Increase of organic carbon burial promoted the glacial decrease of atmospheric CO2: A case study from the Bengal-Indus fans

Elucidating the burial mechanism of organic carbon (OC) in the Bengal-Indus Fans, the principal sink for weathering and erosion products from the Himalayas, is essential for deciphering the global carbon cycle and climate change. This study investigates the quantitative source-to-sink processes and controlling mechanisms of OC burial throughout Quaternary glacial-interglacial cycles using organic carbon isotope, total organic carbon content, mass accumulation rate, and a three-endmember mixing model to partition contributions from terrigenous C₃/C₄ plants and marine phytoplankton. The results indicate a significantly higher contribution of OC burial from C₄ plants during glacial periods, while C₃ and marine sources show opposing trends. Mass accumulation rates of terrigenous and marine OC increase during glacial periods and decrease during interglacials. Orbital variations in OC burial flux in the Bengal-Indus Fans are primarily influenced by glacial erosion of the Himalayas and monsoonal precipitation. Glacial erosion regulates the transport of terrigenous OC and nutrients to the ocean, thereby affecting marine primary productivity. Simultaneously, monsoonal precipitation influences plant composition in terrigenous regions and modulates the preservation efficiency of OC. Our calculations indicate that during glacial periods, the OC burial flux reached 0.8 × 10¹² mol/year. Assuming a total atmospheric CO₂ decline of ∼80 ppmv during glacials, this burial flux contributed approximately 5 % (∼4 ppmv) to the CO₂ drawdown, with marine OC accounting for 41–45 % of the total. These findings highlight the significant role of OC burial in the Bengal-Indus Fans in atmospheric CO₂ sequestration, thus contributing to global cooling during glacial periods.