A case study of continental shelf waves in the northwestern South China Sea induced by winter storms in 2021

This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.

A study of internal solitary waves observed on the continental shelf in the northwestern South China Sea

Based on in-situ time series data from the acoustic Doppler current profiler （ADCP） and thermistor chain in Wenchang area, a sequence of internal solitary wave （ISW） packets was observed in September 2005, propagating northwest on the continental shelf of the northwestern South China Sea （SCS）. Corresponding to different stratification of the water column and tidal condition, both elevation and depression ISWs were observed at the same mooring location with amplitude of 35 m and 25 m respectively in different days. Regular arrival of the remarkable ISW packets at approximately the diurnal tidal period and the dominance of diurnal internal waves in the study area, strongly suggest that the main energy source of the waves is the diurnal tide. Notice that the wave packets were all riding on the troughs and shoulders of the internal tides, they were probably generated locally from the shelf break by the evolution of the internal tides due to nonlinear and dispersive effects.

Stress field modeling of northwestern South China Sea since 5.3 Ma and its tectonic significance

Tectonically, the northwestern South China Sea （SCS） is located at the junction between three micro-plates, i.e., the Indochina, South China and Zhongsha-Xisha micro-plates, and involves three basins, i.e., the Yinggehai Basin, the Qiongdongnan Basin and Xisha Trough in the east, and the Zhongjiannan Basin in the south. Since the Pliocene （5.3 Ma）, the Yinggehai Basin has experienced repeated accelerating subsidence, high thermal fluid, and widely developing mud-rich overpressure chambers, abundant mud diapers and crust-mantle mixed CO2. While a large central canyon was developed in the Qiongdongnan Basin, new rift occurred in the Xisha ~rough. These characteristics demonstrate a single tectonic unit for the northwestern SCS, for which we have undertaken stress field modeling to understand its plate deformations and sedimen- tary responses. Our results demonstrate that an extension tectonic event occurred after 5.3 Ma in theYingge- hal-Qiongdongnan-Xisha trough area, which is characterized by thinner crust C〈16000 m）, half-graben or graben structural style and thicker sedimentary sequences （〉3 500 m）. A new rift system subsequently was developed in this area; this event was mainly driven by the combined effects of different movement veloc- ity and direction of the three micro-plates, and the far-field effect of the continental collision between the Indian Plate and the Tibetan Plateau, and subduction of the Pacific Plate underneath the Eurasian Plate.

The deep mantle upwelling beneath the northwestern South China Sea:Insights from the time-varying residual subsidence in the Qiongdongnan Basin

Deep hot mantle upwelling is widely revealed around the Qiongdongnan Basin on the northwestern South China Sea margin. However, when and how it influenced the hyper-extended basin is unclear.To resolve these issues, a detailed analysis of the Cenozoic time-varying residual subsidence derived by subtracting the predicted subsidence from the backstripped subsidence was performed along a new seismic reflection line in the western Qiongdongnan Basin. For the first time, a method is proposed to calculate the time-varying strain rates constrained by the faults growth rates, on basis of which, the predicted basement subsidence is obtained with a basin-and lithosphere-scale coupled finite extension model, and the backstripped subsidence is accurately recovered with a modified technique of backstripping to eliminate the effects of later episodes of rifting on earlier sediment thickness. Results show no residual subsidence in 45–28.4 Ma. But after 28.4 Ma, negative residual subsidence occurred, reached and remained ca. -1000 m during 23–11.6 Ma, and reduced dramatically after 11.6 Ma. In the syn-rift period(45–23 Ma), the residual subsidence is ca. -1000 m, however in the post-rift period(23–0 Ma),it is positive of ca. 300 to 1300 m increasing southeastwards. These results suggest that the syn-rift subsidence deficit commenced at 28.4 Ma, while the post-rift excess subsidence occurred after 11.6 Ma.Combined with previous studies, it is inferred that the opposite residual subsidence in the syn-and post-rift periods with similar large wavelengths(>10^(2) km) and km-scale amplitudes are the results of transient dynamic topography induced by deep mantle upwelling beneath the central QDNB, which started to influence the basin at ca. 28.4 Ma, continued into the Middle Miocene, and decayed at ca.11.6 Ma. The initial mantle upwelling with significant dynamic uplift had precipitated considerable continental extension and faulting in the Late Oligocene(28.4–23 Ma). After ca. 11.6 Ma, strong mantle upwelling probably occurred beneath the Leizhou–Hainan area to form vast basaltic lava flow.

Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function

This study presents an analysis of the spectral characteristics of remote sensing reflectance(Rrs)in northwestern South China Sea based on the in situ optical and water quality data for August 2018.Rrswas initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole Rrs were characterized using the empirical orthogonal function(EOF)analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95%of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of Rrs(A-D Rrs-EOF1)significantly contributed to the total variances of each Rrs class.In addition,the correlation coefficients between the amplitude factors of class A-D Rrs-EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class ARrs-EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B Rrs-EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(ag(λ)),whereas the spectral shape of class C Rrs-EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D Rrs-EOF1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.

A Comparative Analysis of Chemical Properties and Factors Impacting Spring Sea Fog over the Northwestern South China Sea

In the present study,we analyzed the chemical properties and factors impacting the sea fog water during two sea fog events over the northwestern South China Sea in March 2017,and compared our results with those of other regions.The sea fog water during these two events were highly acidic and their average pH was below 3,which was related to the high initial acidifying potential and large amounts of NOand SOnot involved in the neutralization reaction.The dominant cations in the sea fog water were Naand NH.The primary anions in the sea fog water over the South China Sea were Cland NO,while that over the North Pacific Ocean was mainly SO,and ratios of the three fog water ions near the Donghai Island were similar.Ions in the sea fog water during the two events were mainly derived from marine aerosols,while the difference was that the first low-level sea fog airflow trajectory passed over Hainan Island.Therefore,the proportion of K+in the first sea fog was much higher than that in sea water and the second.Sulfate was the key to fog water nucleation,which made ion concentration in the sea fog water during the second event higher than that during the first.A decrease in average diameter during the first sea fog formation led to an ion concentration increase,while the average diameter of sea fog water during the second event was lower than that during the first,which corresponded with a moderate ion concentration increase.

Seismic Image Prediction of Cenozoic Reef-Banks in the Northwestern South China Sea

The Cenozoic reef-banks reservoir in Qiongdongnan （琼东南） basin is one of the most profitable targets worthy of prospecting in the deep water area of the northwestern South China Sea. In this study, the characteristics of organic reef-like reflectors in southern uplift area of Qiongdongnan basin are analyzed based on the latest 2D and 3D seismic data. It is found that reef-like reflectors in Qiongdongnan basin show high-amplitude moundy continuous reflection at the top and the bottom, chaotic reflection inside the reef-like reflector and there is obviously speed difference between reef-like reflector body and surrounding rock. Combining the geological setting of reef and comparative analysis, the reef-like reflectors are considered to be the reef-banks. Furthermore, the results show that there are three kinds of reef structures in the southern uplift area of Qiongdongnan basin： the fault controlling structure, the fault flexure structure and the carbonate ramp structure. Each structure has its own grow-units that can reveal the growth process of the reef in order. The distribution of reef-like reflec- tors in space shows an arc belt pattern. According to this, four reef arc belts are identified, and their spatial trends are thought to have a good relationship with the buried fault. The internal structure con- stitution and the growth state of reef-like reflectors are mainly controlled by the geomorphology and monsoon-ocean current. The result has an instructive significance to oil-gas exploration of organic reef not only in Qiongdongnan basin, but also even in deep water areas of the South China Sea.

Reconstruction of paleocoastlines for the northwestern South China Sea since the Last Glacial Maximum

The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal. ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only 1×104 km2, and thus the land-sea distribution remained nearly unchanged. Later in 15-10 cal. ka BP coastline rapidly retreated and area of land loss was up to 24×104 km2, causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×104 km2, and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion of about 10×104 km2.

