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121.
The beam attenuation to chlorophyll ratio: an optical index of phytoplankton physiology in the surface ocean? 总被引:1,自引:0,他引:1
Michael J. Behrenfeld Emmanuel Boss 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1537-1549
The particulate beam attenuation coefficient (cp) is proportional to the concentration of suspended particles in a size domain overlapping that of the phytoplankton assemblage. cp is largely insensitive to changes in intracellular chlorophyll concentration, which varies with growth irradiance (a process termed ‘photoacclimation’). Earlier studies have shown that the ratio of cp:chlorophyll (i.e., cp*) exhibits depth-dependent changes that are consistent with photoacclimation. Similar relationships may likewise be expected in the horizontal and temporal dimensions, reflecting changes in mixing depth, incident irradiance, and light attenuation. A link between cp* and more robust photoadaptive variables has never been explicitly tested in the field. Here we use five historical field data sets to directly compare spatial and temporal variability in cp* with two independent indices of photoacclimation: the light-saturated, chlorophyll-normalized photosynthetic rate, Pbopt, and the light-saturation index, Ek. For the variety of oceanographic conditions considered, a first-order correlation emerged between cp* and Pbopt or Ek. These simple empirical results suggest that a relationship exists between a bio-optical variable that can potentially be retrieved remotely (cp*) and physiological variables crucial for estimating primary productivity in the sea. 相似文献
122.
Hossein Ghaffarian Hervé Piégay Diego Lopez Nicolas Rivière Bruce MacVicar Aurelie Antonio Emmanuel Mignot 《地球表面变化过程与地形》2020,45(10):2219-2234
Wood in rivers plays a major role both ecologically and morphologically. In recent decades, due to human activities in the river channels and along the riparian zone, wood obstruction and jamming has exacerbated flooding hazards and infrastructure damage. Therefore, it is necessary to quantify the wood flux and discharge in rivers to improve wood hazard management. Among the various methods for monitoring the wood flux in a river, the streamside videography technique is effective given its high temporal and spatial resolution. Previous work monitored the wood discharge (m3/s) using this technique in the Ain River (France) during three floods (MacVicar and Piégay, 2012), and the same method is implemented on the Isère River (France) to obtain the statistics of wood discharge for two floods. Comparison between the two sites supports the generalization of both the monitoring technique and the link between wood discharge and flood characteristics. We first show that the maximum wood discharge is observed at bankfull discharge, and we confirm the three stage model proposed by MacVicar and Piégay (2012). Additionally, transverse distributions of the number of wood pieces and corresponding wood length appear to be similar for different flood magnitudes on each site. As a technical contribution, the use of the same technique on two sites allows for recommendations on key decisions related to the location and implementation of the equipment. Both statistical and technical contributions can be used by decision makers to implement this monitoring technique, acquire the wood transport parameters, and evaluate the potential wood hazards at local scale or along a river. © 2020 John Wiley & Sons, Ltd. 相似文献
123.
The large-scale Shiti barite deposit of Shaanxi,being stratiform or stratoid in form,occurs in an early Paleozoic large witherite-barite metallogenic belt of southern Qinling region(China).The ore deposit,hosted in Lower Silurian Daguiping Formation,is composed of a series of carbonaceous chert,carbonaceous slate and carbonaceous sandstone,and is characterized by persistent syn-sedimentary ore beds.Barite,w itherite.barytocalcite and barite-witherite constitute the major ore minerals,with barite being the main one. 相似文献
124.
125.
Jean-Baptiste?RenardEmail author Martyn?P.?Chipperfield Gwena?l?Berthet Fabienne?Goffinont-Taupin Claude?Robert Michel?Chartier Howard?Roscoe Wuhu?Feng Emmanuel?Rivière Michel?Pirre 《Journal of Atmospheric Chemistry》2005,51(1):65-78
Eleven vertical profiles of stratospheric NO3 have been obtained since 1992 using the AMON and SALOMON balloon-borne UV-visible spectrometers. The measurements are compared to the SLIMCAT 3D model and calculations based on the steady-state hypothesis for NO3. The calculations cannot reproduce some parts of the profiles which exhibit strong concentration fluctuations over few kilometres, as a consequence of the dependence of NO3 on local temperature variations. A statistical use of the data allows us to estimate the influence of the temperature dependence of the absorption cross-section on the data analysis, and the validity of the recommended reaction rates available in the literature. Discrepancies exist between the model based on recommended kinetics and observations at warmer temperatures. Nevertheless, the analysis is biased by local temperature inhomogeneities, and only a low-resolution vertical shape of the NO3 profiles can be retrieved. 相似文献
126.
