Distribution of coccoliths in surface sediments of the south-eastern South Atlantic Ocean

Recent coccoliths from 52 surface sediment samples recovered from the south-eastern South Atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns, such as ecological and preservational factors, and their role as carbonate producers. Total coccolith abundances range from 0.2 to 39.9 coccoliths*10**9/ g sediment. Four assemblages can be delineated by their coccolith content characterising the northern Benguela, the middle to southern Benguela, the Walvis Ridge and the deeper water. Distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa, Emiliania huxleyi, Calcidiscus leptoporus, Gephyrocapsa spp., Coccolithus pelagicus and subtropical to tropical species. The coccolith distribution seems to be temperature and nutrient controlled co-varying with the seaward extension of the upwelling filament zone in the Benguela. A preservation index (CEX') based on the differential dissolution behaviour of the delicate E. huxleyi and Gephyrocapsa ericsonii versus the robust C. leptoporus is applied in order to detect the position of the coccolith lysocline. Although some samples were recognised as dissolution-affected, the distribution of the coccoliths in the surface-sediments reflects the different oceanographic surface-water conditions. Mass estimations of the coccolith carbonate reveal coccoliths to be only minor contributors to the carbonate preserved in the surface sediments. The mean computed coccolith carbonate content is 17 wt.%, equivalent to a mean contribution of 23% to the bulk carbonate.

对从南大西洋东南部海域获取的52个表层沉积物样品中的现代颗石藻（coccolith）开展了定性与定量分析，以探究其分布格局的调控机制（包括生态因素与保存因素），以及其作为碳酸盐生产源的作用。颗石藻总丰度范围为0.2~39.9×10^9颗/克沉积物。基于颗石藻组成可划分出4类生物组合，分别对应北本格拉海域、中-南本格拉海域、沃尔维斯海岭（Walvis Ridge）以及深水区域。类群区分基于对优势类群相对丰度所采用的多元排序技术，优势类群包括艾氏颗石藻（Emiliania huxleyi）、薄盘颗石藻（Calcidiscus leptoporus）、桥石藻属（Gephyrocapsa spp.）、浮游颗石藻（Coccolithus pelagicus）以及亚热带至热带类群。颗石藻的分布似乎受温度与营养盐共同调控，并与本格拉海域上升流丝状体带的向海延伸范围协同变化。本研究基于脆弱的艾氏颗石藻（E. huxleyi）与埃里克森桥石藻（Gephyrocapsa ericsonii）相较于坚固的薄盘颗石藻（C. leptoporus）的差异溶解行为，构建了保存指数（CEX'），用于识别颗石藻溶跃面（coccolith lysocline）的位置。尽管部分样品被证实受溶解作用影响，但表层沉积物中的颗石藻分布仍反映了不同的海洋表层水环境特征。对颗石藻碳酸盐的质量估算结果显示，颗石藻仅为表层沉积物中保存的碳酸盐的次要贡献源。计算得到的颗石藻碳酸盐平均含量为17 wt.%，相当于对总碳酸盐的平均贡献占比为23%。