Estimating hydrological characteristics in the Amu Darya River basin under climate change conditions

Under consideration are results of solving the problem of the river water content estimation under conditions of uncertainties of climate change forecasts and the catchment state with a reference to the Amu Darya River basin. When constructing regional climate models, one selected a multimodel approach using the results of several global models and a statistical downscaling method that made the climate scenarios more detailed. The estimates demonstrated that in the medium- and long-term perspective, the Amu Darya River runoff is expected to decrease. As a result of the Bayesian ideology application, using the calculations got with a total probability formula, a prognostic probability curve of an annual river runoff supply of the basin rivers was derived based on different weights given to the estimates of a mean value for different climate scenarios. Prognostic characteristics of the annual runoff for the Amu Darya basin rivers are estimated in a form acceptable for hydrologic and hydroeconomic application.     

Remittances and migration--the commerce of movement

"This paper comments upon the role of remittances in a variety of emigrant situations, traces the way remittance patterns change over time and evaluates the importance of remittance payments for personal and national economies. It considers the concept of 'remittance-societies" in the South Pacific and elsewhere, and briefly examines the various mechanisms involved in the emigration-remittance cycle, including the expectation of interactions and interdependence that exists between migrants and their home-based kin, and the sacrifices and hardships often endured by many migrants to meet obligations back home."     

The effect of sea-ice extent in the North Atlantic on the stability of the thermohaline circulation in global warming experiments

Different climate models simulate different behavior of the Atlantic meridional overturning circulation (MOC) under the same global warming scenario. We propose a plausible explanation for this and argue that a proper simulation of the present-day climate in the subpolar North Atlantic is important. This is illustrated using results from idealized global warming experiments, in which both the radiative forcing scenario and the model employed are the same, with the only major difference being the initial subpolar North Atlantic climate. The initial conditions are made progressively colder, with more extensive sea-ice cover in the northern North Atlantic.The key result is that starting from conditions which are too cold in the North Atlantic and with sea-ice that is too extensive leads to an MOC that is more stable to the radiative forcing. Furthermore, under considerably underestimated sea surface temperatures in subpolar regions, the MOC can even intensify. A reduction of freshwater flux associated with the reduction of sea-ice melt is shown to be important for such unusual behavior of the MOC. Other mechanisms are also considered, but not deemed as important in explaining published inter-model differences.     

高效液相色谱-等离子体质谱技术在溴元素形态分析中的应用

溴是一种在自然水体中都含有的元素,通常以B r-的形式存在。目前最常用的水净化方式就是向水中通入臭氧以杀灭细菌;而臭氧分解的副产物即为B r-转换成的B rO3-,这是一种公认的致癌物质。本实验室曾使用阴离子交换高效液相色谱(HPLC)与等离子体质谱(ICP-MS)联用分析B rO3-和B r-,方法虽能有效地将这两种溴形态分离,但分析每个样品需8 m in。本文试图建立新的方法缩短分析时间,并验证该方法应用于实际水样分析时测定其他含溴化合物的能力。1实验部分1.1高效液相色谱分析条件表1列出了等度淋洗和梯度淋洗两种模式下HPLC的分析条件,完成形态的分离。等度淋洗和梯度淋洗在分析中显示出不同     

地球内核粘滞度的动力学估计

最新的地震学研究指出,地球的内核正在对地球的其余部分作相对旋转。根据数值模拟,这一情形可能是由在液态外核中正在作对流运动的流体所保持。另一方面,由于地幔中质量分布的不均匀,巨大的引力将足以便内核与地幔相匹配。内核的不同旋转会通过在旋转时对自身形状的调整民这些强大的引力保持一致,进面可得出在地球最内部区域内有效粘滞度的一个估计。由推测的旋转率得到的内核粘滞度为小于１０＾１６Ｐａ或大于１０＾２０Ｐａ。     

