El Ni?o事件大气-洋流异常与暖海温传播机理研究

利用1971～2000年逐月SODA (Simple Ocean Data Assimilation) 同化资料（Carton等，2004）、1980～2000年逐月NCEP/NCAR再分析资料（Kalnay等，1996）探讨中部型（暖海水首先出现在120°W以西）和东部型（暖海水首先出现在120°W以东）El Ni?o事件赤道纬向风应力及洋流的异常变化与暖海水信号的传播特征。研究指出:（1）中部型和东部型El Ni?o事件发生时，太平洋上赤道海表最大西风应力距平在西太平洋地区都有显著的东传现象，但中部型El Ni?o事件西风应力距平强度强，造成西太平洋赤道表层的东向流可达东太平洋地区，这类El Ni?o事件强度偏强。（2）中部型El Ni?o事件，赤道表层洋流辐合区及其下沉运动由西太平洋向东太平洋传播，辐合下沉运动抑制了深层冷海水上翻，西太平洋暖水能够传到东太平洋与西太平洋赤道表层洋流辐合区及其下沉运动的东移有关。（3）东部型El Ni?o事件西太平洋赤道表层洋流辐合区及其下沉运动没能直接传到东太平洋地区，东太平洋暖水形成与局地（120°W以东）辐合下沉运动抑制深层冷海水上翻有关；东部型El Ni?o事件暖池次表层的暖水，不是沿着西太平洋赤道次表层向东传播到东太平洋地区，而是由南太平洋西边界流将暖池海水带到40°S左右的西风漂流区， 再由西风漂流平流到东太平洋。     

深水浊积砂体的成因机理及特征

深水浊积砂体及其体系域以其重要的理论意义和作为油气储集层的经济价值始终是沉积地质学研究的主要领域之一。深水浊积砂体是在深水环境下在重力作用下所形成的一个连续过程的组成部分。这个连续部分可以分为五类:泥石流、颗粒流、流体化沉积物流、浊流和滑塌。由浊流过程形成的深水环境下的浊积砂体,具有海相浊积体和湖相浊积体的特征,与海(湖)平面的下隆低水位有关。     

基于弯道超高计算泥石流流速的探讨

泥石流流速是难以实测和准确推算的重要参数。在分析既有各类弯道超高计算公式的基础上,探讨适用于各类泥石流的弯道超高计算模式,进而改进基于弯道超高的粘性泥石流、稀性泥石流和泥流的流速计算公式,用实例加以验证。     

2003年11月超强磁暴热层大气密度扰动及其与焦耳加热和环电流指数的关系——CHAMP卫星观测

本文利用CHAMP卫星加速度仪测量数据，计算和分析2003年11月20～21日大磁暴期间大气质量密度扰动的全球分布特征；研究暴时变化与极区大尺度对流引起的全球焦耳加热总功率及环电流指数SYM H之间的关系.结果表明，磁暴期间400 km高度上热层大气质量密度大幅度上升， NRLMSISE 00模式预测值与此相比有很大差别；暴时大气密度的增大存在昼/夜半球不对称性：白天强于夜晚，且白天随纬度的分布呈现出比较复杂的图像，在赤道附近和南半球中低纬区（10°N ～50°S）大气密度增大较强，并呈双峰分布，两个峰分别位于0°和45°S，另外在极区也出现大气密度扰动的局部极大，而在夜晚，大气密度变化南北半球比较对称，在赤道低纬区大气密度增大较强；互相关分析表明，中低纬区大气密度变化滞后于全球焦耳加热总功率3～7 h，滞后于环电流指数（SYM H）0～3 h，与二者存在很强的相关，表明极区焦耳加热和赤道环电流过程对暴时热层大气密度扰动有重要影响.     

Subtropical to temperate facies from a transition zone, mixed carbonate–siliciclastic system, Palaeogene, North Carolina, USA

Palaeogene passive margin sediments on the US mid‐Atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate–siliciclastic shelves. This study utilizes well cuttings, outcrop, core, and seismic data to document temporal and spatial variations in admixed bryozoan‐rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone. This zone was situated between north‐flowing, warm waters of the ancestral Gulf Stream (carbonate dominated settings) and south‐flowing, cold waters of the ancestral Labrador Current (siliciclastic dominated settings). Some degree of mixing of carbonates and siliciclastics occurs in all facies; however, siliciclastic‐prone sediments predominate in nearshore settings, while carbonate‐prone sediments are more common in more open marine settings of the inner shelf break and deep shelf. A distinctive dual‐break shelf depositional profile originated following a major Late Cretaceous to Palaeocene transgression that drowned the earlier shallow platform. This profile was characterized by prominent mid‐shelf break dividing the shallow shelf from the deep shelf and a major continental shelf/slope break. Incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin. Storm wave base also contributed to the preservation of the dual‐break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid‐shelf break. Sediment fines in deep shelf facies were produced in place, transported downdip from the shallow shelf by storm ebb currents and boundary currents, and reworked from adjacent areas of the deep shelf by strike‐parallel boundary currents. Regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf, with warmer waters and more humid climates favouring carbonate deposition and cooler, more arid conditions favouring glaucony and siliciclastic dominated deposition. Continuous wave and current sweeping of the shallow shelf favoured deposition of mud‐lean facies across much of the shallow shelf. Skeletal components in much of the carbonate‐rich strata formed in warm, nutrient‐rich subtropical waters, as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages. These indicators of warm water deposition within the bryozoan‐mollusk‐rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage; such facies generally are associated with cooler water depositional settings.     

