The Role of Large‐Scale Seasonal Cycle Advection in Maintaining the Mean Ocean Salinity Distribution

Abstract Anthropogenic climate change is projected to intensify the global hydrological cycle, posing substantial risks to human societies. However, monitoring these changes through direct observations remains challenging, particularly over the oceans. Since long‐term shifts in the hydrological cycle are expected to alter ocean salinity distribution, understanding the processes governing its evolution is essential. Salinity distribution is known to result from a balance between freshwater fluxes, which broaden the distribution, and mixing processes, which narrow it. Using a novel diagnostic based on the mean salinity variance budget applied to the Estimating the Circulation and Climate of the Ocean (ECCO), we estimate that the large‐scale salinity flux—primarily driven by the seasonal cycle—contributes approximately 23% to this mixing. Our framework also enables us to understand the regional balances, and to identify the regions where these balances are most significant. Our results suggest that accurately representing the seasonal salinity cycle in ocean and climate models is important for simulating the ocean salinity distribution.