Bulk geochemical analysis and planktonic foraminifera of sediment core GeoB7112-5

A multivariable approach utilising bulk sediment, planktonic Foraminifera and siliceous phytoplankton has been used to reconstruct rapid variations in palaeoproductivity in the Peru-Chile Current System off northern Chile for the past 19000 cal. yr. During the early deglaciation (19000-16000 cal. yr BP), our data point to strongest upwelling intensity and highest productivity of the past 19 000 cal. yr. The late deglaciation (16000-13000 cal. yr BP) is characterised by a major change in the oceanographic setting, warmer water masses and weaker upwelling at the study site. Lowest productivity and weakest upwelling intensity are observed from the early to the middle Holocene (13000-4000 cal. yr BP), and the beginning of the late Holocene (<4000 cal. yr BP) is marked by increasing productivity, mainly driven by silicate-producing organisms. Changes in the productivity and upwelling intensity in our record may have resulted from a large-scale compression and/or displacement of the South Pacific subtropical gyre during more productive periods, in line with a northward extension of the Antarctic Circumpolar Current and increased advection of Antarctic water masses with the Peru-Chile Current. The corresponding increase in hemispheric thermal gradient and wind stress induced stronger upwelling. During the periods of lower productivity, this scenario probably reversed.

本研究采用基于总沉积物（bulk sediment）、浮游有孔虫（planktonic Foraminifera）与硅质浮游植物（siliceous phytoplankton）的多变量分析方法，对过去19000个校准年（cal. yr BP）智利北部外海秘鲁-智利海流系统（Peru-Chile Current System）的古生产力（palaeoproductivity）快速变化开展了重建工作。冰消期早期（19000~16000 cal. yr BP），本研究数据显示该区域上升流（upwelling）强度与古生产力均达到过去19000 cal. yr以来的最高水平。冰消期晚期（16000~13000 cal. yr BP），研究站位的海洋环境发生显著转变，水体团温度升高，上升流强度减弱。全新世早期至中期（13000~4000 cal. yr BP），区域古生产力与上升流强度均处于最低水平；全新世晚期伊始（<4000 cal. yr BP），古生产力逐步回升，这一变化主要由硅质浮游生物主导。本记录中古生产力与上升流强度的变化，可能源于高生产力时期南太平洋副热带环流（South Pacific subtropical gyre）的大规模压缩与/或位移，这与南极绕极流（Antarctic Circumpolar Current）向北扩张、秘鲁-智利海流携带的南极水体平流（advection）增强的现象相一致。半球间温度梯度（thermal gradient）与风应力（wind stress）的相应增强，进一步推动了上升流活动；而在古生产力较低的时期，上述过程则发生逆转。