不同气候情景下中国滨海城市海岸极值水位重现期预估

气候变化背景下,海平面上升叠加台风—风暴潮、天文大潮等产生的海岸极值水位事件趋多增强,对我国滨海城市社会经济可持发展构成了严重威胁。为认识未来我国滨海城市海岸极值水位危害性（强度和频率）的变化,本文首先采用第五次国际耦合模式比较计划（CMIP5）数据,分析了不同气候情景下（RCP2.6, 4.5, 8.5,简称为RCPs）下,未来不同年代（2030年、2050年和2100年）我国滨海城市沿岸海平面变化幅度;其次,基于沿海验潮站的历史观测资料和文献数据,分析了未来热带气旋强度变化对海岸极值水位的影响;最后,利用皮尔逊Ⅲ型（P-Ⅲ）水文概率曲线方法,预估了不同气候（RCPs）情景下未来不同年代（2030年、2050年和2100年）我国9个滨海城市海岸极值水位重现期的变化。结果表明：（1）在不同气候情景下,我国滨海城市沿海平均海平面均呈现上升趋势,其中,到21世纪末,长三角地区沿海海平面上升幅度最大,上升速度比全国平均高出约30%;（2）热带气旋的强度与台风—风暴潮的增水幅度存在正相关关系。预计到21世纪末,热带气旋的整体强度很可能将增强,热带气旋引发的台风—风暴潮的增水幅度较当前很可能有明显提高。（3）未来我国滨海城市沿海极值水位将有显著增高的趋势,当前极值水位的重现期将明显缩短。到21世纪末,我国滨海城市当前百年一遇的极值水位,重现期几乎都将缩短至20年一遇以下,其中,大连、青岛、上海和厦门等城市海岸极值水位重现期很可能缩短为（或低于）1年一遇。本文虽在一定程度上反映了不同气候情景下海岸洪水危害性的变化,但对于未来热带气旋的变化及其影响的研究尚有待进一步深入。     

一种加入空间关系的海岸带遥感图像分类方法

 海岸带作为海洋、陆地和大气共同作用的地带，其地物混杂度大，变化频繁，单纯利用光谱特征分类难以取得理想的精度。 但海岸带地物滨临水体，而水体与地物存在巨大光谱差异，易于识别。据此，本文尝试提出一种简单的加入空间关系的遥感图像分类 方法，即，先准确识别出海水类，然后统计非海水类的每一个像元到最近海水的空间距离。由于不同的海岸带地类距离海水的空间距 离有其自身的特点，因此，利用这一距离信息辅助分类能提高分类精度，尤其是针对那些光谱特征相近而距离相差较大的地类。     

石灰岩腐岩的基本特征及其形成机制

碳酸盐岩风化剖面非饱和带内的白色粉末状物质应属碳酸盐岩腐岩，剖面上部覆盖有一定厚度的土层是此类腐岩发育的必要条件。对昆明富民石灰岩风化剖面的研究表明，石灰岩腐岩呈白色或灰白色，结构疏松，密度、孔隙度和渗透率分别为1．8081g／cm^3、32．65％和774．8139×10^-3 μm^2，其母岩的对应指标分别为2．6966g／cm^3、0．05％和0．0084×10^-3 μm^2，综合差异显著。石灰岩腐岩吸水性强、给水能力差，容水度30％，持水度25％。基于铸体薄片的显微观察发现，腐岩粒间孔隙及溶蚀孔隙发育，面孔率达19％；扫描电子显微镜下，可见泥晶方解石集合体之间的蜂窝状溶孔和方解石颗粒之间的粒间孔。石灰岩向腐岩的转变是通过其结构体风化前锋的扩展实现的。微观尺度上，石灰岩结构体属非连续的颗粒集合体，具有巨大的比表面积和很强的潜在吸附能力。覆盖有土层的非饱和带多属潮湿环境，能保持较高的相对湿度。当在压力及浓度梯度驱动下侵入石灰岩结构体的水汽分子凝结为液态水时，可对方解石颗粒产生楔裂作用，削弱粒间或粒内的结构连接，使其集合体发生一定程度的体膨胀，从而形成腐岩壳。随着时间加长，风化前锋逐渐扩展，岩石结构体最终转化为腐岩结构体。石灰岩腐岩是在高湿度包气带环境中经吸湿膨胀作用形成的，是石灰岩物理风化的产物；渗入水的溶滤作用主要发生在腐岩的演化阶段。     

