Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

Late Quaternary histories of two North American desert biomes—C₄ grasslands and C₃ shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C₄ grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial–interglacial cycle. By contrast, key C₃ desert shrubs appeared somewhat abruptly after 5000 cal. yr BP. Bioclimatic envelopes for select C₄ and C₃ species are mapped to interpret the glacial–interglacial persistence of desert grassland and the mid‐to‐late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C₄ grasses, whereas winters were probably too cold (or too wet) for C₃ desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial–interglacial cycle. Mid‐latitude effects, however, truncated midsummer (July–August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000 cal. yr BP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño–Southern Oscillation variability. Published in 2006 by John Wiley & Sons, Ltd.     

Lake Area Changes and the main causes in the hinterland of Badain Jaran Desert during 1973–2010,China

Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics of lake area changes during 37 years. Results indicated that the nttmber of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km2 during 1973-2010. The desert lake area reduced by different degrees in different periods, but this occurred most rapidly during 1973-1990. According to the statistics of lake area changes, lake area decreases mainly occurred in the lakes with areas less than 0.2 km2, while the areas of lakes greater than 0.9 km2 only fluctuated. The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.     

Runoff generation and sediment yield on homogeneous dune slopes: scale effect and implications for analysis

Data concerning runoff and sediment yield in arid zones is of prime importance for hydrologists, geomorphologists, pedologists, ecologists and landscape engineers. For data comparison and extrapolations, runoff and sediment yield are often presented in mass per unit area. Runoff and sediment yield collected on dune slopes over a wide range of plot sizes during 1990–1994 in the Negev Desert, Israel, showed that the contributing area was mainly confined to a narrow belt at the bottom of the slopes. It was therefore hypothesized that the very short rain bursts, capable of runoff generation, may result in a scale effect (SE). Indeed, average duration of duration of consecutive medium and high rain intensities which are potentially above the surface infiltration rate ranged between 2.2 and 3.0 minutes, implying that flow connectivity is largely limited. Based on the intermittent character of the rain spells capable of runoff generation it is argued that SE is an inherent outcome of the rain properties. Yet, it is further argued that the magnitude of the SE is surface‐dependent. As a result, it is argued that the conventional way for runoff and sediment yield presentation as mass per unit area implies theoretical misconceptions and may cause gross overestimation in extrapolation and the presentation of runoff and sediment yield in mass per unit width of the slope is suggested. The accuracy of the two extrapolation methods are compared to the actual runoff and sediment yield collected in the field. The data show that extrapolation based on runoff (or sediment) yield per plot width deviates from the actual amounts collected by a factor of 1·1 to 1·3 only while deviating by a factor of 4·2 to 5·6 and 10·7 to 11·8 if the extrapolation is based on large and small plots, respectively. Theoretical and practical reasons for presentation of runoff and sediment yield as mass per unit width are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

The characteristics of aeolian sediment flux profiles in the south‐eastern Tengger Desert

Deserts are one of the most important dust sources in the world. Because dust content changes as a function of height at low levels in the atmosphere, this affects long‐term dust transport. In this paper, field data measured above shifting sands in the south‐eastern Tengger Desert were used to analyse the vertical distribution of sediment fluxes in the near‐surface layer (0 to 48 m). It was possible to express horizontal sediment flux as a power function, but aeolian deposition as a function of height could be expressed as an exponential function. There are two curve types for the particle size distributions in the horizontal sediment flux and aeolian deposition: bimodal and unimodal curves. For the horizontal sediment flux and aeolian deposition, heights of 24 m and 32 m, respectively, were the key heights in the size distribution curve; below these heights, the curve was bimodal, whereas above these heights, it was unimodal. At heights of 4 to 16 m, and especially between 8 m and 12 m, the data were particularly interesting because the sediment size, transport mode, degree of sorting, and the skewness and kurtosis change. For the horizontal sediment flux, wind turbulence moved saltating particles higher than expected.     

Palynology and genetic sequence stratigraphy of the reservoir rocks (Cenomanian,Bahariya Formation) in the Salam Oil Field,north Western Desert,Egypt

Twenty-eight samples from the Bahariya Formation of the Salam-17 Well in the north Western Desert were palynologically investigated. These samples are of Cenomanian age. Fair diversity and fair to moderately preserved palynomorph assemblage has been recovered. Among them, the dinoflagellate cysts showed very poor diversity and abundance. Four miospore zones have been informally identified in the lower Cenomanian. Various palynofacies criteria, adopted from previous publications (e.g. relative particle abundance data, brown to black wood ratio, equi-dimensional to lath-shaped black wood ratio, average size of phytoclasts and spores/pollen ratio) are applied as alternative indicators to monitor the proximal–distal trends instead of the marine palynomorphs-based parameters. The method can be applied in the Egyptian Western Desert to overcome the rarity and absence of dinoflagellate cysts in the recovered organic residues. The palynofacies study of the section demonstrates a predominantly regressive phase, characterized by deltaic, distributary or tidal channels, interrupted by short-lived marine incursions. The palynofacies trends within the studied succession indicate six genetic sequences informally described as Genetic Stratigraphic Sequences A through F.     

