This article is adapted from an announcement by the University of Hawaii at Mānoa.
Iron released from industrial processes can alter ecosystems thousands of miles away, according to new a study co-authored by researchers at the University of South Florida College of Marine Science.
Published this week in the Proceedings of the National Academy of Sciences, the study demonstrates that iron derived from coal combustion and steel manufacturing influences phytoplankton blooms in the North Pacific Transition Zone, a region just north of Hawaii that is important for fisheries in the Pacific. Although industrial iron has previously been detected in the North Pacific Transition Zone, the effect of this iron on the ecosystem was previously unclear.
“We understand that humans can have an outsized impact on marine environments,” said Tim Conway, associate professor of chemical oceanography at the USF College of Marine Science and a co-author of the study. “This paper demonstrates just how far some of those impacts can spread. We’ve been able to determine both the source of this industrial iron and its impact on ecosystems in the North Pacific Transition Zone.”
To piece together the seasonal cycle of iron input, phytoplankton growth, and ocean mixing, the researchers analyzed water and phytoplankton samples and studied ocean dynamics during four different expeditions in the Pacific Ocean. They assessed the iron in these waters to determine whether it had the unique isotope signature of iron that is released from industrial processes.
IMAGE ABOVE: Researchers use rosette samplers, such as the one shown here, to sample deep water for trace minerals. Credit: Ryan Tabata.
The team found that phytoplankton in the region are iron-deficient during the spring, so an increase in the supply of iron boosts the spring phytoplankton bloom that is typical in the area. However, a booming bloom depletes other nutrients, leading to a crash in phytoplankton later in the season.
Importantly, the iron isotope signature did, in fact, indicate the presence of industrial iron in the samples collected.
"We can tell that industrial combustion iron is reaching the surface waters in this region by looking at the iron isotope signature, or 'fingerprint' of the iron,” said Conway. “This tells us that the iron has likely come from Asia, thousands of miles away, and is having a dramatic effect on waters near Hawaii."
Read more: Deep-sea discovery shines light on life in the twilight zone
The ocean has boundaries that humans can’t see but are known to marine microbes and animals, according to Nick Hawco, lead author of the study and assistant professor in the Department of Oceanography at the University of Hawaii Mānoa School of Ocean and Earth Science and Technology.
“The North Pacific Transition Zone is one of these boundaries,” he said. “It divides the low nutrient ocean gyres from the high nutrient temperate ecosystems to 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.”
While these shifting boundaries are not bad in all cases, the regions of the Transition Zone that are closer to Hawaii are among those that are losing out.
“It's a one-two punch,” Hawco said. “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.”
The research team is developing new techniques to monitor the iron nutrition of ocean plankton. This will shed light on how changes in iron supply, from both natural or industrial sources, could impact ocean life.