Scientists outline case for next-generation ocean iron fertilization field trials
A view through the porthole during HOT-313 on the UH Research Vessel Kilo Moana. Courtesy of the Hawai'i Ocean Time-series Program.
A team of ocean and climate researchers is calling for a new generation of carefully designed ocean iron fertilization (OIF) field trials to determine whether this marine carbon dioxide removal (mCDR) method can safely and effectively leverage a natural ocean process to pull the greenhouse gas carbon dioxide (CO2) out of the atmosphere. Led by the Woods Hole Oceanographic Institution (WHOI), the authors, including two from the University of Hawai‘i at Mānoa, argue that larger, longer studies with rigorous monitoring and clear “go/no-go” safeguards, are needed to accurately assess OIF as a potential long-term CO2 storage solution to help mitigate human-induced climate change. The paper was published recently in Dialogues on Climate Change.
“The ocean science community must explore all possible means for reducing atmospheric carbon dioxide levels, and identify any unintended ecological consequences,” said David Karl, co-author, Victor and Peggy Brandstrom Pavel Professor of Oceanography and Director of the Center for Microbial Oceanography: Research and Education (C-MORE) in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). “Humans continue to pollute our planet, the time for bold action is now.”
In their peer-reviewed article, the authors note that past OIF field studies found that relatively tiny additions of iron in some parts of the ocean can stimulate the growth of small, plant-like organisms known as phytoplankton that live in the surface ocean. These organisms use sunlight and carbon dioxide dissolved in seawater to grow and multiply, which in turn pulls more carbon dioxide out of the atmosphere into the surface ocean in the process. However, those early experiments were not designed to assess the efficacy, durability, and feasibility of OIF, nor did they specifically evaluate the broader ecological and biogeochemical impacts of large-scale additions of iron.
The next generation of trials would need to be substantially larger and longer than prior studies to capture not only phytoplankton bloom development, but also the process of bloom decay, the fate of newly produced carbon, and any potential ecosystem impacts. The authors propose experiments lasting more than three to six months and spanning an area of about 1,000 square kilometers, with an explicit requirement to document a return to natural conditions after iron additions end as a core “go/no-go” criterion.
Tracking carbon export to the deep
A key objective they identify is to quantify the amount of additional carbon exported to depths beyond what would occur without intervention, largely through natural ocean processes. This “additionality,” as well as the durability, or length of time that carbon would be removed from the surface ocean, are key quantities that they argue need to be the focus of monitoring, reporting, and verification (MRV) systems. In addition, they point to the need for environmental MRV, or eMRV systems tracking ecological and biogeochemical responses to OIF.
“The only possible way to solve the climate crisis is to both cut emissions and pursue the widest possible range of science-based carbon dioxide removal strategies,” said lead author, Ken Buesseler, Executive Director of the ExOIS program and Emeritus Research Scholar at WHOI.
For an initial site, the authors point to the Gulf of Alaska in the Northeast Pacific as a promising location based on the region’s low-iron conditions, the availability of decades of research in the area at Ocean Station Papa, evidence of natural iron-driven blooms in the past, and physical characteristics that may help keep the iron-fertilized patch from dispersing too rapidly.
“The ocean is a dynamic environment, with nested scales of temporal and spatial variability in biological, chemical, and physical factors,” said Angelicque White, co-author and SOEST professor in Oceanography and C-MORE. “Ocean time-series, like the Hawai‘i Ocean Time-series and the work done at Ocean Station Papa, form a baseline by which to evaluate the efficacy of any perturbation experiments. Measuring carbon flux to the deep ocean is no small feat; it has taken decades of research to improve our methods for doing so. OIF experiments will highly need to leverage the deep knowledge base generated by time-series programs.”
Monitoring broader impacts and engaging with community
The field trial concept includes creating and tracking a large patch (on the order of 30–50 kilometers per side) of iron-fertilized surface ocean using established iron delivery methods, paired with modern ocean observation tools, surface drifters, autonomous vehicles, satellite-based sensors, and ship-based measurements of key oceanographic variables. The authors also outline predefined “off-ramps” designed to halt iron release or further experimentation if key environmental thresholds are approached or crossed. Although they were not seen in prior studies, potential concerns include deoxygenation, production of other greenhouse gases, or the onset of a harmful algal bloom. In addition, they emphasize the critical importance of engaging key coastal communities and rightsholder groups near the region of iron fertilization and to consider concerns and input as part of the experimental design.
“In addition to a rigorous science plan, it is important to see that community outreach and engagement are considered early in the process, with impact assessment plans laid out in an open and transparent manner following international protocols for OIF research on the high seas” said Brad Warren, CEO of Global Ocean Health.
Portions of this content are courtesy of WHOI.