DataSheet2_Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5.CSV

The modern precipitation balance in southeastern (SE) Brazil is regulated by the South American summer Monsoon and threatened by global climate change. On glacial-interglacial timescales, monsoon intensity was strongly controlled by precession-forced changes in insolation. To date, relatively little is known about the spatiotemporal distribution of tropical precipitation in SE Brazil and the resulting variability of fluvial discharge on glacial-interglacial timescales. Here, we present X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) from the Doce River basin. This area was sensitive to changes in monsoonal precipitation intensity due to its proximity to the South Atlantic Convergence Zone. The data, obtained from a marine sediment core (M125-55–7) close to the Doce river mouth (20°S), show pronounced changes in the Doce River suspension load’s mineralogical composition on glacial-interglacial and precessional timescales. While the ratio of silicates to carbonates displays precession-paced changes, the mineralogical composition of the carbonate-free fraction discriminates between two assemblages which strongly vary between glacial and interglacial time scales, with precession-forced variability only visible in MIS 5. The first assemblage, dominated by high contents of kaolinite and gibbsite, indicates intensified lowland erosion of mature tropical soils. The second one, characterized by higher contents of the well-ordered illite, quartz and albite, points to intensified erosion of immature soils in the upper Doce Basin. High kaolinite contents in the silicate fraction prevailed in late MIS 6 and indicate pronounced lowland soil erosion along a steepened topographic gradient. The illite-rich mineral assemblage was more abundant in MIS 5, particularly during times of high austral summer insolation, indicating strong monsoonal rainfall and intense physical erosion in the upper catchment. When the summer monsoon weakened in times of lower insolation, the mineral assemblage was dominated by kaolinite again, indicative of lower precipitation and runoff in the upper catchment and dominant lowland erosion.

巴西东南部（SE）的现代降水平衡受南美夏季季风调控，并面临全球气候变化的威胁。在冰期-间冰期时间尺度上，季风强度主要受岁差驱动的日照辐射变化控制。迄今为止，学界对巴西东南部热带降水的时空分布，以及冰期-间冰期时间尺度下河川径流的相应变化仍知之甚少。本文报道了采自多西河（Doce River）盆地150–70 ka时段（海洋同位素阶段（MIS）6至MIS 5）的X射线衍射（X-ray diffraction）衍生矿物学数据。该区域毗邻南大西洋辐合带（South Atlantic Convergence Zone），对季风降水强度的变化极为敏感。数据来源于多西河河口附近（20°S）的海洋沉积岩芯M125-55–7，分析结果显示，多西河流悬浮物的矿物组成在冰期-间冰期和岁差时间尺度上发生了显著分异。硅酸盐与碳酸盐的比值呈现岁差节律性变化，而无碳酸盐组分的矿物组成可区分出两类组合：两类组合在冰期与间冰期时间尺度上差异显著，且岁差驱动的变异性仅在MIS 5中显现。第一类组合以高含量高岭石（kaolinite）和三水铝石（gibbsite）为特征，指示成熟热带土壤的低地侵蚀作用增强。第二类组合以较高含量的有序伊利石（illite）、石英（quartz）和钠长石（albite）为典型，表明多西河上游盆地未成熟土壤的侵蚀作用加剧。MIS 6晚期的硅酸盐组分中高岭石占主导，指示陡峭地形梯度下的低地土壤侵蚀加剧。伊利石占优势的矿物组合在MIS 5中更为发育，尤其在南半球夏季日照辐射较高的时期，这指示季风降雨强盛且上游集水区的物理侵蚀强烈。当夏季季风在日照辐射较低的时期减弱时，矿物组合再次以高岭石为主，表明上游集水区的降水与径流减少，且以低地侵蚀为主导。