Another description of the Mediterranean Sea outflow   总被引：1，自引：0，他引：1  

Claude Millot   《Progress in Oceanography》2009,82(2):101-124

Papers about the outflow in the Strait of Gibraltar assume that (i) it is composed of only two Mediterranean Waters (MWs), the Levantine Intermediate Water (LIW) and the Western Mediterranean Deep Water (WMDW) from the eastern and western basins, respectively, (ii) both MWs are mixed near 6°W, hence producing a homogeneous outflow that is then split into veins, due to its cascading along different paths and to different mixing conditions with the Atlantic Water (AW).A re-analysis of 1985–1986 CTD profiles (Gibraltar Experiment) indicates two other MWs, the Winter Intermediate Water (WIW) from the western basin and the Tyrrhenian Dense Water (TDW) basically originated from the eastern basin. In the central Alboran subbasin, these four MWs are clearly differentiated, roughly lying one above the other in proportions varying from north to south. Proportions also vary with time, so that the outflow can be mostly of either eastern or western origin. While progressing westward, the MWs can still be differentiated and associated isopycnals tilt up southward as much as being, in the sill surroundings, roughly parallel to the Moroccan continental slope where the densest MWs are. The MWs at the sill are thus juxtaposed and they all mix with AW, leading to an outflow that is horizontally heterogeneous just after the sill (5°45′W) before progressively becoming vertically heterogeneous as soon as 6°15′W. There can be little LIW and/or no WMDW outflowing for a while.An analysis of new 2003–2008 time series from two CTDs moored (CIESM Hydro-Changes Programme) at the sill (270 m) and on the Moroccan shelf (80 m) confirms the juxtaposition of the MWs, their individual and generally intense mixing with AW, as well as the large temporal variability of the outflow composition. Only LIW and TDW were indicated at the sill while, on the shelf, only LIW, TDW sometimes denser there than 200 m below, and WMDW were indicated; but none of the MWs has been permanently outflowing at one or the other place.The available data can be analyzed coherently. Intermediate and deep MWs are formed in both basins in amounts that, although variable from year to year, allow their tracing up to the strait. Four major MWs circulate alongslope counterclockwise as density currents and as long as they are not trapped within a basin, which is necessarily the case for the deep MWs. In the Alboran, the intermediate MWs (WIW, LIW and upper-TDW) circulate in the north while the deep MWs (lower-TDW and WMDW) are uplifted, hence relatively motionless and mainly pushed away in the south. Since both the intermediate and deep MWs outflow at the sill, they are considered as light and dense MWs, the light–dense MWs interface possibly intersecting the AW–MWs interface in the sill surroundings. Considering an outflow east of the sill composed of only two (light–dense) homogeneous layers gives significant results. Across the whole strait, the outflow has spatial and temporal variabilities much larger than previously assumed. The MWs are superposed in the sea and lead at the sill to juxtaposed and vertically stratified suboutflows that will cascade independently before forming superposed veins in the ocean. These veins can have similar densities and hydrographic characteristics even if associated with different MWs, which accounts for the features permanency assumed up to now. The outflow structure downstream of the sill depends on its composition upstream and, more importantly, on that of AW in the sill surroundings where fortnightly and seasonal signals are imposed on the whole outflow.  相似文献   

Sources to the East Greenland Current and its contribution to the Denmark Strait Overflow     

Emil Jeansson  Sara Jutterström  Leif G. Anderson  E. Peter Jones  James H. Swift 《Progress in Oceanography》2008,78(1):12-28

Data from the East Greenland Current in 2002 are evaluated using optimum multiparameter analysis. The current is followed from north of Fram Strait to the Denmark Strait Sill and the contributions of different source waters, in mass fractions, are deduced. From the results it can be concluded that, at least in spring 2002, the East Greenland Current was the main source for the waters found at the Denmark Strait Sill, contributing to the overflow into the North Atlantic. The East Greenland Current carried water masses from different source regions in the Arctic Ocean, the West Spitsbergen Current and the Greenland Sea. The results agree well with the known circulation of the western Nordic Seas but also add knowledge both to the quantification and to the mixing processes, showing the importance of the locally formed Greenland Sea Arctic Intermediate Water for the East Greenland Current and the Denmark Strait.  相似文献   

