中国多年冻土制图:进展、挑战与机遇

多年冻土制图是冻土学的基础研究方向之一。通过总结我国多年冻土制图的发展历程,讨论了多年冻土分类系统和多年冻土(区)面积,并从经验模型、物理模型、统计学习3个方面探讨了我国多年冻土制图方法的研究进展。根据制图手段、数据可用性、模型和方法的不同,将我国多年冻土制图分为3个发展阶段:起步阶段(20世纪60～80年代)、遥感和GIS初步应用阶段(20世纪90年代至2010年)和多源观测与综合模型融合阶段(2010年至今)。不同阶段对多年冻土面积的认识有较大差别,随着制图空间分辨率与精度的提高,新的冻土图更接近代表真实的多年冻土面积。在制图方法方面,经验模型与物理模型的发展贯穿3个阶段,经验模型与遥感的结合是目前中国多年冻土制图的主要方法;冻土物理模型发展迅速,通过与其他模型的耦合,特别是与分布式水文模型的耦合,为模拟冻土变化的生态水文效应提供了重要工具;随着地面与遥感观测数据的积累,统计学习方法表现出较大潜力。地球观测系统的发展为冻土监测提供了前所未有的机遇。地面调查的优化、数据积累与开放共享、冻土遥感方法的进一步发展、深化多年冻土深层过程的理解与物理模型的进一步改进及其与观测的融合等,都将有助于突破中国多年冻土制图面临的挑战,促进对中国多年冻土过去、现在和未来变化的认识。     

多年冻土工程地质制图的阶梯发展

多年冻土工程地质制图是区域和历史冻土学研究的基础内容之一.多年冻土工程地质制图是根据需要和制图原则,在特定时空尺度分析多年冻土特征,以及各种自然、工程、环境要素共同影响下的多年冻土属性的量化描述.多年冻土工程地质制图所解决的科学问题从多年冻土的分布、规律和格局、冻土功能,认识不断提高.制图的内容从研究多年冻土的基本要素...     

基于综合调查的西昆仑山典型区多年冻土分布研究

西昆仑山位于青藏高原西北部,地势起伏大,气候干旱严寒.为了解其多年冻土分布状况,以219国道大红柳滩到奇台达坂之间的沿线区域作为西昆仑山典型区,以野外冻土钻探、坑探、物探为主要调查手段,综合分析该区域多年冻土分布的下界.对现场调查数据的初步分析表明,该区域多年冻土阳坡下界在海拔4 800m,阴坡下界在海拔4 650m,东西坡下界在海拔4 700m.依据上述冻土下界的分布规律,以数字高程模型为基础,通过ArcGIS软件建立了西昆仑山典型区的多年冻土分布模型,实现了对研究区域多年冻土分布的模拟.对该区域的研究结果表明:典型区内多年冻土的分布面积为3 136.3km2,占区域总面积的89.4%.结果与青藏高原冻土图在该区域的截图相比,多年冻土的面积略有增加.对比分析模拟图和截图后发现,基于实际调查的多年冻土模拟分布图更准确的描述了河谷的融区,而截图的多年冻土分布界限较为粗糙,缩小了喀喇喀什河支沟融区,人为放大了219国道大红柳滩到奇台达坂之间的宽谷融区.     

地面冻结数模型及其在青藏高原的应用

地面冻结数模型可用于分析、模拟和预测多年冻土的分布, 在高纬冻土地区有比较成功的应用. 然而Nelson提出的地面冻结数模型并不具备明显的物理意义, 往往被归入经验统计范畴. 从Stefan公式出发, 重新推导并详细讨论了地面冻结数模型, 使冻结数F=0.5作为多年冻土与季节冻土的分界线具备明确的物理意义. 重新推导后的模型增加了一个影响冻土形成和发展过程的并取决于岩土冻融性质的因子E, 原Nelson地面冻结数模型可作为E=1时的特例给出. 根据青藏高原实测地面温度资料, 针对不同的E值, 分别模拟了青藏高原的冻土分布情况. 对比分析表明, 处在多年冻土南北界附近的土壤性质较明显影响了多年冻土在这些区域的分布情况, 通过对参数E的调参, 可以更好地模拟多年冻土的真实分布情况.     

