Constraints on spatial variability in soft-sediment communities affected by contamination from an Antarctic waste disposal site

A small-scale (<500 m length) transect-based survey was conducted in December 1998 to examine the spatial distribution of soft-sediment communities and of concentrations of heavy metals and hydrocarbons in sediments in Brown Bay, adjacent to an abandoned waste dump, at Casey Station, Antarctica. Samples were taken along three transects at increasing distances (nine stations) from the shore-line waste dump. A gradient of contamination was detected, but concentrations of contaminants were very variable with "hotspots" or high levels of contaminants at some stations. Multivariate analysis revealed that the distribution of soft-sediment communities was distinctly different between the inner, middle and outer stations. Abundances of most taxa were very variable with few patterns apparent, but some fauna displayed an abundance gradient from the inner to the outer part of the bay. Many taxa had maximum abundances at outer stations and minimum at inner stations. Multivariate correlations between environmental variables and soft-sediment communities indicated that combinations of some metals (Cd, Cu, Sn, Pb) and grain size (mainly finer fractions, fine sands and coarse silts) were the variables that best "matched" the community patterns within Brown Bay. This study indicated that there were significant correlations between the presence of contaminants and the distribution and composition of soft-sediment communities over very small spatial scales.     

密度差随深度变化的不规则截面二度体的重力异常

本文是将Hubbert(1948)的线积分法用于求得密度差随深度呈线性变化的任意截面二度体的重力异常。以N边的多边形代替物体截面,利用任一边的两个顶点坐标来求其相应的重力异常,然后再对各边产生的重力异常进行求和得出总的重力效应。在这里我们还研究了密度差随深度呈指数变化的情况。利用这个方法求得了美国加州San Jacinto地堑的构造,在该地堑内充填的沉积物其密度差是随深度呈指数增加的。     

NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> change over China and its influences

A 3-D chemical transport model (OSLO CTM2) is used to investigate the impact of the increase of NOx emission over China. The model is capable to reproduce basically the seasonal variation of surface NOx and ozone over eastern China. NOx emission data and observations reveal that NOx over eastern China increases quite quickly with the economic development of China. Model results indicate that NOx concentration over eastern China increasingly rises with the increase of NOx emission over China, and accelerates to increase in winter. When the NOx emission increases from 1995 to its double, the ratio of NO2/NOx abruptly drops in winter over northern China. Ozone at the surface decreases in winter with the continual enhancement of the NOx level over eastern China, but increases over southern China in summertime. It is noticeable that peak ozone over northern China increases in summer although mean ozone changes little. In summer, ozone increases in the free troposphere dominantly below 500 hPa.Moreover, the increases of total ozone over eastern China are proportional to the increases of NOx emission.In a word, the model results suggest that the relationship between NOx and ozone at the surface would change with NOx increase.     

Identification of heterogeneous aquifer transmissivity using an AE-based method

Determination of hydraulic head, H, as a function of spatial coordinates and time, in ground water flow is the basis for aquifer management and for prediction of contaminant transport. Several computer codes are available for this purpose. Spatial distribution of the transmissivity, T(x,y), is a required input to these codes. In most aquifers, T varies in an erratic manner, and it can be characterized statistically in terms of a few moments: the expected value, the variance, and the variogram. Knowledge of these moments, combined with a few measurements, permits one to estimate T at any point using geostatistical methods. In a review of transmissivity data from 19 unconsolidated aquifers, Hoeksema and Kitanidis (1985) identified two types of the logtransmissivity Y= ln(T) variations: correlated variations with variance sigma2Yc and correlation scale, I(Y), on the order of kilometers, and uncorrelated variations with variance sigma2Yn. Direct identification of the logtransmissivity variogram, Gamma(Y), from measurements is difficult because T data are generally scarce. However, many head measurements are commonly available. The aim of the paper is to introduce a methodology to identify the transmissivity variogram parameters (sigma2Yc, I(Y), and sigma2Yn) using head data in formations characterized by large logtransmissivity variance. The identification methodology uses a combination of precise numerical simulations (carried out using analytic element method) and a theoretical model. The main objective is to demonstrate the application of the methodology to a regional ground water flow in Eagle Valley basin in west-central Nevada for which abundant transmissivity and head measurements are available.     

鲁西地块新生代断裂体系活动性与深部动力机制

根据野外观察分析,综合前人研究成果,对新生代时期鲁西地块的深、浅部构造特征、地震活动性以及动力学机制进行了分析。结果表明,鲁西地块新生代浅表主体断裂构造格局为NW—NWW走向断裂构成的多米诺式组合,震源机制解和野外观测揭示,其具有左旋走滑性质,并与NE向断裂共同控制了新生代盆地的形成和发育。地球物理资料揭示,鲁西地块深部15~20km处存在一条缓倾滑脱带和大规模低速异常体,浅表多米诺式断裂体系归并到该滑脱带,表现为深浅部构造的脱耦性,深部高低速异常体的过渡区域控制发育了鲁西地区两条NW向中强地震带。动力学成因上与太平洋板块俯冲作用导致地壳减薄、地幔上涌并在地幔楔中发生小尺度对流有关,并造成了鲁西地块的隆起抬升。     

台湾东北部古海湾沉积特征

通过对台湾东北部古海湾及周边356个海底表层沉积样品的粒度分析及碎屑矿物分析,揭示了古海湾及周边陆架自末次盛冰期以来的沉积环境演变特征,并分析了古海湾的成因。结果表明,该古海湾及周边海域沉积环境的演变可划分为3个阶段:(1)末次盛冰期,浊流、滑坡事件在海湾边缘及陆架边缘频繁发生,可携带大量的陆源碎屑物质输运至古海湾内(B-3),下蚀其海床及下伏地层,并塑造了作为浊流通道的两个砾石条带,在B-3内部保留分选差、改造弱的沉积物。在此期间,潮流、波浪和跨陆架流在东亚冬季风的影响下严重侵蚀B-3的湾口及湾缘,并沉积大量的砂、石英及低含量的生物碎屑物质,石英/长石比值也较高;(2)末次冰消期,随着海平面的阶段性上升,古海岸线向陆大幅迁移,导致浊流强度减弱,潮流逐渐成为陆架区主要的作用营力,相关的潮流底应力可改造陆架沉积物,此时期,西部陆架含砾砂-砾质砂区(B-1)和北部陆架含砾砂-含砾泥质砂区(B-2)的地势差异及其所影响的水平海侵速度和潮波强度的差异是造就两者沉积组分、类型、石英、长石、岩屑和生物碎屑的含量及石英/长石比值差异的主因;(3)高水位时期,黑潮强度在本区增强,除侵蚀B-1底床,黑潮底层流也对B区的浅水地带进行冲刷,加之台湾暖流及沿岸流、长江冲淡水对该区的影响较小,使得B区细粒沉积物质含量较低,A区(北部陆架含砾泥质砂沉积区)细粒沉积广布,除与弱潮流作用相关外,弱的底层流的影响也是原因之一,同时来自台湾暖流可能携带部分细粒沉积物在此卸载。对于古海湾的成因而言,末次盛冰期频繁的浊流是将前更新世时期受湾内断裂作用而形成的半地堑地貌的海湾雏形进一步塑造成深凹地貌的主因,它进一步加剧了其深凹的地貌,在后期的冰消期和高水位时期,潮波系统及黑潮逐渐强盛,阻止了细粒沉积物的输入,保留了古海湾的深凹地貌。     

Gold Mineralization in the Eastern Tannu-Ola Ore District of the Altai-Sayan Folded Area (Russia)

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