At a pH of ~8, the majority of dissolved inorganic carbon (DIC) exists as bicarbonate. Inorganic removal of a mole of HCO3- from surface seawater via precipitat

At a pH of ~8, the majority of dissolved inorganic carbon (DIC) exists as bicarbonate. Inorganic removal of a mole of HCO3- from surface seawater via precipitation of CaCO3 yields a mole of CO2 back to the atmosphere. Easier to fix CO2 via the classic silicate weathering reaction, which grabs 2 moles of CO2 per mole of silicate weathered (using CaSiO3 as a trivial example). This is the essential feedback from continental weathering: the Earth's thermostat.