国外高山多年冻土研究概况

近年来,在区域冻土学研究领域中,除了以极地为中心的高纬度多年冻土、海底冻土和古冻土方面有了许多进展之外,有关高山多年冻土的研究引起了国内外许多学者的广泛兴趣,学术活动日趋频繁。1972、1974年藤井理行和埃佛斯(Ives)相继明确提出了高山多年冻土的概念。1976年苏联多年冻土研究所A.P.戈尔布诺夫(Gorbunov)在高加索召开的国际地理学会高海拔地区生态学讨论会上提出了高山多年冻土的分类,并于     

基于年平均地温的青藏高原冻土分布制图及应用

年平均地温是指多年冻土年较差为零的深度处的地温,是冻土分带划分的主要指标之一.利用青藏公路沿线钻孔实测年平均地温数据,进行回归统计分析,获取年平均地温与纬度、高程的关系,并基于该结果,结合TOPO30高程数据模拟得到整个青藏高原范围上的年平均地温分布.以年平均地温0.5℃作为多年冻土与季节冻土的界限,对比分析模拟图与青藏高原冻土图,除个别区域有较明显的差异,模拟结果图较好地体现了青藏高原冻土的分布情况.利用模拟结果,根据青藏高原多年冻土分带指标及寒区工程多年冻土区划指标,对青藏高原多年冻土分布进行了分带划分,并统计各分带面积;根据简化的冻土厚度计算公式,计算了青藏高原多年冻土的厚度分布.最后,利用数值预测方法的结果,在气候年增温0.04℃的背景下,对高原未来冻土分布进行了预测.     

ERA-Interim地表温度数据集在青藏高原冻土分布制图应用的适用性评估

地表温度综合反映了大气、植被和土壤等因素的能量交换状况, 是冻土分布模型和一些寒区陆面过程模式的上边界条件, 对多年冻土分布制图和活动层厚度估算有重要意义. 为了评估ERA-Interim 地表温度产品在青藏高原地区的适用性, 综合比较了青藏高原69个海拔2 000 m以上气象站1981-2013年地面实际观测值与ERA-Interim之间的差异及其分布状况. 结果表明, 两种资料的变化趋势一致, 但是ERA-Interim地表温度在数值上与实际观测值差别显著, 平均偏低7.4℃. 原因之一可能是由ERA-Interim再分析资料格点的海拔高度与气象站实际海拔高度差异引起的. 根据两种温度产品之间海拔的差异, 对ERA-Interim地表温度重新进行模拟, 经过模拟后的ERA-Interim地表温度与实际观测值的差值在大部分气象站变小, 平均偏高0.4℃. 因此, 经过重新模拟的ERA-Interim地表温度基本能够反映青藏高原地表温度的真实情况. 以模拟后的ERA-Interim地表温度作为地面冻结数模型的输入参数模拟了青藏高原冻土分布, 结果表明青藏高原多年冻土区面积为1.14×10⁶ km², 季节冻土区面积为1.43×10⁶km².     

