Wind blown dust from desert regions regularly fertilizes the oceans. So this is a natural process we can study and decide whether its effects are desirable before making a decision. It is not as unnatural as some correspondents have painted it. Iron filings seem the least likely ingredient though. Better to use iron rich rock, ground down and transported in bulk carriers to deposition sites in the oceans. Why use all that energy to refine the iron first . Just follow the natural process. It would still take significant amounts of energy to grind the rock and transport it which would have to be weighed into the equation to see the net benefit to CO2 levels.

A technological approach would be to salinate the waters of the North Atlantic. The point in the North Atlantic circulation that is breaking is the sinking of the cooling water in polar regions to the ccean floor for its return to the equatorial regions. The melting of freshwater ice in Greenland dilutes the salinity of the North Atlantic and makes the water too buoyant to sink, even though its cold. We could carry large amount of mined rock salt into the area using bulk carriers. Longer term we could build a pipeline from nearby regions where there is rock salt (eg. Cheshire UK) and pipe brine from these into the area of the North Atlantic where its going to do some good.