南海东北部末次冰盛期以来的水文气候变化

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。

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

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(δ18Oresidual) as a proxy of sea surface salinity, and finally reconstructed hydroclimatic changes in the northeastern SCS over the last 20000 years.