Re: What is the abundance of CO2 in hydrosphere, atmoshere, rocks...?

In the atmosphere, CO2 at present constitutes about 360 parts per million 
(0.036%) by volume, which amounts to 540 parts per million (0.054%) by 
weight.

The total mass of the atmosphere is about 5.2 x 10^15 tonne, meaning that 
2.8 x 10^12 tonne of CO2 is stored in the atmosphere.

In the oceans, CO2 is mostly present as bicarbonate ion HCO3-. If we assume 
that it was all turned into CO2 by decreasing the pH of the oceans, it 
would amount to about 110 parts per million (0.011%) by weight.

The total mass of water in the oceans, which is over 99% of all water on 
the planet, is about 1.7 x 10^18 tonne, meaning that 1.8 x 10^14 tonne of 
CO2 is stored in the hydrosphere.

Similarly, in rocks there is almost no CO2 present as such. CO2 is readily 
released from carbonate minerals by acid leaching, so it is usual to count 
all of the CO2 that could be released from carbonates, but not to count 
coal and shale oil, and other reduced carbon minerals. Estimates of the 
amount of carbon present in rocks, both as reduced carbon and as 
carbonates, are much less certain. The distribution is also very uneven.

The continental lithosphere is about 35 km thick, while the oceanic 
lithosphere averages only 5 km. The total mass of the lithosphere has been 
estimated as around 2.4 x 10^19 tonne. Carbonate minerals occur mainly in 
sedimentary rocks close to the surface. I cannot find a good estimate of 
the total amount. It would exceed the total amount stored in the 
hydrosphere, but possibly not by much. Carbon as an element has been 
estimated at 180 parts per million average composition in rocks, but most 
of this might well be reduced carbon rather than carbonates, and the 
estimate is only good to about a factor of 2 anyway.

In summary, the total amounts of CO2 are in the ratio (units of 10^12 
tonne)

2.8 in the atmosphere to 
120 as dissolved bicarbonate in the oceans to 
somewhere between 200 and 16000 as carbonate minerals in the lithosphere.

and the concentrations of CO2 are in the ratio (parts per million by weight 
expressed as CO2)

360 in the atmosphere to
110 as bicarbonate in the oceans to
somewhere between 8 and 700 as carbonate minerals in the lithosphere