Upper-ocean variability in the Equatorial Atlantic across the Mid-Pleistocene Transition

The Mid-Pleistocene Transition (MPT, ~1.2-0.8 Ma) marks a fundamental reorganization of Earth’s climate system, characterized by a shift from 41 kyr to 100 kyr glacial-interglacial cycles, a long-term expansion of global ice volume, and increasingly asymmetric glacial stages. This interval also witnessed widespread aridification, though the underlying drivers varied regionally: in Asia, enhanced dryness was linked to the growth of Northern Hemisphere ice sheets, whereas in Eastern Africa, more arid hydroclimate conditions were tied to a strengthened Pacific Walker Circulation. Despite the global significance of the MPT, paleoenvironmental reconstructions from Brazil are extremely limited, largely due to the scarcity of long, continuous, high-resolution sedimentary archives. As a result, the response of the western equatorial Atlantic to reorganized glacial boundary conditions remains poorly constrained, even though this region plays a key role in tropical ocean-atmosphere dynamics. To address this gap, we investigate paleoclimatic variability along the western tropical South Atlantic margin throughout the MPT and evaluate how large-scale cooling influenced regional hydroclimate and upper-ocean structure. We developed a composite sedimentary record from cores MD23-3677Q and MD23-3678 (3°14.35′S, 36°11.87′W; 1988 m water depth), recovered from a seamount off northeastern Brazil during the AMARYLLIS AMAGAS II expedition. Planktonic foraminiferal geochemistry (δ¹³C, δ¹⁸O and Mg/Ca ratios) was measured in Globigerinoides ruber and Neogloboquadrina dutertrei at 4-cm resolution to reconstruct sea-surface temperatures, atmosphere–ocean coupling, and upper-ocean stratification through the MPT. Ongoing analyses will provide new constraints on tropical hydroclimate variability, SST changes, and the evolution of upper-ocean structure in the western equatorial Atlantic, offering fresh insight into how low-latitude feedbacks evolved under progressively cooler global climates during the MPT.