Crustal activities recorded incoral reefs in the northwestern South China Sea

Coral reefs in the northwest of South China Sea have recorded the information from not only the environmental variation but also the crustal activities there during their development. The main crustal activities correlated with the coral reef development include fault, seismic, and volcano activities, etc. The high-resolution spark seismic profiles in the northwestern South China Sea show that the fault activities in the coral reef region have been clearly recorded, and appear as neonatal faults incising reefs. Earthquakes in the coral reef region are rather intense, especially the two occurring on December, 31, 1994, and January, 10, 1995, around the southwest of Leizhou Peninsula, with the magnitude of 6.1 and 6.2, respectively. They have great influence on the growth of the local coral reefs. Quaternary volcanos are active in the northwestern South China Sea, especially around the southwest of Leizhou Peninsula, and they have obvious control of the coral reef development. Some submarine volcanoes form the substrates of coral reef, while a few emerge above the sea surface and form coral islands.

Growth of a polymetallic nodule from northwestern continental margin of the South China Sea and its response to changes in paleoceanographical environment of the late Cenozoic

In the northern South China Sea,the accumulation of enormous quantities of terrigenous sediment during Cenozoic rendered well-developed polymetallic nodules very rare.In this study,we analyzed a polymetallic nodule from the northwestern continental margin of the South China Sea using microscopic mineralogical observation,electron probes,X-ray diffraction(XRD),ICP-MS,and Be isotope dating.We found the nodule's shell layers rich in different types of microstructures,including columnar,laminar,stack-like,petal-like,and porphyritic structures.The major mineral components of the nodule are MnO2.Unlike nodules from the eastern Pacific basin,this nodule has high contents in Fe,Si,Al,and REEs but low contents in Mn,Cu,Co,and Ni.The Mn/Fe ratio is also low and the average REEs content is 1370.4 ppm.There is a strong positive anomaly of Ce;and the Be(beryllium) isotope dating shows the initial time of growth of the nodule to be about 3.29 Ma.The inner compact layer formed from 3.29 Ma to about 1.83 Ma.The laminar and stack-like structures and the low contents of the terrigenous elements such as Fe,Si,REE,and Al indicate the paleoceanographical environment with weak undersea currents and favorable oxidizing conditions.From 1.83 Ma to 0.73 Ma,the growth rate of the nodule increased by about 3%;the microstructures formed during this period are stack-like and columnar.The contents of Si and Al are increased by nearly 10%,indicating an increase of terrigenous sediment input in the northern South China Sea.The content of Ce is decreased by about 16%,indicating a significant weakening of the oxidizing conditions at the seabed.From 0.73 Ma to 0.69 Ma,the growth rate of the nodule rapidly rose up to 8.27 times that of the nodule's average growth rate,and the contents of Fe,Al,and REEs in the layer also increased,forming a loose layer characterized by oolitic,granular,porphyritic,and petal-like structures,indicating the paleoceanographical environment with a high sedimemtation rate and abundant supply of terrigenous sediment in the northern South China Sea.From 0.69 Ma to 0.22 Ma,the growth rate of the nodule suddenly slowed and the outer compact layer formed.Contents of Fe,Si,REE,Al,Mn,Cu,Co,and Ni in this layer were significantly lower than in other layers.The main structures of the layer are laminar and fissure filling structures.These reflect the paleoceanographical environment with stable undersea currents,poor oxidizing conditions,and other conditions not conducive to nodule growth.The growth process of nodule S04-1DG-1 was found to respond sensitively to the changes of the paleoceanographical environment of the northern South China Sea during the late Cenozoic.

南海西北部蓝圆鲹时空分布及其与环境因子的关系

蓝圆鲹(Decapterus maruadsi)是中国东南近海重要的经济鱼类之一。本研究根据2012—2018年南海西北部捕捞产量数据和海洋环境遥感数据,分析了该海域蓝圆鲹季节平均单位捕捞努力量渔获量(catch per unit effort, CPUE)的时空分布特征,并运用广义可加模型(generalized additive model, GAM)探究了CPUE与环境因子的关系。结果显示,蓝圆鲹的CPUE具有明显的季节性:夏季最高,CPUE达0.848 kg/(kW·d);冬季最低,CPUE为0.087 kg/(kW·d)。2016年CPUE的异常增加可能是受到2015—2016年超强厄尔尼诺事件的影响。GAM分析显示,该海域蓝圆鲹CPUE与经度、海表温度(sea surface temperature, SST)、叶绿素a (chlorophyll a, Chl-a)浓度、海水深度、海表盐度(sea surface salinity, SSS)、涌浪波向、风浪波向及其周期显著相关。相对较高CPUE海域范围为110.5°~114°E,SST为26~30℃,Chl-a为0.2~1.0 mg/m^(3),海水深度<120 m,SSS为33.4~33.8,涌浪波向为75°~120°、150°~175°,风浪波向为50°~75°、120°~135°、175°~190°,风浪周期为3.0~4.5 s;其中,风浪波向对CPUE贡献最高,涌浪波向其次,然后是SST。南海西北部蓝圆鲹的资源丰度变化和其洄游特性与季风变化等引起的环境因子的变动有关。

