Since 1993, oceanographers have tracked sea surface salinity from space and ships alike. This animation shows the monthly global distribution (CMEMS multi-observation product) on the Spilhaus projection, in PSU (practical salinity units), the actual field, not an anomaly, because the structure itself is the story here.

The pattern follows the water cycle almost like a diagram. Salinity peaks in the subtropical gyres of the Atlantic and South Pacific, belts where evaporation far outpaces rainfall, concentrating salt at the surface. It drops toward the poles, diluted by ice melt, river runoff, and net precipitation. And it spikes hardest of all in semi-enclosed seas with limited freshwater input and heavy evaporation, the Mediterranean, the Red Sea, and the Persian Gulf stand out as the saltiest patches on the entire map.

Watch the texture change over time, too. The early-to-mid 1990s look noticeably smoother and coarser than recent years, that's not degraded data, it's a smaller satellite constellation. As more missions came online through the 2000s and 2010s, the finer mesoscale structure, eddies, fronts, filaments, became visible in a way it simply couldn't be with sparser early coverage.

Data: CMEMS multi-observation sea surface salinity