Institutional Repository of South China Sea Institute of Oceanology, CAS
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Satellite observations of sub-mesoscale vortex trains in the western boundary of the South China Sea
No full textThis study uses high resolution MEdium Resolution Imaging Spectrometer (MERIS) satellite data to analyze sub-mesoscale ocean vortex trains (OVTs) in the western boundary of the South China Sea (SCS). Thirteen cases of vortex trains on the lee side of the Phu Quy Island were observed in the boreal summer from May to August of 2005 - 2010. The average diameter of the vortices is 28.1 +/- 13.8 km. The average spacing distance estimated between two consecutive vortices is 66.3 +/- 27.8 km. The dynamic parameters of a case observed on July 26, 2009 were extracted using a theoretical model. The aspect ratio is 2.8. The ratio of the propagation velocity of the vortex to the undisturbed flow velocity is 0.73. We use a nested high-resolution numerical model with the finest grid of 500 m, to analyze the dynamics of OVT induced by the local topography in the western SCS (WSCS). The results give a propagation velocity of vortex 0.49 of m s(-1) and a mean current velocity of undisturbed flow 0.58 m s(-1). Therefore, the ratio is 0.84. The shedding frequency is determined to be 1.14 x 10(-5) s(-1), corresponding to 1.02 day. The results also suggest that the sub-mesoscale cyclonic vortices along the OVT in the WSCS are characterized by low temperature and high Rossby number. The strong vertical vorticity and associated horizontal velocity shear of an individual vortex brings uplifted cold water on its leading side and warm water on its trailing side, which could drive an enhanced vertical exchange between the surface and oceanic interior
Wintertime Phytoplankton Blooms in the Western Equatorial Indian Ocean Associated With the Madden-Julian Oscillation
No full textThis study investigated boreal wintertime phytoplankton blooms in the western equatorial Indian Ocean (WEIO) and the underlying physical mechanisms. The Sea viewing Wide field of View sensor (SeaWiFS) chlorophyll-a (Chla) concentrations show that phytoplankton blooms occur in the WEIO during December-March. The development of these blooms is not only a seasonal process but also consists of 2-3 intraseasonal events induced by the Madden-Julian Oscillation (MJO). During a typical intraseasonal event, enhanced cross-equatorial wind induces strong upwelling and ocean mixing, thus increasing the supply of nutrients to the surface in equatorial regions. Argo profiles clearly show various responses to the intraseasonal wind bursts, including shoaling of the thermocline and deepening of the mixed layer. Further analysis reveals that the former is the dominant mechanism for the blooms along the equator, while the latter controls the high Chla concentrations off the coast of Somalia. Surface ocean circulations not only account for the blooms south of the equator but also modulate the thermocline depth in the WEIO. The shallower thermocline during the early period of the northeast monsoon season provides favorable conditions for a stronger Chla response to intraseasonal forcing
Investigation of hypoxia off the Changjiang Estuary using a coupled model of ROMS-CoSiNE
No full textThe cause for large variability of hypoxia off the Changjiang Estuary has not been well understood partly due to various nutrient sources and complex physical-biological processes involved. The Regional Ocean Modeling Systems (ROMS) coupled with Carbon, Silicate and Nitrogen Ecosystem (CoSiNE) was used to investigate the 2006 hypoxia in the East China Sea, the largest hypoxia ever recorded. The model performance was evaluated comprehensively by comparing a suite of quantitative metrics, procedures and spatiotemporal patterns between the simulated results and observed data. The simulated results are generally consistent with the observations and are capable of reproducing the development of hypoxia and the observed vertical profiles of dissolved oxygen. Event-scale reduction of hypoxia occurred during the weakening of stratification in mid-July and mid-September, due to strong stirring caused by tropical storms or strong northerly wind. Change in wind direction altered the pathway of Changjiang Diluted Water and consequently caused variation in hypoxic location. Increase in river discharge led to an expansion of hypoxic water during the summer monsoon. Sensitivity analysis suggested that the hypoxia extent was affected by the change in nutrient concentration of the Changjiang as well as that of the Kuroshio. Sensitivity analysis also suggested the importance of sediment oxygen consumption to the size of the hypoxic zone. These results demonstrate that a prognostic 3D model is useful for investigating the highly variable hypoxia, with comprehensive considerations of multiple factors related to both physical and biological processes from the estuary to the shelf break of the East China Sea
High density aggregations of the Aurelia sp 1 ephyrae in a Chinese coastal aquaculture pond
