Carbon partition and atmospheric water abundance

In hot hydrogen-rich thermochemical equilibrium, much carbon can be bound in carbon monoxide, consuming oxygen that is unavailable for water. At a C/O ratio near or above one, water can be strongly depleted. Cooler methane-dominated chemistry can release more oxygen for water at the same elemental inventory. Pressure, quenching, dissociation and atmospheric photochemistry can modify this temperature-dependent partition.