Millennial scale coccolithophore paleoproductivity and surface water changes between 445 and 360 ka (Marine Isotope Stages 12/11) in the Northeast Atlantic

A high resolution coccolithophore study was carried out in order to improve the understanding of the paleoceanographic evolution and changes in paleoproductivity occurring off the Iberian Margin (IM) between 445 and 360 ka, i.e. during late Marine Isotope Stage 12 to 11. Coccolithophore assemblages allowed reconstructing surface water changes characterized by millennial-scale oscillations (~1.5 kyr cycles) involving Portugal or Iberian Poleward Currents (PC and IPC) prevalence. Changes in paleoproductivity, possibly related to the upwelling of Eastern North Atlantic Central Waters (ENACW) - of sub-tropical (ENACWst) or sub-polar origin (ENACWsp) - were also recognized. This study also permitted detecting abrupt events (stadial/interstadial-type oscillations) and revealed that changes in paleoproductivity are related to opposite dynamics during glacial and interglacial stages, with the reversed setting being established during the deglaciation. Furthermore, a possible control of half and fourth precessional cycle components, on the occurrence of abrupt changes within the assemblages' structure, during the deglaciation, is proposed on the basis of wavelet analysis results applied to selected taxa.本研究开展高分辨率颗石藻（coccolithophore）研究，旨在深化对伊比利亚陆缘（Iberian Margin, IM）在44.5万至36.0万年前（即晚海洋同位素阶段12至11期，Marine Isotope Stage 12 to 11）的古海洋演化与古生产力变化的认识。颗石藻组合得以重建该区域表层水的变化特征，其表现为以葡萄牙洋流（Portugal Current, PC）与伊比利亚极向洋流（Iberian Poleward Current, IPC）占优为特点的千年尺度振荡（约1.5千年周期）。研究同时识别出可能与东大西洋中央水团（Eastern North Atlantic Central Waters, ENACW）上升流相关的古生产力变化，该水团可分为亚热带起源亚型（ENACWst）与亚极地起源亚型（ENACWsp）。本研究还检测到冰阶/间冰阶型突变振荡事件，并揭示古生产力变化在冰期与间冰期阶段对应相反的动力学过程，且冰消期（deglaciation）确立了反向的环境背景。此外，基于对选定分类单元（taxa）开展的小波分析（wavelet analysis）结果，本研究提出冰消期内颗石藻组合结构的突变事件，可能受岁差周期（precessional cycle）半分量与四分量的调控。