Fertilize the Oceans to fight global warming
People are worried about C02 in the atmosphere released by the burning of fossil fuels. Most of the carbon near the Earth's surface is not in the air, in plants or in fossil fuels. It is in limestone deposited at the Sea bed. More carbon is fixed on land than in the Sea, but carbon fixed on land ends up back in the atmosphere as plants are eaten and metabolized by animals, fungi and bacteria. Some of the Carbon fixed in the Sea goes away forever. Also even if it is swimming or floating around it is not in the atmosphere.
Increased carbon fixation in Oceans would reduce global warming.
The limiting factor for carbon fixation in Oceans is generally believed to be Phosphorus. Marine ecosystems are rich or poor based on the amount of minerals in the water, more photosynthesis occurs the sometimes frozen North and Far South Seas than near the equator, because the melting and freezing stirs up sediment from the bottom and rock powder from glaciers fertilizes the sea.
How about dumping phosphorus in mineral poor equatorial waters ?
44-46% phosphate fertilizer costs $ 418/ton see table 7. Phosphate is about one third phosphorus by Weight (P weighs about 31, 4 Oxygens each 16 plus two hydrogens so 31 out of 97 Phosphorus. The fertilizer is about 14% Phosphorus, so the Phosphorus costs about $ 2,972 per English ton or about $ 3,269.2 per metric ton or about 2,200 Euro per metric ton (ouch).
Phytoplankton contains roughly 106 times as much Carbon as Phosphorous (by number I'm afraid) so roughly 42 times as much be weight. Assuming the phosphorus is not wasted until it falls to the bottom with the carbon, the cost per pound of Carbon fixed would be about Euro 52 per ton of Carbon fixed.
OUCH. The current price of a Carbon emission credit is 20 Euros a Ton.
However, there is hope, because this guy says that the relevant limiting element is Nitrogen not Phosphorous.
Also a problem with pesciculture is that the food (digested and excreted or otherwise) for the fish in cages "enrich" the water around them excessively causing algae blooms. This would be a good thing if it happened in the open Ocean. This would not be economical given how storms would occasionally smash the cages and liberate the fish, but might work with a subsidy justified by the role of the waste in fixing Carbon.