Stable Atmospheric Boundary Layer Over a Uniform Slope: Some Theoretical Concepts

Theoretical arguments are developed to describe the effects of a uniform slope on the development of the stably stratified atmospheric boundary layer (SBL). A maximum sustainable surface buoyancy flux exists for the SBL overlying a uniform, non-sloping surface. In this study it is shown that the SBL overlying a uniform shallow slope (with gradient of the order of 1:1000) also supports a maximum sustainable buoyancy flux, B _max, but that the value of B _max is influenced by the gradient of the slope, γ. It is demonstrated that in the limit γ → 0, results for the SBL over a horizontal surface are recovered.     

云南个旧卡房铜矿床地质地球化学特征及其成因探讨

云南个旧是世界上最大的锡多金属矿田,卡房铜矿是个旧矿田主要的产铜区。卡房铜矿主要的矿床类型有两类:玄武岩层中或玄武岩与大理岩层间的似层状矿体以及花岗岩与围岩接触带矿体。围岩蚀变主要有夕卡岩化、阳起石化和金云母化。电子探针分析结果显示,卡房铜矿夕卡岩中的辉石主要为透辉石-钙铁辉石系列,石榴子石端元组分以钙铝榴石-钙铁榴石为主。流体包裹体及氢、氧同位素研究显示,从主成矿期到后成矿期,流体温度有显著降低(从260～360℃到160～280℃),而流体盐度则基本保持不变(从1.74%～12.51%到1.74%～11.93%)。氢、氧同位素组成表明,早期成矿流体主要以岩浆水为主,而晚期成矿流体可能在上升过程中与地层中的大气降水相混合。硫同位素分析结果表明,卡房铜矿似层状矿体中硫化物的硫来源于三叠系玄武岩,而燕山期花岗岩和三叠纪玄武岩共同为卡房铜矿接触带矿体提供了成矿所需的大部分的硫。铅同位素分析结果显示,卡房铜矿似层状矿体的成矿物质主要来源于三叠系玄武岩,而接触带矿体的铅可能主要来源于燕山期花岗岩。     

Analysis of solitary disturbances over an Antarctic Ice Shelf

Large amplitude, propagating, solitary disturbances have been observed in the atmospheric boundary layer over a gently sloping Antarctic Ice Shelf. The waves are usually trapped within the lowest 40 m and are observed only when the surface layer is strongly stably stratified and prevailing wind speeds are low. It is shown that the waves are trapped due to the combined effects of velocity curvature and stratification. The observed wavelengths can be bounded using simple heuristic arguments based on the Scorer parameter. Properties of the waves are compared with results from the weakly nonlinear numerical model of Rottman and Einaudi (1993).     

A note on mesh selection and sampling efficiency in benthic studies

The effects of using different mesh sizes on interpretation of seasonal changes in the fauna of a sandy station off the north-east coast of England was investigated. Retention of smaller animals depended both upon absolute size, and the tendency of some species to fragment during routine processing of samples in the field. Seasonal effects may lead to difficulties in establishing trends in abundance using a larger mesh size, and the implications for certain types of investigation of this and other sources of sampling error are discussed.     

Chironomid-based water depth reconstructions: an independent evaluation of site-specific and local inference models

Water depth is an important environmental variable that explains a significant portion of the variation in the chironomid fauna of shallow lakes. We developed site-specific and local chironomid water-depth inference models using 26 and 104 surface-sediment samples, respectively, from seven kettlehole lakes in the Plymouth Aquifer, southeast Massachusetts, USA. Our site-specific model spans a depth gradient of 5.6?m, has an $ {\text{r}}_{\text{jack}}^{2} $ of 0.90, root mean square error of prediction (RMSEP) of 0.5?m and maximum bias of 0.7?m. Our local model has a depth gradient of 11.7?m, an $ {\text{r}}_{\text{jack}}^{2} $ of 0.71, RMSEP of 1.6?m and maximum bias of 2.9?m. Principal coordinates of neighbourhood matrices (PCNM) analysis showed that there is no influence of spatial autocorrelation on the site-specific model, but PCNM variables explained a significant amount of variance (4.8%) in the local model. This variance, however, is unique from the variance explained by water depth. We applied the inference models to a Holocene chironomid record from Crooked Pond, a site for which multiple, independent palaeohydrological reconstructions are available. The chironomid-based reconstructions are remarkably similar and show stable water depths of ~5?m, interrupted by a 2-m decrease between 4,200 and 3,200?cal a BP. Sedimentological evidence of water level fluctuations at Crooked Pond, obtained using the so-called Digerfeldt approach, also shows a drop in water depths around that time. The period of reconstructed lower water levels coincides with the abrupt decline in moisture-dependent hemlock in this region, providing further evidence for this major palaeohydrological event. The site-specific model has the best performance statistics, but the high percent abundance of fossil taxa from the long core that are absent or rare in the training set makes the site-specific reconstruction unreliable for the period before 4,400?cal a BP. The fossil taxa are well represented in the local model, making it the preferred inference model. The strong similarity between the chironomid-based reconstructions and the independent palaeohydrological records highlights the potential for using chironomid-based inference models to determine past lake depths at sites where temperature was not an influencing factor.     

Ethnic change and diversity in England, 1981–2001

The paper compares ethnic change and diversity across two recent decades using common group and area definitions. Ethnic minority groups are shown to be growing rapidly at 41 per cent between 1981 and 1991 and 39 per cent between 1991 and 2001. Some groups have grown swiftly (Black Africans, Bangladeshis), while others have seen moderate expansion (Indians, Other Asians). The White population has hardly grown and the White British population has probably declined. Black and Ethnic Minority (BEM) populations remain concentrated in metropolitan areas in 2001 as in 1991 and 1981. Whereas between 1981 and 1991, BEM groups were concentrating into metropolitan areas, between 1991 and 2001 deconcentration began for most groups. The London region stands out as highly dominant, housing more than 50 per cent of BEM populations as a whole in 1991 and 2001. However, between 1991 and 2001, BEM groups grew outside their core areas. The consequence of BEM population growth and spread has been a dramatic increase in ethnic diversity in all regions.