孟加拉湾深海氧同位素2、3期上升流活动——北印度洋冬季风的实证

UPWELLING ACTIONS IN THE BAY OF BENGAL DURING MARINE ISOTOPE STAGES 2 AND 3: EVIDENCE FOR INDIAN WINTER MONSOON

北印度洋季风研究的经典地区是上升流活跃的阿拉伯海和索马里海盆 ,孟加拉湾地区季风强弱的变化则是以浮游有孔虫壳体氧同位素值反映的淡水输入量大小来指示的。文章通过对孟加拉湾的MD771 81岩芯的浮游有孔虫定量分析、氧碳稳定同位素分析 ,对比东经90°海岭的MD81 349岩芯的同类分析结果 ,发现孟加拉湾地区在深海氧同位素 2、3期出现上升流生物种丰度上升、表层水古生产力升高、表层水温度下降、温跃层变浅、盐度增加等指示存在上升流活动的现象 ,说明当时该区东北冬季风增强。特别的是间冰段深海氧同位素 3期各古环境的代用指标都形成记录上最突出的峰值 ,且在同期背景值上叠加着强烈的波动 ,认为此现象应是印度季风区夏季季风和冬季季风强盛期的相互转换、水体的垂直循环运动等环境信号和控制机制在该区的反映。

The correlation of oxygen and carbon isotopes and planktic foraminifera assemblages in core MD77181 collected in the Bay of Bengal with those in core MD81349 from the 90°E ridge indicates that there were upwelling actions during Marine Isotope Stages 2 and 3, because the relative abundance of upwelling species rose, the surface paleoproduction increased, the surface water temperature decreased, the thermoline became shallower, and the salinity rose. The upwelling actions might be related to boosting of the northeast monsoon. Especially in the interglacial phase of Marine Isotope Stage 3, almost all environmental indexes such as paleoproduction and carbonate dissolution showed peak values, and strong fluctuations exist on the high background. It should be a reflection of the vertical movement induced by transform of the Indian summer monsoon-winter monsoon transforming.