Carbonate dynamics in a tropical coastal system in the South China Sea featuring upwelling, river plumes and submarine groundwater discharge

This study examined carbonate dynamics in the northwestern South China Sea(NWSCS),an area jointly influenced by upwelling,river plumes and submarine groundwater discharge.Data were obtained from two cruises conducted in summer 2009 and 2012.In 2009,a high salinity-low temperature water mass occurred nearshore off northeastern Hainan Island,indicative of upwelling,commonly referred to as HNEU.A river plume fueled primarily by local rivers and characterized by low salinity and high temperature was observed in the NWSCS off the mainland roughly along the 30 m isobath.In 2012,coastal upwelling off northeastern Hainan Island was not detectable at the surface,but was observed at a different location off eastern Hainan Island(HEU).River plume waters in 2012 were patchily distributed,with a low salinity zone further westerly than that in 2009 and another on the mid-shelf of the NWSCS sourced from the Pearl River which reached out~250 km from the mouth of the Pearl River Estuary.In 2009,elevated dissolved inorganic carbon(DIC)and total alkalinity(TA)occurred in the coastal plume,where submarine groundwater discharge contributed DIC and TA additions of 38.9±20.5 and 42.5±22.3μmol kg^(−1),respectively,with a DIC/TA ratio of~0.92,which made a minor contribution to the variation of seawater partial pressure of CO_(2)(pCO_(2)),pH and the aragonite saturation state index(Ω_(arag)).Additionally,high surface phytoplankton production consumed DIC of 10.0±10.4μmol kg^(−1) but did not significantly affect TA,which dominated pCO_(2) drawdown in the coastal plume water and increased the pH andΩ_(arag) at surface.Submarine groundwater discharge was also observed in the region influenced by upwelling,but to a lesser degree than that impacted by coastal plume.Lower pH andΩ_(arag) and higher pCO_(2) values than in offshore waters were observed downstream of the upwelling system,attributable largely to organic matter remineralization with a DIC addition of 23.8±8.4μmol kg^(−1).In 2012,submarine groundwater discharge was not detected but high phytoplankton production dominated carbonate dynamics in the coastal plume water with a net DIC consumption of 104.2μmol kg^(−1),which markedly drew down sea surface pCO_(2) and increased pH andΩ_(arag).In the Pearl River Plume,the solubility-driven CO_(2) sink exceeded biological CO_(2) uptake,resulting in an additional decrease of pH andΩ_(arag) and increase of seawater pCO_(2).Taken together,this study demonstrated complex spatial and year-to-year variability,and the controls of the carbonate system under the joint modulations of upwelling,river plumes and submarine groundwater discharge.A first order estimate that considered the rise of atmospheric CO_(2) and seawater temperature further suggested a high risk of ocean acidification in this coastal area by the end of this century,which could be amplified under the stresses of river plumes,submarine groundwater discharge and organic matter remineralization.

南海西北部陆架区鱼类的种类组成与群落格局

根据2006—2007年在南海西北部陆架区海域进行的4航次底拖网调查数据,对该海域鱼类的种类组成和群落格局进行分析。调查共采获鱼类262种,隶属于20目102科。以冬季出现种类数最多,为166种;夏季和秋季次之,分别为161种和155种;春季最少,为135种。运用聚类分析和非度量多维标度(NMDS)方法分析了南海西北部陆架区鱼类群落结构的空间分布。研究表明,该海域鱼类可划分为5个群落,分别为粤西沿岸群落(群落Ⅰ)、海南岛东南沿岸群落(群落Ⅱ)、海南岛东部深海群落(群落Ⅲ)、过渡群落(群落Ⅳ)和混合群落(群落Ⅴ)。ANOSIM检验表明,各群落间鱼类组成的差异极为显著(R=0.847-0.939,P<0.001)。鱼类群落格局的变化与海流和水深关系密切,有较明显的沿水深梯度分布的规律。咸淡水鱼类在雷州半岛东部的冷涡区域,形成群落Ⅰ;南海暖流控制区域内的深海鱼类,形成群落Ⅲ;在南海暖流最为强劲的冬季,研究区域内大部分鱼类集结为混合性群落Ⅴ;琼东南沿岸的上升流区内形成群落Ⅱ;沿岸流强劲的夏、秋季,在沿岸流和上升流交汇处,形成过渡性群落Ⅳ。

