Nd isotopic variations and its implications in the recent sediments from the northern South China Sea

The chondrite-normalized REE distribution patterns in recent sediments from the northern South China Sea and surrounding areas are similar, with the HREE values being almost equal to or slightly higher, and the La_N/Lu_N ratio being lower, than PAAS standards. However, samples from the Xijiang River, a major branch of the Pearl River system, show opposite trends, i.e., with slightly lower HREE values and higher La_N/Lu_N ratio than PAAS. The distribution of Nd isotopes in sediments from the northern South China Sea was controlled by the Pearl River and the inshore area of South China, respectively. The volume of ε_Nd(0) from inshore areas of southern China is apparently higher than that from the Pearl River, and ε_Nd(0) values in offshore sediments and Taiwan Island are between these values. The results clearly show that ε_Nd(0) volume in the northeastern South China Sea is higher than in the southwest part of the northern South China Sea, indicating different source rock types. The main source rock of the Pearl River sediment is carbonate types and affects sediment deposition in the southwest of the northern South China Sea, while the source rock in the inshore area of southern China, mainly Mesozoic and Cenozoic granites, contributes to sediments in the northeastern area of the northern South China Sea. Due to different source rock types, the HREE values and the volume of ε_Nd(0) in recent sediments supplied by the inshore area of southern China are higher than those from the Pearl River. Over 80% of the rapidly accumulated sediments on the northern slope of the South China Sea in the southeast of Dongsha Islands area were derived from Taiwan Island and from inshore areas of South China, with only less than 20% from the Pearl River. Supported by National Natural Science Foundation of China (Grant Nos. 40276019, 40238060 and 40621063), and National Basic Research Program of China (Grant No. 2007CB819501)     

Deep sea pollen record during 12－1.6 Ma from the southern South China Sea and its response to envi-ronmental change

Based on deep-sea pollen results (512-76 m) from ODP Site 1143 in the southern South China Sea (SCS),the climate and vegetation evolution sequence on the surrounding islands and the exposed continental shelf are discussed. The pollen records show that the pollen influx was quite low before 8.15 Ma and increased dramatically afterwards. The influx changes can be ascribed,on one side,to tectonics deformations around the southern SCS resulting in rapid uplift of islands and subsequent increase of the sediment rates and pollen influx and on the other side to climate cooling and monsoon enhancement. Around 2.63 Ma was another obvious boundary,the increasing of pollen and spores influx since this time was mainly related to global climate cooling. Spectrum analysis of pollen influx values shows that 2 Ma,0.67 Ma,and 0.19-0.17 Ma cycles existed during 12-3.0 Ma,while 0.1 Ma and 46.9 ka cycles existed during 3.0-2.0 Ma.     

Carbon isotopic record of foraminifers in surface sediments from the South China Sea and its significance

Since the 1990s, the papers and data involved withthe South China Sea (SCS) have been emerging in largenumbers in the world as people pay more attention to thepaleoceanography of the SCS. There have been more than100 cores mentioned in papers containing p…     

Original component of grain size index in core sediment from southwestern slope of the South China Sea and its paleoenvironmental implication

Traditional grain size analysis was basically used to discriminate sediment type based on its particle dimension for sedimentary naming[1,2] and to analyze the dynamic feature of transport medium, including water current and wind strength[3―5]. Recently, some patency advances havebeen made by using different methods to separate different grain sizes in various original composition from sediments for searching a new way of paleoenvironmental study[6―8]. Grain size analysis is even playing an …     

Late Neogene radiolarian absence event in the southern South China Sea and its paleoceanographic implication

