Subpolar North Atlantic sea surface salinity as an AMOC mean state indicator

The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in regulating global climate. Although subpolar sea surface temperature (SST) covaries with recent AMOC variability, the relatively short timescales considered by previous studies leave room for doubt on whether subpolar SST reliably represents AMOC state. The same doubt arises for the sea surface salinity (SSS), though freshwater flux into the subpolar North Atlantic (SPNA) affects AMOC stability by regulating salinity. Here, we investigate the relationships of SST and SSS with the AMOC mean states in model simulations conducted for paleoclimate modeling. SPNA SSS aligns well with changes in the AMOC mean state under these scenarios, while SST does not. Notably, climate experiments simulating an abrupt quadrupling of CO₂ demonstrate a significant correlation between SPNA SSS and transient AMOC strength. The absence of significant SPNA freshening over the past several decades may imply the AMOC is less fragile than previously postulated, but data remain insufficient to predict its long-term stability.