Records of Toba eruptions in the South China Sea

Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea, were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, layers of A, B, and C, respectively. All of these tephra layers have an average thickness of ca. 2 cm. They were constrained in age of ca. 0.070 Ma, ca. 0.80 Ma, and ca. 1.00 Ma, respectively, by the microbiostratigraphy data. These tephra layers were predominated by volcanic glass shards with a median grain size of 70–75 μm in diameter. Major chemical compositions analyzed by EMPA and comparison with the previous data from other scatter areas suggest that these three layers of tephra can correspond to the three layers of Toba tephra, YTT, OTT, and HDT, respectively, erupting during the Quaternary. The occurrence of these tephra layers in the South China Sea implies that the Toba eruptions often occurred in the summer monsoon seasons of the South China Sea during the Quaternary, and that the strength of eruptions was probably stronger than that previously estimated.     

Responses of foraminiferal isotopic variations at ODP Site 1143 in the southern South China Sea to orbital forcing

The foraminiferal δ ¹⁸O and δ ¹³C records for the past 5 Ma at ODP Site 1143 reveal the linear responses of the Plio-Pleistocene climatic changes in the southern South China Sea to orbital forcing at the obliquity and precession bands. The phase of the δ ¹⁸O variations with the orbital forcing is opposite to that of the δ ¹³C, which may be caused by the frequent El Niño events from the equatorial Pacific. The amplification of the Northern Hemisphere Ice Sheet at ñ3.3 Ma probably affected the development of the 100-ka climatic cycles. Its further spreading may spur the 100-ka climatic cycle to become the dominant cycle in the late Pleistocene. The “Mid- Pleistocene Transition” event has localized influence on the isotopic variations in the southern South China Sea. The foraminiferal δ ¹³C records for the past 5 Ma at Site 1143 are highly coherent with the orbital forcing at the long eccentricity band, and lead the δ ¹⁸O records at the shorter eccentricity band, highlighting the importance of the carbon cycle in the global climate change.     

Responses of foraminiferal isotopic variations at ODP Site 1143 in the southern South China Sea to orbital forcing

1 Astronomical theory One of the greatest achievements of the EarthSciences in the 20th century is the establishment of theMilankovitch theory or the astronomical theory[1]. AsImbrie pointed out[2], the astronomical theory can bedescribed as a simple system model. The input to thesystem can be defined as changes in the geometry ofthe Earth’s orbit or the seasonal and latitudinal distri-bution of incoming solar radiation, whereas the outputto the system can be defined as one or more calc…     

Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144

The history of natural fire and its relationship to climate during the last three gla cial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25′E, 2037 m in water depth). Accord ing to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1-8), which might be correlated with the Marine Isotope Stage 1-8 (MIS1-8)respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low,which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal par ticles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.     

Grain-size records at ODP Site 1146 from the northern South China Sea: Implications on the East Asian monsoon evolution since 20 Ma

273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10–19 μm/1.3–2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2 EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.     

Palynological record during the Pleistocene (between 1.05 Ma and 0.36 Ma) from ODP1144, northern South China Sea

This paper presents the pollen record from the lower section of ODP1144 (depth 501.3-225.7 m, ca. 1.05-0.36 Ma). Two pollen zones (PA and PB) and eleven pollen subzones are recognized. Within zone PB, the 11 pollen subzones (PB21-11) are defined according to the pine, fern and herb variations, and are equivalent to the marine isotope stages 21-11 (MISs 21-11). The interglacial periods are typified by an increase in pine pollen and fern spores, and a decrease in herbaceous pollen, while the patterning during the glacial periods is just the opposite. During the interglacial periods, pollen assemblages were dominated by pine similar to those of the present day, suggesting that the paleoenvironment of the interglacial periods was similar to that of the present day, whereas the glacial periods are marked by an increase in herbaceous pollen, mainly Gramineae and Cyperaceae, indicating that grassland covered the exposed continental shelf when sea level declined. Increased Artemisia percentages and the highest     

Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146)

Measurement of clay mineralogy at ODP Site 1146 in the northern South China Sea (SCS) indicates that illite, chlorite, and kaolinite contents increased during glacials and smectite content increased during interglacials. The smectite/(illite+chlorite) ratio and the smectite abundance were determined as mineralogical indicators for the East Asian monsoon evolution. At a 10 ka timescale, prevailing southeasterly surface oceanic currents during interglacials transported more smectite from the south and east areas to the north, showing a strengthened summer monsoon circulation, whereas dominated counter-clockwise surface currents during glacials carried more illite and chlorite from Taiwan as well as from the Yangtze River via the Luzon Strait to the northern SCS, indicating a strongly intensified winter monsoon. Based on a 100 ka timescale, a linear correlation between the smectite/(illite+chlorite) ratio and the sedimentation rate reflects that the winter monsoon has prevailed in the northern SCS in the intervals 2000–1200 ka and 400–0 ka and the summer monsoon did the same in the interval 1200–400 ka. The evolution of the summer monsoon provides an almost linear response to the summer insolation of Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.     