略论我国西部高山高原区的冻土工程地质勘探问题

现有资料说明,我国西部高山高原区多年冻土的分布具有明显的垂直分带性,而其它各种地方性的地理-地质因素,对冻土的分布也有着重大的影响。我国西部高山高原地区多年冻土的分布情况相当复杂:多年冻土的分布下界是弯曲的;在一个很小的范围内,就可以遇到各种类型的冻土,其稳定性、冷生组构、含冰量和物理力学性质都有很大的差异;在不同的冻土区内,可以出现各种类型的融区,也可以出现种类繁多的冻土现象。有时,一沟之隔,冻土下界的高程可以相差几百米,並且,在几十米的范围内,冻土特征就有很大的变化,     

青藏高原末次盛冰期和全新世大暖期多年冻土边界变化的探讨

位于中低纬的青藏高原多年冻土是第四纪高原隆升和冰期气候叠加的产物,与高纬多年冻土相比,具有厚度薄和不稳定的特点,对全球变化反应敏感.因此,评价冰期-间冰期多年冻土扩张-收缩过程和其范围重建,是研究高原环境变化的重要工作.本文依据青藏高原及周边地区温度数据和《中国冰川冻土沙漠图》,对青藏高原现代大片多年冻土、岛状多年冻土和高山多年冻土分布进行恢复.依据来自冰川、冰缘和湖泊等证据,采用末次盛冰期气温较现代低7℃,全新世大暖期气温较现代高4℃,进行末次盛冰期和全新世大暖期多年冻土分布重建.重建结果表明:末次盛冰期多年冻土扩张明显,面积约为现代冻土面积的195％;末次盛冰期大片多年冻土几乎覆盖整个高原,岛状多年冻土向东扩张明显,向西范围逐渐收缩变窄,高山多年冻土在喜马拉雅山、祁连山和横断山脉等地区扩张明显.全新世大暖期多年冻土明显收缩,面积是现代多年冻土的73％;大片多年冻土收缩幅度较小,岛状多年冻土在高原东南部收缩明显,高山多年冻土在喜马拉雅山脉、祁连山脉、横断山脉等高海拔山地发育.     

祁连山中东部的冻土特征(Ⅰ):多年冻土分布

祁连山地区地势高耸,气候严寒,冰缘现象广布,各类冰缘现象受地形与水分条件的控制,分布具有明显的规律性.祁连山多年冻土属青藏冻土区,阿尔金山-祁连山亚区,分布在海拔3400 m以上的高山、谷地、盆地中.多年冻土分布具有明显的高度地带性,随高度增加,冻土分布呈现出季节冻土-岛状冻土-连续冻土更替,同时,多年冻土下界高程与经度明显相关,自西向东表现出下降趋势,下降率约为每经度150 m,这一变化与降水在东西方向的变化有关.山区微气候因素复杂多变,也造成了冻土分布的复杂性,局地因素对冻土分布影响显著,对比分析了坡向,植被与水分、岩性,季节性积雪等诸因素对多年冻土分布的影响.     

Hydrogen and carbon in solid solution in oxides and silicates

The dissolution of H₂O and CO₂ in structurally dense, nominally anhydrous and non-carbonate oxide matrices such as MgO and CaO is reviewed. H₂O and CO₂ are treated as gaseous oxide components which enter into solid solution with the refractory oxide hosts. They form anion complexes associated with cation vacancy sites. Evidence is presented that OH^? pairs which derive from the dissolution of H₂O are subject to a charge transfer (CT) conversion into peroxy moieties and molecular hydrogen, O ₂ ^2? ... H₂. Because the O ₂ ^2? moiety is small (O^?-O^? distance ≈ 1.5 Å) high pressure probably favors the CT conversion. Mass spectroscopic studies show that molecular H₂ may be lost from the solid which retains excess oxygen in the form of O ₂ ^2? , leading to the release of atomic O. The dissociation of O ₂ ^2? moieties into a vacancy-bound O^? state and an unbound O^? state can be followed by measuring the internal redox reactions involving transition metal impurities, the transient paramagnetism of the O^? and their effect on the d.c. conductivity. Evidence is presented that CO₂ molecules dissolve dissociatively in the structurally dense oxide matrix, as if they were first to dissociate into CO+O and then to form separate solute moieties CO ₂ ^2? and O ₂ ^2? , both associated with cation vacancy sites. In the CO ₂ ^2? moiety (C-O^? distance 1.2–1.3 Å, OCO angle ≈ 130°) the C atom probably sits off center. The transition of the C atom into interstitial sites is accompanied by dissociation of the CO ₂ ^2? moiety into CO^? and O^?. This transition can be followed by infrared spectroscopy, using OH^? as local probes. Further support derives from magnetic susceptibility, thermal expansion, low frequency dielectric loss and low temperature deformation measurements. The recently observed emission of O and Mg atoms besides a variety of molecules such as CO, CO₂, CH₄, HCN and other hydrocarbons during impact fracture of MgO single crystals is presented and discussed in the light of the other experimental data.     