Large-offset approximation to seismic reflection traveltimes 总被引:4,自引:0,他引:4
Conventional approximations of reflection traveltimes assume a small offset-to-depth ratio, and their accuracy decreases with increasing offset-to-depth ratio. Hence, they are not suitable for velocity analysis and stacking of long-offset reflection seismic data. Assuming that the offset is large, rather than small, we present a new traveltime approximation which is exact at infinite offset and has a decreasing accuracy with decreasing offset-to-depth ratio. This approximation has the form of a series containing powers of the offset from 1 to −∞. It is particularly accurate in the presence of a thin high-velocity layer above the reflector, i.e. in a situation where the accuracy of the Taner and Koehler series is poor. This new series can be used to gain insight into the velocity information contained in reflection traveltimes at large offsets, and possibly to improve velocity analysis and stacking of long-offset reflection seismic data. 相似文献
127.
Geologically Constrained Probabilistic Mapping of Gold Potential, Baguio District, Philippines 总被引:1,自引:0,他引:1
Binary predictor patterns of geological features are integrated based on a probabilistic approach known as weights of evidence modeling to predict gold potential. In weights of evidence modeling, the log
e
of the posterior odds of a mineral occurrence in a unit cell is obtained by adding a weight, W
+ or W
– for presence of absence of a binary predictor pattern, to the log
e
of the prior probability. The weights are calculated as log
e
ratios of conditional probabilities. The contrast, C = W
+ – W
–, provides a measure of the spatial association between the occurrences and the binary predictor patterns. Addition of weights of the input binary predictor patterns results in an integrated map of posterior probabilities representing gold potential. Combining the input binary predictor patterns assumes that they are conditionally independent from one another with respect to occurrences. 相似文献
128.
Using land cover changes and demographic data to improve hydrological modeling in the Sahel
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Jean Emmanuel Paturel Gil Mahé Pierre Diello Bruno Barbier Alain Dezetter Claudine Dieulin Harouna Karambiri Hamma Yacouba Amadou Maiga 《水文研究》2017,31(4):811-824
At the beginning of the drought in the Sahel in the 1970s and 1980s, rainfall decreased markedly, but runoff coefficients and in some cases, absolute runoff increased. This situation was due to the conversion of the land cover from natural vegetation with a low annual runoff coefficient, to cropland and bare soils, whose runoff coefficients are higher. Unless they are adapted, hydrological conceptual models, such as GR2M, are unable to reproduce this increase in runoff. Despite the varying environmental and climatic conditions of the West African Sahel, we show that it is possible to increase the performance of the GR2M model simulations by elaborating a time‐varying soil water holding capacity and to incorporate this value in the annual maximum amount of water to be stored in reservoir A of the model. We looked for interactions between climate, rural society, and the environment. These interactions drive land‐cover changes in the Sahel, which in turn drive the distribution of rainfall between infiltration, evaporation, and runoff and hence the water resources, which are vital in this region. We elaborated several time series of key indicators linked to these interactions. We then integrated these changes in the runoff conditions of the GR2M model through the maximum value of the reservoir capacity. We calculated annual values of water holding capacity using the annual values of four classes of land cover, natural vegetation, cultivated area, bare soil, and surface water. We then used the hydrological model with and without this time‐varying soil value of A and compared the performances of the model under the two scenarios. Whatever the calibration period used, the Nash–Sutcliffe index was always greater in the case of the time‐varying A time series. 相似文献
129.
130.
James Lovell-Kennedy Emmanuel Roquette Stefan Schröder Jonathan Redfern 《Basin Research》2023,35(1):187-213
Over 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of north-west Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across north-west Africa indicate significant and sustained shifts in source regions in Meso-Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from north-west Africa—often described as the ‘Mesoproterozoic Gap’, which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa. 相似文献