Metals from Chinese Smokestacks Are Landing Far Away in the Pacific Ocean

October 27, 2020

Emissions from coal-fired power plants in China are seeding the North Pacific Ocean with metals including iron, a nutrient important for marine life, according to a new study. The authors say the particles, borne on long-distance winds, could alter the balance of carbon in the atmosphere, or change the ocean ecosystem, though it’s unclear whether it would be for better or worse. The study was published last week in the Proceedings of the National Academy of Sciences.

The study shows that winds blowing from Asia toward North America carry emissions from Chinese power plants and other human sources to the surface waters of the North Pacific Ocean. Peak measurements show that early 60 percent of the iron in one vast swath emanates from smokestacks.

“We know these power plants are putting lots of carbon dioxide into the atmosphere,” said lead author Paulina Pinedo-Gonzalez, a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory. “This is the first study to show that they’re also putting a lot of iron into the ocean.” Iron is a key limiting factor for marine plant growth–the base of the food chain–for about one-third of the world’s oceans. That includes this region, so that means the iron could be increasing the amount of photosynthetic algae that take up carbon from the air. “It’s a big deal to see that you’re adding all that iron to parts where it might make more algae grow, and suck up some of that carbon dioxide that we are producing,” she said.

Crew and scientists aboard the Marcus G. Langseth prepare to sample the surface of the north Pacific Ocean for metals. (Randi Bundy)

While wind-blown mineral dust from deserts has long been considered an important source of iron to open ocean waters, previous studies have come up with widely divergent estimates about how much iron is carried from land to the ocean, especially from human sources. The new study shows that human activities contribute an unexpectedly high amount to this region.

During a 17-day research cruise on the Lamont-Doherty research vessel Marcus G. Langseth, the team measured metals in samples of surface seawater in a remote region hundreds of miles north of Hawaii, about midway between Japan and California. The region is downwind of industrial emissions in east Asia. The team took samples along a north-south transect at latitudes between 25 degrees and 42 degrees north. They found peak iron concentrations in about the middle. The peak concentrations are about three times greater than background ocean measurements, the study shows.

Lead author Paulina Pinedo-Gonzalez tends to instruments that track seawater conductivity, temperature and depth. (Nicholas J. Hawco)

The scientists also found elevated lead concentrations coinciding with the iron hot spots. Other research has shown that most lead at the ocean surface comes from human sources, including cement plants, coal-fired power plants and metal smelters. The scientists ruled out upwelling from the deep ocean as a source by testing water at greater depths. Moreover, the metals in the seawater samples bear telltale isotopes pointing to Chinese industrial sources.

The study may have wider implications for marine life: Human-sourced fertilization with iron or other nutrients could alter the ecosystem. “You move around one factor, and maybe that has consequences for something else that you didn’t predict, said Pinedo-Gonzalez.

“Iron-containing particles released during coal burning impact algae growth in the ocean, and therefore the entire ecosystem, for which algae form the base of the food chain,” said study coauthor Seth John, of the University of Southern California. He said that in the short term, the iron might seem to be beneficial, because it stimulates phytoplankton growth, offsetting some of the carbon dioxide released during coal burning. But he said, iron and other metals “could help some marine life thrive while harming other life. There are inevitable tradeoffs when the ocean water’s chemistry changes.”

Other coauthors are based at the University of Washington; Massachusetts Institute of Technology; the National Oceanography Center of the United Kingdom; and the University of Hawaii at Manoa. The research was supported by the Simons Foundation.

Adapted from a press release by the University of Southern California.

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