DataSheet3_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的调节，并受到全球气候变化的威胁。在冰川-间冰期的时间尺度上，季风强度受到由视差引起的日照变化强烈控制。迄今为止，关于巴西东南部热带降水的时空分布及其在冰川-间冰期时间尺度上引起的河流径流变率，了解相对较少。在此，我们展示了来自多斯河盆地的150至70千年前（海洋同位素阶段6至5）的X射线衍射获得的矿物学数据。该地区由于靠近南大西洋辐合带，对季风降水强度的变化敏感。从靠近多斯河入海口（20°S）的海洋沉积岩芯（M125-55-7）中获得的数据显示，多斯河悬浮物质的矿物组成在冰川-间冰期和视差时间尺度上发生了显著变化。虽然硅酸盐与碳酸盐的比例显示出视差同步的变化，但无碳酸盐部分的矿物组成区分了两种在冰川和间冰期时间尺度上强烈变化的集合体，其中视差引起的变异性仅在海洋同位素阶段5中可见。第一种集合体，以高含量的高岭石和三水铝石为主，表明成熟热带土壤的低地侵蚀加剧。第二种集合体，以较高含量的有序伊利石、石英和长石为特征，指向多斯河上游盆地的土壤侵蚀加剧。在海洋同位素阶段6后期，硅酸盐部分中高岭石含量占主导地位，表明沿陡峭的地形梯度上低地土壤侵蚀显著。富含伊利石的矿物集合体在海洋同位素阶段5更为丰富，尤其是在南半球夏季日照量高的时候，这表明强烈的季风降雨和上游流域的强烈物理侵蚀。当夏季季风在日照量较低时减弱，矿物集合体再次以高岭石为主，这表明上游流域降水量和径流减少，低地侵蚀占主导地位。