Spatial precipitation shifts in the Doce Basin (SE Brazil) during MIS 6-5

Precipitation patterns in present-day southeastern Brazil are mainly regulated by the South American Summer Monsoon. The southeast Brazilian Doce Basin is expected to suffer from droughts and flooding as a result of future climate induced shifts in the monsoonal precipitation pattern. Data on past spatiotemporal precipitation shifts are scarce but valuable, especially for climate sensitive regions. We analysed X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) on samples obtained from marine sediment core M125-55-7 close to the Doce river mouth (20°S). Within the river-derived fraction, we discriminated between two mineral assemblages with varying abundances between glacial and interglacial times and precession-forced variability only visible in MIS 5. The first assemblage has high contents of kaolinite and gibbsite and indicates intensified lowland erosion of mature tropical soils. The second one has higher contents of well-ordered illite, quartz and albite and points to intensified erosion of immature soils in the upper Doce Basin. Prevailing high kaolinite contents in late MIS 6 indicate pronounced lowland soil erosion and weak monsoonal activity. The dominance of the illite-rich mineral assemblage in MIS 5, particularly during times of high austral summer insolation, indicates strong monsoonal rainfall and physical erosion in the upper catchment. In times of lower insolation in MIS 5, the summer monsoon weakened, leading to decreased precipitation and runoff in the upper catchment and dominant lowland erosion as indicated by an increase in the abundance of the kaolinite-rich mineral assemblage.