Impact of surface-water temperature on South American Summer Monsoon dynamics during the past ~850 kyrs

季风引起的降水直接影响到约三分之二世界人口的生计。因此，预测季风系统在全球变暖条件下的未来行为具有重大的社会经济意义。然而，数值模式仍然不能可靠地模拟气候变暖下季风系统复杂的时空变化。在热带海面温度上升对季风降水量和空间分布的影响方面，这一缺点尤为突出。为了提高对不同气候边界条件下季风驱动的降水变率的理解，有必要对过去的历史进行连续的替代记录。在这个项目中，我们计划研究巴西东部中更新世至晚更新世期间的南美夏季风(SASM)动力学，以破译热带南大西洋西部海温变化对大陆降水模式的影响。特别是巴西东部，水分供应有明显的季节和年际变化，因此从生态和社会经济角度来看，这是一个高度敏感的地区。为了更好地了解热带海洋如何影响季风降水变化，我们的项目旨在(I)重建热带大西洋西部的水文变化和(Ii)将这些变化与巴西东部不同(即，冰川-间冰期)气候状态下大陆湿度变化的重建联系起来。为了实现这一目标，我们将研究位于巴西东部附近的两个岩心，它们靠近里约多斯河和里约热内卢孔塔斯海峡的入海口。两个岩心的海洋表面温度(SST)将基于对浮游有孔虫(红色球藻，粉红色)的镁/钙测量而重建。XRF岩心扫描获得的沉积物地球化学数据(如K/Al、Fe/Al比值、元素累积率)将提供有关各河流流域河流径流和风化状态的信息。由于岩心扫描和Mg/Ca-SST将来自同一岩心材料，因此有必要对海洋和陆地环境的变异性进行直接比较。综合来自两个核心的替代数据将允许研究巴西东部地区降雨量的区域尺度变异性及其与海温变化的关系。新记录覆盖的整个时间间隔(即过去850KYR)将使巴西东部地区现有的、通常不连续的降雨量变异性记录至少延长600个基尔。新的数据将允许限制以前间冰期的大陆水分平衡，这些间冰期的温度比工业化前的全新世(如MIS5和MIS11)要高。因此，我们期望我们项目的结果能够作为基准，预测未来气候变化对南美洲热带东部降水模式的影响及其所有社会经济意义。

Monsoon-derived precipitation directly affects the livelihood of about two thirds of the world population. Predicting the future behavior of monsoonal systems under global warming conditions is therefore of great socio-economic relevance. However, numerical models still fail to reliably simulate the complex spatial and temporal rainfall variability of monsoonal systems under a warming climate. This shortcoming is particularly prominent with regard to the impact of rising tropical sea-surface temperatures (SST) on the amount and spatial distribution of monsoonal precipitation. In order to improve the understanding of monsoonally driven precipitation variability under different climatic boundary conditions, continuous proxy records of the past are necessary. In this project we propose to investigate South American Summer Monsoon (SASM) dynamics in E Brazil during the mid to late Pleistocene in order to decipher the impact of SST changes in the western tropical South Atlantic on continental precipitation patterns. Particularly E Brazil is subjected to distinct seasonal and interannual changes in moisture availability and, thus, a highly sensitive area from an ecological and socio-economic perspective. To better understand how the tropical ocean affects monsoonal rainfall variability, our project aims to (i) reconstruct hydrographic changes in the western tropical Atlantic and (ii) to link these changes to reconstructions of continental moisture variability in E Brazil across different (i.e., glacial-interglacial) climate states. To achieve this goal we will study two cores located off E Brazil close to the mouths of the Rio Doce and Rio de Contas. Sea surface temperatures (SST) will be reconstructed for both cores based on Mg/Ca measurements on planktic foraminifera (Globigerinoides ruber, pink variety). Sediment geochemical data (e.g. K/Al, Fe/Al ratios, element accumulation rates) derived from XRF core scanning will provide information about fluvial run-off and weathering state in the respective river catchment. As core scanning and Mg/Ca-SST will be obtained from the same core material a direct comparison of marine and terrestrial environmental variability is warranted. Integrating proxy data from both cores will allow to study the regional-scale variability of rainfall in E Brazil and its relation to SST changes.The entire time interval covered by the new records (i.e., the past ~850 kyr) will extend the yet available, often discontinuous records of rainfall variability in E Brazil by at least 600 kyrs. The new data will allow to constrain the continental moisture balance during previous interglacials with warmer temperatures than the pre-industrial Holocene (e.g., MIS 5 and 11). We therefore expect the results of our project to serve as benchmarks for predicting the influence of future climate change on precipitation patterns in eastern tropical South America with all their socio-economic relevance.