闽江口外海域MIS 5和MIS 3的地震地层学特征和古环境

通过闽江口外海域进行的高分辨率浅地震剖面(拖筏)调查,揭示了MIS 6末期以来最大厚度约90 m的沉积地层。研究了MIS 5和MIS 3地震层序的反射波结构特征,基于地震相分析识别沉积地貌类型;结合深海氧同位素海平面变化曲线,阐述了两时期研究区的沉积环境、特殊地貌的分布和体系域阶段;最后简要探讨了海侵视强度(视高度)及其影响因素。在MIS 5,研究区主要为滨浅海环境,在MIS 5.3和MIS 5.1局部发育了赛江水下三角洲、潮流沙脊和滨海沙坝等沉积地貌;在初期和低海面亚期为陆相环境,发育了闽江和赛江河道,分别经南部和东北部向东入海(台湾海峡)。在MIS 3,研究区普遍为海水覆盖,以滨浅海环境为主,局部发育闽江水下三角洲叶瓣和潮流沙脊。MIS 5的海平面远高于MIS 3,但是典型地震剖面的研究表明,前者的海侵视强度(视高度)低于后者,推断这一现象主要与构造沉降有关,沉积物压缩也有一定的影响,这也可以解释南部海区MIS 5.2的古闽江河道要远低于当时海平面的现象。     

VARIABILITY IN THE CHEMICAL COMPOSITION OF IN SITU SUBGLACIAL MELTWATERS

Meltwaters collected from boreholes drilled to the base of the Haut Glacier d'Arolla, Switzerland have chemical compositions that can be classified into three main groups. The first group is dilute, whereas the second group is similar to, though generally less concentrated in major ions, than contemporaneous bulk glacial runoff. The third group is more concentrated than any observed bulk runoff, including periods of flow recession. Waters of the first group are believed to represent supraglacial meltwater and ice melted during drilling. Limited solutes may be derived from interactions with debris in the borehole. The spatial pattern of borehole water levels and borehole water column stratification, combined with the chemical composition of the different groups, suggest that the second group represent samples of subglacial waters that exchange with channel water on a diurnal basis, and that the third group represent samples of water draining through a ‘distributed’ subglacial hydraulic system. High NO⁻₃ concentrations in the third group suggest that snowmelt may provide a significant proportion of the waters and that the residence time of the waters at the bed in this particular section of the distributed system is of the order of a few months. The high NO⁻₃ concentrations also suggest that some snowmelt is routed along different subglacial flowpaths to those used by icemelt. The average SO²⁻₄: (HCO⁻₃ + SO²⁻₄) ratio of the third group of meltwaters is 0.3, suggesting that sulphide oxidation and carbonate dissolution (which gives rise to a ratio of 0.5) cannot provide all the HCO⁻₃ to solution. Hence, carbonate hydrolysis may be occurring before sulphide oxidation, or there may be subglacial sources of CO₂, perhaps arising from microbial oxidation of organic C in bedrock, air bubbles in glacier ice or pockets of air trapped in subglacial cavities. The channel marginal zone is identified as an area that may influence the composition of bulk meltwater during periods of recession flow and low diurnal discharge regimes. © 1997 by John Wiley & Sons, Ltd.     

Footwall dip of a core complex detachment fault: thermobarometric constraints from the northern Snake Range (Basin and Range,USA)

