San Francisco Bay: The Ocean’s Watershed
By Chelsea Leu at Bay Nature:
“When it comes to the water in the San Francisco Bay, the ocean doesn’t get nearly the credit it deserves. At least, that’s the opinion of oceanographer John Largier, who studies the ocean’s complex dance with the Bay. Sure, the Bay is where the Delta empties into the sea, the final resting place of water that flows all the way from the Sierra and the furthest reaches of the watershed. But the Bay is, it’s worth pointing out, mostly seawater. Whatever’s in it is affected by what’s happening in the ocean, particularly the active upwelling just off our coast.
By bringing cold water up to the surface, upwelling helps create conditions for the fog that often blankets San Francisco. And it also acts like fog’s underwater equivalent, Largier says. Just as the fog flows into the city as a dense, low-lying layer of cloud, ocean upwelling can lead to “cold ocean water pushing in like a wedge underneath the Bay waters.”