Science Advisory Report  2010/012

Ocean Fertilization: Mitigating Environmental Impacts of Future Scientific Research


  • Ocean fertilization has been proposed as a geoengineering method that in some regions of the world ocean may enhance ocean uptake of carbon dioxide from the atmosphere. The US National Academy of Sciences defines geoengineering as “options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry”.
  • Ocean fertilization represents one geoengineering approach undertaken by humans with the principal intention of stimulating primary productivity in the oceans. Fertilization proposals are loosely divided into 'micronutrient' and 'macronutrient' additions.
  • Addition of the micronutrient iron is by far the best studied artificial ocean fertilization technique; nitrogen is the most likely option for macronutrient fertilization.
  • Expected consequences of large-scale ocean fertilization include changes in phytoplankton community composition and food web structure, vertical export of biogenic material, reduction of subsurface oxygen, and production of climate active gases such as nitrous oxide.
  • Results from the ocean iron fertilization experiments conducted so far have not determined at what scale fertilization will result in persistent alterations of the ecosystem. However, there is scientific confidence that a “threshold scale” can be determined such that fertilization up to this scale would likely not cause persistent changes to an ecosystem.
  • Large-scale fertilization of coastal waters with nitrogen entails high ecological risks and potentially irreversible ecosystem disruptions.
  • The London Convention/London Protocol Draft Assessment Framework provides a mechanism for assessing, on a case-by-case basis, proposals for ocean fertilization to determine whether they represent legitimate scientific research.
  • It is recommended that there be an examination of the knowledge base for development and application of criteria for conducting environmental assessments of fertilization experiments, and for defining a "threshold scale" below which proposals could be exempted from a full assessment.
  • A concern over the capacity of a single nation to implement the Assessment Framework suggests that if possible an international body should be available to assist with assessments.
  • Fertilization experiments have been highly valuable for the study of the dynamics and functioning of ocean ecosystems and biogeochemical cycles, but it is unlikely that individual experiments will ever resolve critical questions about the long-term consequences of ocean fertilization for climate change mitigation.
  • Future scientific research on ocean fertilization should be encouraged to improve our understanding of the ocean’s response to nutrient addition.

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