Upwelling in the ocean, in which the deep, cold water rises to the surface, provides a very nutrient-rich environment for the marine ecosystem. But there are detrimental effects related to the upwelling system, too. As Tessa Hill of the University of California, Davis explains, when this water gets pulled back up to the surface, it’s also bringing up very carbon dioxide-rich water, which is increasing due to human activities and changing the chemistry of the water itself.

"We call this ocean acidification because when you add that carbon dioxide into the sea water, it changes the acidity of the water. The ocean soaks up that carbon from the atmosphere, so about 30 percent of what we put into the atmosphere ends up in the ocean. And so on top of all the cycling of carbon that would normally happen in the ocean, including things related to that upwelling system, there’s now a human fingerprint on top of that."

Acidic waters are affecting how oysters and mussels build their shell, so Hill is helping to monitor conditions off the Pacific coast, which helps hatcheries decide when to spawn.