Late Holocene vegetation changes in Greenwater Valley,Mojave Desert,California

Small-scale late Holocene vegetation changes were determined from a series of 13 modern and fossil packrat middens collected from a site in the Greenwater Valley, northern Mojave Desert, California. Although the site is above the modern lower limit of Coleogyne ramosissima (black-brush), macrofossils of this shrub are only present in samples younger than 270 yr B.P. In order to measure changes more subtle than presence vs absence, macrofossil concentrations were quantified, and principal components and factor analyses were used to distinguish midden plant assemblages. Both the presence/absence data and the statistical analyses suggest a downward shift of 50 to 100 m for Coleogyne (blackbrush) communities between 1435 and 1795 A.D.     

A general radar equation for the bistatic acoustic sounder

A radar equation which can be applied to any bistatic acoustic sounder is derived. The equation reduces to the expression normally used for the special case of the monostatic sounder. Numerical results using this equation are given for specific acoustic sounders, including the relative contributions to the scattering from the temperature and velocity parameters (C _T ² and C _V ²), the effect of wind speed on the scattered intensity and the measurement of horizontal wind velocity.Now with the Department of Electrical and Electronic Engineering, Portsmouth Polytechnic, Anglesea Road, Portsmouth PO1 3DJ.     

Futher reflections on the Isimila Acheulian

Uranium series dates on bone from the Isimila Prehistoric Site, Tanzania, indicate that this East African Acheulian site may be older than originally estimated. They raise the possibility that the Middle Pleistocene sediments containing Acheulian occurrences span a longer range of time than had been supposed. This could add to the plausibility of a contention by Hansen and Keller that differences between artifacts in the uppermost Acheulian horizon and in lower-lying beds are primarily a reflection of change through time rather than a result of different human activities.A summary of the artifact content and associations of the several archeological stratigraphic units is given, and, although a sort of “developmental sequence” can be seen, the existence of discrepant occurrences suggests that an interpretation of directional change as a “function of time” does not, in fact, well accommodate the evidence.Quantitative changes in artifact class proportions in aggregates seem just as likely to be related to local exploitation potentials for early man which were produced during the process of basin in-filling, while observed qualitative differences in the lower-lying horizons may be due to samples biased because of limited exposures which are restricted to a single sedimentary environment.     

Internal migration in Peru

"E. G. Ravenstein proposed 'laws of migration' to explain the movement of population in the British Isles from data in the 1881 census. Here, migration in Peru is studied using data from the 1981 census to ascertain the extent to which Ravenstein's 'laws' hold for a different country at a different time.... In conclusion, it is a salutory exercise to apply Ravenstein's seven laws and other findings to Peru and to see how, in a different environment a good time ago, someone could produce a model with wide applicability."     

Sensitivity of the global atmospheric cycle of mercury to emissions

A systematic investigation of the impact of current uncertainties in Hg emissions from specific source categories on global air Hg concentrations is presented. First, the uncertainties in different emission source categories are discussed and then the results of a base simulation and three sensitivity simulations conducted with a global chemical transport model for mercury (CTM-Hg) are presented. The total Hg emissions in the four scenarios range from 6600 to 9400 Mg/a. The sensitivity studies investigate the impact of the range in uncertainty in natural emissions, emissions of previously deposited Hg, and anthropogenic emissions both in China and worldwide, while taking into account constraints imposed by available data (current/pre-industrial emission ratio of 2–4). In one case, natural emissions and emissions of previously deposited Hg were changed to represent a mid point of the range of values found in the literature. This lead to a 16% increase in background emissions, i.e., natural emissions and emissions of previously deposited Hg combined. Increasing natural emissions by 16% or Chinese anthropogenic emissions by 100% yielded atmospheric Hg concentrations comparable with those measured across the globe without any changes to the atmospheric chemistry. Increasing natural emissions and emissions of previously deposited Hg by 16% and all anthropogenic emissions by 100% as compared to the base scenario yielded atmospheric Hg concentrations that were not compatible with measurements and changes in the chemical behavior of Hg in the atmosphere would be required to yield results that are consistent with observed Hg concentrations. The current uncertainty in total Hg emissions at the global scale is placed at about a factor of two.     

Geotechnical and mineralogical characteristics of marl deposits in Jordan

Marls and marly limestone deposits cover most of Northern Jordan, where Amman City and its suburbs are located. These deposits serve as foundations for most buildings and roads as well as fill material for structural back filling, especially road bases and sub-bases. The present study aims at investigating the geotechnical characteristics and mineral composition of the marl units of these deposits through field investigations and laboratory testing. Using X-ray diffraction technique along with chemical analysis, representative samples of marl horizons were tested for mineral composition, and for a set of index and geotechnical properties including: specific gravity, grain size, Atterberg limits, Proctor compaction and shear strength properties. The test results show a positive linear relationship as expected between the clay content and both liquid and plastic limits. The tests results also show an inverse linear relationship between the clay content and the maximum dry density in both standard and modified compaction. This is attributed to the adsorption of water by the clay minerals. The relationship is more prominent in the case of modified compaction test. The results also indicate a similar relationship for the angle of internal friction. No clear correlation between cohesion and clay content was apparent.     

Lithological controls on biological activity and groundwater chemistry in Quaternary sediments

Depth profiles of solute chemistry and sulfate isotopic compositions are presented for groundwater and pore water in a sequence of Quaternary glacial outwash sediments. Sand units show evidence for hydraulic connection to the surface and thus modern sources of solutes. Finer‐grained sediments show a general pattern of increasing solute concentrations with depth, with sulfate derived from ancient rainwater and pyrite oxidation in the soil/drift. In these sediments sulfate has undergone bacterial sulfate reduction (BSR) to produce biogenic sulfide. In clay sediments, with d₁₀ ≤ 1·6 µm, high concentrations of sulfate and acetate now co‐exist, implying that BSR is inhibited. The correlation with smaller sediment grain size indicates that this is due to pore size exclusion of the sulfate reducing bacteria. Mechanical restriction of microbial function thus provides a fundamental limitation on microbial respiration in buried clay‐rich sediments, which acts as a control on the chemical evolution of their pore waters. Copyright © 2009 John Wiley & Sons, Ltd.