Reconstructing hydrological changes in (sub)tropical South America over the last 36 kyrs: insights into the low-latitude expressions of high-latitude climate forcing

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The hydrological cycle in tropical South America depends strongly on the intensity of the South American Summer Monsoon (SASM) and the latitudinal migration of the Intertropical Convergence Zone (ITCZ). Particularly in eastern Brazil, precipitation is extremely seasonal, with an eight-months-long dry season between March and October and a relatively rainy season between November and February. The exceptionally long dry season makes this region highly sensitive to changes in the amount of the rainfall received. This does not only entail a very high vulnerability of the region's terrestrial ecosystems to prolonged draughts, but has also severe societal consequences via its effects on agriculture and the availability of hydroelectric power. As NE Brazil currently experiences historic droughts, it is essential to constrain the natural climatic variability in that region, thereby assessing the potential impacts of future climate change on continental moisture availability. Considering that the expected rate of global warming is paralleled by only few periods of earth's history, this project particularly aims to assess the hydrological variability in South America by studying analogue periods of extremely rapid climatic shifts during the last glacial and the deglaciation.To achieve this goal, this study aims to disentangle the impact of insolation and abrupt oceanic forcing on continental moisture availability via reconstructing river run-off in climatically highly sensitive regions of tropical South America during the last 36 kyr. The project relies on marine cores from strategically located positions that have become available during METEOR cruises 78/1 (March 2009) and, very recently, M125 (March/April 2016, with participation of the PI). Core M78/1-235-1 captures the outflow of the Orinoco River, thereby reflecting climate variability in the northern extent of the area influenced by the insolation-driven shifts of the ITCZ. In contrast, core M125-35-3 records the outflow of the Paraíba do Sul River in southern East Brazil, south of the ITCZ influence, but affected by the SASM and the South American Convergence Zone (SACZ). Reconstructions will be based on high- resolution multi-proxy data comprising foraminiferal Ba/Ca, Mg/Ca, d18O, XRF- and color-scanning. Focus will be on critical time intervals with high rates of climate change, i.e. the late Pleistocene/early Holocene transition, the Last Glacial Maximum and Marine Isotope Stage 3 with Dansgaard-Oeschger cycles 5-7. As both sites are strongly influenced by abrupt climate shifts originating from the high-northern and high-southern latitudes, novel insights will be gained about the sensitivity of the continental hydrological cycle during climatically highly dynamic periods.