There was an interesting pilot study done in the tropical pacific a decade or so ago. (BTW, tropical waters are clear because they're nutrient-poor, everything is tied-up and thus, unavailable for phytoplankton, the base of the pelagic food pyramid).

So some folks thought, what if we provide tropical algae with the limiting nutrient, would it spark an algal bloom, increase photosynthesis, and thus facilitate carbon sequestration?

So they loaded a small vessel with iron ore and sailed into the equatorial waters of the Pacific and let fly the iron ore over a huge area. Sure enough, phytoplankton bloomed like crazy, zooplankton entered a feeding planktonic populations enetered exponential growth providing a food surplus for filter feeders, etc. The end product was lots of fishy doo-doo raining down upon the abyssal depths, locked into the organic mud of the sea floor.

Also, there's this business of giving power companies carbon credits for reforestation. In this instance power companies plant trees or pay folks to plant trees and everybody agrees not to harvest them for some number of years. Trees are carbon. So, when you harvest the trees the wood goes into construction and gets locked into buildings for decades longer.

Finally, some of the greatest carbon sinks on the planet are the marshy estuaries of the temperate regions. For example in my area 30 to 60 percent of the outer coastal marsh is organic mater locked-up at slow decomposition rates in marsh peat. By enhancing marsh formation you get pollutant filtration, wildlife and fish habitat, tropical storm protection and carbon sequestration. I should also mention that when you allow marsh to be destroyed you lose each of those benefits.

B