North Atlantic–Pacific salinity contrast enhanced by wind and ocean warming

High salinities in the Atlantic and low salinities in the Pacific are critical ocean features, impacting ocean circulations and climate. Here, using observational data, we reveal that the Atlantic–Pacific salinity contrast has amplified during the past half-century. Notably, in the 0–800 m, 20°–40° N band, the Atlantic–Pacific salinity contrast increased by 5.9% ± 0.6% since 1965. A decomposition of heaving and spicing modes suggests vital contributions of wind and ocean warming, in addition to known surface freshwater fluxes. Specifically, ocean surface warming leads to poleward migration of thermocline outcrop zones, while surface wind changes cause upper-layer convergence in mid-latitudes. These processes lead to substantial upper-layer salinity increases in the North Atlantic but have much weaker signatures in the North Pacific, determined by the inter-basin difference in climatological salinities. This work highlights the complexity of ocean salinity response to climate change, underscoring the unexpected importance of wind- and heat-driven processes in the Atlantic–Pacific salinity contrast. Ocean salinity changes are thought to be dominated by freshwater fluxes. Here the authors show that amplification of the Atlantic–Pacific salinity contrast also involves wind- and ocean warming-driven processes, with larger salinity increases in the North Atlantic, relative to the North Pacific.