A companion piece to the recent Spilhaus animation of monthly salinity: this globe shows the 1993-2025 mean sea surface salinity (CMEMS multi-observation), in PSU. Land is grey.

The surface both is colored and deformed by salinity, but here the reference point isn't zero, it's the ocean's own global mean. Water saltier than that average bulges outward; fresher water sinks in. As with the rest of this series, that's a visual device, not a physical measurement.

The pattern traces the global water cycle almost like a textbook diagram. The subtropical gyres of the Atlantic and South Pacific bulge out as the saltiest open-ocean water on Earth, belts where evaporation strips away far more freshwater than rain returns. Polar waters sink in, diluted by ice melt and river runoff. And the sharpest bulges of all sit in three semi-enclosed seas with heavy evaporation and little freshwater input, the Mediterranean, the Red Sea, and the Persian Gulf, unmistakable even on a globe this size.

Data: CMEMS multi-observation sea surface salinity