南海海盆东-西部地质特征存在巨大差异

南海中部存在巨大的中南断裂将南海海盆分割为东-西两部分,至少自1亿年以来,在沉积环境与沉积厚度、洋陆边界的属性与特征、大陆破裂的时代、岩浆活动的来源与程度、减薄大陆架和大陆坡的宽度、洋壳年龄与磁性层结构、磁异常条带特征、岩石化学等诸多方面都存在巨大差异,它们主要受控于早期地质构造背景的差异、东西部大陆减薄伸展速率的变化以及海底扩张的构造环境的不同,并深刻影响了之后的区域沉积分区和沉降特征。     

南海表面海温异常对南海季风影响的数值模拟

采用P-σ混合坐标系区域气候模式模拟了4－7月南海季风的爆发、演变过程，并进行了3组敏感性数值试验，研究南海表面海温异常对南海季风的影响，得到以下结论：（1）南海4月份海温异常对南海季风的爆发日期影响不大，但对季风爆发后的强度有所影响，异常增温造成南海季风增强，异常降温则南海季风减弱。（2）南海季风爆发和强度的变化与南海本身的海温变化情况有密切的关系，尤其是5月份南海海温异常。5月份南海异常增温可以使南海季风提前爆发，季风增强，南海海温异常降低时，南海季风爆发的时间推迟，季风减弱。（3）南海海温持续异常可以影响南海及中国大陆的高低空环流变化，海温持续异常增温可以使南海季风提前爆发，显地加强南海季风，并有利于南海季风向北推进，但当海温在6月份进一步持续增温时，则有利于季风维持在较南地区，阻碍季风向北发展；当海温持续异常降低时，南海季风推迟爆发，且明显减弱。     

Passive seismic experiment and ScS wave splitting in the southwestern subbasin of South China Sea

The seismic experiment of 3D array of OBS in the southwestern sub-basin of the South China Sea(SCS) is briefly introduced in this paper.The data analysis of broadband OBS shows that totally 93 earthquakes with magnitude of Ms 6.0-6.9 and 10 earthquakes with magnitude above Ms 7.0 were recorded in high quality during this experiment,especially the catastrophic earthquake Ms 9.0 occurred in the east sea area of Japan on March 11,2011.The anisotropy parameters inversion of ScS wave of four events above Ms 7.0 indicates that the fast direction of shear wave is N58°E parallel to the ceased spreading ridge of the southwestern sub-basin of SCS(the slow direction is S35°E perpendicular to the spreading ridge),which means the spreading ridge is under compressing stress at present and the cessation of seafloor spreading is related to such stress field as well.     

Magnetic recording of the Cenozoic oceanic crustal accretion and evolution of the South China Sea basin

We review and discuss some of the recent scientific findings made on magnetic data in the South China Sea (SCS). Magnetic anomalies bear extremely rich information on Mesozoic and Cenozoic tectonic evolution. 3D analytical signal amplitudes computed from magnetic anomalies reveal very precisely relict distributions of Mesozoic sedimentary sequences on the two conjugate continental margins, and they are also found very effective in depicting later-stage magmatism and tectonic transitions and zonation within the SCS oceanic crust. Through integrated analyses of magnetic, gravity and reflection seismic data, we define the continent-ocean boundary (COB) around the South China Sea continental margin, and find that the COB coincides very well with a transition zone from mostly positive to negative free-air gravity anomalies. This accurate outlining of the COB is critical for better tracing magnetic anomalies induced by the oceanic crust. The geometrically complex COB and inner magnetic zonation require the introduction of an episodic opening model, as well as a transform fault (here coined as Zhongnan Fault) between the East and Southwest Sub-basins, while within the East and Southwest Sub-basins, magnetic anomalies are rather continuous later-ally, indicating nonexistence of large transform faults within these sub-basins. We enhance magnetic anomalies caused by the shallow basaltic layer via a band-pass filter, and recognize that the likely oldest magnetic anomaly near the northern continental margin is C12 according to the magnetic time scale CK95. Near the southern continental margin, magnetic anomalies are less recognizable and the anomaly C12 appears to be missing. These differences show an asymmetrical opening style with respect to the relict spreading center, and the northern part appears to have slightly faster spreading rates than to the south. The magnetic anomalies C8 (M1 and M2, ~26 Ma) represent important magnetic boundaries within the oceanic basin, and are possibly related to changes in spreading rates and magmatic intensities. The magnetic evidence for a previously proposed ridge jump after the anomaly C7 is not clear. The age of the Southwest Sub-basin has yet to be further examined, most favorably with deep-tow magnetic surveys and ocean drilling. Our magnetic spectral study shows that the shallowest Curie points are located around the eastern part of the Southwestern Sub-basin, whereas within the East Sub-basin Curie depths are smaller to the north of the relict spreading center than to the south. This pattern of Curie depths is consistent to regional heat flow measurements and later-stage volcanic seamount distributions, and we therefore reason that Curie-depth variations are closely associated with later-stage magmatism, rather than with crustal ages. Although magnetic anomalies located around the northern continent-ocean transition zone (COT) are relatively quiet, this area is not a typical magnetic quiet zone since conceptually it differs markedly from an oceanic magnetic quiet zone. The relatively quiet magnetic anomalies are seemingly associated with a shallowing in Curie isotherm and thinning in magnetic layer, but our comprehensive observations suggest that the well-preserved thick Mesozoic sedimentary rocks are major causes for the magnetically quiet zone. The high similarities between various low-pass filtered marine and air-borne magnetic anomalies and satellite magnetic anomalies clearly confirm that deeper magnetic sources (in the lower crust and the uppermost mantle) have contributions to long-wavelength surface magnetic anomalies in the area, as already inferred from magnetically inversed Curie depths. The offshore south China magnetic anomaly (SCMA) becomes more prominent on low-pass filtered marine and air-borne magnetic anomalies and satellite magnetic anomalies, indicating very deeply-buried magnetic sources beneath it.     

