Selection of scale can reverse the importance of stochastic controls on community assembly

Reconciling the long-standing debate on the importance of niche-related and neutral factors on community assembly, recent research suggests that both deterministic and stochastic processes operate simultaneously along a continuum in many biogeographical systems. In particular, stochastic processes seem to lose importance under stressful conditions, which results in the increasing influence of deterministic counterparts. In this paper, I show that, at local scales, this stochasticity–stress relationship can be reversed along the environmental stress gradients within a salt marsh: stochasticity manifested under harshness. Here, low-lying, more stressful sites contained all of the plant species of the local pool (i.e. a greater chance of ecological drift), whereas high-elevation, less stressful sites exhibited reduced species richness due to competitive exclusion (i.e. a lower chance of ecological drift). I conclude that determining whether the importance of stochasticity in shaping community structure is greater under benign or harsh conditions depends on the scale of interest.     

深海多金属硫化物采矿研究进展及其前景探讨

随着陆地金属矿产资源的日渐枯竭,深海多金属硫化物逐渐成为海洋矿产资源勘探的新趋势。文章介绍了全球主要海底多金属硫化物矿床的成因及分布特点,阐述了多个国际矿业公司和国际海洋组织对西南太平洋、大西洋和印度洋海底块状多金属硫化物勘探活动的最新进展。从海底多金属硫化物的金属品质、深海采矿的法律政策和环境保护等方面对海底多金属硫化物的开发前景进行探讨,并提出积极投身国际海底资源开发规章制定,进一步细化国内法律制度,为深海采矿提供良好的法律制度环境;提升深海治理能力,增强我国在深海领域的话语权;完善深海技术装备体系,提高深海开发创新能力等建议。     

Threshold sediment flux for the formation of river deltas in Hainan Island,southern China

Journal of Geographical Sciences - The knowledge of geomorphological evolution from an estuary to a river delta is necessary to form the formulation of comprehensive land-ocean interaction...     

Effects of aspect on weathering: anomalous behaviour of sandstone gravestones in southeast England

Rocks in the humid temperate zone tend to weather more severely on faces exposed to the prevailing winds than on their more sheltered leeward faces. In southeast England, however, gravestones composed of a non‐local, quartz‐rich sandstone exhibit a reverse weathering pattern. The east‐facing, lee sides exhibit a much greater depth and areal extent of weathering than the west sides which face the westerly wind and rain. Possible reasons for the asymmetric pattern of weathering are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

长江中下游成矿带铁-铜成矿系统结构的地球物理探测: 综合分析

成矿系统是在深部过程驱动下形成的、具有自组织的能量及物质迁移-汇聚系统。系统在形成和演化过程中,在岩石圈不同尺度上留下“痕迹”,这种“痕迹”可以通过地球物理、地球化学和遥感等方法进行探测或观测。文章尝试在成矿系统理论框架下,对近10多年来在长江中下游成矿带进行的多尺度地球物理、地球化学探测结果进行分析,识别典型陆内成矿系统“源区”“通道”“场所”的地球物理、地球化学“痕迹”,尝试构建陆内成矿系统的空间结构模型。主要结论有:(1)长江中下游晚中生代的大规模铁、铜多金属成矿作用是一个完整的成矿系统。该系统包括3个子系统,分别为与高钾钙碱性岩浆岩有关的夕卡岩-斑岩成矿子系统、与橄榄安粗岩有关的陆相火山岩铁(硫)成矿子系统和与碱性岩有关的铜-金(铀)成矿子系统。(2)成矿系统的“源区”来自富集地幔的熔融、底侵,并在壳/幔边界与下地壳物质的混合,具有多级分布特点。幔源岩浆与地壳物质混合的比例决定了成矿金属的类型。(3)成矿带发育的“鳄鱼嘴”构造是铁铜成矿系统的主干“通道”。成矿系统“末端”矿质沉淀的“场所”主要受近地表褶皱、断裂、层间滑脱断层,以及由它们形成的断裂(裂隙)网络控制。(4)区域磁异常、放射性和地球化学异常是成矿系统残留“痕迹”的响应和“标识”。通过分析不同尺度的“标识”特征,可以深入认识成矿系统的空间结构,并可用于深部成矿预测。     

Hydrogeochemistry of shallow groundwater in an upland Scottish catchment

The hydrogeochemistry of shallow groundwater has been characterized in the Allt a'Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the influence of groundwater on the quality and quantity of stream flow. Shallow groundwater in superficial drift deposits is circumneutral (pH∽7·1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (>900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of baseflow in the catchment and also buffers the chemistry of stream water at high flows: groundwater may account for as much as 50–60% of annual runoff in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. © 1998 John Wiley & Sons, Ltd.     

