Climate-driven changes to the distribution of micronutrients across the global ocean may reduce the efficiency iron delivery to marine habitats, weakening the base of marine food chains, new research has warned. Crucially, over time this could mean fewer krill and fewer whales, seals, and penguins.

Marine phytoplankton are tiny algae that sit at the very bottom of ocean food webs. These organisms rely on iron, a vital micronutrient, to grow and function. Iron reaches the oceans mainly through airborne dust from deserts and dry regions, as well as through meltwater released by glaciers.

The research – led by scientists from Rutgers University – shows that when iron is scarce, phytoplankton waste energy and photosynthesis falters. In turn, the phytoplankton grow more slowly, capture less sunlight, and remove less carbon dioxide from the atmosphere. 

To gain an understanding of real-world conditions, lead author Heshani Pupulewatte spent 37 days at sea in 2023 and 2024. During the voyage she measured fluorescence, which reflects the energy released by phytoplankton when photosynthesis breaks down. She also added nutrients to see if photosynthesis resumed when conditions were restored.

The results showed that when iron was scarce, as much as 25% of the proteins that capture the light become “uncoupled” from the structures that convert energy into usable chemical forms. This disconnect reduces how efficiently phytoplankton can photosynthesise.

Encouragingly, when iron became available again, the algae were able to reconnect these systems.

Paul G. Falkowski, one of the study’s co-authors, said that growing evidence indicates that climate change is reshaping ocean circulation patterns and reducing the amount of iron delivered to the sea. This, he says, could have serious consequences for marine ecosystems.

“Phytoplankton are the primary source of food for krill, the microscopic shrimp that are the main source of food in the Southern Ocean for virtually every animal, including penguins, seals, walruses and whales,” said Falkowski. “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 added.

Scientists are now looking to gain a deeper understanding of how iron controls photosynthesis at the molecular level. Pulpewaite has suggested that by deciphering nature’s clues into this process, researchers could better anticipate changes in ocean productivity as well as shifts in the global carbon cycle.

Click here for more from the Oceanographic Newsroom.