张娜,
党皓文^,,
翦知湣
同济大学海洋地质国家重点实验室, 上海 200092

基金项目: 国家自然科学基金项目（批准号：41630965）和国家重点基础研究发展计划项目（批准号：2018YFE0202400）共同资助


详细信息

作者简介: 张娜, 女, 25岁, 硕士研究生, 海洋地质专业, E-mail:1731651@tongji.edu.cn

通讯作者: 党皓文, E-mail:hwdang@tongji.edu.cn

中图分类号: P722.7;Q915.811⁺.1;P595

收稿日期:2020-02-28
修回日期:2020-03-31
刊出日期:2020-05-30

Mid- to Late-Pleistocene orbital-scale changes in the upper-ocean structure of the northern South China Sea: Planktonic foraminiferal oxygen and carbon stable isotope records of IODP Site U1501

Zhang Na,
Dang Haowen^,,
Jian Zhimin
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092



More Information

Corresponding author: Dang Haowen,E-mail:hwdang@tongji.edu.cn

MSC: P722.7;Q915.811⁺.1;P595

--> Received Date: 28 February 2020
Revised Date: 31 March 2020
Publish Date: 30 May 2020


摘要
摘要:文章以南海北部IODP U1501站（18°53.09'N，115°45.95'E，水深2846 m）上部46 m沉积物岩芯为研究材料，基于浮游有孔虫混合层种Globigerinoides ruber壳体氧同位素建立了本站位1.5 Ma以来的氧同位素地层年代框架，结合次表层种Pulleniatina obliquiloculata壳体的氧、碳稳定同位素数据，分析了中-晚更新世以来南海北部上层水体结构的轨道尺度变化。结果表明南海北部浮游有孔虫δ¹⁸O冰期极盛期最重值在0.9 Ma和0.4 Ma之后发生阶段性变重；表层-次表层种之间的δ¹⁸O差值（Δδ¹⁸O_P-G）反映的上层水体温度梯度在0.9 Ma和0.6 Ma阶段性减小，冰期-间冰期变化幅度在0.9 Ma和0.4 Ma后阶段性增大，反映了北半球冰盖扩张和东亚冬季风增强的阶段性变化特征。中更新世转型（MPT）δ¹⁸O的主要变化体现在冰期极正值的增加，同时次表层海水的降温可能更为显著；中布容事件（MBE）期间表层δ¹⁸O变重，次表层δ¹⁸O维持稳定；MBE之后表层δ¹⁸O在间冰期显著负偏，而次表层δ¹⁸O则在冰期明显变重。MBE前的MIS 13期，表层δ¹⁸O显著正偏，可能反映南海北部偏冷，与中国黄土指示该期偏暖湿的特征相联系，可能指示东亚中-低纬度之间的差异减小。U1501站记录的约0.5 Ma的碳同位素重值事件（δ¹³C_max-Ⅱ），表现出两种浮游有孔虫δ¹³C的同步正偏的特征，可能与陆地储存更多¹²C、或者营养盐输入增多改变了大洋有机/无机碳比例有关；同时表层-次表层种之间的δ¹³C梯度显著减小，可能反映上层水体混合增强的现象。
关键词: 上层海水结构/
氧碳同位素/
中更新世气候转型/
中布容事件/
南海北部

Abstract:After the mid-Pleistocene Transition(MPT)and the mid-Brunhes Event(MBE), the Late Quaternary glacial cycle with a powerful ca.100-ka cycle was finally established. Tropical forcing involving the global carbon reservoir, sea surface and thermocline temperature changes in the tropical Pacific has been proposed to have a significant impact on global climate change. However, studies about the changes in the thermocline of the northern South China Sea(SCS), especially that of the MBE, are relatively short, not to mention that there still lacks any in-depth exploration that links the monsoon evolution and the upper-ocean dynamics. Here we analyze the oxygen and carbon stable isotopes of surface-dwelling and subsurface dwelling planktonic foraminifera, Globigerinoides ruber and Pulleniatina obliquiloculata, respectively, from the sediment records of Site U1501 (18°53.09'N, 115°45.95'E; 2846 m depth)drilled by the International Ocean Discovery Program(IODP)Expedition 368. In this work, we analyzed a total of 230 samples from the depth range of 0~46 m at Hole U1501C. The age model, covering the last 1.5 Ma, was established by comparing the planktonic foraminiferal δ¹⁸O record of U1501 with the LR04 stack and the planktonic δ¹⁸O of ODP1146. Using the stable isotopes of the two planktonic foraminifera, the Middle- to Late-Pleistocene orbital-scale variations in the upper-water structure of the northern SCS was reconstructed. The results show that the peak glacial values of both the surface and subsurface δ¹⁸O gradually became heavier after 0.9 Ma and 0.4 Ma, accompanying with an increase in their glacial-interglacial ranges, while their difference indicates that the upper-water temperature gradient decreased at around 0.9 Ma and 0.6 Ma. These trends consistently suggest a response of the northern SCS upper-ocean to the expansion of the Northern Hemisphere ice sheet and the enhancement of the East Asian winter monsoon. During the MPT, changes in glacials were stronger than those in interglacials, and the subsurface seawater temperature decreased more significantly than the surface. During the MBE period, the surface seawater became colder and the subsurface water remained relatively stable. After MBE, both the surface and subsurface δ¹⁸O fluctuate more strongly on the glacial-interglacial cycle, and the surface seawater became significantly warmer during the interglacial periods while the subsurface seawater became colder during the glacial period. In MIS 13, an important interglacial just before MBE, the relatively more positive surface δ¹⁸O in U1501C reflects a relatively cold interglacial, which is apparently contrary to the warm and wet conditions recorded in Chinese Loess Plateau, and thus indicating a reduced latitudinal gradient over the East Asia during MIS 13. The synchronous heavier δ¹³C of the two planktonic foraminifera at ca. 0.5 Ma(δ¹³C_max-Ⅱ)in Site U1501 suggests that the carbon isotope maximum events(δ¹³C_max)may be related to an increased land reservoir of ¹²C due to enhanced summer monsoon, or a change in the ratio between oceanic organic/inorganic carbon pools due to increased terrigenous nutrient input. The greatly decreased surface-subsurface δ¹³C gradient in the U1501C records may suggest an enhancement of upper-ocean mixing in the northern South China Sea during δ¹³C_max-Ⅱ.
Key words:upper-oceanstructure/
oxygen and carbon isotopes/
mid-Pleistocene Transition/
mid-Brunhes Event/
northern South China Sea



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