Controls on Upper Ocean Salinity Variability in the Eastern Subpolar North Atlantic During 1992–2017

Abstract

The upper ocean salinity in the eastern subpolar North Atlantic undergoes decadal fluctuations. A large fresh anomaly event occurred during 2012–2016. Using the ECCOv4r4 state estimate, we diagnose and compare mechanisms of this low salinity event with those of the 1990s fresh anomaly event. To avoid issues related to the choice of reference salinity values in the freshwater budget, we perform a salt mass content budget analysis of the eastern subpolar North Atlantic. It shows that the recent low salt content anomaly occurs due to the circulation of anomalous salinity by mean currents entering the eastern subpolar basin from its western boundary via the North Atlantic Current. This is in contrast to the early 1990s, when the dominant mechanism governing the low salt content anomaly was the transport of the mean salinity field by anomalous currents.