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

• Applicant: Privatdozent Dr. André Bahr
• Subject Area: Palaeontology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 390321344

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.

• DFG Programme: Research Grants