The only geoengineering approach I see discussed in the media is this sulfur dioxide aerosol method. Does anyone know why seeding iron filings in the Southern O

The only geoengineering approach I see discussed in the media is this sulfur dioxide aerosol method. Does anyone know why seeding iron filings in the Southern Ocean doesn't get more consideration? That's always seemed a more straightforward route to me, and one that could be pursued more cautiously. For those that don't know, coccolithophores are single-celled phytoplankton that grow a calcium carbonate shell, of sorts. When they die, their shells sink to the ocean floor. It's posited that their population growth in the Southern Ocean is inhibited by the availability of iron in the water — the theory is that if you dumped some iron filings in the ocean, you'd get a coccolithophore bloom, sucking out carbon for their shells, and then sinking it permanently.