Why are Galician waters so cold in summer?

Galician waters can stay cold in summer because coastal upwelling brings deeper, colder, nutrient-rich water toward the surface. Northerly winds are the usual driver: they push surface water offshore and the replacement water has not been warmed like a still summer surface layer. Air temperature can rise while the sea still reflects that deeper Atlantic water. The same process also feeds phytoplankton, which is why cold summer water here often sits with high marine productivity rather than with a stagnant warm layer.