Constraining the timing of alluvial fan response to late quaternary climatic changes, southern Tunisia

The evolution of the Oued es Seffaia alluvial fan during the last 50,000 years is analyzed in the light of chronometric data derived from AMS radiocarbon and optical dating techniques. These ages have enabled the temporal constraint of the distalward progression of the intersection point (the upper limit of the locus of deposition) which has resulted in the telescopic segmentation of the fan. Comparison of these data with the Late Quaternary climatic history of the Maghreb highlights several problems of interpretation; due both to our limited knowledge of regional palaeoclimates and of the response of dryland fluvial systems to climate changes. However, our data provide some evidence to suggest that fan incision and formation of telescopic segments occurs in response to changes from arid to less arid conditions, supporting the conclusions of some of the work from other areas.     

Water resource conflicts in the Middle East

This article discusses the causes and sources of water resource conflict in the 3 major international river basins of the Middle East: the Tigris-Euphrates, the Nile, and the Jordan-Yarmuk. The physical geography of the Middle East is arid due to descending air, northeast trade winds, the southerly location, and high evaporation rates. Only Turkey, Iran, and Lebanon have adequate rainfall for population needs. Their mountainous geography and more northerly locations intercept rain and snow bearing westerly winds in winter. Parts of every other country are vulnerable to water shortages. Rainfall is irregular. Water resource conflicts are due to growing populations, economic development, rising standards of living, technological developments, political fragmentation, and poor water management. Immigration to the Jordan-Yarmuk watershed has added to population growth in this location. Over 50% of the population in the Middle East lives in urban areas where populations consume 10-12 times more water than those in rural areas. Water is wasted in irrigation schemes and huge dams with reservoirs where increased evaporation occurs. Technology results in greater water extraction of shallow groundwater and pollution of rivers and aquifers. British colonial government control led to reduced friction in most of the Nile basin. Now all ethnic groups have become more competitive and nationalistic. The Cold War restrained some of the conflict. Israel obtains 40% of its water from aquifers beneath the West Bank and Gaza. Geopolitical factors determine the mutual goodwill in managing international water. The 3 major water basins in the Middle East pose the greatest risk of water disputes. Possible solutions include conservation, better management, prioritizing uses, technological solutions, increased cooperation among co-riparians, developing better and enforceable international water laws, and reducing population growth rates.     

The Electrostatic Lunar Dust Analyzer (ELDA) for the detection and trajectory measurement of slow-moving dust particles from the lunar surface

Micron and submicron-sized dust particles can be lifted from the lunar surface due to continual micrometeoroid bombardment and electrostatic charging. The characteristics of these dust populations are of scientific interest and engineering importance for the design of future equipment to operate on the lunar surface. The mobilized grains are expected to have a low velocity, which makes their detection difficult by traditional methods that are based on momentum transfer or impact energy. We describe a newly developed instrument concept, the Electrostatic Lunar Dust Analyzer (ELDA), which utilizes the charge on the dust for detection and analysis. ELDA consists of an array of wire electrodes combined with an electrostatic deflection field region, and measures the mass, charge, and velocity vector of individual dust grains. The first basic prototype of the ELDA instrument has been constructed, tested and characterized in the laboratory. The instrument is set up to measure over a velocity range 1–100 m/s and is sensitive to particles from an approximate mass range from 2×10⁻¹⁶ to 10⁻¹¹ kg, depending on the charge state and velocity.     

The role of playas in pedogenic gypsum crust formation in the Central Namib Desert: a theoretical model

The formation of Namibia's extensive pedogenic gypsum crusts (CaSO₄·2H₂O) is interpreted in a new light. It is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration, such as inland playas, and that deflation of evaporitic‐rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricrusts on the coastal gravel plains of the Namib Desert surrounding these playas. This study establishes the nature, extent and distribution of playas in the Central Namib Desert and provides evidence for playa gypsum deflation and gravel plain deposition. Remote sensing shows the distribution of playas, captures ongoing deflation and provides evidence of gypsum deflation. It is proposed that, following primary marine aerosol deposition, both inland playas and coastal sabkhas generate gypsum which through the process of playa deflation and gravel plain redeposition contributes to the extensive pedogenic crusts found in the Namib Desert region. Copyright © 2001 John Wiley & Sons, Ltd.     

Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.