安达曼海浮游有孔虫群落对全新世海洋环境变化的响应

通过对安达曼海重力柱ADM-C1的浮游有孔虫群落分析, 探讨了该区全新世以来的海洋环境演化。研究发现, 该区浮游有孔虫群落总体以热带暖水种Globigerinoides ruber、Globigerinoides sacculifer、Neogloboquadrina dutertrei和Pulleniatina obliquiloculata等为主。其中G. ruber的相对丰度从早全新世至今呈逐渐降低的趋势, G. sacculifer则呈大致相反的变化趋势。N. dutertrei的相对丰度从11—7.9ka BP较高, 到7.9—3.8ka BP偏低, 3.8ka BP以来又逐渐升高。而P. obliquiloculata的变化趋势则与N. dutertrei大致相反。研究认为, 安达曼海不存在与冲绳海槽类似的晚全新世普林虫低值事件。浮游有孔虫群落Q型因子显示全新世海洋环境呈现三个明显的阶段变化: 早全新世 11—7.9ka BP期间, 浮游有孔虫群落以G. ruber、N. dutertrei与G. bulloides为主, 反映了该阶段较强的夏季风降水会导致表层水体盐度较低, 同时冬季风的影响相对较强; 7.9—3.8ka BP期间, 以G. ruber、P. obliquiloculata和Globigerinella aequilateralis为主, 指示水体盐度仍然较低, 同时次表层属种显著增多, 对应了该阶段强盛的印度夏季风, 上层海水混合强烈; 3.8—0ka BP期间, 以G. sacculifer、N. dutertrei和P. obliquiloculata为主要特征属种, 而G. ruber相对丰度明显下降, 表明该时期表层海水的盐度有显著上升, 对应了印度夏季风降水的明显减弱。安达曼海浮游有孔虫群落所呈现的全新世海洋环境阶段性变化和陆地夏季风记录有很好的一致性, 也与该孔敏感粒级组分所反映的印度季风的强度变化一致, 表明热带边缘海区的有孔虫群落组合可以很好地响应区域海洋环境变化。

Response of planktonic foraminifera to Holocene marine environmental changes in the Andaman Sea

Through analysis of planktonic foraminifera in a gravity core ADM-C1 from the Andaman Sea, the response of planktonic foraminifera to Holocene marine environmental changes in the sea was discussed. The result shows that the planktonic foraminiferal communities in this region are dominated by tropical warm-water species Globigerinoides ruber, Globigerinoides sacculifer, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata. The relative abundance of G. ruber shows a gradual decreased trend from the early Holocene to present, which is roughly opposite to that of G. sacculifer. The relative abundance of N. dutertrei is higher during 11 to 7.9 ka BP (before present), generally lower during 7.9 to 3.8 ka BP, and then gradually increases after 3.8 ka BP. P. obliquiloculata shows an almost opposite trend to that of N. dutertrei. Our result indicates no obvious Pulleniatina Minimum Eventduring the late Holocene, occurs in the Andaman Sea. Q-mode factor analyses of planktonic foraminifera in the core ADM-C1 identify three stages in marine environmental changes during the Holocene. During the early Holocene (11-7.9 ka BP), planktonic foraminifera assemblage was dominated by G. ruber, N. dutertrei and G. bulloides, which reflected that strong summer monsoon and precipitation led to lower sea surface salinity, while the influence of winter monsoon was also strong during this stage. During 7.9-3.8 ka BP, G. ruber, P. obliquiloculata and Globigerinella aequilateralis dominated, indicating lower sea surface salinity during this period. Meanwhile, there was obviously increase in abundance of subsurface water species, reflecting strong mixing in the upper-ocean waters, possibly due to the strong Indian Ocean summer monsoon at this stage. After 3.8 ka BP, G. sacculifer, N. dutertrei and P. obliquiloculata became the dominant species. The abundance of G. ruber declined obviously, indicating that the salinity of surface sea water significantly increased during this period, which was consistent with the reduced Indian Ocean summer monsoon precipitation. The phase change of the Holocene marine environment reflected by the planktonic foraminiferal assemblages in the Andaman Sea is well consistent with the terrestrial records on the Indian Ocean summer monsoon, and it also shows good consistent with the wind intensity variation in Indian Ocean summer monsoon reflected by sensitive grain size proxy of the same core, suggesting rapid response of planktonic foraminifera to marine environmental changes in the tropical marginal seas.