Down-core variations of radiolarians at ODP Site 1143 in the southern South China Sea （SCS） are presented for the last 12 Myr. The fluctuations of radiolarian abundances since the Late Miocene can be divided into three stages： a high abundance stage at 12-5.96 Myr, a radiolarian absent stage at 5.96-3.30 Myr and a gradual increasing stage after 3.30 Myr. The three stages correspond to the forming and vicissitudes of the Western Pacific Warm Pool （WPWP） and the Eastern Asian Summer Monsoon （EASM）. The radiolarian absence event （RAE） was also absent of diatom and occurred nearly simultaneously with the closures of the Panama Isthmus and the Indonesian seaway, which probably caused the reorganization of oceanic circulation systems. Accompanied this circulation reorganization was the weakening of the WPWP and the EASM, which probably led to a weakened upwelling in the southern SCS. In addition dissolved silica （Dsi） content in surface seawater might be very low during 5.96-3.30 Myr due to the ＂biogenic bloom＂ event, which consumed a large amount of Dsi in the surface seawater. All these factors together might lead to a great decrease of siliceous production in the southern SCS and consequently caused the RAE. Moreover, the dissolution of siliceous skeletons might also influence the abundance of radiolarians.     

Late Neogene radiolarian absence event in the southern South China Sea and its paleoceanographic implication

Down-core variations of radiolarians at ODP Site 1143 in the southern South China Sea (SCS) are presented for the last 12 Myr. The ?uctuations of radiolarian abundances since the Late Miocene can be divided into three stages: a high abundance stage at 12–5.96 Myr, a radiolarian absent stage at 5.96–3.30 Myr and a gradual increasing stage after 3.30 Myr. The three stages correspond to the forming and vicissitudes of the Western Paci?c Warm Pool (WPWP) and the Eastern Asian Summer Monsoon (EASM). The radiolarian absence event (RAE) was also absent of diatom and occurred nearly imultaneously with the closures of the Panama Isthmus and the Indonesian seaway, which probably caused the reorganization of oceanic circulation systems. Accompanied this circulation reorganization was the weakening of the WPWP and the EASM, which probably led to a weakened upwelling in the southern SCS. In addition dissolved silica (Dsi) content in surface seawater might be very low during 5.96–3.30 Myr due to the ‘‘biogenic bloom” event, which consumed a large amount of Dsi in the surface seawater. All these factors together might lead to a great decrease of siliceous production in the southern SCS and consequently caused the RAE. Moreover, the dissolution of siliceous skeletons might also in?uence the abundance of radiolarians.     

Observational study of the circulation in the southern South China Sea

CTD data from two oceanographic survey cruises, conducted by “Shiyan No. 3” R/V during two reversing monsoons, were employed to calculate and analyze the distributions of temperature, salinity and geopotential anomaly in the southern South China Sea (SSCS). Based on these distributions, the horizontal structures of the SSCS circulation are described systematically. Study results show that the SSCS circulation structure could be classified as a two-layer (the upper and the lower) pattern, and that the main circulation in the upper layer (0–400 m) is driven by the South China Sea monsoons and is opposite in direction to the reversal of the monsoons. The distributions of principal current systems and their features are presented. Two important local phenomena, local eddy and oceanic front, were observed.     

基于ISCCP卫星资料的南中国海云量特征分析

为较准确地了解掌握可以反映南中国海天气和气候特征的云量分布演变特征,利用1999年1月至2009年12月的ISCCP卫星云量资料,通过物理量特征提取、对比分析等方法,研究了南中国海总云量及高、中、低云量的分布演变特征,以及其与其他海域各季节云量季节性变化特征。结果表明:南中国海低云量四季中均表现为由海区向沿岸递减,总云量和中、高云量夏秋季高于冬春季,低云量则相反。对于不同海域的云量细节特征要依据各季节大气和海洋环流变化来细致区分,这样有助于在掌握规律基础上有效制作海域上空云的预报。     

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.     

Identification of the thick-layer greigite in sediments of the South Yellow Sea and its geological significances

Magnetic minerals in sediments of the continental shelf are sensitive to environmental changes. Therefore, to determine the exact phases of magnetic minerals is the prerequisite to investigate the paleoenvironmental significances. In this study, a comprehensive rock magnetic investigation, coupled with mineralogical studies, was carried out on the long core NHH01 （with a length of 125.64 m） from the central continental shelf of the South Yellow Sea. Single-domain greigite was identified as the dominant magnetic carrier in sediments between 44.90 and 51.80 m, and terrigenous magnetite is the major magnetic phase in the adjacent layers. The existence of greigite unambiguously indicates an anoxic environment. We tentatively interpreted that such an environment could be formed by the fast sea level changes, longexisting of the cold eddies during warm stages, or in a lake which might be related to locally tectonic uplifting. Therefore, the occurrence of the thicklayer greigite could supply a new perspective to paleoenvironmental or even tectonic studies.     