南海西北部新生代沉积基底构造演化

在综合分析地质、地球物理、地球化学、古生物学等多方面资料的基础上,将南海西北部海域控制新生代主要沉积盆地的基底划分为5个区:北部湾古生界断堑基底区、莺歌海古生界走滑拉分基底区、琼东古生界断陷基底区、西沙北古生界裂谷基底区、西沙南古生界走滑伸展基底区.通过区域地质分析,初步重建了该海域的大地构造演化历史.该海域新生代沉积基底在前新生代时期与其北面陆上云开地区和其南面的南沙地区同处于特提斯构造域中,经历过古特提斯和中特提斯的发育历程,晚古生代以来可初步分为5个阶段:(1)D-P1,古特提斯东段多岛洋体系发育阶段;(2)P2,中特提斯(古南海)开始出现、古特提斯开始消减阶段;(3)T-K1,古特提斯东段多地块缝合阶段;(4)K2-N11,现代南海形成、中特提斯(古南海)消亡时期;(6)N21以来南海扩张停止、澳大利亚板块向北俯冲挤压阶段.

红河活动断裂带在南海西北部的反映

红河断裂带是一条走滑的活动断裂带 ,它控制着南海西北部的构造活动 ,也控制着莺歌海盆地的形成和演化。根据南海西北部中穿过莺歌海盆地的地震剖面和历史资料进行解释 ,结果表明 ,莺歌海盆地的形成可分 3个阶段 :自 50MaB .P .开始 ,沿红河断裂带的左旋错动和在印支地块的顺时针旋转的应力作用下 ,形成了莺歌海盆地的雏形 ;2 4MaB .P .之后在左旋压扭应力场作用下 ,形成了盆地西北部的反转构造 ;5MaB .P .之后发生了右旋错动 ,盆地内快速沉降 ,发育巨厚沉积层。根据盆地内最老和最新的沉积中心之间的距离 ,推测沿红河断裂带的左旋位错约 2 0 0km。该断裂带发展到现代 ,其活动性大为减弱 ,曾发生 1 0次小于 5级地震。

无井条件下建立碎屑岩储层地震地质模型研究

常规的储层建模以井数据为基础,建立孔隙度、渗透率和含油饱和度等储层属性参数模型,并通过油田开发生产数据进行拟合,得到最佳地质模型.在南海西北部深水区无井控制的情况下,针对中央峡谷浊积水道储层,采用确定性建模与连续型随机建模相结合的方法,建立碎屑岩储层地震地质模型,应用地震正演模拟和相似性分析方法,确定浊积水道砂体最佳模拟参数.文章首先分析了碎屑岩储层特征,应用连续型随机建模的方法模拟储层空间分布.然后分析实际地震、地质资料,应用层序地层学思想,对研究区划分沉积体系域,建立层序地层格架;基于波阻抗和多种地震属性,采用人机交互的方法对浊积水道储层框架结构进行精细解释,建立储层结构模型;将储层结构模型与砂泥互层随机介质进行"交"、"并"运算,利用连续型随机模拟方法对储层内部介质进行精细刻画,建立中央峡谷浊积水道随机介质储层模型;通过对模型正演模拟、常规处理和相似性分析等建立最佳储层模型.文章研究了在无井条件下建立储层地震地质模型的方法,揭示南海西北部深水区中央峡谷浊积水道储层的空间展布和内部结构特征.