Coastal seafloor observatory at Xiaoqushan in the East China Sea

The seafloor observation system is becoming an important infrastructure for marine research because it is transforming oceanic research from temporal investigation to long term observation.The East China Sea coastal seafloor observatory,located between 30°31′44″N,122°15′12″E and 30°31′34″N,122°14′40″E,is constructed near the Xiaoqushan Island outside the Hangzhou Bay on the inner continental shelf of the East China Sea.The observatory is connected by a submarine optical fiber composite power cable that is more than one kilometer long and consists of a special junction box that transmits power and communication signals to different instruments.The special junction box has a variety of waterproof plugs and connects to three different instruments installed in a trawl preventer.The submarine optical fiber composite power cable is landed on the platform by The East China Sea Branch,State Oceanic Administration and the power is continuously supplied by the solar panels and solar battery on the top of the platform.The real time data are directly sent through the cable to the platform and are transmitted by CDMA wireless to the receiver at the State Key Laboratory of Marine Geology of Tongji University.Measurements at the observatory have been taken since April 20,2009 after installation and the results have been interpreted.The characteristics of the near bottom boundary are constrained by a sediment suspension model using portion of the observed data.In particular,discussion is provided on the sea surface height anomaly at Xiaoqushan Island influenced by the tsunami driven by the 2010 Earthquake in Chile.The successful establishment of the coastal seafloor observatory is the first step toward future development of seafloor observation systems in China.It not only accumulates experiences in technology and engineering,but also paves the way for performing important oceanic research using the long term continuous observation platform.     

Diatoms from the southwestern continental slope, South China Sea, and their paleoenvironmental significance since the last glacial times

A quantitative study was undertaken on diatoms from cores (SA08-34) obtained from the southwestern continental slope of the South China Sea (SCS). A total of 165 diatom species belonging to 45 genera were identified. We constructed a stratigraphic subdivision and correlation according to the characteristics of diatom assemblages together with ¹⁴C dating and carbonate analysis. We also discuss the sedimentary environment in the sea area since the last glacial times. The research shows that the diatom assemblages coincide with interglacial and glacial times, and changes in diatom abundance reflect the instability of the climate in the southern part of the SCS, such that short-term, temperature descending events correlate with the interglacial interval. The abundance of diatoms is relevant to interglacial and glacial times, since high abundance values were associated with an interglacial interval, and low abundance values with the last glacial maximum. We assume that strong upwelling developed in the interglacial interval, the development of which was influenced by variations of monsoons in the East Asian region.     

Rifting process and formation mechanisms of syn-rift stage prolongation in the deepwater basin,northern South China Sea

Based on the latest seismic and geological data, tectonic subsidence of three seismic lines in the deepwater area of Pearl River Mouth Basin （PRMB）, the northern South China Sea （SCS）, is calculated. The result shows that the rifting process of study area is different from the typical passive continental margin basin. Although the seafloor spreading of SCS initiated at 32 Ma, the tectonic subsidence rate does not decrease but increases instead, and then decreases at about 23 Ma, which indicates that the rifting continued after the onset of seafloor spreading until about 23 Ma. The formation thickness ex- hibits the same phenomenon, that is the syn-rift stage prolonged and the post-rift thermal subsidence delayed. The formation mechanisms are supposed to be three： （1） the lithospheric rigidity of the northern SCS is weak and its ductility is relatively strong, which delayed the strain relaxation resulting from the seafloor spreading; （2） the differential layered independent extension of the lithosphere may be one reason for the delay of post-rift stage; and （3） the southward transition of SCS spreading ridge during 24 to 21 Ma and the corresponding acceleration of seafloor spreading rate then triggered the initiation of large-scale thermal subsidence in the study area at about 23 Ma.     