No full textBlooms of the Moon Jellyfish Aurelia sp.1 medusae have occurred in the harbors and coastal waters of the Bohai and Yellow Seas. However, the occurrence and distribution of Aurelia sp.1 ephyrae is relatively unknown. Mass occurrence of scyphozoan ephyrae in a coastal aquaculture pond (Shidao) in northern China was first recorded in April 2015. Based on morphological characteristics, the ephyrae collected in the aquaculture pond were mostly similar to the ephyrae collected in Atlantic French waters, which were identified as Aurelia sp.1. This was further confirmed by phylogenetic analyses of the mtDNA 16S regions of the sampled ephyrae. Surprisingly, the blooms of Aurelia sp.1 ephyrae formed an obvious reddish color similar to "red tides" in the surface water of the aquaculture pond. The mean density of ephyrae in the reddish color zone of the aquaculture pond was estimated to be 7.38 x 10(6) individuals m(-3). Seawater temperature and wind are the key factors for the formation of Aurelia sp.1 ephyra bloom in the aquaculture pond. Finally, we speculate that artificial structures may provide more substrates for the polyps and enhance the Jellyfish blooms in Chinese aquaculture ponds
3D gravity anomaly separation method taking into account the gravity response of the inhomogeneous mantle
No full textIn order to ensure that the gravity data processing and inversion are consistent with the actual geology, we propose that, in integrated geophysical research, 3D gravity anomaly separation (GAS) should take into account the gravity response of the inhomogeneous mantle. This is an effective method by which the residual gravity anomaly (RGA) may be obtained, as well as an important basis for the inversion and interpretation of gravity data. Aimed at the petroliferous basin structure, evolution of continental margin, ocean continental transition zone and other widely discussed geological problems, we extensively investigate the upper mantle structure in many regions around the world, and the results show that the lateral inhomogeneity of the mantle is widespread. In many comprehensive studies based on gravity and seismic data, the gravity anomaly modeling and separation are typically performed within the crust (above the Moho), which actually relies on an assumption of homogeneous mantle. Although this assumption simplifies the difficulty of the gravity modeling and separation, it ignores gravity anomalies caused by inhomogeneities of the deep mantle. The RGA, along with the inverted density structure and other interpretations, involves the risk of deviating from the actual geology. On the basis of the 2D forward calculation of several typical interface models, we implement the quantitative analysis of the effect that the inhomogeneous mantle has on the Bouguer gravity anomaly. In case studies of the southeastern United States and the Sichuan Basin, taking the shear wave velocity (Vs) structure of the upper mantle as the constraint condition, we calculate the gravity anomaly caused by the inhomogeneous mantle by means of the forward method. It is found that the gravity response of the inhomogeneous mantle cannot be neglected. Therefore, we conduct 2.5D joint simulation combining gravity and seismic data in the Sichuan Basin. The fitting results after separating the gravity response of the inhomogeneous mantle are clearly superior to those of the homogeneous mantle hypothesis. On the basis of the 3D depth data of several sedimentary strata, the Moho and the mantle high-velocity bodies, we implement 3D GAS, obtain the RGA of the basement in the Sichuan Basin, and discuss the geological origin of the "Dazu high gravity"
Seasonal wind patterns influence the configuration and geomorphology of insular reef systems: Yongxing Island, Xisha Islands, China
No full textYongxing Island is a coral reef island formed by the growth and accumulation of corals and other skeletal fragments on a reef platform. The reef flat is developed around the entire island. The southeast reef flat and the north and northwest reef flat are asymmetrical in proportions, showing significant differences in reef-flat width, patterns of sedimentary and ecological zonation, fore-reef slope gradients, and submarine geomorphic features. Through application of an underwater survey, measurements and statistics were recorded on the extensional pattern of the Yongxing reef platform, the reef pool, and the spur-groove systems incised on the reef crests and forereefs. It is demonstrated that the Yongxing reef platform is an irregular ovoid in form with a distinct NW-SE elongation that includes gently and steeply sloping forereefs and fore-reef slopes. A gradual transition to the deep sea basin occurs in the southeast part of the Yongxing reef platform, whereas a steep forereef and fore-reef slope that rapidly transition to the deep-water basin are more characteristic of the north and northwest sectors of the Yongxing reef platform. The width of the reef platform in the southeast direction is much greater than that in the northwest direction. Correspondingly, the developmental pattern of the north and northwest reef crest and forereef is different from that of the southeast reef crests and forereefs. The southeast reef crest and forereef are characterized by