Planktonic foraminiferal assemblages of DSDP Hole 75-532@en

Qualitative and quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project site 532 shed light on hydrographic changes over the Walvis Ridge during the past 500,000 years. From changes in distribution of foraminiferal assemblages, two major hydrographic regimes (coastal and geostrophic branches of the Benguela Current and the Angola Current) can be distinguished at site 532. It is suggested that the hydrographic situation on the northeastern Walvis Ridge was characterized by intensified upwelling and a westward expansion of the coastal upwelling cells during several global cooling pulses. During glacial stages 2-4, the middle part of stage 6, sporadically from the lower stage 8 through upper stage 10, and during stage 12, site 532 was located beneath the coastal branch of the Benguela Current because faunal distribution patterns indicate intensified upwelling. The Angola Current probably intruded the area of study during the lower stages 5, sporadically 6-8, and 11, as documented by the increased abundance of Neogloboquadrina dutertrei.对深海钻探计划（Deep Sea Drilling Project）532站位的浮游有孔虫组合（planktonic foraminiferal assemblages）开展定性与定量分析，阐明了过去50万年间沃尔维斯海岭（Walvis Ridge）区域的水文变化过程。基于有孔虫组合的分布变化特征，可在532站位区分出两种主要水文环境：本格拉洋流（Benguela Current）的近岸分支与地转流分支，以及安哥拉洋流（Angola Current）。研究显示，在数次全球变冷脉冲事件期间，沃尔维斯海岭东北部的水文环境以上升流增强、近岸上升流单元向西扩张为典型特征。在第2至4冰期、第6冰期中期、第8冰期早期至第10冰期早期的零星时段，以及第12冰期，因生物群分布模式指示上升流增强，532站位处于本格拉洋流近岸分支的影响范围内。德氏新抱球虫（Neogloboquadrina dutertrei）丰度升高的记录表明，安哥拉洋流可能在第5冰期早期、第6至8冰期的零星时段以及第11冰期侵入了本研究区域。