FY 2021

Untangling the relationship between AMOC variability and North Atlantic upper-ocean temperature and salinity

Chiang, J.C.H., W. Cheng, W.M. Kim, and S. Kim

Geophys. Res. Lett., 48(14), e2021GL093496, doi: 10.1029/2021GL093496, View online (2021)

The relationship between Atlantic meridional overturning circulation (AMOC) variability and high-latitude North Atlantic buoyancy changes is complicated by the latter both driving, and responding to, AMOC changes. A maximum covariance analysis applied to a 1,201-year preindustrial control simulation reveals two leading modes that separate these two distinct roles of North Atlantic temperature and salinity as related to AMOC variability. A linear combination of the two modes accounts for most of the variation of a widely used AMOC index. The same analysis applied to another control simulation known to possess two distinct regimes of AMOC variability—oscillatory and red-noise—suggests that the North Atlantic buoyancy-forced AMOC variability is present in both regimes but is weaker in the latter, and moreover there is pronounced multidecadal/centennial AMOC behavior in the latter regime that is unrelated to North Atlantic buoyancy forcing.

Plain Language Summary. Atlantic meridional overturning circulation (AMOC) variations cause significant changes to the global climate. High-latitude North Atlantic temperature and salinity variations modify the AMOC through changing the buoyancy of the upper ocean. However, this identification is complicated by the reverse relationship, that North Atlantic temperature and salinity changes with AMOC. When we apply maximum covariance analysis—a spatiotemporal analysis designed to find coupled patterns between two climate fields—to a preindustrial control simulation of a fully coupled climate model, it extracts the two coupling relationships. Moreover, the combination of these two behaviors is sufficient to characterize the AMOC variations. When we apply the same analysis method to another control simulation exhibiting two regimes of AMOC variability—oscillatory and red-noise—it reveals that the red-noise regime has a marked reduction to the AMOC variability resulting from North Atlantic buoyancy forcing, and a corresponding increase in multidecadal/centennial AMOC variations of undetermined origin.