reef pools with various shapes, different water depths, and discontinuous tidal channels on the outer reef flat. In contrast, the north and northwest reef crest and forereef developed a typical spur-and-groove system. The former is related to coral reef growth and construction, whereas the latter is shaped by wave or tide flow scouring that contributes to substrate erosion. Similar geomorphic features are known from examples of Indian-Pacific and Caribbean-Atlantic reef crests and forereefs, but the occurrence of such features in different parts of the same reef platform provides a new example of reef crest and forereef development. The differences in slope gradient of forereef and fore-reef slopes (gentle vs. steep in transition), the development of contrasting submarine platform widths in different directions, as well as other submarine geomorphic features on reef crests and forereefs around the reef flats of Yongxing Island may be related to the confluence of several factors. These include the tectonic uplift of reef platform, the island's initial underwater topography, the windward and leeward positions, the direction and strength of winter and summer monsoon, the sea-water dynamics, and the substrate characteristics related to coral reef growth
The Overview of Acoustic Seabed Sediment Classification Base on Chirp Sub-Bottom Profile Sonar Data
No full textChirp sub-bottom profile data not only can be used for the interpretation of seabed geological information, but also can be used for seabed sediments classification. At present, there are mainly two kinds of seabed sediment classification methods base on SBP (sub-bottom profile) sonar data: (1) the echo signal statistical characteristics classification; (2) acoustic parameter inversion method. The first classification methods are similar, which is based on statistics, unknown sediment type can be concluded according to the statistical characteristics of known sediment. Seabed acoustic characteristic parameters are inversed and thus seabed sediment can be classified. Under the condition of limited data, the comprehensive utilization of the two methods provides a more accurate remote sensing method for seabed sediment classificatio
Controls on modern erosion and the development of the Pearl River drainage fa in the late Paleogene
No full textThe Pearl River and its tributaries drains large areas of southern China and has been the primary source of sediment to the northern continental margin of the South China Sea since its opening. In this study we use a combination of bulk sediment geochemistry, Nd and Sr isotope geochemistry, and single grain zircon U-Pb dating to understand the source of sediment in the modern drainage. We also performed zircon U-Pb dating on Eocene sedimentary rocks sampled by International Ocean Discovery Program (IODP) Expedition 349 in order to constrain the source of sediment to the rift before the Oligocene. A combination of Nd and Sr isotopes shows that the Gui, Liu and Dong Rivers are likely not important sources. Single grain zircon dates emphasize the importance of the westernmost tributaries (Hongshui and Yu Rivers), which drain the highest topography and tectonically active areas, as the primary sediment producers. Our data indicate that climate is not the primary control on erosion patterns and intensities. Zircon dating also shows that the Gui and Liu Rivers are not generating large sediment yields. Discrepancies between these new data and earlier samples make the role of the Dong River hard to determine, although Nd isotopes suggest that it is not dominant. The source of sediment during the Eocene at IODP Site U1435 appears to have been a relatively local basement source, or a regionally restricted river only draining nearby areas of the Cathaysia Block, similar, but not identical, to the modern Dong River. There is no evidence for a large regional river and we exclude sediment transport from the southwest (Indochina). Our data are consistent with small drainage systems dominating the basin until the end of the Oligocene (similar to 24 Ma), after which the Pearl River expanded towards its modern state as a result of headwater capture largely towards the west
确定致密储层空气渗透率上限方法的改进与应用
No full text致密储层空气渗透率上限是评价致密油资源量和优选致密油藏合理开发方式的重要参数,但现有的计算与确定方法尚不能全面准确地反映致密油藏地质及开发特征,尤其是不能较好反映致密油渗流特征和当前国内外有关致密油在开发方式上的统一认识。在调研国内外致密油储层物性上限确定方法的基础上,以渗流理论为指导,从致密油藏开发生产实践入手,应用致密油储层启动压力梯度与空气渗透率之间的幂函数关系建立了致密储层空气渗透率上限计算模型。研究表明,基于在开发方式上的统一认识,认为致密油储层开发虽然存在一定困难,但是通过技术攻关可以实现有效经济动用,或在目前开发技术条件下难以实现经济动用的储层,这一认识决定了致密储层物性上限计算与确定方法必须要全面准确反映受启动压力梯度影响致密油出现非达西渗流的特征;该新方法完整地立足于致密油非达西渗流理论及其开发实践,因而具备充分的致密油渗流及开发理论依据;同时,该新方法从纯数学计算的角度入手,因而较以往的计算方法可靠、合理、实用,更具推广价值
柴达木盆地北缘上石炭统碎屑岩—碳酸盐岩高频转换过程及驱动机制
No full text碎屑岩和碳酸盐岩分别产自"外源、浑水"与"内源、清水"环境,二者的交替互层沉积可反映古水体性质、物源供给及气候等环境要素的频繁改变。晚石炭世,柴达木盆地北缘构造相对稳定,盆内发育巨厚的、多级次嵌套的"碎屑岩—碳酸盐岩混积层系",记录了"冰室地球"冰川活动下的古海平面大幅度升降和古气候、古环境频繁交替信息。文中以柴达木盆地北缘连续完整露头剖面和钻井取心剖面为研究对象,结合区域地质资料、前人研究成果,通过详细的岩心、露头及镜下薄片观察,在研究区重点层段识别出下切谷充填型碎屑岩沉积和碳酸盐岩台地沉积组成的频繁互层序列。碎屑岩—碳酸盐岩互层组合序列在垂向上的有序叠加,构成了复合海平面变化旋回层序,其从碳酸盐岩—改造型台地沉积开始,向上依次发育碎屑岩下切谷充填序列的底部冲积河道沉积、中部河口湾序列和顶部代表海泛面的泥岩沉积,最后转变为碳酸盐岩向海到向陆台地亚相,反映了一个显著的早期海退—中期逐渐海侵—后期再次海退的旋回过程。冰川期急剧变冷的气候和冰川型高频的大幅度海平面升降,驱动滨线及相带迁移,影响到碎屑岩供给速率和碳酸盐生产率,造成了碎屑岩—碳酸盐岩的高频转换