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In addition to nutrients such as nitrogen and phosphorus, iron plays a vital role in the development of microscopic phytoplankton in the ocean. However, a recent investigation led by oceanographers at the University of Hawai‘i at Mānoa and partners at the University of Washington uncovered that iron emitted from industrial activities, including coal burning and steel production, is modifying the ecosystem in the North Pacific Transition Zone. This area, positioned just north of Hawai‘i, is significant for Pacific fisheries.

The study was released on June 2 in the Proceedings of the National Academy of Sciences.

“We identified a link between human actions and the position of critical ecosystem boundaries in the ocean vital for marine life,” remarked co-author Randie Bundy, a UW associate professor of oceanography. “I hope this research underscores that human activities can influence the ocean in various ways, not only through climate change. It also emphasizes the necessity of monitoring significant ocean ecosystem boundaries over time, enabling us to better comprehend how this could affect marine organisms.”

Iron from human endeavors ascends into the atmosphere and can be transported to remote regions or oceans before being removed from the skies by rain. Industrial iron has been previously identified in the North Pacific Transition Zone, but its impact on the ecosystem was not entirely clear.

To unravel the seasonal cycle of iron input, phytoplankton development, and ocean stratification, the researchers examined water and phytoplankton samples and investigated ocean dynamics during four distinct expeditions to this segment of the Pacific Ocean. They also evaluated the iron in these waters to ascertain whether it bore the unique isotopic signature of iron released from industrial sources.

The team discovered that phytoplankton in the area are iron-deficient during spring; thus, an increase in the iron supply stimulates the spring phytoplankton bloom typical of the region. However, due to this abundant bloom, they quickly deplete other nutrients, leading to a decline in phytoplankton later in the season. Notably, the iron isotope signature confirmed the presence of industrial iron in the Pacific, thousands of miles away from its origin.

“The ocean has boundaries that are imperceptible to us but recognized by various microbes and creatures that inhabit it,” stated Nick Hawco, lead author and assistant professor at the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology. “The North Pacific Transition Zone is one of these boundaries. It separates the low-nutrient ocean gyres from the high-nutrient temperate ecosystems to the north. As more iron enters the system, that boundary is shifting northward, and we also anticipate observing these boundaries moving north as the ocean warms.”

That’s not necessarily negative, according to Hawco. Unfortunately, the sections of the transition zone nearer to Hawai‘i are among those experiencing the most significant losses.

“It’s a dual threat: Industrial iron is disrupting the foundation of the food web, while the warming ocean is pushing these phytoplankton-rich waters further away from Hawai‘i,” Hawco noted.

The research group is developing innovative methods to monitor the iron availability for oceanic plankton, shedding light on how fluctuations in iron supply—whether from natural or industrial origins—might affect marine life.

“A project of this magnitude is genuinely the result of teamwork among scientists with varied expertise,” stated co-author Sacha Coesel, a UW research scientist in oceanography. “Thanks to these collaborations, we successfully integrated satellite observations—which reveal large-scale, multi-year trends—with ship-based data gathered over several years at the same sites. This integration allowed us to correlate broad environmental trends with the intricate molecular details of gene expression in key organisms responding to iron availability. While each dataset stands alone in value, together, they provide the depth and precision needed to yield robust, predictive insights into ecosystem dynamics.”

Other UW co-authors include Ginger Armbrust and Mora Groussman. For afull list of authors, see the paper.

This investigation was financed by the Simons Foundation and the National Science Foundation.

This article is adapted from a release by the University of Hawai‘i Mānoa School of Ocean and Earth Science and Technology.

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