中-晚更新世南海北部上层水体结构的轨道尺度变化:IODP U1501站浮游有孔虫氧碳稳定同位素记录  

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

作　　者：张娜[1] 党皓文[1] 翦知湣[1] Zhang Na;Dang Haowen;Jian Zhimin(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《第四纪研究》2020年第3期605-615,共11页Quaternary Sciences

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

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δ^18O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δ^18O差值(Δδ^18OP-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)δ^18O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δ^18O变重,次表层δ^18O维持稳定;MBE之后表层δ^18O在间冰期显著负偏,而次表层δ^18O则在冰期明显变重。MBE前的MIS 13期,表层δ^18O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(δ13Cmax-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。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 foraminiferalδ^18O record of U1501 with the LR04 stack and the planktonicδ^18O 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 subsurfaceδ^18O 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 mor

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 

分 类 号：P722.7[天文地球—海洋科学] P915.8111