渐新世以来南海北部陆坡区沉积演化及其对构造的响应

通过对南海北部陆坡下部ODP1148站位沉积物中陆源矿物组分的含量、堆积速率、粒度、石英氧同位素及石英扫描电镜的分析,探讨南海沉积演化及其构造响应.结果显示,根据综合指标的变化特征可将南海海盆的沉积演化划分为5个阶段:扩张初期 (34~28.5 Ma)、构造活动剧烈期(28.5~23 Ma)、构造活动减弱期(23~16.5 Ma)、热沉降期(16.5~3.5 Ma)和台湾隆升形成期(3.5 Ma~现今).其中28.5~23 Ma为物源转换期,陆源矿物组成和石英氧同位素值发生了明显改变,对应南海渐新世以来演化过程中构造活动最为活跃的时期.在此之前的渐新世南海扩张初期,研究区的沉积物主要来源于南部(很可能来自巴拉望陆块);随着南海的不断扩张,尤其是南海扩张轴在25~23 Ma发生向南跳跃后,南部巴拉望陆块不断远去,而此时由于青藏高原隆升导致的区域地貌变化还没有波及到云贵高原和华南地区,珠江等大河尚未发育,因此研究区以北的华南大陆的影响还很小或根本没有影响到研究区,结果陆源矿物沉积速率极低.随后由于青藏高原隆升的高度不断增加,河流发育,溯源侵蚀增加,华南内陆古老的沉积岩区成为南海北部主要物源区,南海北部转为以远源沉积为主,直到3.5 Ma前后由于台湾岛的抬升,大量物质进入南海北部,成为主要物源.物源转换期间在南海不断扩张的构造运动背景下由于物源供应匮乏,加上海平面的上升和较强的底流作用导致了ODP1148站位渐新世晚期的沉积间断.     

Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146) —— Implications for oceanic current transport and East Asian monsoon evolution

The East Asian monsoon system is a thermodynamic atmospheric circulation induced by the different potential heating between the 揥estern Pacific Warm Pool?(WPWP) and the Asian continent. The circulation patterns dominate seasonal patterns of winds, preci…     

Neogene oxygen isotopic stratigraphy, ODP Site 1148, northern South China Sea

A detailed stable isotopic study based on benthic foraminifera from 1165 samples of ODP Site 1148 (18° 50.17.3’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea, provides an excellent oxygen isotopic record with an average resolution of 30 ka. It contains the most continuous δ¹⁸O data with highest resolution for the whole Neogene sequence in the world. The δ¹⁸O curve shows a step-like increasing upwards and records 5 increases, 3 decreases and 2 stable stages during the Neogene, reflecting the general trend of global cooling. Among these events the δ¹⁸O decrease at 17.2–14.5 Ma, and two δ¹⁸O increases at 14.5-13.6 and 3.0-2.4 Ma are most marked and globally comparable. The intervals at 13.6-10.2 and 6.0-3.0 Ma with the lowest-amplitude and least fluctuation in δ¹⁸O represent the most stable bottom water periods for the South China Sea.     

Paleoceanographic evolution recorded in the northern South China Sea since 4 Ma

The late Pliocene-Pleistocene is of great interest for understanding the Earth’s climate system, because not only the late Pliocene is the latest period with tem-perature significantly higher than the Holocene, but also during the Pliocene/Pleistocene transition the Earth’s environment changed from a warm and uni-form climate state into an extreme one with typical glacial-interglacial cycles. During this period the Earth’s climate experienced through the grandly phased rising of the Qing…     

