Reconstruction of the provenance and distribution of terrigenous sediments off NE South America over the last 30ka

We investigate the redistribution of terrigenous materials in the northeastern (NE) South American continental margin during slowdown events of the Atlantic Meridional Overturning Circulation (AMOC). The compilation of stratigraphic data from 108 marine sediment cores collected across the western tropical Atlantic shows an extreme rise in sedimentation rates off the Parnaíba River mouth (about 2°S) during Heinrich Stadial 1 (HS1, 18-15 ka). Sediment core GeoB16206-1, raised offshore the Parnaíba River mouth, documents relatively constant 143Nd/144Nd values (expressed as epsilonNd(0)) throughout the last 30 ka. Whereas the homogeneous epsilonNd(0) data support the input of fluvial sediments by the Parnaíba River from the same source area directly onshore, the increases in Fe/Ca, Al/Si and Rb/Sr during HS1 indicate a marked intensification of fluvial erosion in the Parnaíba River drainage basin. In contrast, the epsilonNd(0) values from sediment core GeoB16224-1 collected off French Guiana (about 7°N) suggest Amazon-sourced materials within the last 30 ka. We attribute the extremely high volume of terrigenous sediments deposited offshore the Parnaíba River mouth during HS1 to (i) an enhanced precipitation in the catchment region and (ii) a reduced North Brazil Current, which are both associated with a weakened AMOC.本研究探讨了大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）减缓事件期间，南美东北部（NE）大陆边缘陆源物质的再分配过程。对热带大西洋西部108个海洋沉积物岩心的地层数据整合分析显示，在Heinrich期1（Heinrich Stadial 1, HS1，18-15 ka）期间，帕纳伊巴河（Parnaíba River）河口外海域的沉积速率出现极端上升。取自帕纳伊巴河河口外的沉积物岩心GeoB16206-1记录了过去30 ka间相对稳定的¹⁴³Nd/¹⁴⁴Nd比值（以εNd(0)表示），这一均一的εNd(0)数据支持帕纳伊巴河的河流沉积物来源于近岸同一物源区；而HS1期间Fe/Ca、Al/Si及Rb/Sr比值的上升，则表明帕纳伊巴河流域的河流侵蚀作用显著增强。相比之下，取自法属圭亚那（French Guiana）外海的沉积物岩心GeoB16224-1的εNd(0)值显示，过去30 ka间该区域物质来源于亚马逊河流域。我们将HS1期间帕纳伊巴河河口外海域陆源沉积物的极端高沉积量归因于两个因素：（i）流域降水增加；（ii）北巴西洋流（North Brazil Current）减弱——两者均与AMOC的减弱相关。