Millennial-scale paleoclimatic and -oceanographic variability of the western tropical South Atlantic during the last glacial

One focus of recent paleoclimate research is the interaction between high and low latitudes during abrupt climate changes. In particular, there is a lack of understanding of mechanisms originating in the tropics. Here we present results from sediment cores of the northeast Brazilian continental slope, based on foraminiferal stable isotopes and magnesium/calcium ratios, alkenone and X-ray fluorescence analyses, suggesting mechanisms of interhemispheric exchange of climate variations. The North Atlantic Bond Cycles and Dansgaard/Oeschger cycles are closely mirrored in our benthic carbon records, suggesting deep ocean conditions of the western tropical South Atlantic are primarily controlled by NADW production variability. Surface ocean and thermocline oxygen isotopes, however, are related to more complex interactions of regional changes in temperature, salinity and upper ocean stratification. Furthermore, our thermocline oxygen isotopes may represent an imprint of South Atlantic Central water oxygen isotopes. Sea surface temperatures (SST), as indicated by alkenones and magnesium/calcium ratios, show warming during some Heinrich events and Dansgaard/Oeschger cycles, but cooling during others. In context of the "seasaw theory", this suggests the western tropical South Atlantic is part of a transition area between the North and South Atlantic, being influenced by northern hemisphere cooling during some stadials and by southern hemisphere warming during others. Different amplitudes of SST variability in the alkenone and magnesium/calcium records point to different sedimentation or preservation conditions of these proxies. Bulk sediment titanium/calcium (Ti/Ca) ratios point to variations in precipitation on the adjacent South American continent, probably caused by repeated southward displacements of the Intertropical Convergence Zone. Pollen records from the same region and contrasting Ti/Ca records from the Cariaco Basin underline this suggestion. Ti/Ca ratios show a pattern similar to the GISP2 oxygen isotope record, suggesting also a strong coupling of tropical and high northern latitudes via the atmosphere.