My guess would be 'very'. Dead plankton will fall to the floor of the ocean and will be removed from circulation that way. After all, that is how the oceans were cleared from iron sulphate in the first place.
Only a tiny part of the dead plankton will make it to the bottom, most falls apart in the top layers and the CO2 will stay in circulation. The effect is tiny, thus it takes a long time to naturally have an influence.
Comments
My guess would be 'very'. Dead plankton will fall to the floor of the ocean and will be removed from circulation that way. After all, that is how the oceans were cleared from iron sulphate in the first place.
Only a tiny part of the dead plankton will make it to the bottom, most falls apart in the top layers and the CO2 will stay in circulation. The effect is tiny, thus it takes a long time to naturally have an influence.