Tracking denudation and sediment production and transport with cosmogenic 10Be in arid,high-altitude Himalayan half-grabens,Zanskar, northern India

Understanding the extent to which local factors, including bedrock and structure, govern catchment denudation in mountainous environments as opposed to broader climate or tectonic patterns provides insight into how landscapes evolve as sediment is generated and transported through them, and whether they have approached steady-state equilibrium. We measured beryllium-10 (¹⁰Be) concentrations in 21 sediment samples from glaciated footwall and hanging wall catchments, including a set of nested catchments, and 12 bedrock samples in the Puga and Tso Morari half-grabens located in the high-elevation, arid Zanskar region of northern India. In the Puga half-graben where catchments are underlain by quartzo-feldspathic gneissic bedrock, bedrock along catchment divides is eroding very slowly, about 5 m/Ma, due to extreme aridity and ¹⁰Be concentrations in catchment sediments are the highest (~60–90 × 10⁵ atoms/g SiO₂) as colluvium accumulates on hillslopes, decoupled from their ephemeral streams. At Puga, ¹⁰Be concentrations and the average erosion rates of a set of six nested catchments demonstrate that catchment denudation is transport-limited as sediment stagnates on lower slopes before reaching the catchment outlet. In the Tso Morari half-graben, gneissic bedrock is also eroding very slowly but ¹⁰Be concentrations in sediments in catchments underlain by low grade meta-sedimentary rocks, are significantly lower (~10–35 × 10⁵ atoms/g SiO₂). In these arid, high-elevation environments, ¹⁰Be concentrations in catchment sediments have more to do with bedrock weathering and transport times than steady-state denudation rates. © 2020 John Wiley & Sons, Ltd.     

甘东南地区水氡浓度的临界慢化现象研究

本文将临界慢化理论应用于甘东南地区水氡浓度观测资料的处理中,以2008年5月12日汶川M_S8.0地震、2013年7月22日甘肃岷县—漳县M_S6.6地震为例,计算表征临界慢化现象的自相关系数和方差。计算结果表明,甘东南地区多个台站的水氡浓度观测资料在两次地震前均存在较明显的临界慢化现象。并从空间分布、持续时间、变化形态方面分析了异常点水氡浓度变化的临界慢化特征,结合水氡异常的水动力学机制和异常点所在构造,认为2次地震前的临界慢化现象与地震的发生有一定关系。     

中国西部区域GRACE卫星重力变化

针对研究中国西部长期重力变化的问题,该文利用GRACE月重力场模型,基于Slepian变换构建中国西部区域局部重力场,并采用GIA和GLDAS等模型扣除相应误差,通过时间序列分析方法得到该区域2003—2013年卫星重力变化。结果表明,东天山呈现负重力变化,可能由区域冰川消融引起的;西天山的正重力变化,应与冰川小幅增加和构造运动引起的壳幔物质积累有关;青藏高原内陆正重力变化可能由区域地壳抬升、粘弹性地壳的构造应变以及壳幔物质的质量迁移与积累引起;青藏高原边界区域的负重力变化,应与冰川加速消融以及地下水抽取有关。Slepian方法较好地克服了滤波平滑处理带来的重力变化信号压制及细节平滑,可为中国西部的地壳运动、地震活动和气候变化等研究提供数据支撑。     

中国东海叶绿素浓度变化分析及其海水温度响应

海洋叶绿素浓度时空格局分析及与海水温度的响应研究对于海洋资源的开发和保护及赤潮的预防具有重要意义。本文基于2004—2018年东海叶绿素浓度和海水温度数据运用趋势分析及ArcGIS10.2软件,对东海叶绿素浓度作了时空分析研究,并结合海水温度进行了回归分析,以探究叶绿素对海水温度变化的响应机制。结果表明：①东海叶绿素浓度在2004—2018年间没有明显的年际变化特征。年内则随时间上下波动,冬季为波峰,夏季为波谷。离海岸带越近,叶绿素浓度越高。②东海海域海水温度在年际尺度上呈波动式起伏变化。在季节尺度上夏秋两季温度较高,春季次之,冬季最低。从沿海到外海海域海温逐渐升高。③就空间相关性而言,东海海域叶绿素浓度与海水温度整体呈负相关,在不同海域相关程度不同。长江口和外海区域叶绿素浓度与海水温度具有很强的相关性;在沿海区域,由于受到城市环境、经济发展及人类生产生活的影响,海水温度与叶绿素浓度的相关性不明显。     

长江口深水航道三维泥沙数值模型相关问题探讨

基于近年来长江口三维水沙盐数值模型及水沙运动机理的研究进展,系统梳理了在长江口实际应用中面临的若干理论和技术难题,其中包括长江口物质输运模拟计算格式的守恒性和稳定性、河口区域河床切应力的准确计算、拦门沙区域近底高浓度泥沙形成机理及数值模型模拟、长江口近底高浓度泥沙横向入槽模式等问题,通过对于上述问题的梳理和总结,表明在长江口这类巨型河口进行三维水沙盐数值模型和水沙机理研究的复杂性,并针对此类区域的模型技术研发和水沙运动理论研究,提出了有科学意义和研究价值的方向和思路。     

Shear strength of soil berm during lateral buckling of subsea pipelines

The soil resistance developed during temperature- and pressure-induced large lateral movements of shallowly embedded subsea flowlines is an important input parameter for the structural design process. A major source of uncertainty in calculation of the soil resistance is the undrained shear strength of the soil berm produced as the flowline moves across the seabed, which is affected by the level of remoulding. To investigate the effect of pipeline embedment and displacement amplitude on the shear strength of the berm, a set of centrifuge model tests was conducted on kaolin clay, involving laterally moving pipelines with constant embedments in the range 5%–35% of the pipe diameter. Back-analysis of the test results, using finite element limit analysis, showed that the shear strength of the soil berm is a function of pipe displacement amplitude, pipe embedment, and soil sensitivity. On the basis of these results, we propose that the overall berm undrained shear strength may be determined as a convolution of the shear strengths of its constituent soil elements. Finally, a formula is presented for calculating the shear strength of soil elements within the soil berm, and this is used to back-analyse the overall soil berm resistance from the model tests.     

