Every spring and summer the sea along the coast of California turns cold. This video shows sea surface temperature from March to October 2021 at about 4 km resolution. In spring, steady north-westerly winds start to blow along the coast. Because of the Earth's rotation, the wind does not push the surface water straight ahead but to its right, away from the coast. Cold water from 50 to 100 metres down rises to replace it. This is coastal upwelling. Cold plumes stream out from the capes, Cape Mendocino, Point Arena and Point Sur, and all season the water at Point Arena stays colder than the open ocean 250 km offshore, by up to 5 °C in summer. The cold water carries nutrients from the deep. It feeds plankton, fish, seabirds and whales, and it is the reason the California Current is one of the most productive seas in the world. It also explains the summer fog over San Francisco. In autumn the winds weaken and the upwelling fades.
Source: Data: NASA JPL Multi-scale Ultra-high Resolution (MUR) SST v4.1, via NOAA CoastWatch ERDDAP, shown at 0.04° (about 4 km) every 3 days. Coastline: GLOBE land mask. Visualisation by The Moving Sea
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