Microscopic algae in the ocean, vital for producing much of Earth's oxygen, depend on iron to fuel photosynthesis, according to new research from Rutgers University. When iron is limited, these phytoplankton waste energy, potentially disrupting marine food chains amid climate change. Field studies in the Southern Ocean highlight how this micronutrient shortage could lead to declines in krill and larger marine animals like whales and penguins.
Phytoplankton, tiny marine algae at the base of ocean ecosystems, generate a significant portion of the oxygen humans breathe through photosynthesis. This process requires iron, sourced primarily from desert dust and glacial meltwater. A study published in the Proceedings of the National Academy of Sciences reveals that iron limitation causes inefficiencies in energy use, slowing oxygen production and carbon capture.
"Every other breath you take includes oxygen from the ocean, released from phytoplankton," explained Paul G. Falkowski, a co-author and the Bennett L. Smith Chair in Business and Natural Resources at Rutgers-New Brunswick. "Our research shows that iron is a limiting factor in phytoplankton's ability to make oxygen in vast regions of the ocean."
To investigate real-world effects, lead author Heshani Pupulewatte conducted fieldwork over 37 days in 2023 and 2024 aboard a British research vessel. The expedition traversed the South Atlantic Ocean to the Weddell Gyre's ice zone and back, starting from the South African coast. Using custom fluorometers developed in Falkowski's lab, Pupulewatte measured fluorescence in phytoplankton samples, indicating energy waste during iron stress.
Findings showed that under iron scarcity, up to 25% of light-capturing proteins decouple from energy-conversion structures, leading to excess fluorescence and reduced efficiency. Adding iron to samples restored connectivity, boosting photosynthesis. "We demonstrated the results of iron stress on phytoplankton out in the ocean, without even bringing back samples to the lab," Pupulewatte noted.
Climate-driven changes, such as altered ocean circulation, may decrease iron inputs, Falkowski warned. This could diminish phytoplankton growth, affecting krill populations and, in turn, predators like seals, penguins, and whales. "When iron levels drop and the amount of food available for these upper-level animals is lower, the result will be fewer of these majestic creatures," he said. The research underscores iron's molecular role in sustaining ocean productivity and the global carbon cycle.