Ocean Iron Fertilization and Potential Toxic Diatom Production

A new study on the potential impacts of ocean iron fertilization (OIF), one of the potential “long wave” geoengineering options, has been published this week inĀ  PNAS: Trick, et al., Iron Enrichment Stimulates Toxic Diatom Production in High-Nitrate, Low Chlorophyll Areas, PNAS Early Edition (March 15, 2010) (open access).

The researchers examined the potential impact of stimulation of the growth of toxigenic diatoms, and its conclusions should give proponents of geoengineering further pause about pursuing OIF as one of the potential schemes for adoption. Among the take-aways from study:

  1. In most of the OIF experiments to date, large diatom blooms generated by the experiments have been predominated by Pseudonitzschia, a species that has the capacity to produce the potent neurotoxin, domoic acid (DA), a toxin that has generated massive toxic harmful algal blooms in coastal waters.
  2. While past OIF experiments failed to find measurable quantities of DA, this may have been due to the use of laboratory cultures that may mask this potential impact;
  3. Bottle-type growth experiments introducing iron and copper amendments resulted in increases of DA by approximately 160% relative to unamended control bottles. Although these levels might not be high enough to generate acute toxicity, it’s unclear whether higher concentrations could result from the persistent introductions of iron that would occur with large-scale deployment of OIF. This threat might be further pronounced by the fact that whereas all mesoscale enrichment experiments to date have used expensive reagent-grade iron substrates, it’s likely that OIF would use industrial-grade iron substrates that may contain copper or other trace metals that would enhance bloom toxicity;
  4. Large-scale OIF could yield DA toxin levels that have been heretofore sufficient to close shellfish fisheries and cause acute toxic effects in seabirds and marine mammals in near-shore waters;
  5. Toxic diatom blooms could have impacts on stressed fisheries that depend on High Nutrient-Low Chlorophyll regions, the regions where OIF operations would occur.

Lots of potential discussion could flow from this article, including:

  1. How do we weigh potential risks of geoengineering strategies against harms that might occur under a business as usual emissions scenario?
  2. Is there any downside to continue to permit small-scale OIF experiments?
  3. Would it be possible to develop an effective compensation mechanism that would permit us to deploy OIF if we become desperate in the future in terms of potential impacts of climate change while still ensuring that those that might be injured by OIF would have redress for damages?
  4. Should we have more trepidation about geoengineering strategies that might be largely driven by private companies seeking carbon credits, vs other potential geoengineering strategies, e.g. sulfur injection or cloud seeding that likely would be developed by governments?

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