Revisiting the Conundrum of Interior Downwelling in Munk’s Abyssal Recipes: An Unsteady Perspective Linked to a Cooling AABW

Walter Munk’s seminal work, Abyssal Recipes, has established a foundational framework for comprehending abyssal water upwelling for almost 60 years. While it has profoundly influenced theoretical, laboratory, and observational studies of deep-ocean processes, discrepancies arise when compared with long-term observational data. One prominent paradox is known as the interior downwelling conundrum: When Munk's framework is applied to conditions of bottom-intensified mixing, it predicts downwelling rather than upwelling, which contradicts the mass balance in the abyssal ocean. This study revisits this challenge by investigating the unsteady dynamics of abyssal isopycnals. We demonstrate that under a cooling regime in the abyssal ocean, which is linked with the formation of the Antarctic Bottom Water (AABW) in the last little Ice Age more than 1000 years ago, rising water parcels can co-exist with downward diapycnal velocities. This reconciliation aligns Munk’s theory with the observed mass balance and resolves the longstanding paradox. These findings provide fresh insights into the conundrum and contribute to advancing our understanding of the closure of the global thermohaline and overturning circulations.