Stable isotope ratios on 3 sediment cores from Tagus prodelta off Lisbon

A high-resolution sedimentary sequence recovered from the Tagus prodelta has been studied with the objective to reconstruct multi-decadal to centennial-scale climate variability on the western Iberian Margin and to discuss the observations in a wider oceanographic and climatic context. Between ca. 100 BC and AD 400 the foraminiferal fauna and high abundance of Globorotalia inflata indicate advection of subtropical waters via the Azores Current and the winter-time warm Portugal Coastal Current. Between ca. AD 400 and 1350, encompassing the Medieval Climate Anomaly (MCA), enhanced upwelling is indicated by the planktonic foraminiferal fauna, in particular by the high abundance of upwelling indicator species Globigerina bulloides. Relatively light d18O values and high sea surface temperature (SST) (reconstructed from foraminiferal assemblages) point to upwelling of subtropical Eastern North Atlantic Central Water. Between ca. AD 1350 and 1750, i.e. most of the Little Ice Age, relatively heavy d18O values and low reconstructed SST, as well as high abundances of Neogloboquadrina incompta, indicate the advection of cold subpolar waters to the area and a southward deflection of the subpolar front in the North Atlantic, as well as changes in the mode of the North Atlantic Oscillation. In addition, the assemblage composition together with the other proxy data reveals less upwelling and stronger river input than during the MCA. Stronger Azores Current influence on the Iberian Margin and strong anthropogenic effect on the climate after AD 1750 is indicated by the foraminiferal fauna. The foraminiferal assemblage shows a significant change in surface water conditions at ca. AD 1900, including enhanced river runoff, a rapid increase in temperature and increased influence of the Azores Current. The Tagus record displays a high degree of similarity to other North Atlantic records, indicating that the site is influenced by atmospheric-oceanic processes operating throughout the North Atlantic, as well as by local changes.本研究对从塔霍河前三角洲（Tagus prodelta）获取的高分辨率沉积序列展开分析，旨在重建伊比利亚西部陆缘数十年至百年尺度的气候变率，并在更广阔的海洋学与气候学框架下探讨相关观测结果。约公元前100年至公元400年期间，有孔虫动物群及高丰度的膨抱环棱螺（Globorotalia inflata）指示亚热带水团经亚速尔海流（Azores Current）与冬季温暖的葡萄牙沿岸流（Portugal Coastal Current）平流输送至研究区域。约公元400年至1350年（涵盖中世纪气候异常期（Medieval Climate Anomaly, MCA）），浮游有孔虫动物群——尤其是高丰度的上升流指示种泡抱球虫（Globigerina bulloides）——显示上升流活动显著增强。较轻的δ¹⁸O值与较高的海表温度（sea surface temperature, SST，由有孔虫组合重建所得）表明亚热带东大西洋中央水团发生上升流。约公元1350年至1750年，即小冰期的绝大部分时段，较重的δ¹⁸O值、较低的重建海表温度，以及高丰度的异盖新拟抱球虫（Neogloboquadrina incompta），均指示冷水团平流输送至该区域、北大西洋亚极锋向南偏移，同时北大西洋涛动（North Atlantic Oscillation）模态发生改变。此外，相较于中世纪气候异常期，该时段的有孔虫组合特征与其他代用指标均显示上升流减弱、河流输入作用增强。公元1750年之后，有孔虫动物群指示亚速尔海流对伊比利亚陆缘的影响进一步增强，同时气候受到强烈的人为活动干扰。约公元1900年，有孔虫组合显示表层水体环境发生显著变化，包括河流径流量增加、温度快速升高以及亚速尔海流影响增强。塔霍河沉积记录与其他北大西洋沉积记录具有高度相似性，表明该站位受整个北大西洋范围内的大气-海洋过程调控，同时也受到局地环境变化的影响。