Late Holocene coccolith assemblage data of sediment core GeoB8323-2 from the Benguela Upwelling System

Coccolith occurrences in sediment core GeoB 8323-2, from the Benguela Upwelling System off south-western Africa, were analysed to reconstruct the temporal changes in surface water conditions, upwelling intensity and associated productivity during the late Holocene (last 2.25ka BP). Absolute numbers of total coccolithophores are low throughout the core, reaching a maximum of 320 x 10^6 coccoliths/gram sediment around 770 years BP. Despite the low abundance of coccoliths, coherent patterns of a changing assemblage composition can be identified. These suggest a consistent paleoceanographic development of highly variable Late Holocene environmental change during the last three millennia. Phases of decreased upwelling in the Benguela Upwelling System are indicated by elevated abundances of Florisphaera profunda alongside reduced occurrence of Coccolithus pelagicus and C. braarudii from 2.25-2.00ka BP, ~ 1.00ka BP and during the last 200 years, also accompanied by a reduced species diversity. Sea surface temperatures estimated with a Gephyrocapsa-based transfer function are in the order of 18-20°C. These phases are intersected by periods of colder sea surface temperatures of 16-17°C and increased productivity, as indicated by an opposing trend for the aforementioned species. Given the climatological and oceanographical complexity of the area, deciphering a single driving mechanism for these changes proves difficult. Synchronous changes in the Antarctic sea ice extent, however, give credit to the conceptual model of latitudinal migration of the westerly wind belt and its interaction with the south-easterly trade winds as an important driver for oceanographic changes in the area.

对西南非洲外本格拉上升流系统（Benguela Upwelling System）沉积岩芯（sediment core）GeoB 8323-2中的颗石藻（coccolith）出现情况进行分析，旨在重建晚全新世（最近2.25千年BP）期间地表水条件、上升流强度及相关生产力的时间变化。

整个岩芯中总颗石藻的绝对数量较低，在约770年BP时达到最大值，为320×10^6颗石/克沉积物。尽管颗石藻丰度较低，但仍可识别出组合成分变化的连贯模式，这些模式表明过去三千年晚全新世环境变化高度可变的一致古海洋学（paleoceanographic）演化过程。

本格拉上升流系统上升流减弱的阶段由Florisphaera profunda丰度升高、Coccolithus pelagicus和C. braarudii出现减少所指示，这些阶段发生于2.25-2.00ka BP、约1.00ka BP及最近200年，同时伴随物种多样性降低。基于Gephyrocapsa的转换函数（transfer function）估算的海面温度（sea surface temperature）约为18-20°C。这些阶段被海面温度较低（16-17°C）且生产力增加的时期所穿插，而上述物种的趋势与此相反。

鉴于该区域气候与海洋学的复杂性，难以破译这些变化的单一驱动机制。然而，南极海冰范围的同步变化支持了西风带纬度迁移及其与东南信风相互作用作为该区域海洋学变化重要驱动因素的概念模型。