深水沉积研究前缘问题   总被引：27，自引：0，他引：27       下载免费PDF全文

庞雄  陈长民朱明何敏  柳保军申俊 连世勇 《地质论评》2007,53(1):36-43

深水沉积研究经历了50年，争论也持续了50年。从浊流及鲍玛序列开始，随着对浊流定义的过分使用，到今天对鲍玛序列作为浊积岩相序及相关的扇模式普遍持否定态度，深水沉积研究经历了一个认识的旋回。主要问题和争论的焦点是：是否所有深水砂岩都是浊流成因，鲍玛序列能否代表浊积岩相序；是否所有的深水扇水道下方都能形成席状的、平行的、加厚的、具有丘状外形的浊积砂岩沉积；是否可以利用地震方法识别深水扇的砂岩储层。对“浊流”概念的过分使用把深水扇模式内几乎所有深水沉积都解释成浊流成因，导致了曾经为之建立模式的学者纷纷撰文抛弃原有扇模式。深水沉积研究面临着对过往认识的否定和如何建立新的理论模式。尽管浊流及相关的深水扇模式研究走向穷途末路，石油工业却从浊流理论和相关模式中获得了许多油气发现，勘探家们仍然希望通过这些模式寻找更多的油气，科学理论和应用出现了分化。对深水沉积过程和流态的认识及沉积模式的建立是当今深水沉积研究的难点，实现深水砂岩储层的有效预测是深水沉积研究的主要目的。我国深海油气勘探在即，深水沉积的科学问题同样不可逾越。  相似文献   

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, as reflected by marine palynology   总被引：1，自引：0，他引：1  

Michael L. Prauss   《Cretaceous Research》2006,27(6):872-886

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, has been analysed palynologically by high resolution sampling to reconstruct changes in relative sea-level and water mass character within photic zone waters. Based on changes in the ratio of terrigenous sporomorphs to marine palynomorphs (t/m index), the distribution of the organic-walled algal taxa as well as of selected dinocyst taxa and groups the section can largely be subdivided into pre-“plenus-bed” and post-“plenus-bed” intervals, reflecting different stages of third-order relative sea-level cycles and/or changes in water mass influence in the photic zone. Accordingly, the pre-“plenus-bed” interval is placed in a transgressive systems tract starting at the “facies change” event (C. guerangeri/M. geslinianum ammonite Zone boundary) with the maximum flooding surface at the top of the “Chondrites II” bed (top of R. cushmani Biozone). A highstand systems tract is suggested from the base of the “plenus-bed” up the base of the “fish-shale” event. Within the “fish-shale” event interval, a transgressive systems tract is suggested to start at the base of the thin, grey-green marly interbed. The Cenomanian/Turonian boundary proper, as defined by the first occurrence of Mytiloides spp., as well as the lowermost Turonian are located within the initial phase of a transgressive systems tract. With respect to water mass characteristics within photic-zone waters, the pre-“plenus-bed” interval is predominantly characterized by warm water masses that changed gradually towards the deposition of the “Chondrites II” bed, where a strong influence of cool and/or salinity-reduced waters is indicated by various palynological proxies. Within the post-“plenus-bed” interval a mixture and/or alternation of warmer and cooler waters is indicated, with the warmer water influence increasing gradually towards and within the Lower Turonian stage. The increased proportions of prasinophytes within the “Chondrites II” bed and parts of the “fish-shale” interval may indicate availability of reduced nitrogen chemospecies, especially ammonium, within photic-zone waters as a function of a vertical expansion of the oceanic O₂-minimum zone.  相似文献   

Infrared luminosities of local-volume galaxies     

I. D. Karachentsev  A. M. Kutkin 《Astronomy Letters》2005,31(5):299-307

Based on data from the Two-Micrometer All-Sky Survey (2MASS), we analyzed the infrared properties of 451 Local-Volume galaxies at distances D ≤ 10 Mpc. We determined the K-band luminosity function of the galaxies in the range of absolute magnitudes from ?25^m to ?11^m. The local luminosity density within 8 Mpc is 6.8 × 10⁸L_⊙ Mpc^?3, a factor of 1.5 ± 0.1 higher than the global mean K-band luminosity density. We determined the ratios of the virial mass to the K-band luminosity for nearby groups and clusters of galaxies. In the luminosity range from 5 × 10¹⁰ to 2 × 10¹³L_⊙, the dependence log(M/L_K) ∝ (0.27 ± 0.03) log L_K with a dispersion of ～0.1 comparable to the measurement errors of the masses and luminosities of the systems of galaxies holds for the groups and clusters of galaxies. The ensemble-averaged ratio, 〈M/L_K〉 ? (20–25) M_⊙/L_⊙, was found to be much smaller than the expected global ratio, (80–90)M_⊙/L_⊙, in the standard model with Ω_m = 0.27. This discrepancy can be eliminated if the bulk of the dark matter in the Universe is not associated with galaxies and their systems.  相似文献   