Comparative urbanization in Ghana and Kenya in time and space

There are few inter-African country urban analyses because of the continent’s enormous size and socioeconomic diversity, language barriers, and wide variations in national and regional urban research capacity. Nevertheless, comparative urban studies are critical in understanding contemporary African urbanization. In this comparative spatial and temporal analysis of Ghana and Kenya’s urbanization, we find that both countries are urbanizing rapidly and are faced with many common urban problems. Moreover, Ghana is more urbanized than Kenya and has a larger indigenous urban imprint and a more widely dispersed urban pattern. Besides their physiographic and population conditions, we trace these countries’ convergent and divergent urban trends to their shared but unique experiences of colonialism, nationalism and globalization.     

煤中气孔和镶嵌结构及其在煤变质研究中的意义

河南省禹县、新密和荥巩煤田山西组Ⅱ₁煤的贫煤和无烟煤中,气孔发育。气孔形态有椭圆状（图版1）、圆状及不规则状（图版2）,有的几个气孔连在一起呈大的朵状气孔(图版3)。此外,在荥巩煤田西部无烟煤中还发育有镀嵌结构(图版4)。      

岩溶地区现代土壤与洞穴石笋中单甲基支链烷烃与烷基环己烷对比研究

利用GC-MS（气相色谱—质谱仪）,对采自湖北清江流域和尚洞洞顶的土壤样品与洞内石笋样品进行分析,发现土壤中存在的七个系列单甲基支链烷烃在所有的石笋样品中均可以找到,呈现相似的分布模式,石笋中七个系列支链烷烃有可能来自洞穴滴水携带的土壤中的支链烷烃,但是也不能排除石笋原地生长的微生物的贡献。烷基环己烷的分布在土壤与石笋中呈现了相似的分布模式,但是主峰碳数有所变化,高碳数部分与低碳数部分的相对含量也发生了变化。主要原因可能是微生物选择性降解的结果,也有可能是土壤与石笋中微生物种类分布差异所造成的。本次研究初步显示了相对封闭稳定的洞穴沉积物与上覆土壤层中生物标志化合物的异同。      

Geogenic and anthropogenic zinc in epiphytic and terricolous lichens in Finland

At 31 sites in Finland the Zn content was determined of the epiphytic lichen Hypogymnia physodes (L.) Nyl. growing on pine and birch, the terricolous lichen Cladina spp. in pine bark, and the inner part of birch bark. The anomalous contents of Zn in H. physodes on pine and Cladina spp. in soil appeared to be strongly related to sulphide ore deposits. Anthropogenic Zn correlated closely with S and Fe in H. physodes on pine and with Fe in Cladina spp. The binding of geogenic Zn was related to iron hydroxides, and was attributed to the different uptake mechanism of S in these lichens. Elevated values of Zn in H. physodes on birch were due to both geogenic and anthropogenic sources. Zinc in pine bark increased with the Zn content in H. physodes and reached a limiting value.     