南海成因模式述评

南海的构造演化与其周边的板块构造运动有密切关系,一直是地学研究的热点问题。现对中外学者关于南海成因模式的观点、模式进行综述分析,讨论涉及主动成因10种,被动类成因7种,涉及代表性观点20个,每一观点都能合理解释一些宏观地质现象,也都与另一些地质现象相悖,还需要进一步修正、发展或用新的资料来验证。这是南海研究日趋成熟的表现,未来将会逐渐各个学说融合发展。从史学的角度讨论了"南海观点"之演变,认为未来主要趋向是研究方法多元化、精细化、定量化,认为南海与周围地块之间主被动关系研究、东南亚盆地群响应序列之间对比、岩石圈结构学、区域岩石发展史、不同学说的动力学定量对比与评价是未来的主要研究关注点,并充分考虑外围被动因素,融合南海的发育历史,并将中生代南海的岩石圈禀赋及历史融于其中是南海成因模式研究的重要方向。     

南海深海塑料垃圾污染

渔业捕捞及商业航运活动的塑料排放是南海深海塑料污染的主要来源。南海深海微塑料污染始于20世纪80年代,具有明显陆源输入的特征,陆架近岸区域微塑料污染严重。陆坡深海峡谷是塑料/微塑料向深海盆地输运的主要通道,近底浊流在输运中发挥了重要作用。综述了南海海底塑料垃圾深潜研究的最新进展,首次提出了深海塑料垃圾生态系统的概念。     

南海深海盆的沉积充填

依据大洋钻探井及地震剖面资料,定量确定南海同扩张期和后扩张期深海盆沉积充填差异及沉积物来源变化。研究显示,南海深海盆自渐新世(32 Ma)开始形成,随着南海二次扩张海盆范围逐渐扩大,海盆内主要充填火山碎屑角砾岩及火山灰,碳酸盐岩、超微化石软泥,泥质粘土、粉砂质粘土、泥岩及粉细砂岩。深海盆充填主要沉积物为晚中新世(11.6Ma)以来的陆源碎屑沉积,丰富陆源碎屑的供给与南海闭合过程中同期区域构造事件(如青藏高原快速隆升、菲律宾板块俯冲)密切相关,也与晚中新世以来东亚季风增强以及源区强烈的风化剥蚀有关。     

The deep thermal characteristic of continental margin of the northern South China Sea

Heat flow plays an important role in the study of thermal structure and thermal evolution of continental margin of the northern South China Sea. The analysis of heat flow value shows that margin heat flow in the northern South China Sea is relatively high setting, but the percentage of crustal heat flow is lower than 35% in terrestrial heat flow. The terrestrial heat flow exhibited a current of rise from the Northern Continental Margin to the Southern Central Basin. However, the proportion of crustal heat flow in terrestrial heat flow slowly dropped down in the same direction. It is suggested that the main factor causing high heat flow setting is the moving up of hot material from asthenosphere.     

Seasonal features of the Sverdrup circulation in the South China Sea

Based on the Sverdrup relation, using climatological wind stress data, the basin scale Sverdrup transport in the South China Sea(SCS) is calculated and the basic seasonal features of the Sverdrup circulation are obtained. A comparison of these calculated features with observations proves that the wind-driven circulation in the SCS is very important for the formation of the SCS upper oceanic circulation in winter, summer and fall. It is shown that the non-uniform sea surface wind is one of the causes to form multi circulation centers in the basin of the SCS. The westward current at 18°N is caused by the local wind, which is stronger in fall and winter. The seasonal variation of circulation in the southern SCS is much more remarkable than that in the north. The wind in spring is helpful to the seasonal reversal of the circulation in the central SCS. The northward transport of the cyclonic circulation reaches the maximum in fall.     

The 1997-1998 warm event in the South China Sea

A strong warm event happens during spring 1997 to spring 1999 in the South China Sea. Its intensity and duration show that it is the strongest event on the record over the past decades. It also corresponds with the severe flood over the valley of the Yangtze River and a couple of marine environmental events. This note addressed the evolution process by using several data sets, such as sea surface temperature, height and wind stress in addition to subsurface temperature. The onset of the warm event almost teleconnects with the El Ni?o event in the tropical Pacific Ocean. Summer monsoon is stronger and winter monsoon is weaker in 1997 so that there are persistent westerly anomalies in the South China Sea. During the development phase, the warm advection caused by southerly anomalies is the major factor while the adjustment of the thermocline is not obvious. Subsequently, the southerly anomalies decay and even northerly anomalies appear in the summer of 1998 resulting from the weaker than normal summer monsoon in 1998 in the South China Sea. The thermocline develops deeper than normal, which causes the downwelling pattern and the start of the maintaining phase of the warm event. Temperature anomalies in the southern South China Sea begin to decay in the winter of 1998-1999 and this warm event ends in the May of 1999.     