南海西北部重磁场及深部构造特征

通过对南海重磁数据的重新处理,得到南海西北部自由空间重力异常图、布格重力异常图、磁异常图和化极磁异常图,并对所反映的地球物理场特征加以分析。根据重力场资料对研究区的地壳结构进行了反演计算,结果表明地壳厚度在10～38km之间,总的趋势由陆向洋逐渐减薄,对应于地壳类型从陆壳、过渡壳到洋壳的分布特征。根据磁力资料计算了居里面深度,其埋深变化于11～27km之间,在陆区居里面是下地壳顶界面和莫霍面之间的另一个物性界面,而在海区则接近于莫霍面埋深。

热带风暴“天鹰”对南海西部浮游植物叶绿素浓度的影响

南海是著名的寡营养盐低生产力区,同时也是热带气旋频发的海域,强的热带气旋通常会给海洋上层带来强烈的扰动,可能引起营养盐的卷入并引起海洋上层浮游植物的急剧增加。由于移动速度较快的弱台风及热带气旋对深水海域生态系统的影响通常较为有限,以往相关的研究通常关注强度较强、移动较慢的台风对深水海区生态系统的影响。文章研究了一个强度较弱、移动较快的跨陆架区热带风暴"天鹰"对陆架区浮游植物的影响,通过对比强风事件前后风场及背景环境要素的变化特征,探讨了这种弱热带气旋事件对陆架区海洋浮游植物的可能贡献。研究结果表明,2005年7月"天鹰"形成前南海西北部夏季叶绿素浓度通常较低(<0.12mg·m 3),气旋过境后浮游植物叶绿素浓度显著增加(>0.14mg·m3),平均大约增加33%。这种叶绿素浓度短期迅速增加与同期风场的变化有关。对强风事件期间垂向温度、声学多普勒海流剖面(ADCP)数据以及营养盐水平分布的分析表明,短暂的强风事件在营养盐跃层较浅的陆架区能导致较强的卷吸混合及惯性振荡流,诱发生源物质由下至上的输送,以及风暴引起的强降水在有利流向作用下将营养物质由近到远的输运,导致海南岛东南部海域浮游植物的迅速增加。

南海西北部珊瑚礁记录所反映的新构造运动

珊瑚礁是发育于热带海洋环境中由生物作用和地质作用共同形成的地质体,具有独特的新构造运动意义。南海西北部珊瑚礁记录所反映的新构造运动主要有火山活动、地壳升降运动和地震活动等。珊瑚礁区第四纪火山活跃,到现代已停止活动,部分火山构成珊瑚礁的基座,个别出露海面为火山岛;地壳升降运动差异较大,雷州半岛西南部珊瑚礁呈上升趋势,上升率为0.02~0.05mm/a;西沙群岛等岛礁地壳运动则呈下降趋势,下降率为-0.07^-0.10mm/a,岛礁中的造礁石珊瑚生长率、礁顶和灰沙岛的堆积率均相当于或大于地壳下降率与现代海平面上升率的总和;南海西北部珊瑚礁区内地震活动较强,尤其是1994年12月31日和1995年1月10日在雷州半岛西南部海域发生了6.1级和6.2级地震,这两次地震对该区珊瑚礁的发育有较大的影响。

西沙群岛石岛浅部基底地壳应力测量及其地球动力学意义分析

西沙群岛独特的构造位置决定了其构造运动背景和地壳应力场动力源的复杂性.位于西沙群岛石岛、深达1268.07m的西科1A井在1257.52m钻遇花岗岩基底.在1125.8~1262.0m开展5次水压致裂地应力测量,获得最大水平主应力为17.09~20.85MPa,最小水平主应力为15.97~18.29MPa,估算垂直主应力为22.86~26.68 MPa,地壳应力结构为SV〉SH〉Sh,以垂直主应力为主导,该应力结构特征有利于正断层活动,表明西沙群岛地壳基底处于拉张的应力环境.受西沙海槽断层影响,水平应力值较低.印模测试显示基底地壳应力方向以近东西-北西向为主,与已有的GPS测量、横波分裂和面波反演结果较为吻合,显示西沙群岛岩石圈尺度上变形一致性较好.西沙群岛地壳应力场的力源受板块运动和地幔物质上涌作用联合制约.综合南海西北部实测地应力数据分析,显示该区域主应力方向较为一致,应处于统一、稳定的构造运动背景之中.西科1A井水压致裂试验是我国首次涉海深孔地壳应力测量,具有重要的地球动力学意义,提供了研究南海地球物理场的宝贵基础资料.