In photosynthesis, plants -- including phytoplankton -- convert CO2 from the atmosphere into their tissues, and produce the oxygen that we breathe. Other animals up the food chain feed off of this carbon that was pulled out of the atmosphere by the miniscule plants. A lack of iron appears to slow this process down, which could affect the food supply for other ocean life, and reduce the amount of heat-trapping carbon dioxide the ocean can soak up.
It's still unclear exactly how the new findings will play out in the complex mixture of organisms in the ocean, with many competing changes caused by acidification and warming.
For instance, most of the iron in the ocean comes from dust, and climate change may increase the amount of dust that settles over the ocean, supplying extra iron and counteracting the new findings, Buesseler noted. Or, other organisms that are not limited by iron may fill the voids left by iron-starved phytoplankton.
"We're just at the beginning of research on ocean acidification," Morel said. "This is the first study published of its kind that looks at the uptake of a critical nutrient."