Late Quaternary change in sources and burial of organic carbon off Northeastern Brazil

The export and burial of continental organic carbon (OCcont) in marine sediments are modulated by vegetation, soils, and climate. This study analyzes the marine sediment core GL-1248 to assess how millennial-scale precipitation variability during the late Quaternary influenced OCcont export and burial along the Northeastern Brazilian margin. We used lignin phenols, plant wax n -alkanes, and branched glycerol dialkyl glycerol tetraethers (brGDGTs) as biomarkers. During Marine Isotope Stage (MIS) 4, prolonged wet conditions was associated with Atlantic Meridional Overturning Circulation (AMOC) slowdowns and Intertropical Convergence Zone (ITCZ) southward shifts, enhanced erosion and fluvial transport of both soil-derived OC (brGDGTs) and plant-derived (long-chain n -alkanes ΣC 27 -C 35 ). Simultaneously, sea-level regression and coastal plain expansion promoted the burial of additional labile carbon from wetlands, evidenced by elevated concentrations of medium-chain n -alkanes (∑C 23 –C 25 ) and p -hydroxyacetophenone. The predominance of this labile material intensified lignin remineralization toward the end of MIS4. At the onset of MIS3, OCcont inputs shifted toward more refractory woody sources, and burial events became more episodic. Contrary to the expectation of uniform OCcont increases across all MIS3 Heinrich Stadials (HS), only HS5 and HS4 exhibited substantial enrichment in OCcont burial, dominated by vascular vegetation biomarkers (lignin phenols and n -alkanes ΣC 27 -C 35 ). These results suggest that although OCcont quality influenced initial degradation, long-term OCcont burial was strongly modulated by reduced benthic oxygenation during AMOC slowdowns. Our results show that ocean circulation, precipitation, sea level, and vegetation jointly controlled OCcont burial at the land–ocean interface, linking millennial-scale climate variability to carbon sequestration along the Northeastern Brazilian margin.