Linking past vegetation, fire, and climate dynamics in the semiarid Northeastern Brazil: insights from marine sediments

• Applicant: Dr. Thomas Akabane
• Subject Area: Geology ; Palaeontology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566258564

Northeastern Brazil (NEB) is mostly dominated by a semiarid climate where thrives a unique triple ecotone that encompasses the world’s most biodiverse xeric vegetation, savanna, and rainforest. Currently, NEB supports a population of 55 million people that partially relies on environmental services provided by these ecosystems. However, future projections point to an intensification of the already expanding aridity and wildfires in the region due to global warming and human activities, with potentially severe impacts for society and ecosystem sustainability. Further uncertainties in projections arise from a potential slowdown of the Atlantic Meridional Overturning Circulation (AMOC) that could shift the Intertropical Convergence Zone (ITCZ) southwards, leading to increased rainfall in the region. To anticipate the complex responses of the interlinked ocean-climate-vegetation-fire systems, it is essential to understand the mechanisms controlling their interactions. Thus, this project aims to reconstruct ecosystem responses to past natural climate and ocean variability using a multiproxy approach based on marine sediment records retrieved off NEB. Vegetation dynamics will be reconstructed through pollen and long-chain n-alkanes δ13C, fire regimes through microcharcoal and polycyclic aromatic hydrocarbons (PAHs), hydroclimate using long-chain n-alkanes δ2H, and sea-surface temperatures with unsaturated n‐C37 alkenones (UK’37). These records offer a unique opportunity to investigate the still-elusive natural environmental responses to contrasted past climate and ocean conditions in the period between 155,000–95,000 years ago and during the last 11,700 years. These periods span conditions similar to those expected in the coming decades: the globally warmer-than-present Last Interglacial period (LIG, 129,000–116,000 years ago) and the preceding period of strong AMOC slowdown called Heinrich Stadial 11 (HS11, 136,000–129,000 years ago). In addition, the investigation of the Holocene record (last 11,700 years) will serve as a benchmark for the LIG. This project will be carried out at MARUM - Center for Marine Environmental Sciences, University of Bremen. The findings will improve our understanding of vegetation and fire dynamics in NEB in response to climate and ocean changes and serve as a critical reference for the expected environmental responses to the ongoing climate changes.

• DFG Programme: WBP Position