Does the Drake Passage play an essentially important role in the Cenozoic Cooling?

The Drake Passage is the seaway between South America and Antarctica. It is widely believed that the thermal isolation effects caused by the opening of the Drake Passage played an important role in the abrupt cooling that occurred at the Eocene-Oligocene boundary in the Cenozoic. These effects are also thought to be independent of the geometry of the passage. Here, the authors demonstrate that the climate impacts of the Drake Passage depend on the passage geometry by comparing the climate’s sensitivity to the opening of the Drake Passage under the present and the Early Eocene land-sea configurations. These experiments show that the thermal isolation effects caused by the passage are much stronger under the present land-sea configuration. In comparison, under the Early Eocene land-sea configuration, the weak anomalies in heat transport caused by the opening of the narrow and shallow Drake Passage are not strong enough to thermally insulate Antarctica. The climate effects of the Drake Passage on the Cenozoic cooling have been overestimated in previous sensitivity studies carried out using the present land-sea configuration. Thus, it is unlikely that the opening of the Drake Passage played an essential role in the abrupt Cenozoic cooling, especially in the abrupt cooling at the Eocene-Oligocene boundary.     

南沙头通道及横沙通道对长江口深水航道的影响分析

根据长江口南沙头通道、横沙通道和南北槽分汊口的断面水深变化及长江口南北港和南北槽的分流比变化实测资料,分析了长江口北槽深水航道淤积的原因。结果表明,北槽深水航道上段淤积受多种因素影响,其中,南沙头通道和横沙通道的发展对深水航道影响最大。南沙头通道的发展在加大落潮流量的同时,对南港南岸会产生一定的冲刷,后经沙洲的阻挡,把泥沙带向南港北岸,在北槽进口段处落淤,直接影响了进入深水航道的落潮量;横沙通道由于直接贯通了北港北槽的水沙交换,因而削弱了南港和北槽之间的水沙交换,促使北槽深水航道上段产生淤积,这也是南槽河道上段刷深的一个主要原因,而南槽河道的发展必然减少了进入北槽的落潮量,进一步加剧了北槽深水航道上段的淤积。同时,科氏力与北槽南导堤分流口鱼咀工程对深水航道也造成了一定的不可忽视的影响。研究成果对治理北槽深水航道淤积问题保障深水航道正常运行具有十分重要的科学实践意义。     

长江河口北槽水沙过程对航道整治工程的响应

北槽大型航道整治工程确定了南北槽分汊口分流界线, 阻碍了北槽和邻近滩槽的水沙自由交换过程, 使北槽水沙动力过程发生调整。基于工程前后北槽主槽纵向同步水沙观测数据的统计分析表明:入口段落潮优势显著减弱;上段枯季时落潮优势显著减弱, 而洪季时落潮优势有所增强;中段(弯曲段拐点附近)落潮优势略有减弱;下段落潮优势明显加强。北槽主槽水沙纵向输移机制分析表明:欧拉余流、潮泵作用、斯托克斯效应和垂向环流为悬沙输移的主要驱动力, 其中欧拉余流输沙指向海, 斯托克斯输沙和垂向环流输沙指向陆, 而潮泵输沙随着季节而变化。洪季, 欧拉余流输沙和潮泵输沙在工程前后的变化使大潮期河床冲淤由中段和下段普遍落淤转化为中上段集中落淤。枯季, 工程前后稳定的潮流辐散输沙作用使大潮期河床以冲刷为主, 但工程后在入口段和上段潮泵的向上游输沙占优势, 使悬沙在入口段落淤。     

Influencing factors and evaluation application of regional crustal stability in the Bohai Strait

Due to the extremely complex geological conditions in the Bohai Strait, active faults is very developed and earthquake activity occurs frequently. It is of great importance to evaluate the regional crustal stability for the planning and construction of the Trans-straits Passage. In this study, the authors carry out the evaluation by means of buffer analysis, topology analysis and overlay analysis based on ArcGIS software. The evaluation mainly analyzed six assessment factors of Bohai Strait including neotectonic activity, active faults distribution, seismicity, tectonic stress fields, Bouguer gravity anomaly and geological disasters. In brief, the crustal stability of the eastern North Yellow Sea Basin is best, while that of the Bohai Basin and southwest Bohai Strait is poor. Meanwhile, small and frequent earthquakes in the southern Strait and geological disasters developed in the northern and central Strait such as tidal ridge and shallow gas which may adversely impact on the Trans-straits Passage construction.     

