Hydrodynamic dispersion during absorption of water by soil: 2. Immobile water model     

M.J.L. Robin  K.B. Laryea  D.E. Elrick 《Journal of Hydrology》1983,65(4):333-348

The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m³ m^?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient.  相似文献   

Polar ice sheets: Developments since Wegener     

Dr. G. de Q. Robin 《International Journal of Earth Sciences》1981,70(2):648-663

Wegener's expeditions pioneered many measurements that are now essential for computer modelling of ice sheets. Advances in knowledge of accumulation, thickness, temperature, crystal fabric and surface mapping of ice sheets and of impurities, gas content and isotopic ratios of ice cores from these ice sheets are outlined before computer modelling work is discussed. The value of such studies in providing large scale tests of geophysical concepts is emphasized. The paper concludes by suggesting that the drag of continental ice sheets on the top of continental blocks might be of comparable magnitude and tend to balance forces on the base of these blocks by motion of the asthenosphere. Apart from providing a possible reason for the aseismic nature of the Antarctic and Greenland land masses, the hypothesis provides a suitable link for this volume between Wegener's interest in continental ice sheets and continental drift.

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Zusammenfassung Wegeners Expeditionen haben viele Messungen angeregt, die zu Ergebnissen geführt haben, die nunmehr reif sind für Computer-Modelle von Eisdecken. Es werden die Fortschritte in der Kenntnis von Akkumulationsraten, Mächtigkeit, Temperatur, Kristallstruktur, Oberflächenkartierung von Eisdecken und Verunreinigungen umrissen. Danach wird die Arbeit mit dem Computer-Modell diskutiert. Der Wert solcher Untersuchungen für großmaßstäbliche Tests geophysikalischer Konzepte wird betont. Die Ergebnisse lassen erwarten, daß die Schubkräfte der kontinentalen Eisdecken auf dem Top der kontinentalen Blöcke in derselben Größenordnung liegen könnten wie die aus der Bewegung der Asthenosphäre an der Basis dieser Blöcke. Letztere könnten damit kompensiert werden.Unabhängig davon, daß die aufgestellte Hypothese mögliche Argumente für die aseismische Natur der Antarktischen und Grönland-Massen aufzeigt, verbindet sie im Rahmen dieses Bandes Wegeners Interesse an kontinentalen Eisdecken mit der Kontinentaldrift.

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Résumé Les expéditions de Wegener ont suscité de nombreuses mesures qui ont fourni des données aujourd'hui mûres pour établir des modèles de couvertures glaciaires par la voie de calculatrices. Mais avant de discuter ce procédé, mention est faite des progrès accomplis dans la connaissance de l'accumulation, de l'épaisseur, de la température, de la structure cristalline et de la cartographie des couvertures glaciaires ainsi que de leurs impuretés, leur teneur en gas et les rapports d'isotopes dans les carottes qui y ont été prélevées, études dont il convient de souligner la valeur par les données à grande échelles qu'elles ont fourni à l'appui de concepts géophysiques. Le mémoire conclut sur la suggestion que les forces d'entrainement des couvertures glaciaires continentales sur la surface des blocs continentaux doit être d'un ordre comparable aux forces agissant à la base de ces blocs dans leur mouvement sur l'asthénosphère et qu'ils tendent à égaler. Outre qu'elle donne une raison possible de la nature asismique du continent antactique et du Groenland, cette hypothèse, dans ce volume, forme un trait d'union dans les intérêts que Wegener a portés aux couvertures glaciaires continentales et à la dérive des continents.

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Increasing Flash Floods in a Drying Climate over Southwest China     

Chan XIAO  Peili WU  Lixia ZHANG  Robin T.CLARK 《大气科学进展》2018,35(8):1094-1099

In a globally warming world,subtropical regions are generally expected to become drier while the tropics and mid–high latitudes become wetter.In line with this,Southwest China,close to 25?N,is expected to become increasingly prone to drought if annual mean precipitation decreases.However,despite this trend,changes in the temporal distribution of moisture supply might actually result in increased extreme rainfall in the region,whose climate is characterized by distinct dry and wet seasons.Using hourly and daily gauge observations,rainfall intensity changes since 1971 are examined for a network of 142 locations in the region.From the analysis,dry season changes are negligible but wet season changes exhibit a significantly strong downward trend [-2.4%(10 yr)~(-1)],particularly during the past 15 years [-17.7%(10 yr)~(-1)].However,the intensity of events during the wettest of 5% hours appears to steadily increase during the whole period [1.4%(10 yr)~(-1)],tying in with government statistical reports of recent droughts and flooding.If the opposing trends are a consequence of a warming climate,it is reasonable to expect the contradictory trend to continue with an enhanced risk of flash flooding in coming decades in the region concerned.  相似文献   

