Reconstructing past vegetation and carbon-cycle responses to monsoon variability is critical for understanding tropical land–ocean interactions. This study presents a multiproxy record from sediment core E87-32B in the central northern Indian Ocean, integrating geochemical, isotopic, and palynological data to reconstruct organic carbon (OC) sources, vegetation dynamics, and Indian Summer Monsoon (ISM) variability since ~37 ka (MIS3–1). The results show that OC derived from mixed terrestrial and marine sources, with its preservation primarily controlled by sedimentation rate and monsoon-driven sediment supply, and secondarily influenced by redox conditions. Pollen assemblages reveal an expansion of humid C₃ forests and enhanced OC burial during strong ISM phases (MIS3 and early Holocene), contrasting with a marked increase in C₄ grasslands and reduced OC preservation during weaker monsoon intervals (MIS2 and late Holocene). Despite intensified Holocene monsoon rainfall and elevated marine productivity, TOC concentrations remained lower than in MIS3, reflecting post-glacial sea-level transgression that caused extensive shelf trapping and enhanced remineralization, limiting terrestrial OC transfer and preservation. Sliding-correlation analyses reveal strong coupling between terrestrial and marine inputs during MIS3, driven by vigorous monsoon-driven sediment flux, whereas weaker correlations in MIS2–1 reflect decoupling associated with aridity and post-glacial depositional reorganization. Cross-core comparisons further demonstrate that monsoon strength and sea-level change were the dominant controls on OC burial efficiency in the Bengal Fan, with redox state exerting a secondary influence on preservation. This integrated record underscores the coupled influence of monsoon variability and sea-level change on late Quaternary land–ocean carbon dynamics in the tropical northern Indian Ocean.