To try and rationalize the behaviour of CO2 inside the gas chamber shown in Figure is depleted of bicarbonate (and consequently of CO2), then CO2 can diffuse into the channel from the gas chamber, effectively adsorbing CO2. This also explains why CO2 is depleted more strongly in the bottom channel, since here there is no direct influx of CO2 from the gas chamber. When bicarbonate accumulates in the top channel, then an excess of CO2 is produced, resulting in a CO2 flux into the gas chamber, thereby desorbing the CO2.