North Atlantic ventilation change over the past three decades is potentially driven by climate change

The North Atlantic Meridional Overturning Circulation (AMOC) ventilates a large part of the world ocean via the formation of mode waters and North Atlantic Deep Water. The extent to which human activities have impacted this ventilation system remains unclear. To assess the temporal variations of ocean ventilation in the North Atlantic, we calculated the "age" of seawater, that is, the duration since its last contact with the ocean surface, from both observed and simulated chlorofluorocarbon-12 and sulfur hexafluoride concentrations. Our results indicate that, despite fluctuations in ventilation strength in the Labrador Sea over the past decades, the North Atlantic waters are generally aging. By integrating observations with model simulations, we propose that this aging trend is indicative of a climate change signal rather than natural variability.