西藏羊八井热田地热流体成因及演化的惰性气体制约

地热流体中惰性气体的相对丰度和同位素组成，不仅可以揭露热田的热源性质，而且还能够揭示深，浅层地热流体的内在联系和演化过程等。在西藏羊八井热田的地热气体中，已检测出大量的^4He组分，3He/^4He值是大气的0．087－0．259倍，表明深部地壳物质的局部熔融为热田提供能量，浅层地热流体的3He/4He 值自西北向东南呈降低趋势，与热储温度的变化相一致，反映出侧向运移时补充了更多的壳源氦，热田北区深层地热流体具有稍高的3He/4He值，是浅层地热流体的母源，气体中氪和氙的相对丰度具有大气降水成因的特征，结合现有的实际资料，建立了热田地热流体的概念模型。     

Characterization of Damage in Sandstones along the Mojave Section of the San Andreas Fault: Implications for the Shallow Extent of Damage Generation

Following theoretical calculations that suggest shallow generation of rock damage during an earthquake rupture, we measure the degree of fracture damage in young sedimentary rocks from the Juniper Hills Formation (JHF) that were displaced 21 km along the Mojave section of San Andreas Fault (SAF) and were not exhumed significantly during their displacement. In exposures adjacent to the fault, the JHF typically displays original sedimentary fabrics and little evidence of bulk shear strain at the mesoscopic scale. The formation is, however, pervasively fractured at the microscopic scale over a zone that is about a 100 m wide on the southwest side of the SAF near Little Rock. The abundance of open fractures, the poor consolidation, and the shallow inferred burial depth imply that the damage was generated close to the surface of the Earth. The spatial correlation of this damage with a seismically active trace of the SAF suggests that it was generated by SAF slip events that by assumption were of a seismic nature throughout the displacement history of the JHF. Thus the JHF provides a very shallow upper bound for the generation of brittle damage in a seismic fault zone. The fracture fabric is characterized by preferred orientations of fractures that split grains between contact points and is consistent with overall deformation under directed compression. However, the available results cannot be used to distinguish between proposed off-fault damage mechanisms. Fracture orientations are compatible with a maximum compressive stress oriented at a high angle to the fault at about 10 m, and at a lower, more variable angle farther away from the fault. The fracture distribution and fabric are consistent with observations made of the microscale damage characteristics of the Hungry Valley Formation in the northwestern section of the SAF in the Mojave, and with previous observations of exhumed, ancestral strands of the SAF.     

Estimation of surface roughness (z0) over a stabilizing coastal dune field based on vegetation and topography

Accurate knowledge of the surface roughness and the resultant wind speed are important for many applications, such as climatic models, wind power meteorology, agriculture and erosion hazards, especially on sand dunes in arid and semi‐arid environments, where vegetation cover is scarce. In this study we aimed at quantifying the effects of vegetation cover and topography on surface roughness over a stabilizing dune field on the southern coast of Israel. Forty‐six wind measurements were made at various distances from the coastline, ranging from 10 to 2800 m, and z₀ values were calculated from the wind measurements based on the ratio between the wind gust and the average wind speed. We estimated vegetation cover using the soil adjusted vegetation index (SAVI) from Landsat satellite images for the upwind sector at various lengths, ranging from 15 to 400 m, and based on digital elevation models and differential GPS field measurements we calculated the topographic variable of the relative heights of the stations. z₀ values were positively correlated with the winter SAVI values (r = 0·87 at an upwind length of 200 m) and negatively correlated with the relative height (r = ?0·68 at an upwind length of 200–400 m for the inland dune stations). Using these variables we were able to create a map of estimated z₀ values having an accuracy of over 64%. Such maps provide a better understanding of the spatial variability in both wind speed and sand movement over coastal dune areas. Copyright © 2007 John Wiley & Sons, Ltd.     

Salinity-Temperature Relations and Morphotypes of a Mixed Population of Coccoid Cyanobacteria from a Hot, Hypersaline Pond in Israel

Abstract. A mixed population of unicellular and colonial cyanobacteria was transferred into culture from a hypersaline helio-thermal pond in the vicinity of the Dead Sea. The entire complex of strains, incubated in Dead Sea water of varying salinity and temperature, showed a pronounced shift of the maximal growth from a salinity of 72 g l^-1 at 30 ^oC up to 142 g 1^-1 at 50 ^oC. Over the above range of salinities and temperatures, these cyanobacteria were capable of about four divisions per day, providing that any increase in salinity was coupled with the suitable increase in temperature. The above peculiar adaptation can explain the prominent success of this group of microorganisms in the extreme and unstable ecological conditions of hypersaline habitats. Amounts of slime accumulating in the cultures were proportional to the incubation temperature.     

The Effect of Salinity and Temperature Gradients on the Distribution of Littoral Microalgae in Experimental Solar Ponds, Dead Sea Area, Israel

Abstract. Several species of cyanobacteria, diatoms and one euglenid alga populated the littoral zone of hypersaline solar ponds investigated over a period of three years. The composition of the microalgae community changed with salinity and temperature. In the shallow marginal zone the diatoms predominated in winter and spring, at salinities of 30–72 g-1^-1 and at temperatures not exceeding 30o°C, whereas in summer, cyanobacteria were the most abundant. In the deeper zone, at higher salinities and temperatures, cyanobacteria predominated throughout the year. The depth limit of algal growth was 60-80cm, where salinity and temperature exceeded 211 g-1^-1 and 48°C.
The most euryhaline and eurythermal among cyanobacteria were Aphanolhece halophytica F remy and Phormidium hypolimneticum C ampbell , among diatoms Nitzschia sp. aff. N. rostellata H ustedt , Amphora coffeaeformis (A gardh ) K utzing , and Navicula massadaea E hrlich .     

