The evidence for the existence of methane seepages in the northern South China Sea: abnormal high methane concentrations in bottom waters   总被引：1，自引：1，他引：0  

YIN Xijie  ZHOU Huaiyang  YANG Qunhui  WANG Hu  CHEN Jian 《海洋学报(英文版)》2008,27(6):62-70

The methane concentration of water samples at five stations collected by the CTD rosette water sampler in the areas of southwest Dongsha Islands and the Xisha Trough was analyzed by the gas-stripping method on aboard ship. It shows abnormal high methane concentrations in near bottom water samples at three stations. In the southwest Dongsha Islands area, the methane conc.entration of 4. 25 and 10. 64 nmol/dm3 occurs in near bottom water samples at Stas E105A and El06, respectively. In the Xisha Trough area, the high methane concentrations of 5. 17, 8.48 and 8.70 nmol/dm3 in water depths of 1 750, 1 900 and 2 050 m, respectively, have been observed at Sta. F413. It is believed that the abnormal high methane concentrations are generated from the leakage of methane from sediments. Combining with previous geophysical and geochemical data from these two areas, this was probably related to the submarine gas hydrates decomposition and cold seep system. In May 2007, gas hydrate samples were successfully obtained by the drilling in the Shenhu Sea area located in the southwest Dongsha Islands area. It is called for further drilling surveys to confirm the existence of gas hydrate and cold seep system in the Xisha Trough as early as possible.  相似文献   

Wet season fine sediment dynamics on the inner shelf of the Great Barrier Reef     

Eric Wolanski  Katharina E. Fabricius  Timothy F. Cooper  Craig Humphrey 《Estuarine, Coastal and Shelf Science》2008,77(4):755-762

Fine sediment dynamics were recorded in February 2007 in coastal waters of the Great Barrier Reef during a moderate flood of the Tully River. An estuarine circulation prevailed on the inner continental shelf with a surface seaward velocity peaking at 0.1 m s⁻¹ and a near-bottom landward flow peaking at 0.05 m s⁻¹. Much of the riverine mud originating from eroded soils was exported onto a 10 km wide coastal strip during the rising stage of the river flood in the first flush. In coastal waters, suspended sediment concentration peaked at 0.2 kg m⁻³ near the surface and 0.4 kg m⁻³ at 10 m depth during calm weather, and 0.5 kg m⁻³ near the surface and 2 kg m⁻³ at 10 m depth during strong winds when bottom sediment was resuspended. Diurnal irradiance at 4 m depth was almost zero for 10 days. The sedimentation rate averaged 254 (±33) g m⁻² d⁻¹ over the 28-day study period, and concentrations of dissolved and particulate nutrients originating from the river were high. The observed low irradiance would have prevented coral photosynthesis, while the sedimentation rate would have been lethal to some juvenile corals. The mud may ultimately be minnowed out over long periods, however, flushing of the mud occurs at time scales much longer than the flood event and the mud is likely to affect coral physiology for significant periods after the flood has subsided. The data show the need to better control erosion on farmed land for the conservation of coral reefs on the inner shelf of the Great Barrier Reef.  相似文献   

Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge   总被引：2，自引：1，他引：1  

Willard S. Moore  William Ussler III  Charles K. Paull   《Marine Chemistry》2008,109(3-4):421