Low‐angle detachment faults are common features in areas of large‐scale continental extension and are typically associated with metamorphic core complexes, where they separate upper plate brittle extension from lower plate ductile stretching and metamorphism. In many core complexes, the footwall rocks have been exhumed from middle to lower crustal depths, leading to considerable debate about the relationship between hangingwall and footwall rocks, and the role that detachment faults play in footwall exhumation. Here, garnet–biotite thermometry and garnet–muscovite–biotite–plagioclase barometry results are presented, together with garnet and zircon geochronology data, from seven locations within metapelitic rocks in the footwall of the northern Snake Range décollement (NSRD). These locations lie both parallel and normal to the direction of footwall transport to constrain the pre‐exhumation geometry of the footwall. To determine P–T gradients precisely within the footwall, the ΔPT method of Worley & Powell (2000) has been employed, which minimizes the contribution of systematic uncertainties to thermobarometric calculations. The results show that footwall rocks reached pressures of 6–8 kbar and temperatures of 500–650 °C, equivalent to burial depths of 23–30 km. Burial depth remains constant in the WNW–ESE direction of footwall transport, but increases from south to north. The lack of a burial gradient in the direction of footwall transport implies that the footwall rocks, which today define a sub‐horizontal datum in the direction of fault transport, also defined a sub‐horizontal datum at depth in Late Cretaceous time. This suggests that the footwall was not tilted about the normal to the fault transport direction during exhumation, and hence that the NSRD did not form as a low‐angle normal fault cutting down through the lower crust. Instead, the following evolution for the northern Snake Range footwall is proposed. (i) Mesozoic contraction caused substantial crustal thickening by duplication and folding of the miogeoclinal sequence, accompanied by upper greenschist to amphibolite facies metamorphism. (ii) About half of the total exhumation was accomplished by roughly coaxial stretching and thinning in Late Cretaceous to Early Tertiary time, accompanied by retrogression and mylonitic deformation. (iii) The footwall rocks were then ‘captured’ from the middle crust along a moderately dipping NSRD that soled into the middle crust with a rolling‐hinge geometry at both upper and lower terminations.     

Seasonal distribution of rainfall in Australia analysed by Fourier methods

Summary A harmonic or Fourier analysis of mean monthly rainfall data is found useful in objectively describing and mapping the seasonality of rainfall within Australia. Over large areas the seasonal component is well described by the first and second harmonic terms, leaving as a residual variance only a small proportion of the observed total variance. Care must be taken in the interpretation of second harmonic contributions within those areas of tropical Australia under strong monsoonal influences. This is because pecularities in the form of the annual rainfall regime make the first harmonic term inadequate in itself to fully describe the annual trend. The technique is found particularly useful in defining the boundaries of areas of similar seasonality, and maps based upon the first and second harmonic amplitudes are shown to bear a close relationship with known physical controls.

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Zusammenfassung Zur objektiven Beschreibung der jahreszeitlichen Schwankung der Regenfälle in Australien und ihrer kartenmäßigen Darstellung wird mit Erfolg die harmonische Analyse der mittleren Monatsmengen des Niederschlags angewendet. Über weiten Gebieten wird die jahreszeitliche Schwankung durch die ersten beiden harmonischen Schwingungen gut dargestellt; die Reststreuung macht nur einen kleinen Bruchteil der beobachteten Gesamtstreuung aus. Vorsicht erscheint jedoch geboten bei der Interpretation des Anteils der zweiten Harmonischen in den Gebieten des tropischen Australien, die unter starkem Monsuneinfluß stehen. Hier machen Besonderheiten im Niederschlagsregime selbst die erste Harmonische ungenügend zur Beschreibung des Jahresganges. Die angewandte Methode ist besonders geeignet, die Grenzen zwischen Gebieten mit gleichartigem Jahreszeiteneinfluß festzulegen. Karten, die auf der ersten und zweiten harmonischen Schwingung beruhen, zeigen einen engen Zusammenhang mit bekannten physikalischen Faktoren.

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Résumé Afin de décrire objectivement les variations saisonnières des précipitations en Australie, on se sert avantageusement de l'analyse harmonique des sommes mensuelles moyennes. Cette méthode est également utilisée pour la représentation cartographique des dites variations. Les amplitudes saisonnières sont bien rendues par les deux premières harmoniques et cela pour de grandes étendues. L'amplitude qui reste ne représente qu'une faible fraction de l'amplitude totale observée. Il faut cependant procéder avec prudence lors de l'interprétation de la part revenant à la seconde harmonique dans les contrées tropicales de l'Australie, contrées qui subissent fortement l'influence de la mousson. Dans ce cas précis, les particularités du régime des précipitations ne permettent même pas d'utiliser la première harmonique pour décrire l'évolution des pluies au cours de l'année. La méthode proposée est surtout intéressante pour délimiter les régions soumises aux mêmes régimes. Des cartes basées sur la première et la seconde harmonique montrent un rapport étroit entre les précipitations et certains facteurs physiques connus.

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With 9 Figures