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1.
During landward migration, ridge and runnel systems are subjected to asymmetric oscillatory and/or unidirectional flow regimes, depending on the stage of development reached by these systems. In the early stages of evolution, when the ridge is situated in the upper shoreface, the whole system is subjected to asymmetric oscillatory flow. The runnel is under lower flow regime conditions and the ridge may be under upper or lower flow regime according to water depth and wave energy. Later, when the ridge has migrated to a position on the foreshore, the runnel is largely under a unidirectional lower flow regime while the ridge itself is under oscillatory upper flow regime. When the ridge welds to berm, it is largely emergent and exposed to high-tide swash action under upper flow regime conditions. The runnel is eventually filled with sand and transformed into a low-lying area. All these types grade laterally into each other. One or more ridge and runnel systems can occur at the same time. Wave energy, tide level and position of the ridge control the variations in the characteristics of the ridge and also the position of the zones of bedforms found at the upper shoreface. 相似文献
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T. Losada B. Rodríguez-Fonseca I. Polo S. Janicot S. Gervois F. Chauvin P. Ruti 《Climate Dynamics》2010,35(1):45-52
On the frame of the AMMA-EU project, sensitivity experiments for an Atlantic Equatorial mode (AEM) which origin, development and damping resembles the observed one during the last decades of the 20th century, has been analysed in order to investigate the influence on the anomalous summer West African rainfall. Recent studies raise the matter of the AEM influence on the next Pacific ENSO episodes and also on the Indian Monsoon. This paper evaluates the response of four different atmospheric global circulation models, using the above-mentioned AEM sensitivity experiments, to study the tropical forcing associated with the Atlantic Niño mode. The results show a remote signal in both the Pacific and Indian basins. For a warm phase of the AEM the associated southward location of the ITCZ, with rising motions over the Equatorial Atlantic, leads to a global subsidence over the rest of the tropics, weakening the Asian Monsoon and favouring the La Niña conditions in the central Pacific. Although ocean–atmosphere coupled experiments are required to test the latter hypothesis, the present studies shows how the AEM is able to influence the rest of the tropics, a result with important implications on ENSO seasonal predictability. 相似文献
3.
The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral‐associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by 13C‐NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra‐macroaggregate SOM, which is then separated by density. Finally, intra‐microaggregate SOM is isolated from mineral‐associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral‐associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted‐aliphatic material, most probably lipid biopolymers. 相似文献
4.
Zazo C. Dabrio C.J. Borja F. Goy J.L. Lezine A.M. Lario J. Polo M.D. Hoyos M. Boersma J.R. 《Geologie en Mijnbouw》1998,77(3-4):209-224
The stratigraphic relationships, genesis and chronology, including radiocarbon dating, of the Quaternary sandy deposits forming the El Asperillo cliffs (Huelva) were studied with special emphasis on the influence of neotectonic activity, sea-level changes and climate upon the evolution of the coastal zone. The E-W trending normal fault of Torre del Loro separates two tectonic blocks. The oldest deposits occur in the upthrown block. They are Early to Middle Pleistocene fluviatile deposits, probably Late Pleistocene shallow-marine deposits along an E-W trending shoreline, and Late Pleistocene and Holocene aeolian sands deposited under prevailing southerly winds. Three Pleistocene and Holocene aeolian units accumulated in the downthrown block. Of these, Unit 1, is separated from the overlying Unit 2 by a supersurface that represents the end of the Last Interglacial. Accumulation of Unit 2 took place during the Last Glacial under more arid conditions than Unit 1. The supersurface separating Units 2 and 3 was formed between the Last Glacial maximum at 18 000 14C yr BP and ca. 14 000 14C yr BP, the latter age corresponding to an acceleration of the rise of sea level. Unit 3 records wet conditions. The supersurface separating Units 3 and 4 fossilised the fault and the two fault blocks. Units 4 (deposited before the 4th millennium BC), 5 (> 2700 14C yr BP to 16th century) and 6 (16th century to present) record relatively arid conditions. Prevailing wind directions changed with time from W (Units 2–4) to WSW (Unit 5) and SW (Unit 6). 相似文献
5.
V. González-Quiñones A. de la Torre M. P. García A. Polo R. Jiménez-Ballesta 《Environmental Geology》2007,53(3):527-531
In the region of Castilla-La Mancha (Spain), over half of the soils are under cropping. This vast agricultural activity, combined
with other anthropological uses, has led to a deterioration of the soil quality and virtual degradation. Therefore, it was
deemed to assess the quality of these soils, which was achieved by applying two different methods. Three soils, representative
of typical conditions in this community, were sampled and diverse properties were analysed in order to apply two different
approaches. The first soil evaluation was carried out by a traditional method developed by FAO using a productivity index,
whereas the second method consisted of the application of a new method called SINDI, developed in New Zealand. Both approaches
make an evaluation based on a number of indicators that differs in each case. These differences explain why each method ranked
the soils studied in different order reaching diverse conclusions on their quality. 相似文献
6.
