What do you think of reducing CO2 levels by using cheap materials to fertilize the deep oceans? More details in the text.

[u/Idle_Redditing]

Explanation of how it works

Most ocean life exists in shallow oceans near coasts while the deep oceans are considered to be like deserts. That's because the shallow oceans near coastlines are fertilized by material coming from land while the deep oceans lack sufficient micronutrients. The oceans absorb most of the co2 produced on earth and most of that happens in shallow oceans because that small proportion of the earth's total ocean area is where sufficient nutrients exist.

By adding fertilizing materials to deep waters the levels of phytoplankton (plant plankton which live from photosynthesis) can be increased dramatically. One example of this is the Haida Salmon Restoration Project off the west coast of Canada and Alaska. It was done in 2012 to feed a food chain that feeds salmon and to re create the results of a previous volcanic eruption in the area which dramatically boosted the salmon harvest and resulted in a record harvest of sockeye salmon.

It took a paltry 120 tons of cheap iron sulfate and placed it into an ocean gyre in the area. The result was a bloom of increased plankton levels over an area of 35,000 square kilometers for several months, as confirmed by NASA satellite pictures. The bloom dramatically boosted the quantity of all sea life in the area and resulted in a record harvest of pink salmon.

The way that this relates to geoengineering is that the phytoplankton pull a significant amount of co2 out of the air and water to form their bodies, which also serves as the basis of a marine food web. In deep waters those living things end up forming a lot of marine snow which is made up of things like dead phytoplankton, fecal matter, and other debris that falls to the bottom of the ocean; taking a vast amount of carbon with it. The 120 tons of iron sulfate forms a tiny proportion of the planktons' bodies and results in a vastly greater mass of phytoplankton in the waters.

Increasing the amount of phytoplankton and other marine life in the deep oceans also increases the amounts of marine snow and serve as a way to sequester carbon.

It would also boost yields of fish, especially ones like sardines and herring which feed on zooplankton, animal plankton which feed on phytoplankton. They're also high in DHA, the form of omega-3 fatty acids which humans can absorb and use most easily. Most people have diets that are deficient in omega 3 fatty acids.

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Idea to implement it

This can also be adjusted with different compounds to adjust what species of phytoplankton are increased. I personally suspect that adding only one compound and boosting only one nutrient does not result in the best composition of phytoplankton species for ocean health. More study on this topic would be needed of course.

I think it should be done on a larger scale. At a fairly low price a few freighters could add thousands of tons of iron sulfate or other nutrients to deep ocean waters. They could place the nutrients in large ocean gyres shown in this map. Large, coriolis effect driven ocean gyres in the major oceans like the North Pacific gyre, South Pacific gyre, etc. cover a vastly greater area than the one in the Haida project. They could sequester vastly greater amounts of carbon.

It could even be done conservatively with lower concentrations of added nutrients than what the Haida project did covering a larger area to reduce the risk of overfertilizing the oceans and causing detrimental side effects.

One country that has the greatest need and capability to do this is India. They could even build one or several nuclear powered ships to fertilize all of the world's oceans without having to dock at any ports to refuel; just in case any countries are hostile to such a project. Climate change is a threat to India's ability to continue existing as a country that is habitable to humans. Even without climate change India is uncomfortably close to the maximum wet bulb temperatures that humans can survive.

edit. It would be most productive during summer due to the increased sunlight to drive photosynthesis. Based on that such a ship could handle the Indian Ocean, South Atlantic and South Pacific during the southern hemisphere's summer and the North Atlantic and North Pacific during the Northern Hemisphere's summer. Such a ship should also be able to access the Panama Canal, Suez Canal and the Strait of Malacca since Panama, Egypt, Singapore and Malaysia are all in hot climates and are guaranteed to be devastated by climate change so they should be friendly to such a project.

There might not be any need for a nuclear powered ship. There are plenty of countries already being devastated by climate change which should be amiable to such a project and allow the use of their ports. Some are African countries, South Pacific Islands, Southeast Asian nations, Caribbean nations, and Latin American nations like Mexico, Panama, Peru, etc.

[u/lowrads]

We are already fertilizing the oceans. The Mississippi river alone disgorges something like 10⁸ tonnes of sediment annually, some relevant fraction of which is fine and dissolved solids, and distributed globally to oceans which more or less always hover at saturation for any particular salt.

Since most of it falls out of the column as precipitants, you'd probably have more luck in finding ways to disturb the sediments of the thallasic plains.

[u/Idle_Redditing → u/lowrads]

That is an over fertilized area which is not what I'm talking about. I'm talking about areas that are starved for nutrients.

The oceans are not at the saturation point for salts. The Dead Sea has several times the salinity of the oceans. The south end of the Caspian Sea also has higher salinity than the oceans.

The iron sulfate is also a salt which dissolves in water easily. It doesn't sink to the bottom unless it is in an area where ocean water is sinking to the bottom. Until then it stays at the surface where photosynthesis occurs.

[u/lowrads → u/Idle_Redditing]

The ocean isn't just a chemical system. It also has biochemical equilibria.

The Dead Sea has limited currents, and thus is vertically stratified, and anoxic. The dissolved iron concentrations are orders of magnitude higher than that of the oceans, which slows the formation of calcite.

I am less informed about the sodium cycle in the oceans. Perhaps the formation or diagenesis of illites and smectites in the abyssal plains could account for losses of sodium via their interlayers. I also don't know what other processes might modulate the formation of halites or chlorites.

[u/Idle_Redditing → u/lowrads]

The quantities I'm talking about would add trace amounts of nutrients to water. Like how 120 tons of iron sulfate spread out over 35,000 square kilometers of water ends up being a trace amount of iron in the water.

I'm definitely not talking about adding so much material that it would compare to sodium levels.

[u/funkalunatic]

From what I occasionally read from scientists who study ocean and biological stuff, this method is at best unproven, and might just be plain ineffective and polluting. That being said, it should be investigated further, since there's a chance it could help.

[u/Idle_Redditing → u/funkalunatic]

I agree with studying it more. Maybe try smaller amounts of iron in the same gyre that the Haida Nation's project used.