We measured significant activities of short-lived radium isotopes, ²²³Ra (half-life = 11 days) and ²²⁴Ra (half-life = 3.7 days), around the margins of the Hawaiian Islands to water depths of 3500 m. These measurements suggest fluid inputs from the basalt to the surrounding ocean. In general ²²³Ra activities were considerably greater than ²²⁴Ra in spite of the expected higher production rate of ²²⁴Ra activity in basalt. The ²²³Ra was not supported by dissolved ²²⁷Ac. The highest enrichments of ²²³Ra were measured over the Puna Ridge (2100 m depth) east of Hawaii. Here ²²³Ra activities reached 19 dpm/m³, similar to activities measured near sites of active submarine groundwater discharge in the South Atlantic Bight. To explain the high activities of ²²³Ra unaccompanied by ²²⁴Ra, we postulate that thermally-driven circulation of seawater through the Puna Ridge deposits ²³¹Pa on basalt surfaces. With time the ²³¹Pa produces ²²⁷Ac and ²²³Ra; and ²²³Ra desorbs into the circulating fluids. These fluids then transport ²²³Ra into the overlying ocean. Based on the inventory of ²²³Ra above the Puna Ridge, we estimate the flow of fluids through the ridge to be on the order of 20–60 cm³ cm^− 2 day^− 1. In less than 1000 years the incoming seawater could provide enough ²³¹Pa to basalt surfaces to balance the inventory of ²²³Ra above the ridge if only 8% of the ²²³Ra was transported to the overlying water. These observations on the flanks of a volcanically-active ocean island have significant implications for quantifying fluid fluxes from the flanks of the mid-ocean ridge system. By mapping ²²³Ra inventories in the ocean above ridge flanks and measuring the activity of ²²³Ra in the emerging fluids, the fluid flux can be obtained.  相似文献   

南海礼乐盆地礁体水热循环及其对地温场的影响          下载免费PDF全文

任自强  施小斌  杨小秋  谌永强  盛冲  许鹤华 《地球物理学报》2021,64(2):612-627

南海礼乐盆地自渐新世以来持续发育碳酸盐岩礁体,礁体区地温场可能受到礁体与周围低温海水间水热循环的扰动.为了解礁体与周围海水间的热交换过程及其对礁体区地温场的影响,以便从位于礁体区的钻井测温数据中提取深部热信息,本文以过礁体区S-1井的地震剖面为基础,在流热耦合条件下对礁体内的水热活动进行数值模拟.结果表明,礁体与海水间...  相似文献   

微温传感器测量近地面大气湍流分布的建议   总被引：1，自引：0，他引：1  

候金良  苏洪钧 《天文研究与技术》1996,(Z1)

根据大气湍流温度结构函数的基本定律，推导了用于测量近地面大气湍流强度分布以及对天文视宁度贡献的关系式；提出了进行该项测量的具体方案以及数据处理过程。  相似文献   

四川盐源地区晚二叠纪双峰式火山岩的厘定及其地质意义     

程建康  孙宝伟  霍加庆  肖亮  王彬  朱凯宁 《地质论评》2024,70(1):2024010013-2024010013

四川省盐源县柏林山一带广泛分布着一套基性岩、酸性岩的火山岩组合,两类火山岩在时空上紧密伴生,二者之间缺失中性火山岩,构成典型的双峰式火山岩组合。通过对区内双峰式火山岩的空间分布调查,基性岩主要为致密块状玄武岩、斑状玄武岩,酸性火山岩主要为碱流岩,碱流岩位于玄武岩顶部,为晚二叠纪峨眉山大火成岩省的组成部分。在地质背景、岩石学、地球化学等方面研究的基础上,对区内双峰式火山岩的成因和形成环境进行了探讨,表明玄武岩的原始岩浆来自富集型地幔源区,为地幔橄榄岩小程度部分熔融的产物,形成于洋岛构造环境,碱流岩主要为玄武岩浆极度分离结晶后的酸性残余岩浆形成,形成于陆内拉张构造环境。柏林山地区晚二叠纪双峰式火山岩的发现和厘定为峨眉山玄武岩的演化提供了新的线索和依据,为区域成矿研究以及稀有稀土找矿提供了新的启示。  相似文献   