Changes in tropical Atlantic interannual variability from a substantial weakening of the meridional overturning circulation 总被引：1，自引：1，他引：0
In response to a substantial weakening of the Atlantic Meridional Overturning Circulation (AMOC)—from a coupled ocean–atmosphere general circulation model experiment—significant changes in the interannual variability are found over the tropical Atlantic, characterized by an increase of variance (by ~150 %) in boreal late spring-early summer and a decrease of variance (by ~60 %) in boreal autumn. This study focuses on understanding physical mechanisms responsible for these changes in interannual variability in the tropical Atlantic. It demonstrates that the increase of variability in spring is a consequence of an increase in the variance of the El Niño-Southern Oscillation, which has a large impact on the tropical Atlantic via anomalous surface heat fluxes. Winter El Niño (La Niña) affects the eastern equatorial Atlantic by decreasing (increasing) cloud cover and surface wind speed which is associated with anomalous downward (upward) short wave radiation and reduced (enhanced) upward latent heat fluxes, creating anomalous positive (negative) sea surface temperature (SST) anomalies over the region from winter to spring. On the other hand, the decrease of SST variance in autumn is due to a deeper mean thermocline which weakens the impact of the thermocline movement on SST variation. The comparison between the model results and observations is not straightforward owing to the influence of model biases and the lack of a major MOC weakening event in the instrumental record. However, it is argued that the basic physical mechanisms found in the model simulations are likely to be robust and therefore have relevance to understanding tropical Atlantic variability in the real world, perhaps with modified seasonality. 相似文献
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Cari Zazo Norbert Mercier Pablo G. Silva Cristino J. Dabrio Jos Luis Goy Elvira Roquero Vicente Soler Francisco Borja Javier Lario Dolores Polo Luis de Luque 《Geomorphology》2005,68(3-4):269-290
The coastal evolution of the El Abalario area (Huelva, southern Spain) during the Late Pleistocene and Holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence (OSL) dating. New data come from the analysis of soft sediment deformation, palaeosols, geomorphological mapping, and published seismic surveys on the onshore and offshore Gulf of Cadiz.The present structure of El Abalario dome resulted from the complex interaction of littoral-catchment processes and sea-level changes upon an emergent coastal plain, conditioned by the upwarping of the underlying Pliocene–Pleistocene prograding deltaic sequence. Upwarping is probably related to escape of over-pressurized fluids, accompanied by dewatering, prior to (?) and during OIS (Oxygen Isotopic Stage) 5. Continued upwarping produced the large NW–SE gravitational fault of Torre del Loro (TLF) in the southwestern flank of the dome, roughly parallel to the present coastline during OIS 5–OIS 4. The resulting escarpment favoured the accumulation of aeolian sand dunes (units U1, U2, and U3) from OIS 5 to early OIS 1. Unit U1 (OIS 5) ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions. Unit U2 accumulated mainly during OIS 4 and OIS 3 with prevailing W/E winds. The supersurface between U2 and U3 records a part of OIS 2, with relative low sea level. Sedimentation of unit U3 took place during the Last Deglaciation (radiocarbon and OSL ages) with prevailing W/SW winds, under a temperate moist climate, that became more arid towards the top (Holocene). A major supersurface with an iron crust-like layer (SsFe) developed during the Holocene Climatic Optimum (OIS 1) under wetter and more temperate conditions than before, fossilizing the TLF. The supersurface is covered by younger aeolian dunes (U4, U5, U6, and U7) transported by W–SW winds since the Late Neolithic–Chalcolithic cultural period (5.0 ky cal BP). 相似文献
10.
Marta Martín-Rey Belén Rodríguez-Fonseca Irene Polo Fred Kucharski 《Climate Dynamics》2014,43(11):3163-3178
Atlantic and Pacific El Niño are the leading tropical oceanic variability phenomena at interannual timescales. Recent studies have demonstrated how the Atlantic Niño is able to influence on the dynamical processes triggering the development of the Pacific La Niña and vice versa. However, the stationarity of this interbasin connection is still controversial. Here we show for the first time that the Atlantic–Pacific Niños connection takes place at particular decades, coinciding with negative phases of the Atlantic Multidecadal Oscillation (AMO). During these decades, the Atlantic–Pacific connection appears as the leading coupled covariability mode between Tropical Atlantic and Pacific interannual variability. The mode is defined by a predictor field, the summer Atlantic Sea Surface Temperature (SST), and a set of predictand fields which represent a chain of atmospheric and oceanic mechanisms to generate the Pacific El Niño phenomenon: alteration of the Walker circulation, surface winds in western Pacific, oceanic Kelvin wave propagating eastward and impacting on the eastern thermocline and changes in the Pacific SST by internal Bjerknes feedback. We suggest that the multidecadal component of the Atlantic acts as a switch for El Niño prediction during certain decades, putting forward the AMO as the modulator, acting through changes in the equatorial Atlantic convection and the equatorial Pacific SST variability. These results could have a major relevance for the decadal prediction systems. 相似文献