热带地区碳酸盐岩上覆红色风化壳的成因机理及元素演化

开展热带岩溶地区红色风化壳元素地球化学演化规律研究,有助于丰富碳酸盐岩风化成土理论的认识。在越南北部选取典型的碳酸盐岩风化剖面,分析热带气候条件下碳酸盐岩上覆红色风化壳中主量元素的物质来源和演化特征。结果表明:无论Ti/Zr的元素比值分析,Hf-Zr、Nb-Ta及Sm-Nd的元素对协变分析,还是上地壳元素平均值(UCC)标准化分析,两个剖面的上覆风化壳均显示原地残积的特征,即两个剖面是碳酸盐岩的原位风化产物。碳酸盐岩风化成土过程中,CaO、MgO淋失明显,Al_2O_3和Fe_2O_3发生富集,显示两个剖面均经历较强的风化过程,但是白云岩和灰岩剖面有一定的分异特征。越南北部白云岩风化剖面从基岩到上部土层显示出稳定的Ti-Fe元素共富集特征,而灰岩剖面中Fe的增长速率明显超过Ti。白云岩上覆风化壳经历了强烈的风化作用,其脱硅作用弱于灰岩风化剖面,而富集铝的作用强于灰岩。迁移系数的演化规律说明两个剖面中长石成分(钾长石、钠长石等)或次生矿物(伊利石等)在风化成土过程中逐渐分解,同时Al、Fe、Si等稳定元素的在风化剖面中不断富集。     

钼的地球化学性质与成矿

钼在硅酸盐地球中的丰度很低,作为中度不相容元素,简单的岩浆形成、演化过程很难使之从地壳丰度直接富集到工业品位。我们研究结果显示钼的成矿主要通过两阶段富集过程来实现:一是与风化、沉积有关的表生过程;二是与板块俯冲或深埋熔融有关的岩浆过程。钼是变价元素,在寒武纪大气氧再次升高以后,钼在地表化学风化过程中容易被氧化为水溶性的Mo O42-,进入地表径流和海洋湖泊中,并且在还原条件下进入富含有机质的黑色页岩等沉积物(岩)中。富钼沉积物(岩)在随板块俯冲到地幔或深埋等条件下可以因升温变质,进而发生部分熔融,形成富钼的原始岩浆,在俯冲条件下往往形成斑岩铜(金)钼矿床,氧逸度低于斑岩铜矿,而斑岩钼矿的氧逸度更低。具有高化学风化速率、大的流域面积的封闭、半封闭型水域和河口地区是表生过程中钼富集的最佳区域,是大型钼矿形成的基础。     

Cavernous Weathering in Aeolian Sandstones: An Example from the Yongningshan Hill of the Loess Plateau, Northwest China

Cavernous weathering is commonly found on sandstone slopes in different environments. Either a single dominant process or polygenetic agents require to be invoked in order to interpret the development. The Yongningshan hill of the central Loess Plateau is representative of cliff dwellings in Northwest China, which is characterized by well-developed cavernous weathering features and provides a good opportunity for the better understanding of sandstone weathering in the Loess Plateau. Multiple methods, including field survey, in-situ rock strength measurement, along with experiments on samples for microscopic observation, element composition and salt chemistry, were employed to investigate the controlling factors of cavernous weathering. The results show that cavern development is different on the four slopes with the western slope hosting massive honeycombs, tafoni and hardened surfaces. The porous and permeable aeolian sandstones are fundamental, because they provide space and pathways for the transportation of water and salt, honeycombs dominantly aligning within the lamination of cross-beds. The environmental factors such as the seasonal wetting and drying cycle, aeolian salt, moisture and water vapor are key factors for the development of cavernous weathering forms. The northern and northwestern wind-blown dust storms have brought abundant salts, the lengthier dry periods of the wetting and drying cycle being beneficial for salt accumulation within caverns, favoring salt weathering.     