新一代天气雷达晴空回波反射率因子特征分析     

陈亚军  梁海河  张乐坚  文浩  张林  叶飞  张骞 《气象科技》2022,50(3):303-313

本文基于新一代天气雷达、地面自动站、探空资料和卫星资料,综合利用天气雷达反射率因子和气象要素等资料分析了晴空回波的特征。结果表明:我国不同地域（华北、华中、华东和华南）晴空回波具有明显的日变化和年变化特征,具体表现为每年的春秋两季天气雷达可探测到明显的晴空回波,而且晴空回波主要出现在傍晚到第2天清晨之间。进一步的分析表明雷达探测的晴空回波和折射指数的涨落关系密切,此外逆温层和高湿区的存在也与雷达是否能够探测到晴空回波存在较高的相关性。  相似文献   

条带状铁建造(BIFs)研究的几个问题   总被引：8，自引：0，他引：8  

李碧乐  霍亮  李永胜 《矿物学报》2007,27(2):205-210

前寒武纪条带状铁建造(BIFs)中拥有全球最重要的铁矿资源,BIFs中以及包括BIFs在内的含铁岩系还含有丰富的金、铜、锌、钴、铂族等有用元素。本论文主要针对BIFs形成过程中与成矿有关的几个关键问题进行评述和探讨,包括BIFs的成矿系列,地幔柱与BIFs的关系,微生物在BIFs形成中的作用等。认为BIFs内部以及包括BIFs在内的含铁岩系均构成贱、贵金属成矿系列;地幔柱与BIFs之间存在密切的时、空和成因联系;在早前寒武纪缺氧的环境下,厌氧的细菌类生物通过光合作用为BIFs中铁质沉淀提供了氧。希望该研究对包括BIFs的成矿作用在内的前寒武纪地质研究以及拓展找矿思路有所启示。  相似文献   

Statistics of velocity centroids: effects of density–velocity correlations and non-Gaussianity     

A. Esquivel  A. Lazarian  S. Horibe  J. Cho  V. Ossenkopf  J. Stutzki 《Monthly notices of the Royal Astronomical Society》2007,381(4):1733-1744

We continue with our previous work on statistics of velocity centroids, to retrieve information about the scaling properties of an underlying turbulent velocity field from spectroscopic observations. We use synthetic data sets with extreme effects of velocity–density correlations that we create artificially, which also have a non-Gaussian distribution of fluctuations. We confirm that centroids can be used to obtain the scaling properties of the turbulent velocity when the ratio of the density dispersion to the mean density is less than unity, regardless of velocity–density correlations and non-Gaussianity. It was found that extreme velocity–density correlations can distort the statistics of velocity centroids, impeding the recovery of the turbulent velocity spectral index from centroids. We show that such correlations introduce high-order moments to the maps of centroids, which we disregarded in previous work, but that they are only important when the density dispersion is large in comparison with the mean density. It was also found that non-Gaussian velocity and/or density distort the statistics of centroids too, but to a lower degree than extreme cross-correlations.  相似文献   

Modelling the optical turbulence boiling and its effect on finite-exposure differential image motion     

A. Berdja  J. Borgnino 《Monthly notices of the Royal Astronomical Society》2007,378(3):1177-1186

It is usually accepted that whenever dealing with astronomical observation through the atmosphere, the optical turbulence temporal evolution can be sufficiently described with the so-called frozen turbulence hypothesis. In this model, turbulence is supposed to be equivalent to a series of solid phase screens that slide horizontally in front of the observation field of view. Experimental evidence shows, however, that an additional physical process must be taken into account when describing the temporal behaviour of the optical turbulence. In fact, while translating above the observer, turbulence undergoes a proper temporal evolution and affects differently the astronomical and, more specifically, the astrometric observations. The proper temporal evolution of the turbulence-induced optical turbulence observable quantities is here called the optical turbulence boiling. We are proposing through this paper a theoretical approach to the modelling of the optical turbulence temporal evolution when the turbulent layer horizontal translation and the optical turbulence boiling are both involved. The model we propose, as a working hypothesis though, has a direct relevance to differential astrometry because of its explicit dependence upon the optical turbulence temporal evolution. It can also be generalized to other techniques of high angular resolution astronomical observation through the atmospheric turbulence.  相似文献