Multidecadal Variability of Ocean Climate and Circulation of the North Atlantic Ocean

The North Atlantic's surface has been heating up for decades. There was concern that the thermohaline circulation and essential climate variables, such as the seawater temperature and salinity, could endure substantial changes in response to this surface warming. The Atlantic Meridional Overturning Circulation (AMOC) has changed noticeably over the last century and possibly slowed down in recent decades. Therefore, concerns about the trajectory of the North Atlantic Ocean climate are warranted. The key to understanding the North Atlantic current climate trajectory is to identify how the decadal climate responds to ongoing surface warming.  We address this issue using objectively analyzed in-situ data from the World Ocean Atlas covering 1955-2017 and from the Simple Ocean Data Assimilation reanalysis data for 1980-2019 as fingerprints of the North Atlantic three-dimensional circulation and AMOC’s dynamics. We have found that although the entire North Atlantic is systematically warming, the climate trajectories in different sub-regions of the North Atlantic reveal diverse regional decadal variability, although the thermohaline geostrophic circulation in the North Atlantic during the most recent decade has slowed down. The warming trends in the subpolar North Atlantic lag behind the subtropical gyre and Nordic Seas warming by at least a decade. The climate and circulation in the North Atlantic remained steady from 1955 to 1994, while the last two decades (1995-2017) demonstrated a noticeable reduction in AMOC strength, which may be closely linked to changes in the geometry and strength of the Gulf Stream system.