Mechanisms Driving the Extensive Antarctic Bottom Water in the Glacial Atlantic

Paleo-proxy data indicate that during the Last Glacial Maximum (LGM), the volume of Antarctic Bottom Water (AABW) in the Atlantic was nearly four times greater than it is today. We employed an ocean-only model to simulate the galcial ocean and sea-ice conditions. Our simulations reveal two key mechanisms driving its greater volume. First, while present-day sea ice formation is driven largely by seasonal changes, the glacial mechanism is the substantial export of sea ice toward lower latitudes. The glacial sea ice formation was more than quadruple current levels, providing a steady source of Dense Shelf Water (DSW) crucial for AABW expansion. Second, weaker mixing between North Atlantic Deep Water (NADW) and AABW during the LGM allows the latter to maintain the colder, denser properties of its DSW origin. Together, these factors clarify how glacial conditions supported significantly greater AABW volumes, aligning well with paleo-proxy evidence.