The Meandu Creek Bentonite,Queensland

New data on the source of sands found in desert alluvia and adjacent dunes have led to a revival of the suggestion that the sand ridges of the Australian dunefields, and specifically those of the Great Victoria and Simpson Deserts, are predominantly of erosional origin. In this paper, geological and morphological evidence are cited against this wind rift hypothesis. In the Great Victoria Desert several arguments put for a local derivation of dune sand are incompatible with regional and local geology. In the Simpson Desert, the distribution, shape and colour of dunes, and the topographic relation of dunes to substrates argue against an erosional origin. Long‐distance transport of sand from numerous local depocentres and under a bidirectional wind regime better accounts for the field evidence.     

Positive Ion Contained in Tamarix Cone Sedimentary Veins and Climatic and Environmental Change in Southern Region of Taklimakan Desert

Based on the research on Tamarix cone sedimentary veins in three different places which are Andier Ancient City, Andier Meadow, and Damagou Township in the southern region of the Taklimakan Desert, the relationship between the characteristics of the positive ion content in Tamarix fallen leaves and climatic change during the past 400 years is systematically analyzed. The results show: the order of four kinds of positive ion content’s change range in three sampling sites is Ca²⁺> K⁺> Mg²⁺> Na⁺. The correlation coefficient between Ca²⁺ content and the total positive ion content is higher, which indicates that Ca²⁺ content or the total positive ion content can reflect the change trends. There is an inverse correlation between positive ion content in Tamarix fallen leaves and the local temperature. According to the change of positive ion content, the climate in the southern region of the Taklimakan Desert can be divided into cold and warm periods during the past 400 years, among which the period of 1590-1691 is warm period, of 1692-1896 is cold period (warm fluctuations are 1799-1808,1825-1829,1878-1881,1887-1891), of 1897-2010 is warm period (cold fluctuations are 1939-1941,1992-1998); Precipitation has a poor correlation with the positive ion content; There is a better correspondence between the changes of positive ion content and the regional flood events. This research provides a kind of research method for the environmental evolution in the southern region of the Taklimakan Desert,and it is of great help to environmental change research of the arid desert regions. It has further perfected the feasibility of using positive ion content in Tamarix cone sedimentary veins to reveal the environmental change, and fills up the blank of high resolution climatic change during the past 400 years in the southern region of the Taklimakan Desert.     

Mapping the distribution of the main host for plague in a complex landscape in Kazakhstan: An object-based approach using SPOT-5 XS,Landsat 7 ETM+, SRTM and multiple Random Forests

Plague is a zoonotic infectious disease present in great gerbil populations in Kazakhstan. Infectious disease dynamics are influenced by the spatial distribution of the carriers (hosts) of the disease. The great gerbil, the main host in our study area, lives in burrows, which can be recognized on high resolution satellite imagery. In this study, using earth observation data at various spatial scales, we map the spatial distribution of burrows in a semi-desert landscape.The study area consists of various landscape types. To evaluate whether identification of burrows by classification is possible in these landscape types, the study area was subdivided into eight landscape units, on the basis of Landsat 7 ETM+ derived Tasselled Cap Greenness and Brightness, and SRTM derived standard deviation in elevation.In the field, 904 burrows were mapped. Using two segmented 2.5 m resolution SPOT-5 XS satellite scenes, reference object sets were created. Random Forests were built for both SPOT scenes and used to classify the images. Additionally, a stratified classification was carried out, by building separate Random Forests per landscape unit.Burrows were successfully classified in all landscape units. In the ‘steppe on floodplain’ areas, classification worked best: producer's and user's accuracy in those areas reached 88% and 100%, respectively. In the ‘floodplain’ areas with a more heterogeneous vegetation cover, classification worked least well; there, accuracies were 86 and 58% respectively. Stratified classification improved the results in all landscape units where comparison was possible (four), increasing kappa coefficients by 13, 10, 9 and 1%, respectively.In this study, an innovative stratification method using high- and medium resolution imagery was applied in order to map host distribution on a large spatial scale. The burrow maps we developed will help to detect changes in the distribution of great gerbil populations and, moreover, serve as a unique empirical data set which can be used as input for epidemiological plague models. This is an important step in understanding the dynamics of plague.     

Quitovac Oasis: A Sense of Home Place and the Development of Water Resources

Agricultural development at Quitovac, a Sonoran Desert oasis that is an ancestral home of the Tohono O’odham people, was first interpreted in the literature as a typical example of an indigenous community succumbing to the economic pressures of industrial society. However, a humanistic analysis of the cultural and historical context and the results of ethnographic fieldwork leads to a radically different interpretation of recent community actions. Community-initiated institutional and economic changes can be understood as creative and resilient adaptations, and perhaps a resolution, to a complex social and religious challenge to the community’s identity. Notwithstanding the economic failure of part of the development efforts, the overall effects are interpreted as strengthening the residents’ sense of their home place and ensuring the continuation of religious rites associated with this sacred place.     

巴丹吉林沙漠典型沉积物年代学研究评述

巴丹吉林沙漠内几种典型近地表沉积物,如风成沙、湖相沉积、冲洪积物等构成了巴丹吉林沙漠复杂多变的地貌景观.这些典型沉积物的年龄是探讨巴丹吉林沙漠地貌过程及其机理的最直接证据和基础数据.前人发表的这几种典型沉积物年龄,主要涉及380余个14C年龄和释光年龄,这些数据涵盖了170 ka至今的大部分时段.其中12 ka以来年龄...