation of habitat use patterns could help clarify whether lionfish are using the mangrove areas of San Salvador as nurseries. The aim of the present study is to determine temporal trends in lionfish relative abundance in mangrove and reef systems in San Salvador, and to further assess whether there is evidence suggesting an ontogenetic shift from mangroves to reef areas. Accordingly, we collected lionfish from mangrove and reef habitats and calculated catch per unit effort (a proxy for relative abundance), compared body size distributions across these two systems, and employed a combination of stable isotope, stomach content, and genetic analyses of prey, to evaluate differences in lionfish trophic interactions and habitat use patterns. Our results show that populations may have increased in San Salvador during the last 4 years, and that there is a strong similarity in body size between habitats, stark differences in prey items, and no apparent overlap in the use of habitat and/or food resources. These results suggest that there is not evidence an for ontogenetic shift from mangroves to reefs, and support other studies that propose lionfish are opportunistic forages with little movement across habitats. 相似文献
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Galvis-Castro Ayda Catalina Colmenares Julio E. Garcia-Leal Juan C. 《Geotechnical and Geological Engineering》2022,40(3):1485-1497
Geotechnical and Geological Engineering - Understanding the compression behavior of volcanic ash soils is essential in the assessment of settlements in such materials. A series of one-dimensional... 相似文献
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During the Cretaceous, high global sea-level and low latitudinal temperature variations led to the growth of epeiric carbonate platforms. Platform-scale dolomitization of these platforms is not common, reflecting the low Mg/Ca ratio of seawater and a humid climate. This study describes the processes governing pervasive dolomitization of a land-attached carbonate platform within the Iberian Basin. Dolomite is planar to sub-planar with a geochemical signature consistent with dolomitization from penesaline seawater. Dolomitization was most pervasive during a 1 Myr period in the middle Cenomanian, by repeated reflux of seawater from brine pools formed on the top of a southward-prograding carbonate platform. Tilting and structural reorganization in the Upper Cenomanian led to a reversal in polarity of the platform, and dolomitization was restarted by the northward reflux of seawater. Rising relative sea-level and oceanic acidification led to back-stepping of the platform such that the supply of dolomitizing fluids was cut off. In the Lower Turonian, pervasively dolomitized rudist rudstone facies in the south of the study area indicate that dolomitization restarted, either penecontemporaneously or later, from highly evaporated Campanian–Maastrichtian seawater. A systematic increase in dolomite crystal size up-section ties broadly, but not entirely, to stratigraphy. It is possible that these textural differences reflect changes in fluid chemistry, limestone permeability or precursor rock texture. However, the lack of stratigraphic conformance, and the preservation of the earliest-formed dolomite only in the oldest sediments, could indicate a progressive recrystallization of early-formed dolomite through repeated reflux of brines. As such, the succession appears to preserve a fossilized record of dolomite recrystallization through time during the Cenomanian–Turonian. The results of this study therefore provide a record of the progressive dolomitization of a carbonate platform and demonstrate the important interplay of climate and basin-scale tectonics on dolomite distribution and crystallinity. 相似文献