Rutgers marine scientists use tools created in New Jersey to quantify how iron stress in Southern Ocean phytoplankton slows the process of converting light energy into oxygen
The next time you breathe, consider this: photosynthesis of algae, powered by iron dust in the ocean, made it possible.
Now, a new Rutgers University study published in the Proceedings of the National Academy of Sciences pulls back the curtain on this vital process.
Iron is a critical micronutrient for marine phytoplankton, the microscopic algae that form the foundation of the ocean's food webs. It is deposited into the world's oceans as dust from deserts and arid areas as well as from glacial meltwater.
"Every other breath you take includes oxygen from the ocean, released from phytoplankton," said Paul G. Falkowski, the Bennett L. Smith Chair in Business and Natural Resources at Rutgers-New Brunswick and a co-author of the study. "Our research shows that iron is a limiting factor in phytoplankton's ability to make oxygen in vast regions of the ocean."
When iron is absent or reduced, photosynthesis - the process of turning light energy into chemical energy, with oxygen as a byproduct - is slowed or halted. This limits the growth of these organisms and affects how efficiently they capture sunlight and remove carbon dioxide from the atmosphere.
Evidence suggests climate change is altering patterns of ocean circulation and reducing iron deposition, Falkowski said. While humans can still breathe easily - reduced iron levels in the world's oceans won't mean that humans will suffocate - the trend could have significant effects on marine life, he said.
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.
Paul Falkowski
Bennett L. Smith Chair in Business and Natural Resources
"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," Falkowski said. "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."
Researchers have long suspected that iron is crucial to photosynthesis, but little is known about how the process is affected in nature. Most previous studies have been conducted only in the laboratory.
To address this gap, Heshani Pupulewatte, a graduate research assistant in the Department of Chemistry and Chemical Biology conducting research in Falkowski's lab and lead author of the study, spent 37 days in 2023 and 2024 aboard a British research vessel sailing through the South Atlantic Ocean and Southern Ocean, covering a transect from the South African coast to the marginal ice zone of the Weddell Gyre and back.
Using custom fluorometers built by Max Gorbunov from the Falkowski Lab on Cook Campus in New Brunswick, Pupulewatte tested samples for fluorescence - a measure of energy re-released by phytoplankton when the photosynthesis process breaks down. She then added nutrients to samples collected along the route to determine if doing so could restart the photosynthesis process.
"We wanted to know what really happens to the energy transfer process at the molecular level of phytoplankton in natural environments," she said.
What she found was that iron limitation causes up to 25% of light-harvesting proteins to become "uncoupled" from the energy-producing centers, effectively reducing energy conversion. When iron is resupplied, phytoplankton reconnect their internal light-harvesting systems, improving their efficiency and potential for growth.
"We demonstrated the results of iron stress on phytoplankton out in the ocean, without even bringing back samples to the lab to perform molecular extractions using fluorescence measurements carried out at sea," she said. "By doing so we were able to show that much more energy is wasted as fluorescence when iron is limiting."
Understanding how iron influences photosynthesis at the molecular level could help scientists predict future ocean productivity and global carbon cycles, she added.
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