Stable isotope record of planktonic foraminifera from sediment core MD96-2085

A high-resolution (~4-5cm/kyr) giant piston core record (MD962085) retrieved during an IMAGES II-NAUSICAA cruise from the continental slope of the southeast Atlantic Ocean reveals striking variations in planktonic foraminifer faunal abundances and sea-surface temperatures (SST) during the past 600 000 yr. The location and high-quality sedimentary record of the core provide a good opportunity to assess the variability of the Benguela Current system and associated important features of the ocean-climate system in the southeast Atlantic. The planktonic foraminifer faunal abundances of the core are dominated by three assemblages: (1) Neogloboquadrina pachyderma (right coiling) + Neogloboquadrina dutertrei, (2) Globigerina bulloides, and (3) Globorotalia inflata. The assemblage of N. pachyderma (right coiling) + N. dutertrei shows distinctive abundance changes which are nearly in-phase with glacial-interglacial variations. The high abundances of this assemblage are associated with major glacial conditions, possibly representing low SST/high nutrient level conditions in the southwestern Africa margin. In contrast, the G. bulloides and G. inflata assemblages show greater high-frequency abundance change patterns, which are not parallel to the glacial-interglacial changes. These patterns may indicate rapid oceanic frontal movements from the south, and a rapid change in the intensity of the Benguela upwelling system from the east. A single episode of maximum abundances of a polar water species N. pachyderma (left coiling) occurred in the beginning of stage 9 (~340-330 kyr). The event of the maximum occurrence of this species shown in this record may indicate instability in the Benguela coastal upwelling, or the Antarctic polar front zone position. A winter season SST estimate using transfer function techniques for this record shows primarily glacial-interglacial variations. The SST is maximal during the transitions from the major glacial to interglacial stages (Terminations I, II, IV, V), and is associated with the abundance maxima of a warm water species indicator Globigerinoides ruber. Cross-spectral analyses of the SST record and the SPECMAP stack reveal statistically significant concentrations of variance and coherencies in three major orbital frequency bands. The SST precedes changes in the global ice volume in all orbital frequency bands, indicating a dominant southern Hemispheric climate effect over the Benguela Current region in the southeast Atlantic.高分辨率（约4~5厘米/千年）的巨型活塞岩心记录（MD962085）由IMAGES II-NAUSICAA科考航次在东南大西洋大陆坡采集所得，该记录揭示了过去60万年中浮游有孔虫（planktonic foraminifer）动物群丰度与海表温度（Sea-Surface Temperature, SST）的显著变化。该岩心的采样位置与高质量沉积记录，为评估东南大西洋本格拉洋流系统的演变，以及该区域海洋-气候系统的关键特征提供了绝佳契机。该岩心的浮游有孔虫动物群丰度主要由三个组合构成：（1）粗厚新抱球虫（右旋）+ 杜氏拟抱球虫，（2）球室抱球虫，（3）膨胀拟抱球虫。右旋粗厚新抱球虫+杜氏拟抱球虫组合的丰度变化呈现显著特征，其变化周期几乎与冰期-间冰期旋回同步。该组合的高丰度时段对应大规模冰期环境，可能指示西南非洲陆缘区域的海表温度偏低、营养盐浓度偏高的状态。与之相反，球室抱球虫与膨胀拟抱球虫组合则呈现出更高频的丰度变化模式，且该变化与冰期-间冰期旋回并不一致。这类变化模式可能指示来自南部的海洋锋面快速移动，以及来自东部的本格拉上升流系统强度的快速变化。在第9气候阶段初期（约34万~33万年前），出现了一次极地冷水种左旋粗厚新抱球虫的丰度峰值事件。该记录中显示的该物种丰度峰值事件，可能指示本格拉沿岸上升流的不稳定性，或是南极极锋带的位置变动。本研究利用转换函数技术对该记录进行的冬季海表温度估算结果，同样以冰期-间冰期旋回变化为主要特征。海表温度在大规模冰期向间冰期的过渡阶段（终止期I、II、IV、V）达到峰值，且与暖水种指示物种红拟抱球虫的丰度峰值相对应。对海表温度记录与SPECMAP堆叠曲线进行的交叉频谱分析显示，其在三个主要轨道频率波段中存在统计学意义显著的方差聚集与相干性。在所有轨道频率波段中，海表温度的变化均早于全球冰量变化，这表明东南大西洋本格拉洋流区域的气候主要受南半球气候过程主导。