德雷克海峡夏季海雾的分析研究

本文利用中国第三次南极考察的海上实测水文气象资料 ,以及智利南极弗雷气象中心和阿根廷所发布的每日高空和地面天气图 ,对海雾进行了天气学分析 ,指出了夏季影响德雷克海峡地区的海雾过程主要是平流冷却雾。通过分析这种海雾生消时的气压场和其它要素场特征 ,得出一些有益的结论 ,从而为本区海雾的预报提供了依据。     

内通承压地质构造系统在热液铀成矿中的作用及其找矿意义

本文阐述了热液铀矿床的一个重要成矿构造模式——内通承压地质构造系统。所谓内通承压地质构造系统,即在地壳浅部或较深部位对地下水(包括热液)具有承压运移作用,并与地壳深部(深熔带)有断裂沟通的构造通道,以及与之相通的次级透水构造等的统称。主要包括补给区、承压运移通道、深部通道、混合区、泄水区和上、下隔水层等。内通承压地质构造系统对热液铀成矿具有重要的作用:有利于含铀热液的形成;为含铀热液的运移提供了动力条件;控制着铀矿化产生的特定部位;控制了铀矿化类型、矿体的形态、产状和埋藏深度。     

Transparency change of the ionosphere for cosmic radio waves caused by acoustic pulse of ultra low frequency range

The simulation of the passage from the lithosphere through the atmosphere to the ionosphere of acoustic waves produced by seismic eruption or explosion shows that there is an acoustic coupling among these layers. This in turn is the cause of change in the transparency of the ionosphere for cosmic radio waves. Underground displacements produce Very Low (VLF) and Extremely Low Frequency (ELF) acoustic waves. In their passage through the lithosphere, the VLF wave is subject to nonlinearity that leads to frequency down-conversion, namely, increasing the ELF acoustic component at the Earth's surface. In turn, the nonlinear propagation of ELF acoustic wave in the atmosphere and the ionosphere leads to the emergence of ultra low frequency (ULF) acoustic waves in the ionosphere. An ultra low frequency acoustic wave (ULF) brings influence into the density of F-layer of the ionosphere and causes the transparency change of the ionosphere for cosmic radio waves.     

Variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang （Yangtze River） Estuary

Dissolved inorganic nutrient elements were analyzed from the samples collected in the South Passage of the Changjiang (Yangtze River) Estuary in March 2003, including NH4 , NO3-, NO2- and PO43-. The water samples were collected with a Niskin sampler hourly at the near-surface, middle and near-bottom depths at the three stations -A1, A2 and A3-during two complete tidal cycles of neap tide and spring tide. Results showed that 1) the concentrations of NH4 , NO3- and NO2- were a little higher respectively during the neap tide than those during the spring tide, while PO43- showed an opposite trend, and each was higher in the ebb tide than in the flood tide, either for the neap tidal cycle or the spring tidal cycle; 2) higher stratification of the nutrients existed obviously in this area, with the concentrations of which increased from the bottom to the surface, especially for NH4 and NO3-; 3) the coefficient of variation (C.V.) values of all dissolved inorganic nutrients varied from 4.06% to 36.8% beyond different influences of the tidal current and Changjiang runoff; 4) with increasing suspended matter in the water column, the concentrations of PO43- became lower in the filtered water; and 5) the total transport of each tidal cycle was much more in the spring tide than in the neap tide, and the positive values indicated that the nutrients had been exported to the East China Sea. Studies on the variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang Estuary will provide the scientific basis for the study of the mechanism of red tide in the East China Sea.     

长江口南北槽分流口洪季水沙变化过程研究

河口分流口的水沙变化过程是影响河口三角洲发育的核心环节,对下游河势的稳定起着关键性的作用。本文通过对北槽二、三期工程前后的南北槽分流口河段洪季大潮期间的同步水沙观测数据进行分析,以探讨长江口深水航道工程整治对分流口水沙过程的影响。结果表明:(1)北槽二期工程到三期工程后,分流口洪季以落潮优势流、优势沙为主的格局基本没有发生改变,但南槽优势流、优势沙出现略有变大,而北槽略有变小现象;(2)分流口洪季的水体输移主要受控于欧拉余流的变化,除北槽入口段水体净输移量一直较小外,其他河段在二、三期工程实施期间均有大幅提升,其中斯托克斯余流变化不大,拉格朗日余流与欧拉余流变化相一致,南槽呈波动状上升,北槽先增后减;(3)在二期到三期工程期间,北槽分流比明显减小,入口段落潮流速减小,含沙量较高,水体输移量降低,输沙强度减弱,由此导致二期工程以来北槽入口河段淤积强度加重。     

1959～2013年长江河口南槽动力地貌演变过程

南槽作为长江口入海四口之一,是长江水沙输运向海的主要通道。在长江入海水沙急剧变化和长江口大型涉水工程的影响下,南槽的动力地貌过程成为当前长江河口研究的重点内容之一。分析和揭示近50年来南槽的动力地貌变化过程对理解长江河口响应人类活动和自然驱动作用的变化具有重要意义。基于此,本文通过1959~2013年长时间序列的南槽地形资料,研究长江入海水沙变化及南槽落潮分流分沙比影响下的南槽动力地貌演变过程。结果表明,南槽在1989年江亚南沙并滩前后呈现两种不同的地貌演化阶段:江亚南沙并滩前,南槽普遍发生淤积,两侧浅滩不断淤涨,河槽总体呈缩小态势,河槽拦门沙呈现"双峰"状态;江亚南沙并滩后,南槽呈现出"上段冲蚀加深、中段微冲、下段河槽束窄、两侧浅滩淤积"的状态,拦门沙向"单峰"发展。此外,周边涉水工程的实施对近期南槽地貌的冲淤演变过程有较大的影响。