陆地硅的生物地球化学循环研究进展

地球表层硅（Si）的生物地球化学循环与大气CO2浓度变化、大洋生物泵作用以及海岸带富营养化等过程密切相关,因此成为全球环境变化研究的核心问题之一。在地质时间尺度上,硅酸盐矿物的化学风化是地球表层所有次生Si的来源。陆地生态系统各次生Si库具有不同的形成机制和驱动因子,这导致各Si库的贮存量和循环周期存在明显差异。土壤Si库中的黏土矿物Si、溶解硅（DSi）和淀积在其他矿物表面的无定形Si都源自硅酸盐矿物的化学风化过程;植物生长过程中吸收土壤中的DSi形成生物Si,然后经微生物分解过程返还给土壤;地表径流将流域陆源Si以悬移质Si和DSi的形式输入河流、海洋。迄今,陆地不同形态Si库的大小及其对全球Si循环的贡献仍不确定。因此,在研究陆地Si的生物地球化学循环过程中,综合考虑各种地表过程及其耦合作用是非常必要的。     

The possible role of magnetic measurements in the discrimination of Sahara/Sahel dust sources

The mineral magnetic properties of deposited dusts collected along a broadly north‐to‐south transect across Niger have been investigated on both a bulk and particle size‐specific basis. Dusts display a general north‐to‐south gradient in fine‐grained ferrimagnetic mineral (magnetite/maghemite) concentrations, with samples south of the Sahara/Sahel transition (south of ~15·5^o N) generally containing greater concentrations than dusts from further north where the climate is much drier. This distinction is seen especially clearly in the clay (< 2 µm) fraction, which harbours the products of weathering and pedogenesis. This gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils/sands across a similar latitudinal range. We suggest that the regional distinction in both dust and surface soil/sand magnetic properties can be related to differences in weathering regime between the arid Saharan parts of the transect and the Sahel sites where higher rainfall has permitted stronger weathering and pedogenesis. Given that the weathering‐related magnetic signatures in the clays dominate the magnetic properties of the < 16 µm fractions in these samples, and that this particle size component is most likely to be involved in long‐range transport, magnetic measurements hold out the potential of discriminating Sahara and Sahel dusts deposited in remote areas. Copyright © 2011 John Wiley & Sons, Ltd.     

In‐situ gamma‐ray spectrometric study of weathered volcanic rocks in Hong Kong

In‐situ gamma‐ray spectrometry (GRS) measurements were conducted at 35 sites in Hong Kong where volcanic rocks with varying extent of weathering were exposed. Elemental analyses using X‐ray fluorescence spectrometry and inductively coupled plasma–mass spectrometry were carried out on samples collected from these 35 plus 22 other locations to assess the feasibility of using the GRS method to quantify the extent of weathering. The Parker weathering index, varying within a range of 0·0–0·8 for the samples studied, was used as a geochemically based reference scheme for correlating the gamma‐ray spectrometric results with the extent of weathering. For the former 35 sites, the concentrations of the three major radioelements, K, U and Th, determined by in‐situ GRS were compared to laboratory‐determined values from the samples. The study reveals that no significant change occurs to the contents of the three radioelements during the initial state of weathering. But once the rocks become highly weathered, further progression of weathering is accompanied by a systematic removal of K and an increased dispersion of U and Th. The results show that K content, which is indicative of the extent of weathering, can be retrieved reliably with the gamma‐ray spectrometry technique. The study has given support to the potential use of the downhole spectral gamma method for evaluation of weathering grade and the detection of subsurface clay‐rich levels. Copyright © 2002 John Wiley & Sons, Ltd.     

广东惠东地区离子吸附型稀土矿床地球化学特征

摘要：运用岩石地球化学方法,对广东惠东地区离子吸附型稀土矿床的地球化学特征进行研究。结果显示,风化壳中元素含量及配分特点总体上取决于母岩,但稀土元素在继承母岩稀土元素的基础上含量进一步富集,且各风化层中元素含量变化与风化作用之间具有一定相关性。WIG指数相较于CIA指数能更有效地描述风化壳风化强度,风化壳中稀土元素迁出富集与WIG指数及元素迁移系数具有一定规律性,轻稀土元素多在全风化层上部富集,而重稀土元素在全风化层下部及半风化层明显迁入富集,Ce、Eu均具明显负异常。