Upper pycnocline turbulence in the northern South China Sea

The first regional mapping of the averaged turbulent kinetic energy dissipation rate <εp> in the upper pycnocline of the northern South China Sea is presented and discussed.At φ=20°N and to the north of this latitude,<εp> appears to be more than two times larger than that to the south of 20°N.It is suggested that this asymmetry is associated with the predominant northwestward propagation and dissipation of the internal waves originated in the Luzon Strait area.An approximately linear relationship between <εp> and the available potential energy of the waves P IW,suggests a characteristic time of the P IW dissipation of about 6 h.     

The 1997–1998 warm event in the South China Sea

A strong warm event happens during spring 1997 to spring 1999 in the South China Sea. Its intensity and duration show that it is the strongest event on the record over the past decades. It also corresponds with the severe flood over the valley of the Yangtze River and a couple of marine environmental events. This note addressed the evolution process by using several data sets, such as sea surface temperature, height and wind stress in addition to subsurface temperature. The onset of the warm event almost teleconnects with the El Niño event in the tropical Pacific Ocean. Summer monsoon is stronger and winter monsoon is weaker in 1997 so that there are persistent westerly anomalies in the South China Sea. During the development phase, the warm advection caused by southerly anomalies is the major factor while the adjustment of the thermocline is not obvious. Subsequently, the southerly anomalies decay and even northerly anomalies appear in the summer of 1998 resulting from the weaker than normal summer monsoon in 1998 in the South China Sea. The thermocline develops deeper than normal, which causes the downwelling pattern and the start of the maintaining phase of the warm event. Temperature anomalies in the southern South China Sea begin to decay in the winter of 1998–1999 and this warm event ends in the May of 1999.     

析南海问题中的美国因素

冷战结束后,美国一改其过去所持的中立立场,开始积极介入南海问题,以从政治、军事上遏制中国,并掠夺南海的石油资源,美国对南海问题的介入,无疑会增加争端解决的难度,使我国的周边安全环境趋于恶并改变亚太地区原有的战略均势。     

南海北部三参量风浪频谱数值模拟

基于Open FOAM开源程序,采用侯一筠的三参量风浪频谱构造了适用于中国南海北部海域的不规则波浪。首先,在waves2Foam程序中开发了解析松弛法进行消波处理并选用速度入口法造波,进而选用JONSWAP谱进行计算以验证不规则波造波程序的准确性;其次,以适用于中国南海北部海域的三参量风浪频谱为理论基础进行编程,将三参量风浪频谱嵌入到waves2Foam程序中,替换JONSWAP谱,通过设定风区长度、风速等参量构造模拟南海北部的不规则波浪。经验证,构造的不规则波的模拟值与理论值之间的误差在精度允许范围内,表明该方法能较好地模拟南海北部真实海况下的不规则波浪。     

南海生物礁碳酸盐台地演化

南海碳酸盐台地分布自早中新世开始发育,至中中新世达到鼎盛,再到晚中新世大量台地被淹没而逐渐消亡。从分布看,南海碳酸盐台地具有南早北晚、东早西晚的发育规律;从堆积速率看,中中新统速率最大。控制这些台地的诞生、发育演化和消亡的因素十分复杂,可能包括构造活动、相对海平面的变化、陆源碎屑物质输入变化、古海洋环境变化。     

The barrier layer in the southern region of the South China Sea

By analysing the CTD data in the southernregion of the South China Sea gathered during six cruisesbetween 1989 and 1999, a barrier layer with seasonalvariation just like what exists in the equatorial oceans isfound in this region. It is the first discovery in such amarginal sea yet. It is strong in autumn and a little weak in summer and winter. The thicker the barrier layer, the higher the average temperature of the upper mixed layer. The region with the thicker barrier layer overlaps the region with thehigher average temperature of the upper mixed layer, andaccords with the thicker region of the warm pool in the South China Sea got from the Levitus data. The barrier layer in the southern region of the South China Sea has significantinfluence on the heat storage of the upper ocean there.     

南海地区对流活动的时空变化特征

利用美国NCEP1958-1998年高斯网格月平均再分析资料,分析了南海地区(0°-20°N,100°-125°E)对流活动(OLR)的时空变化,结果表明:南海地区对流活动具有明显的季节转换特征,南海地区对流活动主要呈一致性的分布形势,且具有多时间尺度的变化特征,不同时间尺度的振动,其周期显著性和强度存在明显的年际差异。