The situation with these experiments is summed up as follows:
Researchers worldwide have conducted 13 major iron-fertilization experiments in the open ocean since 1990. All have sought to test whether stimulating phytoplankton growth can increase the amount of carbon dioxide that the organisms pull out of the atmosphere and deposit in the deep ocean when they die. Determining how much carbon is sequestered during such experiments has proved difficult, however, and scientists have raised concerns about potential adverse effects, such as toxic algal blooms. In 2008, the United Nations Convention on Biological Diversity put in place a moratorium on all ocean-fertilization projects apart from small ones in coastal waters. Five years later, the London Convention on ocean pollution adopted rules for evaluating such studies.
Because Oceaneos’s planned experiment would take place in Chilean waters, it is allowed under those rules. Riedijk says that the foundation will voluntarily follow international protocols for such studies; it is unclear whether that will allay fears that the group is promoting an unproven technology, rather than conducting basic research....
Whether it would help fisheries is a very moot point:
In the meantime, scientists say that it will be difficult to get solid data from the Oceaneos foundation’s planned experiment. The geology off the Chilean coast, and the patterns of currents there, create a mosaic of low- and high-iron waters. Anchovies, horse mackerel and other fish move freely between these areas.
And adding iron could shift the location and timing of phytoplankton blooms to favour fast-growing species, says Adrian Marchetti, a biological oceanographer at the University of North Carolina at Chapel Hill. One of those, the diatom Pseudo-nitzschia, produces domoic acid, a neurotoxin that can kill mammals and birds. Oceaneos’s experiment will probably increase plankton growth in low-iron waters, Marchetti says, “but it’s not to say that that is actually good for the higher levels of the food chain”.