Stereotomography

The following paper presents a new exploration technique called stereotomography. Such a technique appropriately combines stereograms with data from borecores or from drillhole logs. Its purpose will be to show graphically the general trends of data for structural domains, for sectors, or for a whole mine. This method has been originally designed for discrete RQD measurements between boreholes, but it also has many other uses when RQD is substituted by any other physical or geophysical parameter related to the rock mass. In their example case, the authors found that such a so-called stereotomographic technique, supported by a complete structural geology study, will be decisive in the choice of potential mining sites, since it can delimit the discontinuity attitudes present inside the rock mass.     

The Cosmolian program for simulating aeolian dynamics and its application to central Australia

The wide spatial coverage of sand dunes in continental interiors makes the understanding of their activity and accumulation history valuable for palaeoenvironmental reconstructions and the interpretation of landscape evolution. Nevertheless, the study of aeolian landscape development at the million-year timescale is hampered by the complex interaction of factors determining dune migration and the inherently self-destructive nature of their chronostratigraphy, thus limiting the applicability of traditional dating methods. This study presents a standalone program that simulates aeolian transport based on luminescence-derived chronologies coupled with numerical modelling of the accumulation of cosmogenic nuclides. This integrative approach to modelling the history of aeolian landforms reveals phases of emergence of aeolian sand into the landscape, and provides a data-based scheme that facilitates the morphodynamical study of aeolian processes over multiple timescales and up to several millions of years. The application of the program for reanalysing previously reported data from the Australian Simpson Desert reveals multiple pulses of sand dispersion into central Australia at 3.8–3.4, 2.9–2.5 and 1.5–1 Ma, corresponding to pronounced changes in climatic conditions and landscape deformation events. The synchronicity of the results with the established environmental framework that would promote the production and aeolian distribution of sand exemplifies the applicability of process-based modelling in constructing a timeframe of key landscape evolution events in arid environments by studying aeolian deposits. The dependence of the parameters used to determine environmental settings on sand transportation patterns additionally makes the program a powerful tool to further investigate the triggers and mechanisms of aeolian processes.     

1971-2005年西藏主要农区农田蒸散量变化特征及其与环境因子的关系

利用1971—2005年西藏"一江两河"主要农区4个气象站点月平均最高气温、最低气温、降水量、风速、相对湿度、日照时数等资料,应用Penman-Monteith模型计算了农田蒸散量,分析其空间分布、年际和年代际变化特征,并讨论了影响蒸散量变化的气象因子.研究表明:近35a西藏主要农区年蒸散量表现为不同程度的减小趋势,为-16.5～-71.6mm.(10a)-1,以泽当减幅最大;四季蒸散量均呈现为减小趋势,以冬季减幅最明显.土壤水分年亏缺量呈明显的减少趋势,平均每10a减小59.6mm,特别是近25a(1981—2005年)减幅更明显.20世纪70年代至90年代年、季蒸散量均为逐年代减小趋势.90年代与80年代比较,主要农区各季土壤水分亏缺量都有不同程度的减小,尤其是夏季由亏缺转为盈余.日照时数和平均风速的显著下降,以及平均相对湿度的明显增加可能是蒸散量显著下降的主要原因,平均气温日较差的显著减小和降水量的增加在蒸散量减少趋势中也起着重要作用.     

Alpine wetlands in the Lhasa River Basin, China

The Lhasa River Basin is one of the typical distribution regions of alpine wetlands on the Tibetan Plateau. It is very important to get a better understanding of the background and characteristics of alpine wetland for monitoring, protection and utilization. Wetland construction and distribution in the basin were analyzed based on multi-source data including field investigation data, CBERS remote sensing data and other thematic data provided by 3S technology. The results are (1) the total area of wetlands is 209,322.26 hm2, accounting for 6.37% of the total land area of the basin. The wetlands are mainly dominated by natural wetland, with artificial wetland occupying only 1.09% of the wetland area; marsh wetland is the principal part of natural wetland, dominated by Kobresia littledalei swampy meadow which is distributed in the river source area and upstream of Chali, Damshung and Medro Gongkar counties. The ratio and type of wetlands in different counties differ significantly, which are widely distributed in Chali and Damshung counties (accounting for 62% of the total wetland area). (2) The concentrated vertical distribution of wetlands is at an elevation of 3600–5100 m. The wetlands are widely distributed throughout the Yarlung Zangbo River Valley from river source to river mouth into the Yarlung Zangbo River. Marsh wetland is dominant in the source area and upstream of the river, with the mosaic distribution of lakes, Kobresia littledalei and Carex moorcroftii swampy meadow, shrubby swamp and river; as for the middle-down streams, the primary types are river wetland and flooded wetland. The distribution is in a mosaic pattern of river, Kobresia humilis and Carex moorcroftii swampy meadow, Phragmites australis and subordinate grass marsh, flooded wetland and artificial wetland.