Iron released from coal combustion and steel production is altering the ecosystem in a critical part of the North Pacific, a new study has found.
About 39 percent of dissolved iron in the uppermost layer of the ocean is rooted in human industrial activity, according to the study, published on Monday in the Proceedings of the National Academy of Sciences.
Iron is essential for the growth of microscopic phytoplankton in the ocean, but industrial emissions contain aerosolized iron, which quickly dissolves in the ocean and disrupts nutrient balances, the authors noted.
These airborne metals, they explained, can flow to distant lands or oceans before getting scrubbed from the atmosphere via rain.
“This is an example of the large-scale impact that human pollution can have on marine ecosystems that are thousands of miles away from the source,” lead author Nick Hawco, an assistant professor in oceanography at the University of Hawaii Manoa, said in a statement.
Hawco and his colleagues sampled oceanic water and phytoplankton samples across the North Pacific Transition Zone — an area just north of Hawaii — on four expeditions between 2016 and 2019. They also evaluated the properties of iron in these waters to identify whether the unique “signature” of industry-generated iron was present.
The scientists observed that the phytoplankton in the region tend to be iron-deficient during the spring and that a surge in iron supply boosts their seasonal bloom. But that burst also causes these microscopic marine algae to deplete other nutrients more rapidly, which then leads to a crash later in the season, according to the study.
In tandem with their observations of this boom-and-bust trend, the researchers also confirmed the presence of industrial iron in the region, thousands of miles away from any possible source.
“The ocean has boundaries that are invisible to us but known to all sorts of microbes and animals that live there,” Hawco said.
The North Pacific Transition Zone, he explained, is one of these critical boundaries, as this region separates low-nutrient ocean whirlpools from nutrient ecosystems in the north.
“With more iron coming into the system, that boundary is migrating north, but we are also expecting to see these boundaries shift northward as the ocean warms,” Hawco added.
Similar such effects may have occurred in areas of the North Atlantic during the industrialization of North American and Europe, as coal-powered shipping saw an uptick in the early 20th century, the authors noted.
While Hawco acknowledged that the changes impacting the North Pacific Transition Zone may not necessarily be entirely negative, he warned that regions closer to Hawaii are among those reaping the negatives of these developments.
“It’s a one-two punch: industrial iron is impacting the base of the food web and the warming of the ocean is pushing these phytoplankton-rich waters further and further away from Hawaii,” he said.
Going forward, Hawco and his colleagues added that they are working on developing new techniques to monitor iron nutrition in ocean plankton. Having greater insight into the metal’s presence, they stressed, could help shed light on how changes in iron supply could be influencing ocean life.