Monsoon and deep ocean control of organic carbon burial in the southeastern Bay of Bengal

Marginal seas play a key role in absorbing anthropogenic CO₂, yet drivers of their glacial-interglacial carbon burial remain controversial, especially in deep water. The Bay of Bengal—a global carbon sequestration hotspot—exhibits unresolved spatial heterogeneity, with the southeastern region dominated by marine organic carbon and invaded by deep-ocean waters. Here, we reconstruct organic carbon burial history since the Last Glacial Maximum (LGM) using total organic carbon content (TOC) and isotopes (δ¹³C_org), and discuss their controlling mechanisms by reconstructing paleoproductivity, redox condition and bottom water dynamics using multi-proxy records (authigenic neodymium isotopes and uranium content, biogenic barium content). The organic carbon accumulation rate peaked during the LGM (0.75 % TOC; 200 mg cm⁻² kyr⁻¹) due to enhanced monsoon-driven vertical mixing and oxygen-depleted preservation, then declined to minimal values in the Holocene (0.21 % TOC; 27 mg cm⁻² kyr⁻¹) with enhanced bottom-water oxygenation. These shifts support a “mixing‑oxygenation” mechanism: monsoon intensity governs surface productivity and particle export, while deep-water intrusions regulate oxygen levels and the efficiency of carbon preservation. Our findings highlight the critical role of coupled surface-deep ocean processes in regulating ocean carbon sinks, and contribute to improved understanding and prediction of organic carbon burial processes in marginal sea-ocean transition zones under future global warming and intensified oceanic hypoxia.