Spatial discordance in fish,coral, and sponge assemblages across a Caribbean atoll reef gradient          下载免费PDF全文

Charles Acosta  Robin Barnes  Rebecca McClatchey 《Marine Ecology》2015,36(2):167-177

Certain biodiversity patterns on coral reefs are generally consistent but we still lack fundamental insight into how assemblages vary across spatially heterogeneous reef systems. We compared fish, coral, and sponge assemblages across a symmetrical physiographical gradient (windward forereef, lagoon patch reef, leeward forereef) of the Glover's Reef atoll, Belize. Species richness of fishes and corals was highest in the deep habitat (15 m) on the windward forereef. Sponges were diverse and abundant on both deep windward and leeward forereefs but not on the exposed shallow (5 m) windward forereef. Fish and benthic assemblages were relatively distinct in each reef zone, with the lagoon patch reef communities consisting of a combination of leeward and windward species. Nevertheless, there were no clear patterns in community similarity matrices of fish and benthic assemblages, suggesting that overall coral and sponge assemblages had weak or no direct association with patterns in fish assemblages. A closer examination of fish trophic groups indicated that planktivores and predators were predictably associated with depth, whereas herbivores were associated with shallow protected reefs. None was specifically associated with spatial location along the atoll gradient. These patterns of diversity distribution are important for identifying spatial conservation priorities. A Marine Protected Area (MPA) at Glover's Reef encompasses substantial windward forereef and patch reef habitats. A much lesser extent of protection is afforded the leeward forereef that supports faunal assemblages that are unique and productive, if not as diverse as the windward forereef. Isolated coral atolls can serve as ideal systems to study spatial heterogeneity and biodiversity patterns, but more experimental studies are needed to reveal the mechanistic processes underlying these patterns.  相似文献   

The queen conch fishery on Pedro Bank, Jamaica: discovery, development, management     

Karl A. Aiken  G. Andre Kong  Stephen Smikle  Robin Mahon  Richard Appeldoorn 《Ocean & Coastal Management》1999,42(12):67

The history, methods, problems and regulation of fishing of the last remaining large queen conch resource in the world, located on a Jamaican fishing bank, are examined. The fishery activities for the queen conch, Strombus gigas Linnaeus are briefly described with the main activities in the industrial sector which produce the bulk of the harvest, which is exported. There are a few large producers harvesting the single major fishing ground of Pedro Bank, southwest of Kingston. These fishers harvested at least 1500 t annually between 1992 and 1998. Management is by licensing, individual quotas and a close season from July to October. Regulations related to CITES are thought to greatly assist in making licensed harvesters provide catch data to the Fisheries Division. The industrial operators have provided funding to undertake stock assessment studies in 1994 and again in 1997. We highlight the focus on management on a participatory consensual approach with meetings with all players in the industry. The conch fishery is thought to be one of the few areas of the Jamaica fishery where there is close and successful collaboration between fishers and the Fisheries Division. It provides an example of how rapid, precautionary, participatory action can provide an adequate basis for management until more definitive scientific information becomes available. The status of the conch fishery is thought to be sustainable at present, once reductions are made to the annual quota.  相似文献   

Linking uplift,erosion, and sedimentation using landscape evolution models: Madagascar since the Late Cretaceous     

Ruohong Jiao  Jean Braun  Antoine Delaunay  Cécile Robin  François Guillocheau 《地球表面变化过程与地形》2023,48(1):215-229

We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.  相似文献   

Emplacement age of the Markagunt gravity slide in southwestern Utah,USA     

McKenna E. Holliday  Tiffany Rivera  Brian Jicha  Robin B. Trayler  Robert F. Biek  Michael J. Braunagel  W. Ashley Griffith  David B. Hacker  David H. Malone  Danika F. Mayback 《地学学报》2023,35(1):66-72

The Markagunt gravity slide (MGS) is a large-volume landslide in southwestern Utah that originated within the Oligocene-Miocene Marysvale volcanic field. Gravity slides are single emplacement events with long runout distances and are now recognized as a new class of volcanic hazard. Accumulation of volcanic material on a structurally weak substrate along with voluminous shallow intrusive events led to collapse. Here, ⁴⁰Ar/³⁹Ar data for landslide-generated pseudotachylyte, the landslide-capping Haycock Mountain Tuff and the deformed Osiris Tuff are combined with a Bayesian age model to determine an emplacement age of 23.05 + 0.22/−0.20 Ma for the MGS. The results suggest a lag time of <200 kyr between the caldera-forming eruption of the Osiris Tuff, additional buildup of the unstable volcanic pile and subsequent mass movement.  相似文献