Atmospheric CO₂ and climate variation across the glacial-interglacial cycle, are closely linked to ocean carbon cycle, yet the influence of interglacial variability in ocean overturning circulation on carbon sequestration remains poorly constrained. Here, we investigate the coupling between meridional overturning circulation (MOC) and dissolved inorganic carbon (DIC) using 9 interglacial climate simulations performed with an Earth system model incorporating marine biogeochemistry.
DIC exhibits distinct relationships with the Atlantic and Southern Ocean overturning circulations. In the Atlantic, DIC concentrations show a pronounced vertical dipole relative to Atlantic MOC (AMOC) strength. Stronger AMOC is associated with higher DIC concentrations in intermediate waters (200–2000 m) but lower concentrations below ~2000 m, reflecting enhanced ventilation and upward redistribution of carbon-rich deep waters and associated with mineralization changes. In contrast, the Southern Ocean MOC (SOMOC) produces a south-deep to north-shallow structure, characterized by reduced DIC in Antarctic source regions and enhanced carbon storage in the abyssal Southern Ocean and deep Atlantic through intensified Antarctic Bottom Water formation. These contrasting circulation regimes exert markedly different controls on ocean carbon storage. Stronger AMOC reduces deep-ocean carbon inventories through enhanced ventilation, whereas stronger SOMOC promotes carbon sequestration below 3 km depth.
These results demonstrate that the balance between northern-sourced ventilation and southern-sourced abyssal water formation exerts a major control on carbon partitioning within the ocean interior. Interglacials characterized by weaker AMOC and stronger SOMOC therefore favor enhanced deep-ocean carbon storage, providing a mechanism linking overturning variability to atmospheric CO₂ changes across interglacial climates.