Experimental study on the effects of artificial bed roughness on turbidity currents over abrupt bed slope change

A series of experimental observations are presented in the current study to discuss the effects of artificial bed roughness on the turbidity current flowing in a rectangular channel with an abrupt change in bed slope.For this purpose,two different types of elements,sinusoidal and trapezoidal,with various heights and arrangements are considered as artificial bed roughness.A Vectrino velocity meter was used to measure the velocity and sediment concentration profiles.The effects of inlet sediment concentration on front velocity,body velocity,unit discharge,sediment concentration,and suspended load transport rate also were investigated.Accurate equations were developed for estimation of the velocity of a turbidity current over smooth and rough beds.The unexpected experimental results showed that unlike the effect of roughness height,a change in the roughness arrangement has no significant influence on the velocity of a turbidity current.Also,the effect of bed roughness on the front velocity of a denser current is more significant.     

Quasi-stationary flow structure in turbidity currents

A turbidity current is a particle-laden current driven by density differences due to suspended sediment particles. Turbidity currents can transport large amounts of sediment down slopes over great distances, and play a significant role in fluvial, lake and submarine systems. To better understand the sediment transport process, the flow system of an experimentally produced turbidity current in an inclined flume was investigated using video processing. We observed that the current progresses with constant frontal velocity and maintains an unchanged global interface geometry. In addition, the spatio-temporal profiles of the inner mean and turbulence velocity obtained by ultrasound velocity profiler (UVP) showed that similar distributions were maintained, with low dissipation. The results indicate that the turbidity current progressed in a quasi-stationary state, which enabled long-distance sediment transport. To understand the mechanisms behind the quasi-stationary flow, we analyzed the forces acting on the turbidity current. We found that under particular densities of suspended particles, the gravitational force is balanced by the viscous forces along the slope direction. We conclude that this specific force balance induces the quasi-stationary flow structure, enabling the long-distance transport of a substantial amount of sediment downstream with low dissipation.     

Spatio-temporal characteristics of small-scale wave–current ripples on the Ameland ebb-tidal delta

Ebb-tidal deltas are highly dynamic environments affected by both waves and currents that approach the coast under various angles. Among other bedforms of various scales, these hydrodynamics create small-scale bedforms (ripples), which increase the bed roughness and will therefore affect hydrodynamics and sediment transport. In morphodynamic models, sediment transport predictions depend on the roughness height, but the accuracy of these predictors has not been tested for field conditions with strongly mixed (wave–current dominated) forcing. In this study, small-scale bedforms were observed in the field with a 3D Profiling Sonar at five locations on the Ameland ebb-tidal delta, the Netherlands. Hydrodynamic conditions ranged from wave dominated to current dominated, but were mixed most of the time. Small-scale ripples were found on all studied parts of the delta, superimposed on megaripples. Even though a large range of hydrodynamic conditions was encountered, the spatio-temporal variations in small-scale ripple dimensions were relatively small (height 0.015 m, length 0.11 m). Also, the ripples were always highly three-dimensional. These small dimensions are probably caused by the fact that the bed consists of relatively fine sediment. Five bedform height predictors were tested, but they all overestimated the ripple heights, partly because they were not created for small grain sizes. Furthermore, the predictors all have a strong dependence on wave- and current-related velocities, whereas the ripple heights measured here were only related to the near-bed orbital velocity. Therefore, ripple heights and lengths in wave–current-dominated, fine-grained coastal areas ( mm) may be best estimated by constant values rather than values dependent on the hydrodynamics. In the case of the Ameland ebb-tidal delta, these values were found to be m and m. ©2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

The Wave Energy Concentration at the Agulhas Current off South Africa

The case of a freak wave collision with the ship in the Agulhas current is described. The explanation of the appearance of the freak wave as a result of wind-wave transformation in the Agulhas current is given. Swell is captured and intensified by the counter-current and is located in the neighbourhood of the maximum value of the current velocity, as a result of which there is a great concentration of wave-energy density. The superposition of wind and sea with swell transformed by the current promotes the formation of the freak waves. Using a simple mathematical analysis, an optimal ship track is proposed which could reduce the risk of collision with a freak wave.     

中国红土型金矿床研究综述

对红土型含矿床的勘查现状,矿化特征及成矿规律进行了探讨和总结,认为它形成于第三系－第四系红土风化壳内,可包括狭义的铁帽型金矿床,;概述了红土型金矿床的有效勘查方法和具体勘查方案。