南海北部5万年来的表层海水盐度及东亚季风降水
SEA SURFACE SALINITY AND EAST ASIAN MONSOON PRECIPITATION SINCE THE LAST 50000 YEARS IN THE NORTHERN SOUTH CHINA SEA
范维佳 1陈荣华2
作者信息
- 1. 同济大学海洋地质国家重点实验室,上海,200092
- 2. 国家海洋局第二海洋研究所,杭州,310012
- 折叠
摘要
为了探讨末次冰期以来南海北部区域降水变化对东亚夏季风强度变化的响应,利用南海北部191PC柱状样有孔虫壳体氧同位素和镁钙比值.重建了过去5万以来的表层海水温度和海水氧同位素变化.通过分析南海北部淡水收支的主要影响因素,认为夏季风降水是本研究站位海水盐度的主要影响因素,而海平面变化导致的冲淡效应变化并非主导因素.基于此前提,将剩余海水氧同位素作为区域降水变化的指标,结果表明.南海北部降水量与东亚季风强度在50-10kaB.P.间变化趋势较一致.10kaB.P.以来则呈相反的变化趋势.本文通过对比分析南海和西太平洋相关站位的古盐度变化、东亚陆地的干湿变化,结合数值模拟结果.认为50～10kaB.P.之间.北半球大陆冰盖对东亚夏季风的影响较强,东亚内陆和南海北部降水同时响应北半球高纬气温变化,表现出冷事件时降水少而暖事件时降水多的特点.而在10kaB.P.以来,南海北部和华南地区降水量与东亚季风强度变化趋势相反,表现出东亚-西北太平洋区域降水量分布的海陆差异特征.此现象与中全新世南北半球夏季辐射量不对称变化和海陆热容差异导致的温度、水汽重新分布有关.
Abstract
The marine core 191PC in Northern South China Sea( SCS,19°2. 95 'N.116°13. 22'E, w. d. 25l0m; 7. 2m in length) was studied using oxygen isotope and Mg/Ca of planktonic foraminifera Globigerinoides ruber shells in order to better understand the response of the precipitation in the South China Sea( SCS) to the changes of East Asian Summer monsoon during the last climatic cycle. Chronology of core 191PC was established by correlating the δ18O record with the NGRIP records, based on 3 AMS 14C ages. The bottom age was estimated to ca. 50kaB. P. with an average sedimentation rate of 14. 6cm/ka. The Mg/Ca ratios ranged from 2. 39mmol/mol to 4. 00mmol/mol in the studied intervals. It is revealed that the average sea surface temperature ( SST) during the Last Glacial Maximum could be as low as 23. 8℃ .ca. 3. 5℃ lower than the average SST in the Holocene. Higher and lower sea surface salinity( SSS) was observed during cold and warm intervals . respectively. An exception , however. occurs during the mid-Holocene,when the values of δ18Oresidual were as low as in the H-1 event. We can thus infer that SSS in the Northern SCS was probably elevated during mid-Holocene.Monsoonal precipitation was considered as a crucial factor to the local salinity over the Northern SCS at both the glacial/interglacial and millennial cycles,while the runoff dilution effect regulated by sea-level changes was considered of minor significance. Based on this premise, the precipitation over the Northern SCS during the last glacial was negatively correlated to the speleothem δ18O records from the South China. The two records, however,were observed positively correlated in the Holocene, indicating a decoupled tendency between marine and continental rainfall. This decoupled tendency was also discovered in other marine δ18Oresidual records from the Western Pacific Ocean and some terrestrial hydrological records from the South China coastal region. We thus concluded that the decoupling of marine-continent rainfall in the Holocene could be attributed to differences in the climatic boundary conditions and the regional precipitation-evaporation balance.
关键词
南海/Mg/ca浮游有孔虫/表层海水盐度/东亚季风引用本文复制引用
基金项目
国家重点基础研究发展规划(973计划)(2007CB815901)
出版年
2011
NETL
NSTL
维普
万方数据