The 'Geritol solution' is the idea that supplementing low-iron areas of the world's oceans could allow existing oceanic cyanobacteria's iron-requiring nitrogenases to fix the nitrogen (from dissolved gaseous nitrogen) needed to fix the carbon (from dissolved atmospheric carbon dioxide) needed to reverse the climate crisis. Now that may not be needed.
Biotechnology is beginning to successfully design enzymes. A newly-designed nitrogenase which needed either no metal ion, or needed a metal cation which is more prevalent in the oceans than iron could induce enormous carbon fixation and a rebound in oceanic life, including deepwater fisheries like tuna, if that new nitrogenase was active in widespread cyanobacteria.
Such a nitrogenase, if widespread in cyanobacteria, might help to fix atmospheric carbon at rates that could restore temperature homeostasis on earth, without depriving the biosphere of sunlight energy like shading the earth with satellites or stratospheric smog would. Instead, this approach would increase the amount of sunlight energy entering the biosphere, and thus the amount of living beings and biomass on earth.
But there are risks that increased nitrogenase activity in the deep oceanic iron-poor areas could lead to such increased methane emissions, itself an greenhouse gas, that the climatic crisis would be worsened. Also, contrarily, so much carbon dioxide might be removed that the greenhouse effect might be reduced below levels earth's living being need to survive. It is probable that spreading a non-iron nitrogenase wold be an irreversible step. Therefore careful research is needed.