山东半岛沿岸海域悬浮体时空分布及形成机制分析

依据2015年GOCI(geostationary ocean color imager)卫星影像反演的悬浮体浓度数据,分析了山东半岛沿岸海域表层悬浮体质量浓度和锋面月变化特征,揭示该海域悬浮体的分布特征和扩散格局,并结合风速、波高以及海表温度数据,对其控制因素进行初步探讨。结果显示:研究区内悬浮体质量浓度整体表现为冬季最高,春秋次之,夏季最低的分布特征;悬浮体扩散过程可以划分为4个阶段,冬季稳定外输,春季向岸退缩,夏季近岸贮存,秋季向外扩散。此外,山东半岛近岸存在一条悬浮体质量浓度高于10 mg/L的浑浊带,该浑浊带同样表现出季节变化,它在秋季开始形成,其悬浮体含量、幅宽及延伸范围在冬季达到最大,春季减弱,夏季消失。研究认为山东半岛沿岸海域的表层悬浮体来源主要是海底沉积物的再悬浮。风场、海浪以及沿岸流的强弱变化对悬浮体分布和输运的季节变化有重要的控制作用:风场和海浪影响海水混合搅拌强度,改变海底沉积物再悬浮作用的临界深度,进而影响表层海水悬浮体浓度,致使悬浮体浓度与风浪的月际变化趋势基本一致;沿岸流携带高浓度悬浮体沿山东半岛输运形成沿岸浑浊带,沿岸流的强度变化直接控制浑浊带的季节变化。     

Modelling the spatial dynamics of Mainland China-born migrants in Australia

Over the past two decades, migration from Mainland China (MC) to Australia has become increasingly significant. In contrast to previous migrant waves, post-2000 MC-born migrants in Australia are more likely to be highly skilled and/or financially independent, and often migrate under skilled, business and investment visa programs. Though scholarship has explored various facets of MC-born migrants’ settlement in Australian cities, the spatial dynamics of settlement, and change over time associated with these shifts in socio-economic profile, have remained unexplored. This paper draws on three census periods, and employs a local indicator of spatial autocorrelation together with a geographically weighted regression. We conclude that the settlement patterns of MC-born migrants in Australia do not follow the ‘straight-line’ assumptions of spatial assimilation theory, nor are they tied explicitly to socio-economic factors in the majority of capital cities. Instead, the settlement patterns of MC-born migrants vary by city: Sydney and Melbourne display the most spatially segmented settlement patterns; while Adelaide and Perth exhibit increasing levels of concentration as the number of MC-born migrants grows. Results indicate that while MC-born migrants are somewhat likely to cluster at the early stage of group formation, within-group spatial patterns are articulated by social attributes as the group grows in size and significance in a metropolitan context.     

走向大中小城市协调发展的中国新型城镇化格局——建国以来中国城市规模分布演化与影响因素

为了落实国家新型城镇化规划提出的大中小城市协调发展战略,对1952-2014年中国城市规模分布指数进行演化分析,并在时间序列分析基础上探索了影响因素。结果表明,2000年以来,中国城市规模分布一改长期的分散化趋势,正走向集中化;人口规模增长、政策干预以及城市之间信息和交通成本的节约,都促使城市规模分布分散化;人均GDP长期以来促进了城市规模分布的集中,但近年来开始促进分散化;对外开放水平则主要促进分布的集中。未来应以全国适度均衡发展作为指导方针;远期以市场一体化,近期以共赢互利机制建设为抓手,促进城市群内大中小城市协调分工,优势互补;注意政策的稳定性和长期性,减少城市化格局的人为波动。     

振荡流层移输沙条件下悬沙层泥沙扩散系数垂向分布特征研究

层移输沙是海岸带泥沙运动的主要形式之一,其垂向悬沙浓度分布规律的研究一直是海岸工程关心的重点。一般情况下,经典的纯扩散模型被用来描述和解释悬沙浓度的试验数据,该模型认为周期平均悬沙浓度主要由参考浓度、泥沙沉速和泥沙扩散系数确定。泥沙扩散系数可以由泥沙沉速和悬沙浓度的垂向梯度反演得到。既往研究大多直接给出泥沙扩散系数的结果,对于不同反演计算方法间结果差别的研究较少。本研究汇总了已有振荡流层移输沙试验数据,采用曲线拟合方法和直接差分方法计算了相应的泥沙扩散系数,研究表明两种方法得到的计算结果在垂向位置z 0.15 m处差异不大,随着垂向位置的升高,差分方法的计算结果略微大于拟合方法。考虑到拟合方法可以得到连续的泥沙扩散系数垂向分布,本研究推荐使用幂函数形式的曲线拟合方法求解悬移泥沙扩散系数。基于此,对比分析了层移输沙悬沙层泥沙扩散系数随泥沙粒径、振荡流周期、均方根流速和振荡流类型等物理参数的变化规律。在纯振荡流层移输沙条件下,泥沙扩散系数随泥沙粒径的增大而增大,而振荡流周期和均方根流速几乎不影响泥沙扩散系数。在振荡流和定常流共同作用下,泥沙扩散系数受振荡流周期和定常流流速的影响,泥沙扩散系数随着振荡流周期的增大或定常流流速的减小而增大。