Sedimentological,geomorphological and dynamic context of debris-mantled glaciers,Mount Everest (Sagarmatha) region,Nepal

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. – 2008 Elsevier Ltd. All rights reserved.     

An overview of the Tennessee-Tombigbee Waterway

When the Tennessee-Tombigbee Waterway of Mississippi and Alabama opened to commercial and recreational traffic on January 16, 1985—some 21 months ahead of schedule—it signaled the completion of the largest Army Corps of Engineers Civil Works project ever undertaken, and perhaps the last of its kind After more than a century of studies and re-studies and major funding battles in Congress, the Tennessee-Tombigbee construction faced, predictably, great opposition on environmental grounds The first major project to be completed under the National Environmental Policy Act, it brought environmental design to the same level of prominence as engineering design.     

It's not all about wealth and beauty: Changing perceptions of fatness among Makola market women of Accra,Ghana

Within the African context, body shape preferences may be influenced by culture without necessarily taking into consideration health implications. Thus, fatness is culturally associated with beauty, prosperity, and prestige while thinness is perceived as a sign of ill‐health or poverty. Using a cross section of Makola market women, who traditionally are perceived as fat and affluent, our findings revealed that the perception of fatness as a sign of richness and beauty is changing due to women's access to knowledge and information on the health implications of fatness. The challenge for these women however, is adhering to healthy lifestyles despite living sedentary lives in the market place which is a conducive environment for one to become fat. We recommend that qualified professionals should encourage these women through continuous programmes on regenerative health and nutrition aimed at healthy lifestyle behaviour at the market places. The social groups that women belong to should be targeted, trained and equipped with the right information on healthy living so that they can disseminate this information to other members of their networks.     

Selenium in San Francisco Bay zooplankton: Potential effects of hydrodynamics and food web interactions

The potential toxicity of elevated selenium (Se) concentrations in aquatic ecosystems has stimulated efforts to measure Se concentrations in benthos, nekton, and waterfowl in San Francisco Bay (SF Bay). In September 1998, we initiated a 14 mo field study to determine the concentration of Se in SF Bay zooplankton, which play a major role in the Bay food web, but which have not previously been studied with respect to Se. Monthly vertical plankton tows were collected at several stations throughout SF Bay, and zooplankton were separated into two operationally defined size classes for Se analyses: 73–2,000 μm, and ≥2,000 μm. Selenium values ranged 1.02–6.07 μg Se g^?1 dry weight. No spatial differences in zooplankton Se concentrations were found. However, there were inter- and intra-annual differences. Zooplankton Se concentrations were enriched in the North Bay in Fall 1999 when compared to other seasons and locations within and outside SF Bay. The abundance and biovolume of the zooplankton community varied spatially between stations, but not seasonally within each station. Smaller herbivorous-omnivorous zooplankton had higher Se concentrations than larger omnivorous-carnivorous zooplankton. Selenium concentrations in zooplankton were negatively correlated with the proportion of total copepod biovolume comprising the large carnivorous copepodTortanus dextrilobatus, but positively correlatid with the proportion of copepod biovolume comprising smaller copepods of the family Oithonidae, suggesting an important role of trophic level and size in regulating zooplankton Se concentrations.     

The value of Pacific sardine as forage fish

This paper develops a simple bioeconomic model to investigate the economic and ecological issues associated with the commercial harvest of Pacific sardines relative to their value as forage for commercially, recreationally, and ecologically important predators in the California Current ecosystem. The model was used to evaluate how changes in the net per unit value of sardines, the net per unit value of sardine predators, and the transfer efficiency of predators affect the total net value of sardines, i.e. the net value of catches and the net value from sardine predation. Given recent market conditions for sardines and their commercial predators, and transfer efficiencies derived from predation data of the 1960s, it was found that the value of commercially caught predators and the efficiency by which they convert sardines to exploitable biomass were most important in determining the viability of the sardine fishery. The values assumed for predators that are not commercially caught were of no consequence under these conditions. Taking the value of sardines as forage into account does not necessarily mean an either-or situation for the fishery. As long as there is some measure of net value from the fishery and net value from predation, both benefit society at large.     

