I hate to burst your bubble but ...
I hate to burst your bubble, but the story about the guy who dumped iron off the coast of BC in 2012 is full of holes. We can start with his claim about the size of Fraser River salmon run. Reputable news reports put it at about 21 million, not 72 million as he claimed. There were 72 million was for all of BC, but that is quite a different matter from claiming 72 million for the Fraser River run alone.
The other hole is that the area he dumped the iron in is not nutrient poor. Ocean currents carry nutrients from land and produce phytoplankton blooms, and he dumped his iron right in the middle of one of the richest of these.
There was an exceptionally large salmon run for BC in 2014, but it was due to two factors. One was that salmon populations go in cycles, and 2010 (two years before the iron dump) was an unusually good year. They laid a lot of eggs and the 2014 run is their progeny returning. So in other words, it was due to events which took place 2 years before he dumped iron in the ocean. This larger return was predictable based on existing records, so it should have come as no surprise. I'm getting the feeling though that claiming credit for predictable natural phenomenon is part of his business plan.
The other cause was that unusually warm waters in the Pacific drove the salmon north from US waters into Canada. Salmon don't like warm water and are sensitive to changes of even a couple of degrees. The Americans were left with empty nets while the Canadians got all the fish. Normally, half of the run would go to the US, so warmer ocean temperatures effectively doubled the size of the BC run without actually increasing the total number of fish in the ocean, aside from the above mentioned increase due to the good year in 2010.
Oh but wait, warmer ocean temperatures disrupting fishing? Am I allowed to mention that here?
As for seeding the oceans with iron as a solution for global warming, the Quirks and Quarks podcast (highly recommended, by the way) had an interview with one of the scientists a while ago. His or her (I can't remember which) conclusion about it was that while it may possibly be worth while for increasing fish yields (more research is required to answer that), as a solution for locking up CO2 to prevent global warming it was a drop in the bucket. Very few areas of the ocean are actually limited by lack of iron, and those are mainly near Antarctica. When they did add iron, there was a limited effect because there are so many other bottlenecks to ocean phytoplankton growth.