Ken Buesseler ^1* Daniele Bianchi ² Fei Chai ³ Jay T. Cullen ⁴ Margaret Estapa ⁵ Nicholas Hawco ⁶ Seth John ⁷ Dennis McGillicuddy ¹ Paul J. Morris ^1* Sara Nawaz ⁸ Jun Nishioka ⁹ Anh Pham ² Kilaparti Ramakrishna ¹ David Siegel ¹⁰ Sarah Smith ¹¹ Deborah K. Steinberg ¹² Kendra A. Turk-Kubo ¹³ Benjamin Twining ¹⁴ Romany Webb ¹⁵ Mark Wells ⁵ Angelicque White ⁶ Peng Xiu ³ Joo-Eun Yoon ¹⁶

• ¹ Woods Hole Oceanographic Institution, Woods Hole, United States
• ² University of California, Los Angeles, Los Angeles, California, United States
• ³ Xiamen University, Xiamen, Fujian Province, China
• ⁴ University of Victoria, Victoria, British Columbia, Canada
• ⁵ University of Maine, Orono, Maine, United States
• ⁶ University of Hawaii at Manoa, Honolulu, Hawaii, United States
• ⁷ University of Southern California, Los Angeles, California, United States
• ⁸ American University, Washington, DC, Washington, United States
• ⁹ Hokkaido University, Sapporo, Hokkaidō, Japan
• ¹⁰ University of California, Santa Barbara, Santa Barbara, California, United States
• ¹¹ Moss Landing Marine Laboratories, Moss Landing, California, United States
• ¹² William & Mary's Virginia Institute of Marine Science, College of William & Mary, Gloucester Point, Virginia, United States
• ¹³ University of California, Santa Cruz, Santa Cruz, California, United States
• ¹⁴ Bigelow Laboratory For Ocean Sciences, Boothbay, Maine, United States
• ¹⁵ Columbia University, New York City, New York, United States
• ¹⁶ Korea Polar Research Institute, Incheon, Republic of Korea

There are many approaches to marine carbon dioxide removal (mCDR), of which ocean iron fertilization (OIF) has the longest history of study. However, prior OIF studies were not designed to quantify the durability of carbon (C) storage, nor how wise OIF might be as an mCDR approach. To quantify C sequestration, we introduce a metric called the “centennial tonne”, defined as 1000 kg of C isolated from atmospheric contact for at least 100 years. We set forth the activities needed to assess OIF from a scientific and technological perspective, and additionally, how it might be responsibly studied and potentially deployed. The 5 activities include: field studies in the Northeast Pacific; improved modeling for field studies, data assimilation and predictions at larger scales; improvements in monitoring, reporting and verification (MRV) for C, but also eMRV for tracking ecological and environmental impacts; and developing new iron sources and their delivery, to increase efficiencies and reduce costs. The fifth activity is to understand whether public and community support exists for OIF, and what governance structures might support further research and possible deployment of OIF. This article is written by a multidisciplinary experts group called Exploring Ocean Iron Solutions (ExOIS) that is organized around a responsible code of conduct. Of the mCDR approaches, OIF has the potential to be low cost, scalable, and rapidly deployable. There is an urgency to decide under what conditions OIF might be deployed or not. Now is the time for actionable studies to begin.