中晚更新世以来南海中部深层流演化特征  

Deep current evolution in the central part of the South China Sea since the Middle to Late Pleistocene

作　　者：杨小强 谢一璇 吴双 张庭伟 商圣潭 Xiaoqiang Yang;Yixuan Xie;Shuang Wu;Tingwei Zhang;Shengtan Shang(Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519080,China)

机构地区：[1]中山大学地球科学与工程学院,广东省地质过程与地质灾害重点实验室,珠海519080

出　　处：《科学通报》2024年第18期2660-2673,共14页Chinese Science Bulletin

基　　金：国家自然科学基金(42274090);环南海地质过程与灾害创新团队项目(2016ZT06N331)资助。

摘　　要：太平洋西边界流是南、北半球间输送热量、营养物质等的重要大洋环流.南海深层环流起源于经过吕宋海峡进入南海的西太平洋中深层水,其在地质时间尺度与太平洋西边界流的关系还有待深入研究.本文选择位于南海中央海盆的沉积钻孔,在根据地球磁场相对强度变化确定沉积物年代框架的基础上,对碎屑沉积物的粒度组成进行端元分解,同时结合磁化率椭球体参数的变化,尝试建立能够反映南海深层环流的指标,讨论其演化规律.结果表明,沉积物中可排序颗粒(10~63μm)的含量(SS%)、中值粒径约为17.26μm的端元2组分(EM2)含量以及磁化率各向异性度P均指示了较强的水动力条件,对此3个参数进行主成分分析后获得的PC1组分可以代表南海深层流活动.自250 ka以来,南海深层流活动与太平洋西边界流一致,在氧同位素阶段MIS6和MIS2活动强烈,波动幅度较大,其他时期活动较弱.深层流活动强度与西太平洋温跃层的温度变化密切相关,当温度降低时,深层流活动强烈.可能的机制是强烈的西边界流进入菲律宾海之后,翻转上升,使温跃层温度降低、密度加大,吕宋海峡两侧海水的密度差异增加,导致进入南海的水量和流速均增加,使南海深层流活动加强.The Pacific western boundary current(WBC)is a crucial oceanic circulation that transports heat and nutrients between the Northern and Southern Hemispheres.The deep current in the South China Sea(SCS)originates from intermediate-deep waters in the western Pacific Ocean,entering through the Luzon Strait.The long-term relationship between the WBC and the deep current in the SCS over geological timescales remains uncertain.In this study,we selected a sedimentary core(located at 116.75°E and 15.80°N,at a water depth 3000 m,with a length of~580 cm)from the central basin of the South China Sea to illustrate the evolution of the deep current in the central SCS.The core sediments primarily comprise silty clay,clayey silt and fine silt,exhibiting colors ranging from light greenish gray to dark gray.Notably,there are no distinct signs of erosion or bioturbation.A total of 290 paleomagnetic samples and an equivalent number of powder samples were continuously obtained for paleomagnetic measurements and debris grain size analysis,respectively.Additionally,twenty samples were selected for hysteresis loop determination and first-order reversal curve(FORC)diagram tests.The paleomagnetic and rock magnetic results indicated that single-domain(SD)and pseudodomain(PSD)soft magnetic minerals faithfully record changes in the geomagnetic field.Stable and reliable natural remanence could be achieved after alternating demagnetization in the laboratory.The relative paleointensity(RPI)proxy can be reconstructed using normalized natural remanent magnetization(NRM)with saturation isothermal remanent magnetization(SIRM).The core chronology was established through AMS14C dating of three planktonic foraminifera samples and correlation of the relative paleointensity with the stacked master curve of the geomagnetic field intensity.To gain insights into hydrodynamics,we conducted End-member decomposition of the grain-size composition of detrital sediments.Combining these data with changes in magnetic fabric parameters,we aimed to establish an ind

关 键 词：太平洋西边界流 南海深层流 碎屑沉积物粒度 磁化率各向异性度 

分 类 号：P731.27[天文地球—海洋科学]