The density of carbon in seawater is also higher much than it is in air. The relative concentration of bicarbonate in seawater is a few times lower than in air

The density of carbon in seawater is also higher much than it is in air. The relative concentration of bicarbonate in seawater is a few times lower than in air (as % by mass), but because water is nearly 1000x the density of air the true amount of bicarbonate there per volume is much higher.