西南印度洋中脊活动与非活动热液区沉积物元素地球化学特征对比

龙旂热液区与断桥热液区分别是西南印度洋中脊典型的活动与非活动热液区。为研究两区内表层沉积物地球化学特征,对共59件表层沉积物进行了元素地球化学测试,对其进行物质组分、富集系数与R型聚类等分析。结果表明:两区内普遍含较高的Ca、Sr、Ba等生源元素和Fe、Mg、Si、Al等围岩元素,而构造、围岩和热液活动等因素的不同,使两区沉积物的元素地球化学特征存在差异。龙旂区沉积物出现了源于超基性围岩的组分并体现在元素聚类组合中,其沉积物中热液富集相关元素Cu、Zn、Fe和Co等。断桥区更高的生源元素含量可能指示其热液活动停止后,主要受生物沉积作用的影响,该区热液相关元素与基性围岩联系紧密,表现出Pb与W的明显富集。     

南极布兰斯菲尔德海峡及邻区地壳结构反演及构造解析

南极布兰斯菲尔德海峡及邻区是南极半岛海域火山、地震等新构造运动最活跃的地区,由于前人对资料处理解释的差异,导致盆地的构造格局仍部分存疑。本文以研究区的卫星重力数据为基础,以多道反射地震和部分岩性资料为约束,采用重震联合反演方法构建了三条横跨研究区的地壳结构剖面,并进一步研究布兰斯菲尔德海峡盆地的地壳结构。研究结果表明布兰斯菲尔德海峡盆地莫霍面深度为33—38km。菲尼克斯板块俯冲消减下沉至南设得兰岛弧之下,导致南设得兰海沟的俯冲带后撤,产生3—4km厚的岩浆混染地壳,密度为2.9g/cm~3。分析认为受板块运动和弧后扩张影响,沿布兰斯菲尔德海峡盆地扩张脊分布的海底火山裂隙式喷发,并进一步导致盆地的持续性扩张。     

南海北部深水区东西构造差异性及其动力学机制

This paper overviews research progress in observation, theoretical analysis and numerical modeling of submesoscale dynamic processes in the South China Sea(SCS) particularly during recent five years. The submesoscale processes are defined according to both spatial and dynamic scales, and divided into four subcategories as submesoscale waves, submesoscale vortexes, submesoscale shelf processes, and submesoscale turbulence. The major new findings are as follows.(1) Systematic mooring observations provide new insights into the solitary waves(ISWs) and the typhoon-forced near-inertial waves(NIWs), of which a new type of ISWs with period of 23 h was observed in the northern SCS(NSCS), and the influences of background vorticity, summer monsoon onset, and deep meridional overturning circulation on the NIWs, as well as nonlinear wave-wave interaction between the NIWs and internal tides, are better understood. On the other hand, satellite altimeter sea surface height data are used to reveal the internal tide radiation patterns and provide solid evidence for that the ISWs in the northeastern SCS originate from the Luzon Strait.(2) Submesoscale offshore jets and associated vortex trains off the Vietnam coast in the western boundary of the SCS were observed from satellite chlorophyll concentration images. Spiral trains with the horizontal scale of 15–30 km and the spacing of 50–80 km were identified.(3) 3-D vertical circulation in the upwelling region east of Hainan Island was theoretically analyzed. The results show that distribution patterns of all the dynamic terms are featured by wave-like structures with horizontal wavelength scale of 20–40 km.(4) Numerical models have been used for the research of submesoscale turbulence. Submesoscale vertical pump of an anticyclonic eddy and the spatiotemporal features of submesoscale processes in the northeastern SCS are well modeled.     

长江口南汇边滩冲淤变化规律与机制

根据1842—2004年海图资料分析发现,南汇边滩存在近百年尺度的强烈冲刷—淤积旋回。长江主泓走南港或北港是造成冲刷期"北滩、东滩淤积,南滩、过渡带冲刷"或淤积期冲淤态势反相的主要原因;冲刷期内风暴强度和频数明显多于淤积期,造成冲刷期滩面叠置记忆的是暴风浪成因的"高滩冲刷、低滩淤积"的冲淤态势,而淤积期保存的是弱风浪成因的"高滩淤积、低滩冲刷"叠置增强的剖面特征。尽管三角洲整体冲淤态势的转变主要受流域来沙量的控制,但不同岸段受河口河势分水分沙作用、潮流和波浪等共同作用,明显存在此冲彼淤、冲淤动态调整等特征。已有的入海泥沙含量阈值研究以点代面或以局部代整体,这是造成阈值估算偏高的主要原因。2003年三峡水库开始蓄水后平均年输沙量154 Mt/a已低于低阈值184 Mt/a,但三角洲尚未如预测那样发生由净淤积向净侵蚀的转变。已有的河口水文观察资料显示,水体含沙量也未发生明显下降,这可能是潮控型三角洲潮流对泥沙在河口的再分配起主导作用,并可能由此延长三角洲冲淤转变对入海泥沙量减少的滞后。今后需进一步加强潮控型河口复杂过程的综合研究,提高对泥沙含量阈值估算和应对可能面临的海岸侵蚀及其相关的环境地质灾害的能力。