南海东北部末次冰盛期以来的水文气候变化  

HYDROCLIMATIC CHANGES IN THE NORTHEASTERN SOUTH CHINA SEASINCE THE LAST GLACIAL MAXIMUM

作　　者：陈越 王跃[1] 党皓文[1] 翦知湣[1] CHEN Yue;WANG Yue;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》2021年第4期1031-1043,共13页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41630965、91958208和41976047)资助。

摘　　要：本研究以南海东北部MD18-3569孔(22°09.30'N,119°49.24'E;水深1320 m)上部10.09 m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(δ^(18)O_(c))、Mg/Ca比值计算了表层海水剩余氧同位素(δ^(18)O_(residual)),重建了过去两万年以来(19.88~0.78 ka B.P.,时间分辨率约152 a)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δ^(18)O_(residual)记录的长期趋势呈反相变化关系,即南海北部δ^(18)O_(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δ^(18)O_(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δ^(18)O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δ^(18)O偏轻的季风降水,导致研究区海表盐度降低、δ^(18)O_(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δ^(18)O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δ^(18)O_(residual)主要受夏季风降水影响。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;1320 m water depth,total core length of 40.08 m)during the 2018 Marion Dufresne cruise.For the upper 10.09 m of this core,seven AMS 14C 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 52.4 cm/ka.Based on 126 samples spanning this core segment(with a sampling interval of 8 cm or a time resolution of ca.152 years),we analyzed shell Mg/Ca ratio andδ^(18)O of planktonic foraminifera G.ruber for each sample,then calculated associated residual oxygen isotope of sea water(δ^(18)O_(residual))as a proxy of sea surface salinity,and finally reconstructed hydroclimatic changes in the northeastern SCS over the last 20000 years.Compared with otherδ^(18)O_(residual)reconstructions in the SCS,our results imply that:(1)Long-term trends ofδ^(18)O_(residual)records in the southern and northern SCS are featured by a temporal out-of-phased relationship,in which the sea surfaceδ^(18)O_(residual)and salinity both shifted negatively in the northern SCS during the last deglacial period and then gradually shifted positively during the Holocene,while theδ^(18)O_(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 fro

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 

分 类 号：P593[天文地球—地球化学] P736[天文地球—地质学]