Pleistocene precession forcing of the upper ocean structure variations of the southern South China Sea

The precession plays a dominant role in driving the tropical monsoon variations. Our high resolution, millennial scale marine isotope records from ODP Site 1143 in the southern South China Sea (SCS) present the detailed history of the upper ocean structure variations over the past 1.56 Ma on glacial/interglacial timescale. The cross spectral analyses between the Earth's orbital variations and the isotopic differences reveal a high coherency between the East-Asian-monsoon-related thermocline and nutricline variations of the SCS and the precession. The variations of monsoon-related isotopic difference between species also demonstrate periodicities of 11-, 12- and 14- thousand years near semi-precession which originates in the tropics, highlighting the importance of the precession in driving the east Asian monsoon changes.     

Quaternary high-resolution opal record and its paleoproductivity implication at ODP Site 1143,southern South China Sea

The correlation of opal content and MAR with oxygen isotopic records of benthonic foraminifera at Site 1143, southern South China Sea indicates that,since about 900 ka,the increasing opal content and MAR during the interglacial periods is inferred to reflect the bigher surface productivity ,for the intensified summer monsoon during the interglacial periods would result in the enhanced upwelling and nutrient supply,Time-sequence spectral analyses of oxygen isotopic record ,opal content and MAR at intervals of 0-900 ka reveal that the changes of surface productivity were dominantly forced by the variations of the earth orbital cycles.     

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.     

Geochemical characteristics of pore water in shallow sediments from Shenhu area of South China Sea and their significance for gas hydrate occurrence

The Shenhu area is one of the promise target areas for marine gas hydrate exploration in the northern margin of the South China Sea.Pore water samples were collected from two piston cores (8.75 and 8.52 m) in site HS-A and site HS-B in the Shenhu area,and their major anion and cation contents and trace element contents have been analyzed in this study.Cl- concentrations in pore waters are similar to the seawater value and no systematic change along depth profiles has been found for the Cl- content in both s...     

Deep-water Oligocene pollen record from South China Sea

Leg 184 of ODP recovered a record of deepwater sediments spanning the past 32.8 Ma from the South China Sea (SCS). The sediments of the Ofigocene (32.8-23.8 Ma) at Site 1148 contain relatively abundant fossil pollen. The pollen analysis at Site 1148 has established the first pollen assemblage sequence of deep-water Oligocene in the China Sea. The pollen assemblages of the Ofigocene are dominated by montane conifer tree pollen. The abundances of broad-leaved tree pollen are lower in the assemblages.Both of the montane conifer and broad-leaved tree pollen groups include mainly tropical-subtropical components. The pollen of cold and drought-enduring plants is present in lower content. The distinct change in pollen assemblage sequence of deep-water Oligocene of the SCS occurred at 32.0 Ma, indicative of an important shift of the Oligocene climate in the SCS region. The characteristics of the pollen flora of the deep-water Oligocene indicate the tropical montane ralnforest and lowland ralnforest developed on the areas around the SCS before 32.0 Ma, reflecting the warm and wet climatic condition. In the pollen flora of the Oligocene after 32.0 Ma, the temperate montane conifer and cool and drought-en- during deciduous tree taxa remarkably increased, indicating that the climate in the SCS region became comparatively cool and dry.     

滇池东部第四系浅层湖滨相沉积物磁学特征及其环境意义

为了探究昆明盆地第四纪以来的总体气候特征及滇池湖泊的演化规律。本文综合环境磁学、TOC、pH等指标,对滇池东岸DC1钻孔岩芯沉积物进行了系统研究,测试了包括质量磁化率（χ）、非磁滞剩磁（ARM）、饱和等温剩磁（SIRM）、低频磁化率（χlf）、高频磁化率（χhf）、软剩磁（IRM-300mT）、pH值及总有机碳（TOC）。结果显示：DC1沉积物磁性特征由亚铁磁性矿物主导,反铁磁性的赤铁矿在0.3-3.6 m与14.7-15.6 m两个区段含量相对较高,结合赤铁矿的形成环境,反映了这两个区段对应的沉积环境为湖退时期;另外,结合TOC与磁化率在不同深度上的关系,表明TOC的高值与细颗粒的磁性矿物溶解有关。结合TOC在各区段的含量特征表明整个21 m沉积过程所对应的气候类型以温暖气候为主。     

