Doppler sounder observations of trade winds and sea breezes along the African west coast near 34 ° S, 19 ° E

Summer weather conditions along the west coast of Africa near 34 ° S, 18 ° E are investigated using doppler acoustic sounder profiles. Case studies were selected from a two-year record to form composite analyses over the diurnal cycle. The SE trade wind exhibited a low level jet at the level of the temperature inversion due to a sharp reversal in the thermal wind vector aloft. Mean wind speeds reached 14 m s^–1 just before midnight as the surface and upper inversions strengthened. Seabreezes were categorised by the supporting gradient wind and found to have mean depths of 400 m, speeds of over 6 m s^–1 at the 200 m level, and advance/retreat times of 09 hr and 16–20 hr. During seabreezes and weak on-shore gradient flow conditions, the thermal internal boundary layer (TIBL) was monitored with sounder transects in the first 12 km of the coastal zone. The growth height was observed to be 1:20 in the first 5 km and 1:50 farther inland. The sounder climatology, together with surface network and aerial survey results, illustrate the four-dimensional characteristics of trade winds and seabreezes near Cape Town.     

Fisheries in upwelling regions — with special reference to peruvian waters

The anchovy population that is the basis of the Peru fishery, the world's largest, is a phytoplankton feeding species, supported by an upwelling based ecosystem. The fish is very short-lived and grows rapidly — both criteria for high turnover rate — high yield fisheries. The maximum sustainable yield is around 10 million metric tons. Analysis of the dynamics of the fishery suggests that the fleet is overbuilt, applying too much fishing effort, and slightly overfishing the population. In consequence, the population may be approaching a size and stress level at which it will be unstable.     

Geometric modelling of fades migration: theoretical development of f acies successions and local unconformities

Geometric analysis shows that the angle of migration of coastal sedimentary facies is a function of the relative sea-level change and the thickness of sediment deposited or eroded. The angle of facies migration compared to the slopes on the sediment surface determines the degree of facies preservation and stratigraphic relationships to the surrounding facies. Vertical facies successions generated by radial migration of environments show a great deal of variety because the sediment surface in both marine and non-marine areas is concave-up. Both regressive and transgressive sequences with non-erosive marine-nonmarine contacts can be generated. Transgression at a slightly lower angle can form a ravinement surface cut on non-marine deposits with onlapping barrier sands or shallow marine deposits. Regression with relative sea-level drop generates a minor erosion surface with baselapping isolated shoreline deposits. Disequilibrium conditions occur when sea level varies at a rate exceeding the ability of the system to supply or redistribute sediment, with resulting changes in surficial slopes. Onlapping and downlapping stratal relationships across erosion surfaces result because of differences in slopes between marine and non-marine environments. These discontinuities are generally less than one degree, but could possibly be recognized on high quality multichannel seismic lines. Most of these discontinuities are probably not regionally extensive enough to be regarded as sequence boundaries. Tectonic tilting or differential subsidence of strata during depositional hiatuses is necessary to generate true regional unconformities or sequence boundaries. Where facies climb with respect to horizontal, erosion surfaces produced only by this migration may cut across lithostratigraphic units at higher angles, up to 3 or 4 degrees. Low-angle erosion surfaces relevant to the scales of sequence stratigraphic studies may result only from facies migration, even during a period of relative sea-level rise.     

Framboidal pyrite associated with lead-zinc mineralisation in mid-Wales

Framboidal pyrite occurs in the breccia fragments of country rock found in lead-zinc veins, while it is generally absent from unmineralised rocks. It is thought to be cogenetic with the main mineralisation, representing an early stage of deposition.     

Biocrust landscape-scale spatial distribution is strongly controlled by terrain attributes: Topographic thresholds for colonization in a semiarid badland system

Biological soil crust, or biocrust communities, are the dominating life form in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analysed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LiDAR survey. Our results showed that the spatial distribution of cyanobacteria-dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas of high potential incoming solar radiation. The exception was bare south-aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen-dominated biocrusts, in contrast, colonized near the top of north-aspect hillslopes, characterized by low potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

The unusual and large drawdown response of buried-valley aquifers to pumping

The buried-valley aquifers that are common in the glacial deposits of the northern hemisphere are a typical case of the strip aquifers that occur in many parts of the world. Pumping from a narrow strip aquifer leads to much greater drawdown and much more distant drawdown effects then would occur in a sheet aquifer with a similar transmissivity and storage coefficient. Widely used theories for radial flow to wells, such as the Theis equation, are not appropriate for narrow strip aquifers. Previously published theory for flow to wells in semiconfined strip aquifers is reviewed and a practical format of the type curves for pumping-test analysis is described. The drawdown response of strip aquifers to pumping tests is distinctive, especially for observation wells near the pumped well. A case study is presented, based on extensive pumping test experience for the Estevan Valley Aquifer in southern Saskatchewan, Canada. Evaluation of groundwater resources in such buried-valley aquifers needs to take into account the unusually large drawdowns in response to pumping.     

Evaporative losses from soils covered by physical and different types of biological soil crusts

Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well‐developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils. Copyright © 2011 John Wiley & Sons, Ltd.