赤道MJO活动对南海夏季风爆发的影响

利用1979-2013年NCEP/DOE再分析资料的大气多要素日平均资料、美国NOAA日平均向外长波辐射资料和ERSST月平均海温资料,分析赤道大气季节内振荡(简称MJO)活动对南海夏季风爆发的影响及其与热带海温信号等的协同作用.结果表明,赤道MJO活动与南海夏季风爆发密切联系,MJO的湿位相(即对流活跃位相)处于西太平洋位相时,有利于南海夏季风爆发,而MJO湿位相处于印度洋位相时,则不利于南海夏季风爆发.赤道MJO活动影响南海夏季风爆发的物理过程主要是大气对热源响应的结果,当MJO湿位相处于西太平洋位相时,一方面热带西太平洋对流加强使潜热释放增加,导致处于热源西北侧的南海-西北太平洋地区对流层低层由于Rossby响应产生气旋性环流异常,气旋性环流异常则有利于西太平洋副热带高压的东退,另一方面菲律宾附近热源促进对流层高层南亚高压在中南半岛和南海北部的建立,使南海地区高层为偏东风,从而有利于南海夏季风建立;当湿位相MJO处于印度洋位相时,热带西太平洋对流减弱转为大气冷源,情况基本相反,不利于南海夏季风建立.MJO活动、孟加拉湾气旋性环流与年际尺度海温变化协同作用,共同对南海夏季风爆发迟早产生影响,近35年南海夏季风爆发时间与海温信号不一致的年份,基本上是由于季节转换期间的MJO活动特征及孟加拉湾气旋性环流是否形成而造成,因此三者综合考虑对于提高季风爆发时间预测水平具有重要意义.     

A model study of the summer Southeast Vietnam Offshore Current in the southern South China Sea

The western boundary current in the southern South China Sea (SCS) in summer does not always flow northward along the Indo-China Peninsula, it leaves the southeast coast of peninsula around 10–14°N, forming a strong eastward jet called “Vietnam Coastal Current” or “Southeast Vietnam Offshore Current” (SVOC). It is known that the wind stress curl is the major driving factor responsible for this current. In this paper, we carry on the study of the separation position, strength and forming time of this current. A connected single-layer/two-layer model is employed here to study these problems. According to the numerical experiments and analyses of the vorticity dynamics, it is found that, the local wind stress curl (including the northern cyclonic and the southern anticyclonic wind forcing curl), the nonlinear term, the topographic effect, the planetary vorticity advection and the water exchange between the SCS and Java Sea via the Sunda Shelf have an important effect on both the position where this current leaves the coast and its strength; when there is an inflow via the Sunda Shelf, the current is stronger and the separation position is more northward; whereas the water stratification, the coastline and the inflow of Kuroshio have little effect on its separation. In fact, two opposite flowing currents, the northward SVOC and the southward western branch of the cyclonic eddy to its north near the Indo-China Peninsula, collide with each other, and the strength of these two currents determine the separation position of the SVOC. Origin of the SVOC may be driven by the local negative wind stress curl in the middle SCS in mid-spring, this current flows along the coast of the Indo-China Peninsula and leaves the coast at high latitude, flowing northeastward; once the local positive wind stress curl near the northern Indo-China Peninsula or the negative one near the southern Indo-China Peninsula is large enough, this current will begin to leave the coast at low latitude.     

南海夏季风爆发与南大洋海温变化之间的联系

利用1979-2009年NCEP第二套大气再分析资料和ERSST海温资料,分析南海夏季风爆发时间的年际和年代际变化特征,考察南海夏季风爆发早晚与南大洋海温之间的联系.主要结果为:(1)南海夏季风爆发时间年际和年代际变化明显,1979-1993年与1994-2009年前后两个阶段爆发时间存在阶段性突变;(2)南海夏季风爆发时间与前期冬季(12-1月)印度洋-南大洋(0-80°E,75°S-50°S)海温、春季(2-3月)太平洋-南大洋(170°E -80°W,75°S-50°S)海温都存在正相关关系,当前期冬、春季南大洋海温偏低(高)时,南海夏季风爆发偏早(晚).南大洋海温信号,无论是年际还是年代际变化,都对南海夏季风爆发具有一定的预测指示作用;(3)南大洋海温异常通过海气相互作用和大气遥相关影响南海夏季风爆发的迟早.当南大洋海温异常偏低(偏高)时,冬季南极涛动偏强(偏弱),同时通过遥相关作用使热带印度洋-西太平洋地区位势高度偏低(偏高)、纬向风加强(减弱),热带大气这种环流异常一直维持到春季4、5月份,位势高度和纬向风异常范围逐步向北扩展并伴随索马里越赤道气流的加强(减弱),从而为南海夏季风爆发偏早(偏晚)提供有利的环流条件.初步分析认为,热带大气环流对南大洋海气相互作用的遥响应与半球际大气质量重新分布引起的南北涛动有关.     