Sea surface temperature and terrestrial biomarker records of the last 260 ka of core MD05-2904 from the northern South China Sea

This paper reports high-resolution biomarker records of the last 260 ka for core MD05-2904 from the northern South China Sea （SCS）. The sea surface temperature （SST） record using the U37^k＇, index reveals a minimum of 21.5℃（MIS 2） and a maximum of 28.3℃（MIS 5.5）, for a temperature difference of almost 7℃, and provides the longest high-resolution U37^k＇ SST record in northern SCS. The content of odd-number long chain n-alkanes and several n-alkanes indexes such as the CPI, ACL and the C31/C27 ratio, all reveal generally higher values during the glacials and lower values during the interglaclals. Terrestrial input as Indicated by n-alkane content was mostly controlled by sea-level changes： During the glacials, lower sea-level exposed the continental shelf to enable rivers to transport more terrestrial materials to the slope; and the situation reverses during the interglacials. The n-alkane indexes changes reveal more n-alkanes from contemporary vegetation during glacials as a result of the proximity of the core site to the source region, while the increases in ACL and C81/C27 ratio during glaclals indicate a change to more grassy vegetation. However, the highest values for CPI, ACL and the C81/C27 ratio all occurred during late MIS 3, and it was suggested that this period was characterized by a strong summer monsoon-dominated humid climate which resulted in a denser vegetation for the exposed continental shelf region.     

Oxygen and carbon isotope records of calcareous nannofossils for the past 1 Ma in the southern South China Sea

Oxygen and carbon isotopic analyses have been carried out on calcareous nannofossils from ODP Site 1143 in the southern South China Sea. The results demonstrate that the δ18O values of calcareous nannofossils for the past 1 Ma vary systematically with those of planktonic and benthic foraminifera from the same site. But the average δ18O value of nannofossils is 1.869‰ higher than that of planktonic foraminifera, and is 3.855‰ lower than that of benthic foarminifera. There are systematic differences between the δ13C values of nannofossils, planktonic foarminifera and benthic foraminifera. The average δ13C of nannofossils is 0.756‰ higher than that of benthic foraminifera, and is 0.460‰ lower than that of planktonic foraminifera. The δ13C values of nannofossils exhibit a significant positive shift beginning near isotope stage 14 and lasting until stage 8. This study also finds that there is a close ralationship between the δ13C of nannofossils and the percentage of Florisphaera profunda. This implies that the δ13C of nannofossils can be used as an indicator of sea water surface paleoproductivity.     

Barrier layer in the northeastern South China Sea and its formation mechanism

A VERTICALLY UNIFORM LAYER OF TEMPERATURE(ISOTHERMAL LAYER),SALINITY(ISOHALINE LAYER)AND DENSITY(MIXED LAYER)IS USUALLY FORMED IN THE UPPER OCEAN DUE TO THE WIND STIRRING.UNDERNEATH IS THE LAYER WITH RELATIVELY STRONG VERTICAL GRADIENT AS THE THERMOCLINE,…     

Internal tide characteristics over northern South China Sea continental slope

21-day in-situ ADCP current and CTD data from an anchored observational station by R/V Shiyan 3 are used to investigate the characteristics of intemal tide in the northern South China Sea continental slope. The results show that tide and internal tide are both mixed type in the observed region and dominated by diurnals; the maximum internal tidal major axes of K1, O1 were largest and reached 11 cm/s, 10 cm/s, respectively, and their current vectors rotate anticlockwise. The 300 m-deep internal tide presents obvious quasi-diurnal oscillation and its average amplitude reaches 50 m. Furthermore, internal tide carried high energy; in the upper layers above 140 m, the kinetic energy of intemal tides accounts for 15%--37% of overall kinetic energy, most of internal tide energy concentrates around the thermocline.