南海南部第四纪表层海水古生产力变化的钙质超微化石证据

CALCAREOUS NANNOFOSSIL EVIDENCE FOR VARIATIONS IN QUATERNARY SURFACE WATER PALEOPRODUCTIVITY IN THE SOUTHERN SOUTH CHINA SEA

深海沉积中的钙质超微化石是古海洋表层生产力的替代性标志之一。通过对南海南部 ODP1143站第四纪沉积中超微化石分析 ,从绝对丰度和堆积速率、Florisphaera profunda百分含量及碳同位素三个方面探讨了该区第四纪表层海水古生产力的变化特征。结果显示 ,1.5 6 Ma以来南海南部表层海水古生产力呈现两种不同时间尺度的变化。一是随冰期 -间冰期旋回而变化 ,间冰期时 ,表层海水生产力高 ,而冰期时则降低 ;另一种则是大约 40万年的长周期变化 ,自 1.5 6 Ma以来 ,可以分成四个大的旋回 。

Calcareous nannofossils deposited in deep sea sediments are one of good proxies of surface water paleoproductivity. Quantitatively micropaleontological and stable isotopic analyses have been performed on Quaternary calcareous nannofossils from ODP site 1143 in the southern South China Sea. Changes in absolute abundance, accumulation rate and carbon isotopic record of nannofossils have been applied to understanding the Quaternary evolution of surface water paleoproductivity in the southern South China Sea. The results show that the surface water paleoproductivity displayed significant oscillations on two different time scales during the past 1 56 Ma. One is the fluctuation covarying with glacial interglacial cycles which is marked by the increase of paleoproductivity during interglacial periods and decrease during glacial periods. The other fluctuation of paleoproductivity is the long term changes on a time scale of about 400 ka. Four cycles have been recognized for the last 1.56 Ma in the southern South China Sea. Surface water paleoproductivity changed from lower to higher and then to lower within each cycle.