南海颗石藻记录对大洋碳同位素低值事件的响应

RESPONSE OF COCCOLITH RECORDS IN THE SOUTH CHINA SEA TO CARBON ISOTOPE MINIMUM EVENTS

发生在冰消期时的碳同位素低值事件是晚第四纪以来大洋碳同位素变化的普遍特征。通过对南海北部MD05-2904柱状样(19°27.32′N、116°15.15′E,水深2066m,岩心长度4498cm)930个沉积物样品中颗石藻属种鉴定,发现颗石藻主要属种Florisphaera profunda,Gephyrocapsa oceanica和Emiliania huxleyi相对百分含量与浮游有孔虫碳同位素变化具有相关性。MIS5期以来δ13C值逐渐变重,颗石藻G.oceanica含量增多,下透光带种F.profunda含量逐渐降低,海水初级生产力升高。对应3次δ13C低值期,颗石藻属种含量都发生明显变化,海水初级生产力出现峰值,说明碳同位素低值事件与浮游植物群落和海洋环境变化有密切关系,颗石藻记录能够为研究大洋碳储库的变化提供依据。

The occurrence of carbon isotope minimum events at deglaciations is a common feature of marine carbon isotopic records in late Quaternary. Coccolith analysis has been carried out for 930 sediment samples of the core MD05-2904（19°27.32′N, 116°15.15′E,water depth 2 066 m,core length 4 498 cm）from the northern South China Sea. The results revealed that the relative percentage variations of the predominant coccolith taxa （Florisphaera profunda,Gephyrocapsa oceanica and Emiliania huxleyi） were correlated to the carbon isotope record of planktonic foraminifera. While the δ13C became heavier since MIS5, the percentage of G. oceanica increased and lower euphotic species F. profunda decreased, indicating the rise of primary productivity. Corresponding to the three δ13C minimum events, significant changes occurred in the coccolith assemblages and marine primary productivity peaks appeared in deglaciations. It reflects that carbon isotope minimum events may be closely related to the variations of phytoplankton community and paleoenvironmental change. The present results demonstrate that coccolith records can provide evidence for the research of ocean carbon reservoir.