Experimental study of cohesive sediment consolidation and resuspension identifies approaches for coastal restoration: Lake Lery,Louisiana

The purpose of this study was to evaluate related processes of sediment consolidation and resuspension in a coastal basin and how these processes influence retention of fine sediment delivered by a river diversion. Sediment samples were collected from Lake Lery, a coastal receiving basin of the Caernarvon Diversion from the Mississippi River, Louisiana. Consolidation was tested for six initial sediment concentrations (14.0–105 kg m^–3) in a settling column over 15-day periods. Mud erodibility was tested at seven shear stress regimes (0.01–0.60 Pa) using a dual-core Gust erosion microcosm system, on cores containing suspensions that consolidated for 1, 2, and 4 weeks. Consolidation rates were found to be inversely and exponentially related to initial suspension concentration, over concentrations ranging from fluid mud (10–200 kg m^–3) to hydraulic dredge effluent. Consolidation is best predicted by a function consisting of two exponential terms and one asymptotic constant, describing rates of rapid initial and slower subsequent settling. Coupled resuspension and consolidation tests (concentrations of 20–21 kg m^–3) show that shear stresses generating the highest turbidity peaks increase from ≤0.30 Pa after 2 weeks of consolidation to ≥0.45 Pa after 4 weeks, and this strengthening cannot be attributed solely to increasing sediment concentration over time. Comparison of measured erosion shear stresses with bed shear stresses typical of coastal lakes and bays suggests that this degree of strengthening, if given time to occur, could increase the overall retention of fine sediments deposited on lake and bay floors.     

Contourites in the Gulf of Cadiz: a cautionary note on potentially ambiguous indicators of bottom current velocity

Facies associations in cores collected in the deep part of the Gulf of Cadiz, which is under the influence of the lower branch of the Mediterranean Outflow Water, are investigated in terms of the classical contourite model using grain-size analyses and thin sections of indurated sediment. Cores include both low-energy (contourite drift) and high-energy (channel) environments. The thin sections and grain-size distributions show that clayey fine silts and sandy coarse silts are the most common facies associations in the studied contourite sequences, while coarse-grained, gravelly contourites are less common. Grain-size distributions are unimodal in the fine-grained and bi- or trimodal in the coarser-grained contourites. This change in grain-size composition is related both to the partial removal of the fine-grained fraction and to the replenishment of the coarser-grained one. In addition, most of the contacts between individual facies are sharp rather than transitional. This suggests that the contourite sequence is only in part related to changes in bottom current velocity and flow competency, but may also be related to the supply of a coarser terrigeneous particle stock, provided by either increased erosion of indurated mud along the flanks of confined contourite channels (mud clasts), or by increased sediment supply by rivers (quartz grains) and downslope mass transport on the continental shelf and upper slope. The classical contourite facies association may therefore not be solely controlled by current velocity, but may be the product of a variety of depositional histories. The classical contourite depositional sequence should therefore be interpreted with greater care and in the light of the regional sedimentological background. In addition, the wisdom of exclusively using mean or modal particle size for the interpretation of depositional contourite processes is questioned. Instead, it is proposed that the vertical evolution of grain-size populations in the facies successions forming contourite sequences be assessed.     

NIGHT-FROST MODULATION OF NEAR-SURFACE SOIL-WATER ION CONCENTRATION AND THERMAL FIELDS

The modulation of the soil-water ion concentration and thermal fields resulting from night frost is illustrated with data from temperature-electric potential probes in the upper 15 cm of a sandy loam soil. The relative soil-water ion concentration, calculated from soil electric potential observations, aids in the detection of these modulation effects produced by non-conductive heat-mass transfer processes. The apparent thermal diffusivity, calculated from soil-temperature data, further facilitates the detection and analysis of these non-conductive processes. This new technology demonstrates the distorting effects of soil-water advection to the freezing zone, “ice purification” of soil water in the freezing zone and other coupled mass-heat transport effects produced by night frost. The conversion of electric potential observations to a relative index of soil-water ion concentration and the calculation of the apparent thermal diffusivity from the temperature data matrix are demonstrated as effective methods for the detection and analysis of the magnitude and direction of coupled-flow processes. [Key words: electric potential, frost, soil chemistry, soil temperature, thermal diffusivity.]     

Simulation des changements climatiques au cours du XXIe siècle incluant l'ozone stratosphériqueSimulation of climate changes during the 21st century including stratospheric ozone

Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154.