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

热带南美洲的水文循环在很大程度上取决于南美洲夏季风（SASM）的强度和热带辐合带（ITCZ）的纬向迁移。特别是在巴西东部，降水具有极强的季节性，3月至10月为长达8个月的旱季，11月至2月为相对较多的雨季。异常漫长的旱季使该地区对降雨量的变化高度敏感。这不仅使该地区的陆地生态系统极易受到长期干旱的影响，而且还通过其对农业和水力发电的影响产生了严重的社会后果。由于巴西东北部目前正在经历历史性的干旱，因此必须限制该地区的自然气候变化，从而评估未来气候变化对大陆水分可用性的潜在影响。考虑到全球变暖的预期速度与地球历史上只有少数几个时期是平行的，本项目特别旨在通过研究末次冰期和冰川消退期间极端快速气候变化的类似时期来评估南美洲的水文变异性。为了实现这一目标，本研究旨在通过重建南美洲热带气候高度敏感地区的河流径流来解开日照和海洋突变强迫对大陆水分可用性的影响。该项目依赖于战略位置的海洋核心，这些核心在METEOR巡航78/1（2009年3月）和最近的M125（2016年3月/ 4月，PI参与）期间可用。M78/1-235-1岩芯捕获了奥里诺科河的流出，从而反映了受ITCZ日晒驱动移动影响的北部地区的气候变率。相反，M125-35-3岩心记录了巴西东部南部Paraíba do Sul河的流出，位于ITCZ影响以南，但受到SASM和南美辐合带（SACZ）的影响。重建将基于高分辨率多代理数据，包括有孔虫Ba/Ca， Mg/Ca, d18O， XRF和彩色扫描。重点将放在具有高气候变化速率的关键时间区间，即晚更新世/全新世早期过渡、末次盛冰期和海洋同位素阶段3 （Dansgaard-Oeschger旋回5-7）。由于这两个地点都受到源自高北高纬度和高南高纬度的气候突变的强烈影响，因此将获得关于气候高动态时期大陆水文循环敏感性的新见解。

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.