A Model Based Study of the Emergence of North Atlantic Deep Water During the Cenozoic: A Tale of Geological and Climatic Forcings

Abstract The North Atlantic Deep Water (NADW) is a key component of modern climate systems, redistributing heat from equatorial to polar regions and contributing to the Atlantic Meridional Overturning Circulation. However, the timing of its emergence and the mechanisms driving its formation remain uncertain. This study explores ocean circulation patterns during the middle Eocene (48–38 Ma) and early Miocene (23–16 Ma) using simulations with the IPSL‐CM5A2 climate model. In the middle Eocene simulations, reduced surface salinity in the North Atlantic prevents NADW formation, regardless of atmospheric levels or the presence of an Antarctic ice sheet. Conversely, early Miocene simulations suggest that paleogeographic shifts promote higher Atlantic salinity, enabling NADW formation. Specifically, the closure of the Polish Strait and the narrowing of the Central American Seaway enhance salt retention in the Atlantic and increase salt transport from subtropical to subpolar regions. Additionally, changes in African monsoonal precipitation—characterized by a reduction and eastward shift across Central Africa—reduce freshwater influx into the Atlantic between the middle Eocene and early Miocene. These combined factors weaken North Atlantic stratification, facilitating NADW development during the early Miocene. This research provides a timeline for NADW initiation and insights into the processes driving its formation.