Vertical and lateral organization of a carbonate deep-water slope marginal to a submarine fan system, Miocene, southern Turkey     

Bryan T. Cronin  Kemal GÜrbÜz  rew Hurst  & Nick Satur 《Sedimentology》2000,47(4):801-824

Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments.  相似文献   

节理卸荷岩体非线性本构关系再研究     

刘杰  李建林  王乐华  胡海浪 《岩土力学》2006,27(Z2):39-44

对地质材料模型、石膏模型、砂浆模型、进行了模型试验,通过对模型试验得出的数据进行分析、拟合,得出初步的节理卸荷岩体的增量本构。针对其不足,从参数选择、物理意义等方面进一步进行修正得出一改进的增量本构关系,并在有限元分析程序ADINA中接入该本构关系,对清江隔河岩电站厂房高边坡三维模型进行有限元分析。  相似文献   

节理岩体地基极限承载力研究   总被引：2，自引：0，他引：2  

周小平  张永兴 《岩土力学》2004,25(8):1254-1258

由于节理岩体具有复杂的力学特性,节理岩体地基的极限承载力问题一直都没有很好解决。利用非线性统一强度准则考虑中间主应力影响和岩性、岩体结构特性可以通过参数m,s和σc 来反映的优点,将非连续介质特性的节理岩体等效为连续介质,在确定即时摩擦角后,结合滑移线场理论获得了节理岩体地基极限承载力的封闭形式的理论解,其解考虑了边界条件和基础的几何形状,举例说明了计算裂隙岩体极限承载力的过程和所需的参数。结果表明：节理岩体的材料特性和中间主应力对极限承载力具有重要影响。  相似文献   

珠江口盆地深水区珠海组陆架边缘三角洲特征及其意义     

曾清波  陈国俊  张功成  纪沫  韩银学  郭帅  王龙颖 《沉积学报》2015,33(3):595-606

陆架边缘三角洲发育于大陆架边缘、由物源越过陆架坡折并在陆坡沉积而形成, 分布广、储层发育, 其富油气性已经全球多个地区的勘探实践所证实。基于最新钻井与地震资料综合分析, 首次系统揭示了珠江口盆地深水区珠海组大型陆架边缘三角洲的分布与结构充填, 分析了其发育的主控因素与油气勘探意义。研究表明, 珠海组陆架边缘三角洲剖面上呈S形、斜交或叠瓦状前积结构, 钻井揭示为厚层水下分流河道、河口坝、席状砂与前三角洲泥互层沉积, 平面上北东向展布于白云凹陷至鹤山凹陷一带。白云凹陷段三角洲规模相对较小, 以斜交前积为主;白云南洼东段呈S形前积结构, 顶积层为厚层水下分流河道与河口坝砂岩, 前端深水水道与深水扇发育;南部隆起段以斜交、叠瓦状前积为主, 规模较小;鹤山凹陷段以S形前积结构为主, 发育大型下切谷与深水扇。晚渐新世构造活动相对平静, 深水区形成了稳定的陆架坡折带, 古珠江携带的充沛物源与珠海组时期相对海平面下降促使了陆架边缘三角洲的发育。珠海组陆架边缘三角洲的泥质沉积是一套中等-好的烃源岩, 同时其发育也为海相泥岩带来了丰富的陆源有机质;陆架边缘三角洲的河口坝、水下分流河道、席状砂分布广、纵向厚度大, 是深水区重要的储层类型, 其前端发育的深水扇体是有利勘探目标。  相似文献   

Bacterial diversity and community structure in the East China Sea by 454 sequencing of the 16S rRNA gene   总被引：1，自引：0，他引：1  

董逸  赵苑  张文燕  李艳  周锋  刘诚刚  吴莹  刘素美  张武昌  肖天 《中国海洋湖沼学报》2014,32(3):527-541

The 454 sequencing method was used to detect bacterial diversity and community structure in the East China Sea. Overall, 149 067 optimized reads with an average length of 454 nucleotides were obtained from 17 seawater samples and five sediment samples sourced in May 2011. A total of 22 phyla, 34 classes, 74 orders, 146 families, and 333 genera were identified in this study. Some of them were detected for the first time from the East China Sea. The estimated richness and diversity indices were both higher in the sediment samples compared with in the seawater samples. All the samples were divided by their diversity indices into four regions. Similarity analysis showed that the seawater samples could be classified into six groups. The groups differed from each other and had unique community structure characteristics. It was found that different water masses in the sampling areas may have had some influence on the bacterial community structure. A canonical correspondence analysis revealed that seawater samples in different areas and at different depths were affected by different environmental parameters. This study will lay the foundation for future research on microbiology in the East China Sea.  相似文献