中国陆架海有孔虫Mg/Ca指标研究及其全新世应用

The Mg/Ca ratio of foraminifera is an important proxy in plaeoceanographic studies. The application of this proxy in Chinese shelf seas, however, is very scarce due to the absent of available calibration equation in this region. In this project, we try to build some suitable calibration equations both for planktonic and benthic foraminifera on these shallow shelf seas. Based on modern ecology study of panktonic and benthic foraminifera in these shelf seas, we try to choose some typical planktonic and benthic foraminiferal species from surface sediments across the northern South Chia Sea (SCS) shelf, East China Sea (ECS) shelf and the Yellow Sea (YS) shelf, for Mg/Ca measurments. Then we try to probe factors that influenced the foraminiferal Mg/Ca ratio variation. Through correlation analysis of Mg/Ca ratio with modern physical parameters such as temperature and salinity, species with Mg/Ca ratio sensitive to temperature changes will be screened out, then the Mg/Ca -temperature calibration equations will be built. these calbration equations will then apply into the Holocene paleoenvironmental study in these shelf seas. We plan to choose 3-4 sediment cores with high sedimentation rate from the three shelf seas, through Mg/Ca analysis combined with stable isotpe measurements we try to reconstruct comparable Holocene records both in temperature and salinity, together with foraminiferal and grain size analysis on these cores, we futher expect to uncover the response of Holocene marine environmental changes on Chinese shelf to the east Asian monsoon variation and global climate changes. This project will provide basic scientific data for the study of regional climate response to global changes.

有孔虫Mg/Ca比是古海洋环境重建的重要指标，在中国陆架海区，由于缺乏相应的温度校准方程研究，这方面的应用研究非常欠缺。本项目拟在陆架有孔虫生态调查的基础上，选取横跨南、东、黄海陆架上表层沉积物中的典型浮游和底栖有孔虫属种进行Mg/Ca比值测试，探讨有孔虫Mg/Ca比的主要影响因素；结合现代海洋环境参数分析，筛选出对温度变化显著的浮游和底栖有孔虫属种，建立对应的Mg/Ca比-温度校准方程。进而在以上三个陆架海区挑选3-4个具有较高沉积速率的沉积柱样，应用获得的Mg/Ca经验方程与氧碳同位素结合重建不同岩芯全新世的温度和盐度变化历史；结合有孔虫分析、粒度分析等，探讨全新世从南到北陆架海洋环境对全球变化的区域响应规律。为全球变化区域响应研究提供基础科学资料。

有孔虫Mg/Ca温度指标是古海洋环境研究的重要基础。本项目通过对中国东部陆架海从南到北表层沉积物、捕获器和拖网样品中的现代有孔虫进行了Mg/Ca比值分析，对多种特征浮游有孔虫和底栖有孔虫属种Mg/Ca比值对陆架海表层和底层水体温度指示的可靠性和适用性进行了评估。研究发现在陆架海区，浮游有孔虫G. bulloides与G. ruber对温度反应较为敏感，有建立Mg/Ca-温度校正方程的潜力。据此建立的两个属种的温度校正方程与开放大洋有明显差别，可能与中国陆架海浅水区有机质的保存密切相关。对表层沉积物中多种主要底栖有孔虫Mg/Ca变化与底层温度相关性进行了分析，总体上Ammonia ketienziensis和Elphidium advenum的Mg/Ca变化和温度有较好的相关性。Ammonia beccarri的Mg/Ca变化和温度无明显相关性。结合现代有孔虫的生态，发现有孔虫的季节性变化导致有孔虫Mg/Ca的指示温度亦有明显的季节偏向。在此基础上，通过有孔虫群落及其壳体Mg/Ca和氧碳同位素、粒度等多种指标综合分析，探讨了陆架海全新世环境的时空变化及其控制因素。认为黄海冷水团主要受控于东亚冬季风的变化和ENSO活动的影响：6.9-5.0ka期间，黄海中部冷水团为全新世最强盛期；5.0-2.9ka期间，较前一阶段有所减弱，黄海沿岸流的影响有所加强；2.9ka以来，黄海沿岸流影响明显增强，冷水团影响则为7 ka来最弱。泥质区不同位置开始受到冷水影响的时间具有显著区域差异，10-9千年始形成于泥质区西北缘，其后向东南扩张，7千年来范围最广。总体上冷水团对泥质区的影响在中心位置最强，往北往东南方向冷水团的影响逐渐减小。从西北向东南，随着离岸距离的增加，泥质区受黄海沿岸流的影响逐渐减小。本研究为陆架环境精细研究提供了重要的基础资料。