Re-Os and Pd-Ag systematics in Group IIIAB irons and in pallasites

Using improved analytical techniques, which reduce the Re blanks by factors of 8 to 10, we report new Re-Os data on low Re and low PGE pallasites (PAL-anom) and IIIAB irons. The new pallasite samples nearly double the observed range in Re/Os for pallasites and allow the determination of an isochron of slope 0.0775 ± 0.0008 (T = 4.50 ± 0.04 Ga, using the adjusted λ¹⁸⁷Re = 1.66 × 10⁻¹¹ a⁻¹) and initial (¹⁸⁷Os/¹⁸⁸Os)₀ = 0.09599 ± 0.00046. If the data on different groups of pallasites (including the “anomalous” pallasites) are considered to define a whole-rock isochron, their formation would appear to be distinctly younger than for the iron meteorites by ∼60 Ma. Five IIIAB irons (Acuna, Bella Roca, Chupaderos, Grant, and Bear Creek), with Re contents ranging from 0.9 to 2.8 ppb, show limited Re/Os fractionation and plot within errors on the IIAB iron meteorite isochron of slope 0.07848 ± 0.00018 (T = 4.56 ± 0.01 Ga) and initial (¹⁸⁷Os/¹⁸⁸Os)₀ = 0.09563 ± 0.00011. Many of the meteorites were analyzed also for Pd-Ag and show ¹⁰⁷Ag enrichments correlated with Pd/Ag, requiring early formation and fractionation of the FeNi metal, in a narrow time interval, after injection of live ¹⁰⁷Pd (t_1/2 = 6.5 Ma) into the solar nebula. Based on Pd-Ag, the typical range in relative ages of these meteorites is ≤10 Ma. The Pd-Ag results suggest early formation and preservation of the ¹⁰⁷Pd-¹⁰⁷Ag systematics, both for IIIAB irons and for pallasites, while the younger Re-Os apparent age for pallasites suggests that the Re-Os system in pallasites was subject to re-equilibration. The low Re and low PGE pallasites show significant Re/Os fractionation (higher Re/Os) as the Re and PGE contents decrease. By contrast, the IIIAB irons show a restricted range in Re/Os, even for samples with extremely low Re and PGE contents. There is a good correlation of Re and Ir contents. The correlation of Re and Os contents for IIIAB irons shows a similar complex pattern as observed for IIAB irons (Morgan et al., 1995), and neither can be ascribed to a continuous fractional crystallization process with uniform solid-metal/liquid-metal distribution coefficients.     

Orogenesis in time and space in Mexico

The evolution of the border region of part or all of a craton, on the basis of geological data gathered from Mexico, may best be described in terms of geotectonic cycles. These consist, in chronological order, of (1) an orthogeosynclinal phase (eu- and miogeosynclines) with or without initial magmatic activity, (2) an anatexitic phase consisting of batholith emplacement with attendant regional metamorphism in the eugeosyncline and deposition of a clastic or flysch wedge over the miogeosyncline, (3) an orogenic phase consisting principally of the folding and thrusting of the sediments of the miogeosyncline together with the clastic or flysch wedge against the foreland, and (4) a taphrogenic or block-faulting phase accompanied by (a) accumulation of post-orogenic debris or molasse, (b) subsequent magmatic activity consisting largely of igneous extrusions with fewer intrusions, and (c) final magmatic activity consisting of igneous extrusions. A region that has gone through the above phases of a geotectonic cycle may be termed a structural belt. In the post-Precambrian geologic history of Mexico, three geotectonic cycles are recognized: one occurred along the Pacific border of Mexico between Cambrian and middle Jurassic (?) time (Jaliscoan geotectonic cycle), the second occurred along the present Gulf of Mexico border of the country at the same time (Huastecan geotectonic cycle), and the third occurred over the entire country from the United States border to the Guatemalan border between Late Jurassic and Pliocene time (Mexican geotectonic cycle). The early Mesozoic clastic rocks in northwestern Mexico may signify a fourth geotectonic cycle in that region. In the three recognized geotectonic cycles, however, the geologic record shows only two orogenic phases, one of which occurred in late Paleozoic time in an arcuate belt along the eastern side of Mexico (Coahuilan orogeny), and the other in early Tertiary time in a belt traversing central Mexico from the United States border to the Guatemalan border (Hidalgoan orogeny).     

