Combatting global warming has iron-ic consequences
Toxin-producing algae have been found in areas of the open ocean where iron has been added, increasing concerns about proposals to use oceanic iron fertilization as a way to combat global warming, according to a team of marine scientists.
The findings, reported in this week’s Proceedings of the National Academy of Sciences, show that adding iron from natural or artificial sources stimulates rapid growth of blooms of dangerous diatoms, which scientists had previously thought were limited to coastal waters.
“There have been a lot of ideas about how to remove CO2 from the atmosphere,” said Dr. Claudia Benitez-Nelson, director of the Marine Science Program, a professor in USC’s department of earth and ocean sciences in the College of Arts and Sciences and one of the study’s authors. “One of those proposals has been to fertilize the ocean.”
The idea is similar to adding nutrients to a garden in hopes of improving plant growth. By adding iron to the ocean, the theory is that single-celled algae -- called phytoplankton -- will grow, consuming carbon dioxide. When the algae die and sink to the bottom of the ocean, so the theory goes, they would take with them the CO2 that otherwise would contaminate the atmosphere and contribute to greenhouse gas accumulation.
“It’s an interesting idea,” Benitez-Nelson said. “But this study has shown that when you add nutrients to the ocean, sometimes you have organisms grow that are really bad for you.”
What’s “blooming” is pseudo-nitschia, a diatom that produces a neurotoxin called domoic acid. When large blooms of that same species have occurred in coastal waters, the toxin entered the food chain, causing widespread shutdown of the seafood industry. Domoic acid causes amnesic shellfish poisoning, characterized by both gastrointestinal and neurological disorders. Gastroenteritis usually develops within 24 hours of the consumption of toxic shellfish, with symptoms including nausea, vomiting, abdominal cramps and diarrhea. In severe cases, neurological symptoms may also appear and includes dizziness, headache, seizures, disorientation, short-term memory loss, respiratory difficulty and coma. In 1987, four victims died after consuming toxic mussels from Prince Edward Island, Canada. Until this study, blooms of these algae in the open sea have not been studied.
Iron can be naturally deposited in oceans by dust storms, volcanic eruptions and other airborne sources. Those natural, sporadic occurrences have likely been going on for millions of years, but adding iron to the oceans on a large scale could be dangerous if it causes these neurotoxins to get in the food chain, researchers said.
“This is one of the first studies to convincingly prove one of the detrimental impacts of marine iron addition,” Benitez-Nelson said. “It shows that one solution you think may work, in the long term, it may even be worse than your original problem.”
Benitez-Nelson said fertilizing the ocean with iron is viewed as a serious solution for combating global warming.
“There are companies thinking about all sorts of ways to offset CO2 emissions,” she said. “This is one of several that people were thinking could work. Everyone gets a little worried when you start tinkering with Mother Nature. When you change things dramatically, there can be unforeseen results.”
Benitez-Nelson and fellow USC researcher Emily Sekula-Wood collaborated with researchers from the University of California - Santa Cruz and Louisiana State University. Mary Silver, professor emerita of ocean sciences at UC-Santa Cruz, was the lead author.
The research was funded by the National Science Foundation, U.S. Department of Energy and the U.S. Office of Naval Research.