西北孟加拉湾中更新世早期的硅质生物生产力变化  

Changes in siliceous paleoproductivity during the early Middle Pleistocene in the Northwest Bay of Bengal

作　　者：邹家麒 丁旋[1] ZOU Jiaqi;DING Xuan(School of Ocean Sciences,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)海洋学院,北京100083

出　　处：《海洋地质与第四纪地质》2022年第5期83-93,共11页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金项目“1.2 Ma以来印度季风降水变化——来自孟加拉湾/安达曼海有孔虫的新证据”(41976060)。

摘　　要：西北孟加拉湾位于印度夏季风的核心降水区,是研究印度季风活动及其对环境影响的理想地区。通过对西北孟加拉湾马哈纳迪盆地IODP353航次U1446站位岩芯生物硅含量和沉积通量的分析,重建了研究区早更新世末—中更新世早期(920~370 ka)的硅质生物生产力演变历史,探讨了印度夏季风降水和径流活动对研究区古生产力变化的影响机制。结果显示,西北孟加拉湾在920~370 ka期间,硅质生产力总体上表现为中更新世过渡期(Mid-Pleistocene Transition,MPT)较低,MPT之后呈上升的趋势;具有明显的冰期-间冰期旋回性,冰期时下降,间冰期上升,且在MPT之后波动幅度增大。对比该站位已有的δ_(18)O_(sw)和Rb/Ca比值等夏季风降水和径流指标发现,印度夏季风增强时硅质生产力上升,减弱时硅质生产力下降,推测印度夏季风的增强导致孟加拉湾降水以及周边河流径流量剧增,河流提供的营养物质使得西北孟加拉湾表层硅质生物勃发,硅质生产力迅速升高。而印度夏季风减弱时,营养盐的减少抑制了表层浮游硅质生物的繁殖,从而使得硅质生产力下降。U1446站位生物硅通量的频谱和小波分析也显示,研究区的硅质生产力受轨道周期变化的调控。The Northwest Bay of Bengal (BoB) is located in the core precipitation zone of the Indian Summer Monsoon (ISM),and an ideal area to study Indian monsoon activity and its impact on the environment.We reconstructed the history of siliceous productivity evolution in the study area during late Early Pleistocene to early Middle Pleistocene (920~370 ka) by analyzing biogenic silica content and sediment fluxes of cores from Site U1446 of IODP Expedition 353 in the Mahanadi Basin,Northwest BoB,and explored the mechanism of ISM precipitation and runoff activities on the paleoproductivity changes in the study area.Results indicate that siliceous productivity reflects a trend from low in the MidPleistocene Transition (MPT) to high after MPT in the northwest BoB during 920~370 ka in an obvious glacial-interglacial cycle.It decreased during the glacial period and increased during the interglacial period,and the fluctuation increased after the MPT.A comparison of existing summer monsoon precipitation and runoff indicators such as δ^(18)O_(sw) and Rb/Ca ratio at this site reveals that siliceous productivity increased(decreased) when the ISM strengthened (weakened).It is hypothesized that the enhanced ISM led to a dramatic increase in runoff from the Indian peninsula and precipitation in the BoB,and the nutrients from rivers led to a proliferation of surface siliceous organisms and a rapid upsurge in siliceous productivity in the northwest BoB.However,the weakened ISM and the reduction of nutrients inhibited the flourishing of planktonic siliceous organisms,which then decreased the surface productivity.Spectral and wavelet analyses of biogenic silica fluxes at Site U1446 also indicate that siliceous productivity was modulated by orbital cycle variations in this study area.

关 键 词：中更新世过渡 生物硅 古生产力 印度夏季风 西北孟加拉湾 

分 类 号：P736.21[天文地球—海洋地质]