Argument: Iron-fertilization favors some phytoplankton, destabilizing ecosystems

Issue Report: Geoengineering, iron fertilization of algae blooms


“A scientific critique of oceanic iron fertilization as a climate change mitigation strategy”. Greenpeace Research Laboratories. September 2007 – Ecological Concerns Results of mesoscale iron enrichment studies have generally shown that, after iron is added to HNLC waters, the initially predominant smaller phytoplanktonic species increase their growth rate. However, their growth soon becomes checked by the microzooplankton that consume them. The larger phytoplanktonic diatoms are initially low in abundance in the phytoplankton community but, upon the addition of iron, their growth rate also increases. However, unlike the smaller phytoplanktonic species, the diatoms bloom because they largely escape the grazing pressure of the mesozooplankton that
consume them and whose rate of replication is too slow to keep pace.

  • It is evident from mesoscale iron enrichment studies that, after iron addition to HNLC waters, the phytoplankton community commonly changes from one dominated by smaller phytoplanktonic species to one dominated by diatoms. This is of great concern from an ecological viewpoint because phytoplankton form the base of the marine food chain. Any changes in the phytoplankton community will have unknown and poorly predictable, but potentially highly damaging, impacts on marine ecosystems.