Changes in Equatorial Atlantic deep ocean ventilation during the mid-Pleistocene transition

The mid-Pleistocene transition (MPT—1250ka to 700ka) marked a fundamental change in the global climate system, characterized by modifying the glacial-interglacial cycle rhythm from a 40kyr to 100kyr period. Because no significant changes in orbital forcing were observed, it is proposed that an internal modification in the ocean-atmosphere-continental-ice system must be the fundamental forcing (Clark et al. 2006). Based on studies in the Atlantic Ocean, it has been suggested that a decrease in glacial pCO₂ atmospheric concentrations during the MPT, possibly due to a reduction in ocean ventilation (Pena, Goldstein 2014), contributed to the growth of larger ice sheets in the Northern Hemisphere, and increasing the duration of the glacial cycles (Thomas et al. 2022). However, the expression of changes in deep ocean ventilation during the MPT event and its mechanisms on the Brazilian margin are not fully comprehended, due to the lack of long-term and high-resolution records. In order to fill these gaps, the present work aims to investigate the deep ocean ventilation changes in the Equatorial Atlantic across the MPT. For that, we provide records from a composite of two cores MD23-3677Q and MD23-3678 (3°14.35 S, 36°11.87 W, 1988 water-depth), collected on a seamount at the northeastern Brazilian margin during the AMARYLLIS AMAGAS II scientific expedition. We conducted δ¹³C and δ¹⁸O analysis on benthic foraminifera (Uvigerina sp.) at a 4-cm resolution. An age model covering the Mid-Pleistocene was built based on the δ ¹⁸O results aligned with a deep-sea δ ¹⁸O stack. The δ¹³C and results showed a glacial-interglacial variability for the entire record, with peaks during interglacial periods indicating a more ventilated ocean. A modification in the proxy variabilities and mean values is observed after the MPT, suggesting changes in deep circulation patterns and deep ocean ventilation across this period. Our records will improve the understanding of MPT climatic mechanisms and their influence on global climate.