陈越,
王跃^,,
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、91958208和41976047）资助


详细信息

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

通讯作者: 王跃, E-mail: 163wangyue@tongji.edu.cn

中图分类号: P593;P736

收稿日期:2021-03-08
修回日期:2021-05-22
刊出日期:2021-07-30

Hydroclimatic changes in the northeastern South China Sea since the Last Glacial Maximum

CHEN Yue,
WANG Yue^,,
DANG Haowen,
JIAN Zhimin
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092



More Information

Corresponding author: WANG Yue,E-mail:163wangyue@tongji.edu.cn

MSC: P593;P736

--> Received Date: 08 March 2021
Revised Date: 22 May 2021
Publish Date: 30 July 2021


摘要
摘要:本研究以南海东北部MD18-3569孔（22°09.30'N，119°49.24'E；水深1320m）上部10.09m的沉积物为研究材料，利用浮游有孔虫Globigerinoides ruber壳体的氧同位素（δ¹⁸O_c）、Mg/Ca比值计算了表层海水剩余氧同位素（δ¹⁸O_residual），重建了过去两万年以来（19.88~0.78 ka B.P.，时间分辨率约152a）的表层海水盐度演变历史，结合南海其他站位降水重建记录，分析了研究区的水文气候变化特征。研究表明：1）南海南部和北部δ¹⁸O_residual记录的长期趋势呈反相变化关系，即南海北部δ¹⁸O_residual在末次冰消期逐渐偏负、全新世以来逐渐偏正，指示海表盐度先减小后增大，而南海南部δ¹⁸O_residual则呈现先偏正、后偏负的变化特征。这种南、北反相变化关系表明末次冰消期过程中，随着北半球夏季辐射量逐渐增加，热带海洋上方的大气对流活动增强，包括南海南部在内的暖池区水汽蒸发及相关δ¹⁸O分馏增强，同时东亚夏季风增强、把更多蒸发水汽传输至东亚大陆，途中在南海北部产生更多δ¹⁸O偏轻的季风降水，导致研究区海表盐度降低、δ¹⁸O_residual逐渐偏负。2）在千年尺度上，全新世东亚夏季风于1.4 ka B.P.、2.7 ka B.P.、4.4 ka B.P.、6.2 ka B.P.、7.2 ka B.P.和8.9 ka B.P.共出现6次降水减少事件，平均间隔约1500年，与中国东部石笋δ¹⁸O记录的全新世千年尺度事件一致，可能受太阳辐照度变化影响。因此，末次冰盛期以来，研究区的δ¹⁸O_residual主要受夏季风降水影响。
关键词: 季风降水/
表层海水盐度/
过去两万年/
氧同位素分馏/
南海东北部

Abstract:Sea Surface Salinity derived from paired oxygen isotope and Mg/Ca of planktonic foraminiferal shell is an important indicator for understanding hydroclimatic changes in the East Asian Summer Monsoon(EASM) region. However, mechanism for EASM-related hydroclimatic changes remains controversial since the last deglacial and little attention has been paid to the influence of EASM in the northern South China Sea(SCS), especially with archives of millennium scale high-resolution. In this work, we selected the marine core MD18-3569 that was drilled from the northeastern SCS(22°09.30'N, 119°49.24'E; 1320m water depth, total core length of 40.08m) during the 2018 Marion Dufresne cruise. For the upper 10.09m of this core, seven AMS¹⁴C dating points were used to establish a reliable age model covering from 0.78 ka B.P. to 19.88 ka B.P. with a sedimentation rate of 52.4cm/ka. Based on 126 samples spanning this core segment(with a sampling interval of 8cm or a time resolution of ca. 152 years), we analyzed shell Mg/Ca ratio and δ¹⁸O of planktonic foraminifera G.ruber for each sample, then calculated associated residual oxygen isotope of sea water(δ¹⁸O_residual) as a proxy of sea surface salinity, and finally reconstructed hydroclimatic changes in the northeastern SCS over the last 20000 years.
Compared with other δ¹⁸O_residual reconstructions in the SCS, our results imply that: (1) Long-term trends of δ¹⁸O_residual records in the southern and northern SCS are featured by a temporal out-of-phased relationship, in which the sea surface δ¹⁸O_residual and salinity both shifted negatively in the northern SCS during the last deglacial period and then gradually shifted positively during the Holocene, while the δ¹⁸O_residual in the southern SCS shifted out-of-phased. This reversed relationship may be explained as follows, during the last deglacial period, the increased northern hemisphere summer insolation results in stronger atmospheric convections over the EASM-adjacent tropical oceans and larger oxygen isotope fractionation from ocean to land, with more water vapor evaporation of lighter δ¹⁸O at the expense of heavier δ¹⁸O of the residual sea water(increased salinity) in the warm pool areas(such as the southern SCS). Meanwhile, the enhanced EASM transported more water vapor to the northern SCS, resulting in more monsoonal precipitation of lighter δ¹⁸O in our study area, explaining the negative shift of δ¹⁸O_residual and decreased salinity. (2) At millennial time scales, there are 6 positive shifts in our δ¹⁸O_residual record during the Holocene, centered at 1.4 ka B.P., 2.7 ka B.P., 4.4 ka B.P., 6.2 ka B.P., 7.2 ka B.P., and 8.9 ka B.P., respectively. These millennial-scale events have an average interval of about 1500 years, and resemble those abrupt EASM weakening events of stalagmite δ¹⁸O from China, and may be related to solar irradiance changes. Especially at 4.2~4.6 ka B.P. and 8.7~9.2 ka B.P., drastically decreased monsoon rainfall events were recorded in many regions of East Asia, indicating that severe droughts at that time may influence past evolutions of China civilization. Generally, since the last glacial maximum, the δ¹⁸O_residual proxy of sea surface salinity in our study area is mainly affected by EASM-related hydroclimatic changes at multiple time scales.
Key words:monsoon precipitation/
surface seawater salinity/
the last 20000 years/
oxygen isotope fractionation/
the northeastern South China Sea



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