This specification covers a Mark IIIB carbon dioxide (CO₂) removal plant, and test kit for the plant, capable of removing CO₂ from a submarine atmosphere and discharging this CO₂ overboard against variable submergence pressures. The CO₂ removal shall be accomplished by continuous absorption and desorption of the CO₂ in an aqueous solution of chelated monoethanolamine (MEA) (see 6.6).