Chestnut Hill, Mass. (6/9/2026) – Ice-age sea-level declines may have turned seafloor volcanoes into natural iron fertilizer for plankton, potentially enhancing ocean carbon storage, Boston College researchers report today in the journal Nature Geoscience.
In some ocean regions, major nutrients such as nitrogen and phosphorus are abundant, but phytoplankton growth is limited by a shortage of iron, long viewed as supplied by windblown dust.
The new findings suggest iron released from deep-sea hydrothermal vents could also have fertilized surface waters during ice-age transitions, when lower sea level may have increased ridge volcanism and hydrothermal activity, said report lead-author Boston College Assistant Professor of Earth and Environmental Sciences Xingchen “Tony” Wang.
“The surprising message is that life at the sunlit ocean surface may be connected to volcanic activity thousands of meters below,” Wang said. “The result points to a possible feedback loop connecting sea level, seafloor volcanism, ocean biology, carbon storage, atmospheric carbon dioxide, and climate.”
The team examined whether hydrothermal iron from mid-ocean-ridge volcanic activity could directly stimulate surface-ocean productivity, rather than remaining trapped in the deep ocean. Building on previous findings, the team sought out the connection between ice-age sea-level fall, increased ridge volcanism and iron release, and phytoplankton growth, Wang said.
Using sunlight and nutrients to grow, microscopic phytoplankton help move carbon from the atmosphere into the ocean, part of a cycle that has drawn the interest of researchers looking at how atmospheric carbon can be sequestered, reducing greenhouse gas contributions to climate change.
“In some ocean regions, phytoplankton growth is limited by a shortage of iron rather than major nutrients — like a missing vitamin,” Wang said. “This ‘iron limitation’ is one reason ocean iron fertilization has been discussed as a possible carbon dioxide removal strategy.”
Wang pointed out the study, titled “Ocean iron fertilization from enhanced mid-ocean-ridge volcanism due to ice-age sea-level falls,” did not test deliberate fertilization; instead, it examines how natural iron sources have affected phytoplankton growth and carbon cycling in Earth’s past.
Working with colleagues from Boston University, University of Massachusetts, Boston, National Taiwan University and Princeton University, Wang and his team studied the eastern equatorial Pacific, a large tropical ocean region where phytoplankton growth is limited by iron, and the underlying East Pacific Rise, a major mid-ocean ridge system.
The researchers analyzed sediment samples from this region spanning the past 200,000 years. In fossil shells of foraminifera — tiny marine organisms preserved in seafloor sediments — the team measured nitrogen isotopes, which record how completely phytoplankton consumed nutrients in the surface ocean, according to the report.
The key nitrogen isotope records were generated by Tianshu Kong, a co-first author and recent Ph.D. graduate from Wang’s lab at Boston College.
“The nitrogen isotopes in these fossil shells gave us a way to reconstruct how surface-ocean nutrient use changed through time,” Kong said. “When the 200,000-year record came together, the two deglacial peaks were striking.
“We then compared those nitrogen isotope records with existing records of hydrothermal iron release from the same ridge system,” said Kong. “We also compared against alternative explanations, including dust-borne iron, changes in oxygen-deficient waters, movement of the iron-limited zone, and nutrient changes carried from the Southern Ocean.”
The research found that phytoplankton in the eastern equatorial Pacific appear to have been fertilized by iron from the seafloor. During the last two transitions out of ice ages, phytoplankton in the eastern equatorial Pacific consumed more nutrients at the same times that hydrothermal iron emissions from the East Pacific Rise increased.
This timing supports a mechanism in which lower sea level enhanced mid-ocean-ridge volcanism, releasing more iron-rich hydrothermal fluids.“That iron could then spread through the ocean and be carried upward by mixing and upwelling into sunlit waters, where it stimulated plankton growth,” Wang said. “Other explanations—including dust-borne iron, shifts in the iron-limited zone, oxygen-deficient waters, and Southern Ocean nutrient changes—were less consistent with the data.”
The team also used ocean models to test whether iron released deep along the ridge could move upward toward sunlit waters.
Modeling work was performed by Boston University Assistant Professor Xiaozhou Ruan, a co-first author of the study, which revealed how material released at depth could disperse over time and move upward through the ocean.
“The ocean is not a static container,” Ruan said. “It is moving, mixing, and interacting with seafloor topography. Our modeling suggests that under stronger hydrothermal activity, iron released in the deep ocean could be transported to depths where upwelling and mixing make a connection to surface waters plausible.”
The project began as a test of dust-borne iron fertilization in the eastern equatorial Pacific, Wang said. But when the 200,000-year nitrogen-isotope record emerged, two strong deglacial peaks stood out, and more familiar explanations did not match the timing. The surprising turning point came when the team noticed that these peaks closely matched hydrothermal iron fluxes from the same sediment cores. That unexpected match shifted
the study toward seafloor volcanism as a driver of surface-ocean fertilization.
“This was a natural experiment created by Earth’s own climate cycles,” Wang said. “As sea level fell during ice ages, the pressure on mid-ocean ridge systems decreased, and previous studies suggested that it may have increased hydrothermal iron release during deglaciations.”
Additional BC co-authors of the report include former undergraduate student researcher Thomas C. Lee, Ting-Hsuan Lin, and Professor of Earth and Environmental Sciences Yi Ming, a climate scientist at BC’s Schiller Institute for Integrated Science and Society.
Next, researchers want to test whether the seafloor-to-surface fertilization occurred beyond the eastern equatorial Pacific, especially in the Southern Ocean, where nutrient use has a stronger effect on atmospheric carbon dioxide. The scientists plan to determine whether hydrothermal iron fertilization was a local phenomenon or a broader contributor to glacial–interglacial climate feedbacks.
Nature Geoscience
Experimental study
Ocean iron fertilization from enhanced mid-ocean-ridge volcanism due to ice-age sea-level falls
9-Jun-2026