Biogeography: molecular trails from hitch-hiking snails

Darwin was fascinated by the transportation of land snails across great swathes of open ocean by birds--he even immersed snails in sea water to see how long they would survive. Here we follow a molecular phylogenetic trail that reveals the incredible transequatorial dispersal of the land snail Balea from Europe to the Azores and the Tristan da Cunha islands, and back again. This long-distance dispersal is unexpected for what are proverbially considered the most pedestrian of creatures.     

基于R语言的赏金类软件数据分析

随着赏金类软件的不断发展,人们日常的对话从“今天你吃饭了吗”转变成“今天你领钱了吗”.2017下半年,随着支付宝扫码赚赏金和直播答题赚赏金等活动的兴起,赏金类软件一时风头无两,得到了国民的极高关注.文中利用R软件进行数据的分析处理,旨在了解影响赏金类软件推广的因素,分析用户对赏金类软件的看法,研究其发展所面临的问题.最...     

Imaging the Indian subcontinent beneath the Himalaya

The rocks of the Indian subcontinent are last seen south of the Ganges before they plunge beneath the Himalaya and the Tibetan plateau. They are next glimpsed in seismic reflection profiles deep beneath southern Tibet, yet the surface seen there has been modified by processes within the Himalaya that have consumed parts of the upper Indian crust and converted them into Himalayan rocks. The geometry of the partly dismantled Indian plate as it passes through the Himalayan process zone has hitherto eluded imaging. Here we report seismic images both of the decollement at the base of the Himalaya and of the Moho (the boundary between crust and mantle) at the base of the Indian crust. A significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths. North of the Himalaya, the lower Indian crust is characterized by a high-velocity region consistent with the formation of eclogite, a high-density material whose presence affects the dynamics of the Tibetan plateau.     

Potential methane reservoirs beneath Antarctica

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14?kilometres thick and an estimated 21,000 petagrams (1?Pg equals 10(15)?g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300?metres in West Antarctica and 700?metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.     

应用型本科高校的生物地理学课程改革和创新

针对应用型本科地理科学专业的专业课“生物地理学”教学过程中存在的问题,结合在教学科研中的实际经验,运用结构主义课程理论,对课程理念、教学内容、教学方法进行改革,并建立基于工作过程导向的考核机制。     

Thermochemical structures beneath Africa and the Pacific Ocean

Large low-velocity seismic anomalies have been detected in the Earth's lower mantle beneath Africa and the Pacific Ocean that are not easily explained by temperature variations alone. The African anomaly has been interpreted to be a northwest-southeast-trending structure with a sharp-edged linear, ridge-like morphology. The Pacific anomaly, on the other hand, appears to be more rounded in shape. Mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes. It has not been shown, however, that such models can lead to thermochemical structures that satisfy the geometrical constraints, as inferred from seismological observations. Here we present numerical models of thermochemical convection in a three-dimensional spherical geometry using plate velocities inferred for the past 119 million years. We show that Earth's subduction history can lead to thermochemical structures similar in shape to the observed large, lower-mantle velocity anomalies. We find that subduction history tends to focus dense material into a ridge-like pile beneath Africa and a relatively more-rounded pile under the Pacific Ocean, consistent with seismic observations.     

凤仙花属系统学与生物地理学研究新进展

概述了近10年来凤仙花属系统学与生物地理学研究的新进展,包括花序与花、子房、种子、孢粉学、细胞学、花器官发生学、系统发生学、生物地理学等内容.     

Small-scale convection beneath oceans and continents

Small-scale convection supplies heat flow of ～17 mW m-2 to the base of stable continents where xenolith studies resolve the geotherm.However,effects of small-scale convection are difficult to resolve in ocean basins.On first pass,most seafloor appears to subside to an asymptote compatible with ～40 mW m-2 convective heat flow.These common regions are tracked by hotspots so uplift associated with ponded mantle material is an attractive alternative.Unaffected seafloor in the North and South Atlantic continues to subside with the square root of age as expected from pure conduction.The theory of stagnant-lid convection provides good scaling relationships for heat flow.For linear viscosity,heat flow is proportional to the underlying "half-space" viscosity to the 1/3 power and the temperature to change viscosity by a factor of e to the 4/3 power.The formalism is easily modified to represent convection beneath a lid of highly viscous and buoyant cratonal lithosphere and to represent transient convection beneath thickening oceanic lithosphere.Asthenospheric mantle with linear,strongly temperature-dependent,and weakly depth-dependent viscosity is compatible with both oceanic and continental data.More complicated rheology may allow vigorous small-scale convection under most but not all old ocean basins.Still viable hypotheses require poorly understood global features,including lateral variations of asthenospheric temperature.Seismological studies have the potential to resolve the lithosphere-asthenosphere boundary,including local variations of its depth associated with small-scale convection.     

加快青海省林下产业发展的研究

目前,青海省林地面积为309.66万公顷,孕育了许多特有动物资源、林下以及林缘植物资源。但是通过开发形成养殖产业的品种几乎没有,仍然在原生地采挖,这不但使得野生资源枯竭,同时严重地破坏了高原脆弱的生态环境,结合林下资源的应用现状,提出了根据林下动植物资源的特点,分区域地发展青海地道药用动植物、食用经济动植物、菌类,进行合理种植、养殖,以构建稳定的生态系统,达到林地生物的多样性,同时促进青海地方经济发展的总体思路。     

中国东北上地幔各向异性研究

利用中国数字地震台网记录的地震波形,观测其穿过地球外核和地幔的SKS波分裂特征,确定了快波S波的振动方向和快慢波时间延迟。这种经过地幔传播的SKS震相的横波分裂主要来源于上地幔的各向异性。可以用应变引起的上地幔中矿物质的结晶优势排列来解释。结果表明,对于所分析的10个观测台站均发现了明显的横波分裂现象。时间延迟在0.4～1.8 s。在东部地区,快波振动方向与中国东北西太平洋俯冲带的板块相对运动方向基本一致,说明俯冲的太平洋板块地幔流对各向异性有重要意义。在西部地区,快波振动方向和时间延迟都具有较大差异,说明其总体形变的起因是复杂的,各向异性受到地幔流和历史构造运动的双重影响。