i would still like to know what "controlled experiments" exist. Has anyone done the studies to show it is not worth the while, eg that it does not remove carbon? Although just not removing carbon does not say seeding is not beneficial, carbon neutral aqua culture would be quite beneficial.

There are some natural experiments: the Sahara feeds the Amazon, and the Gobi feeds the Pacific ... Perhaps more directed seeding would be more beneficial. We will never know unless we actually study, or try.