Water-extractable and exchangeable phosphate in Martian and carbonaceous chondrite meteorites and in planetary soil analogs

Aqueous extraction contributes to the formation and weathering of planetary materials and renders electrolytes such as phosphate available for biology. In this context, the solubility of phosphate is measured in planetary materials, represented by the Mars meteorites Nakhla, Dar al Gani 476 (DaG 476), Elephant Morraine 79001 (EETA 79001), and terrestrial analogs, and in the Murchison CM2 and Allende CV3 carbonaceous chondrites. The Mars meteorites contain high levels of phosphate that is readily extracted by water, up to 15 mg kg⁻¹ in Nakhla and DaG 476 and 38 mg kg⁻¹ in EETA 79001, while the terrestrial analogs and the carbonaceous chondrites contain 0.5 to 6 mg kg⁻¹. Correspondingly, high phosphate concentrations of 4 to >28 mg L⁻¹ are obtained in extracts of the Mars meteorites at high solid/solution ratios, exceeding the concentrations of 0.4 to 2.0 mg L⁻¹ in the extracts of the terrestrial analogs. A wide range of planetary conditions, including N₂ and CO₂ atmospheres, solid/solution ratios of 0.01 to 1.0 kg L⁻¹, extraction times of 1 to 21 d, and temperatures of 20 to 121°C affect the amounts of extractable phosphate by factors of only 2 to 5 in most materials. Phosphate-fixing capacity and exchangeable phosphate are assessed by the isotopic exchange kinetics (IEK) method, which quantifies the amount of P isotopically exchangeable within 1 min (E_1min) and between 1 min and 3 months (E_1min-3m) and the amount of P that cannot be exchanged within 3 months (E_>3m). The IEK results show that the DaG 476 Mars meteorite and terrestrial analogs have low P-fixing capacities, while the carbonaceous chondrites have high P-fixing capacities. Aqueous processing under early planetary CO₂ atmospheres has large effects on the available phosphate. For example, the fraction of total P that is exchangeable in 3 months increases from 1.6 to 11%, 13 to 51.6%, and 43.9 to 90.4% in the DaG 476 Mars meteorite, Allende, and Murchison, respectively. The results show that solutions with high phosphate concentrations can form in the pores of planetary lava ash and basalts and in carbonaceous asteroids and meteorites. These solutions can help prebiotic synthesis and early microbial nutrition. The Martian and carbonaceous chondrite materials contain sufficient phosphate for space-based agriculture.     

Amphibole and chlorite in mafic and ultramafic rocks in the lower crust and upper mantle

Stabilities of amphibole and chlorite in mafic and ultramafic compositions have been considered in the model system CaO+MgO+Al₂O₃+SiO₂+H₂O. From topological arguments two petrogenetic grids have been constructed. Although available experimental data in CMASH are compatible with the grid in which amphibole reacts out before chlorite in model ultramafic compositions for the pressure range 6 to 15 kbar, naturally observed mineral assemblages and some experimental data in more complex systems favour the other grid in which chlorite reacts out before amphibole at all pressures. This discrepancy between natural and model systems is due to differential movement of the dehydration equilibria of the two hydrates reflecting the variation of activity of H₂O or of components other than CMASH.     

银川平原地下水资源开发与植被变化

植被状况的变化是反映区域性生态环境状况的重要指标。地下水是影响植被变化的主要因素。宁夏地处干旱半干旱地带,是全国生态系统最脆弱的省区之一。2000年后,随着宁夏黄河引水量的减小,水资源的不合理应用使银川平原的生态植被出现了退化的趋势。本文利用MODIS-NDVI遥感数据,对银川平原2000~2004年间的植被变化趋势进行了研究。在此基础上,对引用黄河水量及多年地下水位的变化对植被的影响进行了分析,并对适宜于植被发育的地下水位埋深进行了探讨。