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CHRISTOPHER S. ROMANEK EUGENE C. PERRY ALLAN H. TREIMAN RICHARD A. SOCKI JOHN H. JONES EVERETT K. GIBSON 《Meteoritics & planetary science》1998,33(4):775-784
Abstract— Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and 18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette. Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ～90% separate. Based on these measurements, end-member iddingsite has a δ18O of 15.6%, which places it among other 18O-enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (～11%) is typical of low-temperature alteration products. A range of crustal fluid δ18O values can be interpreted from the δ18O for end-member iddingsite, assuming isotopic equilibrium was achieved during low-temperature hydrous alteration (<100 °C; Treiman et al., 1993). The calculated range of values, ?15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O-bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO2-carbonate-iddingsite-H2O system at low temperature. The SNC meteorite samples in this study have Δ17O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ17O of ～1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ17O is similar in direction to Δ17O reported for waters extracted from bulk samples of Lafayette (Karlsson et al., 1992). If the Δ17O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago. 相似文献
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Abstract The uncertainties arising from the problem of identifying a representative model structure and model parameters in a conceptual rainfall-runoff model were investigated. A conceptual model, the HBV model, was applied to the mountainous Brugga basin (39.9 km”) in the Black Forest, southwestern Germany. In a first step, a Monte Carlo procedure with randomly generated parameter sets was used for calibration. For a ten-year calibration period, different parameter sets resulted in an equally good correspondence between observed and simulated runoff. A few parameters were well defined (i.e. best parameter values were within small ranges), but for most parameters good simulations were found with values varying over wide ranges. In a second step, model variants with different numbers of elevation and landuse zones and various runoff generation conceptualizations were tested. In some cases, representation of more spatial variability gave better simulations in terms of discharge. However, good results could be obtained with different and even unrealistic concepts. The computation of design floods and low flow predictions illustrated that the parameter uncertainty and the uncertainty of identifying a unique best model variant have implications for model predictions. The flow predictions varied considerably. The peak discharge of a flood with a probability of 0.01 year?1, for instance, varied from 40 to almost 60 mm day?1. It was concluded that model predictions, particularly in applied studies, should be given as ranges rather than as single values. 相似文献
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AMY MILLS 《Geographical review》2005,95(3):441-462
ABSTRACT. Since the foundation of the Turkish Republic in 1923, when the Turkish nation was defined as ethnically Turkish and Muslim, the issue of ethnic minorities has been at the root of a deep insecurity concerning cultural identity and what it means to be Turkish. The movement to “recover” ethnic minority in history and in place is most visible in Istanbul, the city identified as the location of European culture in Turkey and Turkey's most culturally pluralistic city. The movement has gained pace since the formal acceptance of Turkey as a candidate for membership in the European Union and the push for reforms in human rights. It is promoted by a very small cultural and economic elite and works together with gentrification to produce elite spaces in the city, as exemplified by two neighborhoods: Kuzguncuk, a historic minority neighborhood on the Asian shore of the Bosporus; and “French Street,” a new commercial development in Beyoǧlu, on the European side of the city west of the Bosporus. These landscapes articulate a European, cosmopolitan, and multicultural place identity for Istanbul and reflect a particular notion of Turkey as modern and European, providing insight into the contemporary debate in Turkey concerning the tensions embedded at the core of Turkish cultural identity. 相似文献
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The fractal dimension of relative lagrangian motion 总被引：1，自引：0，他引：1
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L. ALLAN JAMES 《地球表面变化过程与地形》1996,21(5):413-432
An empirical evaluation of glacial trough cross-section shape is performed on seven vertical cross-sections in three Sierra Nevada valleys glaciated during the late Quaternary. Power and second-order polynomial functions are fitted by statistical regression. Power functions are very sensitive to subtle valley-bottom topographic features and require precise specification of the valley-bottom-centre location. This dependency is problematic given under-representation of valley bottoms by conventional contour-sampling methods, and the common alteration of valley-bottom morphology by non-glacial processes. Power function exponents vary greatly in response to these and other non-genetic factors and are not found to be reliable indicators of overall valley morphology. Second-order polynomials express overall valley shape in a single robust function. They are applied to both bedrock- and sediment-floored glacial valleys with negligible statistical bias except where side-slopes are stepped or convex-upward or where valley form is asymmetrical. They can describe alluviated or severely eroded valleys, and can objectively identify indi-vidual components of polymorphic valleys, because valley bottom and centre locations need not be specified. Mathematical expressions of parameters useful for geomorphic measurements and glaciological modelling are analytically derived from the polynomials as functions of the three polynomial coefficients. These parameter equations provide estimates of valley side-slopes, mean and maximum depth, midpoint location, width, area, boundary length, form ratio and symmetry. 相似文献
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Chunlei LIU Yazhu YANG Xiaoqing LIAO Ning CAO Jimmy LIU Niansen OU Richard P.ALLAN Liang JIN Ni CHEN Rong ZHENG 《大气科学进展》2022,39(11):1941-1955
The change in ocean net surface heat flux plays an important role in the climate system. It is closely related to the ocean heat content change and ocean heat transport, particularly over the North Atlantic, where the ocean loses heat to the atmosphere, affecting the AMOC(Atlantic Meridional Overturning Circulation) variability and hence the global climate.However, the difference between simulated surface heat fluxes is still large due to poorly represented dynamical processes involving multisca... 相似文献
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Organic sediments exposed in a seacliff near Kalaloch, Washington, contain abundant, well-preserved beetle remains. Fossil assemblages dating from about 48 000 to 40 000 yr BP are dominated by species typical of the lowland and montane forests in the region today. A few species, Micropeplus laticollis, Olophrum consimile, Olophrum boreale, Arpedium cribratum, and Tachinus thruppi are presently not members of the Pacific Northwest fauna. Mean July temperature during this part of the Middle Wisconsinan is estimated to have been about 1°C lower than today. Later Wisconsinan assemblages are dominated by non-arboreal species, indicating a treeless, probably tundra environment. Mean July temperature based mostly on the occurrence of the alpine leaf-beetle species, Asiorestia pallida, is estimated to have been at least 3°C lower than the present day. Palaeoclimatic interpretations based on beetles are in good agreement with those based on pollen. 相似文献