Distinct carbon sequestration in the glacial Pacific despite vigorous deep ocean circulation

The Pacific Ocean holds the largest marine carbon inventory and serves as a vital sink for atmospheric CO₂ during glacial periods. Associated with drastic cooling of the global oceans, the Pacific carbon sequestration has traditionally been attributed to slow deep circulation, similar to the mechanisms possibly occurring in the glacial Atlantic Ocean. Recently, however, this view has come under scrutiny due to a compilation of neodymium isotope records showing a shorter, rather than longer, transit time for deep Pacific water masses. The noted discrepancy suggests the presence of differing carbon dynamics operating in the glacial Pacific, raising the question of whether a larger carbon reservoir could persist under stronger deep ocean circulation. Here, we employ biogeochemical simulations to examine the possible mechanisms driving the enhanced carbon inventory in the glacial Pacific. The results indicate that the proposed rapid movement of deep Pacific water masses may be linked to cooling in the Southern Ocean, which further increases carbon storage primarily by intensifying air-sea disequilibrium at surface and impeding diapycnal mixing within the ocean interior. Essentially, the results suggest that a substantial Pacific carbon inventory can withstand intensified deep circulation. In the context of thermohaline circulation, the glacial North Atlantic plays a crucial role in absorbing atmospheric CO₂, whereas the surface Southern Ocean and North Pacific operate synergistically to inhibit the release of carbon from the ocean.