19万年以来南海北部MD12-3429站浮游有孔虫记录的表层海水环境演化

CHANGES OF PLANKTONIC FORAMINIFERAL ASSEMBLAGES AND MARINE PALEOENVIRONMENT AT MD12-3429 IN THE NORTHERN SOUTH CHINA SEA SINCE 190 KA

南海北部陆坡具有较高的沉积速率,为古海洋和古气候演化提供了绝佳的研究材料。本研究对南海北部陆坡中部MD12-3429站(20°08.52’N, 115°49.84’E,水深903 m)的高分辨率沉积样品中的浮游有孔虫群进行研究,重建了海洋氧同位素期(MIS)6期以来上部水体结构和表层古生产力变化。并与陆坡底部MD12-3432站(19°16.88’N,116°14.52’E,水深2 125 m)对比,旨在进一步探讨南海北部陆坡上部水体环境的时空演化。结果表明:受到冰期冬季风增强和表层环流变化的共同影响,海表温度具有显著的冰期/间冰期旋回,冬季海表温度波动可达7–8°C;MIS2–4期和MIS 6期时, MD12-3429站的温跃层明显比MD12-3432站的深,可能与海平面下降后、河流输入在近岸地区形成的淡水盖层和强冬季风通过埃克曼输送形成的向岸流有关;浮游有孔虫Globigerinoidesbulloides+Neogloboquadrinadutertrei含量和非共生种/共生种比值显示南海北部陆坡初级生产力在MIS 6期晚期和MIS 2期显著增高,这可能是当时较低的海平面和较强的东亚冬季风带来更多的陆源碎屑输入所致。

The northern continental slope of the South China Sea(SCS) has a high sedimentation rate, which provides the ideal material for the paleoclimatological and paleoceanographical study. In this paper, we analysized the planktonic foraminifers from Core MD12-3429(20°08.52’ N, 115°49.84’ E, water depth of 903 m), which is located in the middle northern slope of the South China Sea. Sea surface temperatures(SST) in summer and winter, together with thermocline depth since Marine Isotope Stage 6(MIS 6) were estimated, using planktonic foraminiferal assemblages and transfer functions. Compared with Core MD12-3432(20°08.52’ N, 115°49.84’ E, water depth of 2 125 m), located in the bottom northern slope of the SCS, the temporal and spatial evolution of upper ocean structure were discussed. The results showed that the variations of summer and winter SST embodied prominent glacial-interglacial cycles of 100 ka. During the glacial periods, intensified winter monsoon and altered surface circulation could impel a significant decline in winter SST. During MIS 2–4 and MIS 6, the thermocline depth of MD12-3429 is deeper than that of MD12-3432. By comparing with modern observation data, we ascribed the deepening of thermocline depth to the freshwater blanket formed in the nearshore area by river input when sea level fall and the onshore current formed by Ekman transport of strong winter monsoon. The relative abundance of Globigerinoides bulloides+Neogloboquadrina dutertrei and the ratio of nonsymbiotic and symbiotic species indicated that the primary productivity increased significantly in late MIS 6 and MIS 2, which was influenced by terrigenous detrital input controlled by sea level and Asian monsoon intensity.