Geochemistry of Globigerinoides ruber of sediment core M78/1_235-1@en

Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America dur-ing periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we gen-erated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indi-cate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions pre-vailed in northern South America, while eastern Brazil experienced maximally wet condi-tions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by recon-figurations of surface ocean currents in low latitudes. Our new records demonstrate the ex-treme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions.大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）强度的变化对全球大气环流格局具有显著影响。然而，迄今为止，低纬度地区对高纬度强迫作用的响应节律与机制仍未得到充分约束。为阐明AMOC大幅减弱时期（海因里希冰阶1与新仙女木事件）热带南美洲大气与海洋强迫的相互作用，我们基于钡钙（Ba/Ca）与镁钙（Mg/Ca）比值以及稳定同位素测量，从奥里诺科河外海域获取了一套高分辨率有孔虫多指标记录。该数据清晰表明，基于热带大西洋洋流重构的海因里希冰阶1（HS1）具有三阶段结构。初始阶段（HS1a）以北巴西海流减弱、热带辐合带（Intertropical Convergence Zone, ITCZ）南移以及巴西东北部地区湿润气候为主导特征。在随后的HS1b阶段，北巴西海流进一步减弱甚至发生反向流动，热带辐合带移至其最南端位置。因此，南美洲北部地区普遍出现干旱环境，而巴西东部则处于极端湿润的气候条件。在最后阶段HS1c，气候条件与HS1a相似。新仙女木事件是HS1的小幅振幅版本，其热带辐合带同样发生南移。我们的研究结果表明，低纬度陆域气候对高纬度强迫作用的响应是通过低纬度表层洋流的重构所介导的。我们的新记录证实，在气候不稳定时期，热带南美洲的陆域环境对海洋环流的突然扰动具有极高的敏感性。