南海晚新生代深水古海洋学变迁

This study will synthesize and integrate the paleoceanographic results from the projects funded by the large research program "Evolution of deep-sea processes of the South China Sea", in combination with the post-cruise study of the South China Sea (SCS) IODP Leg 349 in 2014, to reveal the characteristics of the SCS deepwater responses to the basin evolution and the glacial-interglacial changes. This project will adopt new methods of foraminiferal B/Ca ratio and fish teeth’s Nd isotope analysis, combining with carbon stable isotope, microfossils and their shells’ elements, carbonate content and other proxies, to reconstruct the SCS deepwater evolution. On the basis of the comparison with the paleoceanographic records of the SCS upperwater and the Western Pacific deepwater, this study will focuse on: 1) the history of the deepwater exchanges between the SCS and the Pacific at the tectonic and orbital- timescales since the Miocene; 2) the evolution of the SCS deepwater and carbon cycle at the glacial-interglacial and even longer time scales; 3) the carbonate development and the CCD evolution of the SCS since the Miocene. This study will provide an important scientific basis for reconstructing the "life history" of marginal seas, and also make international contribution to explore the mechanisims of deep ocean circulation and carbon cycle.

本项研究将集成综合“南海深海过程演变”重大研究计划已资助项目的古海洋学研究成果，结合2014年南海大洋钻探IODP 349航次后研究，揭示南海作为边缘海，其深部海水对盆地演化和冰期-间冰期旋回的响应特征。该项目将采用有孔虫壳体B/Ca比值和鱼牙Nd同位素分析等新手段，结合稳定碳同位素、微体化石及其壳体元素、碳酸盐含量等其它替代性指标，再造南海深部海水的演变特征，进而与南海上层海水、西太平洋深部水的古海洋学记录比较，着重研究：1）中新世以来构造和轨道时间尺度上南海与太平洋深部海水交换的历史；2）冰期旋回及更长时间尺度上南海深部海水与碳循环的演变；3）中新世以来南海的碳酸盐发育与CCD演变。本项研究将为再造边缘海的“生命史”提供重要的科学依据，同时也为探索大洋深部环流和碳循环演变机制做出国际贡献。

本项研究依托南海深部大计划的多个古海洋学研究项目，采用底栖有孔虫及其壳体化学（氧碳同位素和B/Ca比值）和测年、鱼牙Nd同位素等多种替代性指标，结合IODP第368航次的新材料，对南海新生代深水古海洋学变迁做集成研究，并与太平洋深水古海洋记录做比较，在探讨南海早期构造演变的沉积古环境响应、中中新世以来南海与太平洋深部海水的交换历史、以及晚第四纪冰期旋回中南海深部环流演变及其对海洋碳循环的影响等方面取得了重要进展，为揭示南海作为边缘海的演化历史提供了新的科学依据。主要研究进展如下：.1）获得南海从陆到海的沉积古环境记录，重新确定重要地震界面的年龄，恢复南海早期构造演变的古水深变化，揭示距今约28Ma前的构造沉降和古环境巨变。.2）发现中中新世南极冰盖扩张导致太平洋翻转流PMOC增强和南海深层水13C降低，晚中新世约6.5Ma巴士海峡开始形成导致南海底栖有孔虫13C的南北梯度变化，而上新世以来PMOC增强使得南海深层水[CO32-]降低、并具有40-50万年的偏心率长周期。.3）发现末次冰消期北太平洋中层水NPIW增强、而间冰期PMOC较强，并揭示了冰期南海深部海水通风减弱、深部水文界限下降对海洋碳循环和碳酸盐溶解的影响。