• Two fresh anomalies observed in the eastern subpolar North Atlantic upper ocean during 1992-2017 share similar spatial characteristics. • Salt budget analysis shows the 2012-2016 fresh anomaly in the upper 200 m occurs due to transport of anomalous salinity by mean currents. • In contrast, the fresh anomaly in the 1990s is due to anomalous circulation of the mean salinity field.

The eastern subpolar North Atlantic upper ocean salinity undergoes decadal fluctuations. A large fresh anomaly event occurred during 2012--2016. Using the ECCO state estimate, we diagnose and compare mechanisms of this low salinity event with that of the 1990s fresh anomaly event. To avoid erroneous interpretations of physical mechanisms due to 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 fresh 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 fresh anomaly was the transport of the mean salinity field by anomalous currents across the southern boundary of the subpolar North Atlantic.

Computational Oceanography is the study of ocean phenomena by numerical simulation, especially dynamical and physical phenomena. Progress in information technology has driven exponential growth in the number of global ocean observations and the fidelity of numerical simulations of the ocean in the past few decades. The growth has been exponentially faster for ocean simulations, however. We argue that this faster growth is shifting the importance of field measurements and numerical simulations for oceanographic research. It is leading to the maturation of Computational Oceanography as a branch of marine science on par with observational oceanography. One implication is that ultra-resolved ocean simulations are only loosely constrained by observations. Another implication is that barriers to analyzing the output of such simulations should be removed. Although some specific limits and challenges exist, many opportunities are identified for the future of Computational Oceanography. Most important is the prospect of hybrid computational and observational approaches to advance understanding of the ocean.