One such approach involves the addition of otherwise scarce (limiting) nutrients to surface ocean waters to manipulate marine biological production, thus
Page 9 OCEAN CARBON DIOXIDE REMOVAL METHODS NRDC EDF OCEAN CONSERVANCY Ocean Fertilization: At a Glance Marine plants and algae, like phytoplankton, take up CO2 during photosynthesis, and this can increase the ocean’s uptake of atmospheric CO2. 42 Technical Readiness: OF experiments using iron in the 1990s and 2000s confirmed that fertilization does induce phytoplankton blooms and carbon capture, but scientists found that only some of these blooms led to longer-term carbon storage or atmospheric CO2 drawdown beyond already naturally occurring processes. 49 Page 10 OCEAN CARBON DIOXIDE REMOVAL METHODS NRDC EDF OCEAN CONSERVANCY 36 National Academies of Sciences, Engineering, and Medicine (hereinafter NASEM), A Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration (Washington, D.C.: National Academies Press, 2022), https://doi.org/10.17226/26278.
Iron-based fertilizer may stimulate plankton to pull carbon dioxide from the ocean, driving a carbon-negative process.
• 1988: Fe fertilization proposed as a method of “curing” greenhouse effect (Gribbin, J., Nature 331, 570, 1988) • 1990 Martin suggests iron instrumental in causing lower atmospheric CO2 concentrations in glacial time. • Open ocean diatoms have an Fe-limited C:Fe ~3 x 105 • However, the ratio of phytoplankton C sequestered to Fe added is much lower than this in Iron enrichment experiments: • Ironex II: C:Fe = 3 x 104 (fixed, not necessarily sequestered) • SOIREE: 0.2 - 0.8 x 104 • SOFEX 0.7 x 104 (sequestered below 100m, Buessler etal) • Fe may be used more efficiently – By larger-scale, longer time fertilizations?
Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration.
# Ocean Iron Fertilization: A Promising Path for Carbon Removal? As a marine radiochemist and the director of the non-profit Exploring Ocean Iron Solutions (ExOIS), Dr. Buesseler shared insights on how adding small amounts of iron to the ocean could amplify its natural ability to store carbon, the potential impacts on marine ecosystems, and the path toward responsible research. When scientists compared different climate models' predictions of natural carbon flux in the ocean, the estimates ranged from 5 to 12 billion tons per year. Every marine carbon dioxide removal approach, whether it involves adding minerals, growing seaweed, or fertilizing with iron, will change ocean conditions. We need roughly 5 to 10 billion tons per year of carbon dioxide removal alongside dramatic emissions reductions to address climate change. Ocean iron fertilization might contribute 1 to 2 billion tons annually if deployed widely, though much more research is needed to confirm these estimates and assess full-scale impacts.
DEEP-OCEAN STEWARDSHIP INITIATIVE Fig. 1 Elements of the biological pump (Fig. 1 From McClain (2010) American Scientist) Deep Ocean Climate Intervention Impacts Deep Ocean Climate Intervention Impacts Ocean Fertilization Key Points DECEMBER 2021 Policy Brief Page 2 DOSI Scaling and Effectiveness The subarctic Northern Pacific, Eastern Equatorial Pacific and Southern Ocean are high-nutrient, low-chlorophyll regions where iron scarcity limits phytoplankton growth, and thus have been proposed for OIF (Yoon et al., 2018, GESAMP, 2019). The alteration of natural phytoplankton communities may result in changes in the seasonality of particulate organic carbon flux to the deep-sea floor (benthic-pelagic coupling) and in compositions of phytoplankton species in the marine snow, potentially impacting deep-sea benthic communities that rely on food from the ocean surface (Billet et al., 1983; Gooday, 1988; Graf, 1989; Ruhl and Smith, 2004; Nomaki et al., 2021).
Ocean fertilization could enhance atmospheric CO2 removal by increasing biological productivity, namely by stimulating the growth of