Ocean iron fertilization from enhanced mid-ocean-ridge volcanism due to ice-age sea-level falls

Iron fertilization in high-nutrient, low-chlorophyll regions has been proposed to boost phytoplankton growth and enhance oceanic CO2 sequestration. While dust has long been recognized as a primary external iron source to these waters, recent discoveries highlight hydrothermal activity along mid-ocean ridges as a substantial contributor of iron to the deep ocean. However, it remains unclear whether hydrothermal iron directly impacts upper-ocean productivity. Pleistocene glacial cycles provide a natural test because previous studies suggest that sea-level falls during ice ages led to several-fold increases in hydrothermal activity and iron emissions during glacial deglaciations. Here we compare 200,000-year records of phytoplankton nutrient consumption in the iron-limited eastern equatorial Pacific (reconstructed from foraminifera-bound 15N/14N) with records of hydrothermal iron emissions from the underlying East Pacific Rise mid-ocean ridges. Beginning just before the last two terminations, increases in East Pacific Rise hydrothermal activity coincide with higher eastern equatorial Pacific nutrient consumption, consistent with direct iron fertilization by enhanced ridge volcanism. If corroborated in other iron-limited regions such as the Southern Ocean, this would suggest a broader Earth system feedback linking sea level, ridge volcanism, ocean carbon sequestration, atmospheric CO2 and climate across glacial cycles. Increased hydrothermal iron inputs from mid-ocean ridges, triggered by ice-age sea-level falls, supported higher surface primary productivity during the last two glacial terminations, according to proxy records of nutrient consumption in the eastern equatorial Pacific Ocean.