A new study in Nature Geoscience finds that falling sea levels during ice ages may have triggered more volcanic activity on mid-ocean ridges, releasing iron that fertilized plankton in iron-limited ocean regions. Researchers at Boston College analyzed 200,000-year sediment records from the eastern equatorial Pacific and found that during deglaciations, increased hydrothermal iron from the East Pacific Rise coincided with higher nutrient consumption by phytoplankton. This suggests a natural feedback loop where sea level, seafloor volcanism, ocean biology, and carbon storage are connected. The study used nitrogen isotopes in fossil foraminifera shells to track past nutrient use and ocean models to show how deep-sea iron could reach sunlit surface waters. The findings challenge the assumption that windblown dust is the main iron source for ocean fertilization. While the research does not test deliberate carbon dioxide removal, it highlights a natural mechanism that may have helped lower atmospheric CO2 during past climate shifts. The team plans to investigate whether this effect occurred in other regions like the Southern Ocean.