基于卫星高度计资料分析南海热含量的年际变化特征

本文从海面高度异常与海洋热含量变化的线性关系出发,利用1992～2004年多颗卫星融合海面高度资料,对南海海域的热含量异常进行了计算.这一计算结果与基于气候态温盐资料计算的热含量季节变化具有很好的一致性.本文得到的结果还显示南海热含量异常具有明显的长周期变化,表现为:1992～1998年基本保持比较稳定的年际变化特征,1998年之后,热含量出现明显的跃变,这一跃变一直维持到2001年,在2002年开始出现热含量的递减趋势.对此时间序列进行谐波分析可以看出,南海热含量异常除了具有显著的年变化周期外,还存在明显的0.5、1.5、2.4、4年和6年的变化周期.进一步分析还发现,南海12月份热含量异常可以作为南海夏季风爆发的一种预报指标.     

青藏高原春季积雪在南海夏季风爆发过程中的作用

本文应用欧洲中期预报中心（ECMWF,European Centre for Medium\|Range Weather Forecasts—ERA\|40）资料和美国国家环境预测中心和国家大气研究中心(NCEP/NCAR, National Centers for Environmental Prediction/National Center for Atmospheric Research)资料,研究了青藏高原雪深变化对南海夏季风爆发的影响和ENSO对青藏高原降雪的影响.结果表明：（1）ECMWF的雪深资料是可信的,可以用来研究青藏高原雪深变化对南海夏季风爆发的影响;（2）青藏高原的积雪异常影响到500 hPa以上的温度异常和印度洋与大陆间的气温对比,一方面使上层的南亚高压移动速度发生变化,另一方面也影响到低层大气的运动和东西向风异常,在青藏高原少雪年,东印度洋产生西风异常和一个气旋对,而在青藏高原多雪年,东印度洋产生东风异常和一个反气旋对;（3）ENSO与青藏高原春季积雪关系密切.东太平洋SST正异常时,东印度洋和南海气压偏高,从而导致该区海陆经向压强梯度增强和西风异常.另外,此时青藏高原北部气压偏高,北风偏强,副热带锋面增强,同时,印度洋的SST偏高,为青藏高原降雪提供了水汽保障,这些都有利于青藏高原的降雪.     

Quaternary biogenic opal records in the South China Sea: Linkages to East Asian monsoon, global ice volume and orbital forcing

Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations.     

Stepwise paleoceanographic changes during the last deglaciation in the southern South China Sea Records of stable isotope and microfossils

Quantitative analyses of microfossils and stable isotopic analysis were carried out for Core SCS-12 in the southwestern slope of the South China Sea (SCS). A high-resolution paleoceanographic record for the last 13 ka was revealed with the AMS¹⁴C dates. The southern SCS has experienced stepwise paleoceanographic changes since the last deglaciation. The oxygen isotopic stage 1/2 boundary around 12.05 ka B. P. and the end of the last deglaciation around 7.70 ka B.P. are two rapid change periods (corresponding to the terminationIa and terminationIb, respectively), in between is a slow change period. The authors infer that the sea level stood at - 110 m before the terminationIa, roughly the same as today after the termination I_B, and about - 50 m in between. Subsequently, the average winter sea surface temperature and salinity obviously increased while paleo-productivity decreased since 12.05 ka B.P. The early Holocene CaCO₃ preservation spike, coupled with a high abundance of pteropoda and CaCO₃ content, occurred around 7.70 ka B. P. Project supported by the National Natural Science Foundation of China (Grant Nos. 49576286 and 49732086).     

菲律宾海板块与南海协同构造演化探讨

菲律宾海板块(Philippine Sea Plate,PSP)与南海(South China Sea,SCS)处于欧亚板块、太平洋板块和澳大利亚板块的交汇区域,其构造演化对东南亚、西太平洋乃至全球板块构造重建具有重要意义.虽然PSP和SCS的构造演化模型已经分别建立,但二者之间的协同演化关系还不明确.本文综述了PSP和SCS的古地磁数据、海底磁异常条带资料,并结合地震层析成像以及其他地质结果的约束,对二者的演化关系进行了探讨.PSP四国盆地与SCS在渐新世开始时,受控于统一的地球动力学系统,两者具有地质意义上的亲缘性.早中新世,澳大利亚板块与东南亚地块碰撞,致使PSP发生旋转,四国盆地开始与SCS发生分离,并逐渐向北运动和顺时针旋转,直至演化至现今位置.本文最后提出了这种协同构造演化模式有待解决的问题以及未来的研究展望.

     

Pleistocene radiolarian biostratigraphy in the South China Sea*

Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core. 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea. Project supported by the National Natural Science Foundation of China (Grant No. 49291100) and by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as part of a GermadChinese scientific cooperation program. This is Alfred Wegener Contribution No. 1473.