A team of researchers from USC, Columbia University, University of Washington, MIT and the University of Hawaii, have found that emissions from coal-fired power plants in China are fertilizing the North Pacific Ocean with iron. Their findings, published in the Proceedings of the National Academy of Sciences, questions whether the addition of iron, an important nutrient for marine life, will pose a positive or negative influence on ocean ecosystems.
"It has long been understood that burning fossil fuels alters Earth's climate and ocean ecosystems by releasing carbon dioxide into the atmosphere," said lead author Seth John, who is an assistant professor of Earth sciences at USC. "This work shows fossil fuel burning has a side effect: the release of iron and metals into the atmosphere that carry thousands of miles and deposit in the ocean where they can impact marine ecosystems."
The team measured metals in surface seawater samples from a distant part of the Pacific Ocean located north of Hawaii and between Japan and California. The north-south transect where the team took samples is downwind of industrial emissions in east Asia.
In their samples, the team was able to identify peak iron concentrations roughly three times more than background ocean concentrations. Particularly clear was the association of iron and other metals in the surface waters of the North Pacific Ocean from westerly winds blowing emissions from Asia to North America.
"When we collected samples in the ocean, we found that the iron isotope and lead isotope 'fingerprints' from seawater matched those of anthropogenic pollution from Asia," said study author Paulina Pinedo-Gonzalez, a USC post-doctoral scientist who is now at the Lamont-Doherty Earth Observatory at Columbia University. They showed that almost 60% of the iron in part of the northern section sampled originates from power plants.
Iron is an essential limiting factor for marine productivity for roughly one-third of the world's oceans. This then begs the question, is more iron a good thing? Referring to the micronutrients that plankton and algae need to thrive, John comments, "Certain metal deposits could help some marine life thrive while harming other life. There are inevitable tradeoffs when the ocean water's chemistry changes."
"Microscopic iron-containing particles released during coal burning impacts algae growth in the ocean, and therefore the entire ecosystem for which algae form the base of the food chain," John continues. "In the short term, we might think that iron in pollution is beneficial because it stimulates the growth of phytoplankton, which then take carbon dioxide out of the atmosphere as they grow to offset some of the carbon dioxide released during the initial burning process. However, it's totally unsustainable as a long-term geoengineering solution because of the deleterious effects of pollution on human health. Thus, the take-home message is perhaps a better understanding of an unintended side effect of coal burning and the ways in which that can impact ocean ecosystems thousands of miles away."