A new study in Nature Geoscience shows that ice ages may have triggered volcanic activity on the ocean floor that fed plankton and pulled carbon from the atmosphere. Researchers at Boston College analyzed 200,000 years of sediment from the eastern equatorial Pacific. They found that as sea levels dropped during ice ages, pressure on mid-ocean ridges decreased. This increased volcanic activity and released iron into deep ocean waters. That iron then traveled upward through ocean mixing and upwelling to reach phytoplankton at the surface. The plankton used the iron to grow and absorb more carbon dioxide from the atmosphere. The study points to a previously unknown feedback loop linking sea level, seafloor volcanism, ocean biology, and atmospheric carbon. The researchers found two major peaks in nutrient use during the last two transitions out of ice ages. Those peaks matched periods of elevated hydrothermal iron release from the East Pacific Rise. The findings suggest that natural iron fertilization from seafloor volcanoes may have played a larger role in past climate cycles than previously understood. The next step is testing whether the same mechanism operated in the Southern Ocean, where changes in nutrient dynamics have a stronger effect on atmospheric CO2.
