Generation and propagation of Eastern Subpolar North Atlantic salinity anomalies

Abstract The Eastern Subpolar North Atlantic (E-SPNA) upper ocean experiences pronounced interannual salinity variability, strongly influencing the global overturning circulation. These anomalies often originate upstream and are advected into the region, yet a quantitative understanding of their dynamics remains lacking. Based on an ocean state estimate, we employ a novel approach that integrates salt budget analysis with Lagrangian particle tracking to quantify the generation and propagation of E-SPNA salinity anomalies. Analyzing salinity for each day between 1992 and 2017 reveals that anomalous advection, freshwater forcing, and vertical diffusion contribute similarly to interannual salinity variability. Most anomalies originate during the two years prior to entering the E-SPNA, particularly near the Grand Banks and along the North Atlantic Current. We also examine two salinity extreme events. We find that the 2016 E-SPNA fresh event primarily resulted from circulation changes near the Grand Banks, with a smaller contribution from vertical diffusion at its onset, whereas the 2007 E-SPNA salty event arose from a combination of atmospheric freshwater forcing and circulation changes associated with subtropical gyre expansion along the North Atlantic Current.