We can put all the oceans, atmosphere, and lot of calcite into a single chemical reactor unit and run equilibrium calculations. This chemical system specification is shown in Fig. 4. The amounts and compositions of gas and water phases correspond to the average amounts and composition of the atmosphere and seawater. Calcite has been assumed to consist mainly of CaCO3.

The equilibrium calculations may be carried out at different temperatures and CO2 amounts in the air. The Equilibrium module calculation routine uses the Gibbs Energy Minimization method, which determines the phase amount, and the composition combination where the Gibbs free energy of the chemical system reaches its minimum. This method automatically takes into account all the possible chemical reactions that may occur in this system.

The enthalpy, entropy, and heat capacity data for the pure chemical compounds shown in Fig 4. are based on the extensive HSC 7 thermochemical database. The non-ideal behavior of the water solution is calculated using the HSC Aqua module, Fig. 5, which uses an extensive aqueous solution database. The amounts and compositions of the air and seawater are based on average values available in public encyclopedias and Internet sources.

The current average CO2 content of the atmosphere is some 383 ppm. The average temperature at sea level is 15 °C. The equilibrium pressure of CO2 above the seawater in these conditions is only 157 ppm. This is the thermochemical explanation of why the oceans are the most important carbon sinks, see Fig. 3 and 6.

The chemical potential and activity of the carbon dioxide is lower in cold seawater than in air, and this is the chemical explanation of why carbon goes to the sea in cold areas. If the chemical potential of carbon dioxide were higher in seawater, then seawater would release much more carbon dioxide into the air in hot areas, however, we are lucky and this is not the situation.

On the other hand, at high surface temperatures, like 25 - 35 °C, the oceans may release carbon dioxide because the equilibrium pressure increases rapidly along with the temperature, Figs. 6 and 7. The sun may easily warm up a thin surface layer of the sea and this is enough to increase CO2 emissions. At medium surface temperatures this layer may behave as a barrier which prevents the CO2 dissolution to the seawater.

Figures 6 and 7 also shows the explanation why the CO2 content in the atmosphere within the last 800 000 years has never been lower than 160 ppm, Fig. 1.

The carbon dioxide pressure and chemical potential difference decrease along with an increase in temperature. This simply means that the driving force for carbon dioxide absorption and accumulation in the sea is decreasing radically, Fig. 6. This always happens if the temperature of the oceans increases for any reason. Seawater emit CO2 when surface temperature of seawater is high, because carbon dioxide pressure is higher in seawater than in the atmosphere.

The sea can easily absorb large amounts of carbon dioxide. Figure 7 shows what happens if we change the amount of CO2 in the atmosphere. The result is that if we remove carbon dioxide from the atmosphere, then the sea will release CO2 until the CO2 content reaches 140 ppm. On the other hand, if we double the CO2 amount in the atmosphere, then sea will absorb CO2 until the CO2 level in atmosphere reaches 180 ppm. Of course, in the long-term, the conditions of the whole chemical system will change, but this calculation illustrates the direction of the chemical reactions.

Actually the total CO2 absorption potential of seawater is very high because the equilibrium partial pressure of CO2 decreases along with pressure, see Fig. 8. Ie. carbon dioxide dissolution into seawater increases along with pressure. This promotes formation of limestone, because seawater is generally supersaturated in calcite, CaCO3. The shells of marine organisms made of calcite can form limestone sediments, because calcite do not dissolve into seawater. The limestone is the most important destination for the carbon, Fig. 3.

However, at very high pressure also calcite starts to dissolve into seawater, usually this happens about 4500 meters below sea level. This depth is called carbonate compensation depth (CCD) or lysocline. Below this depth limestone sediments may dissolve.

Fig 6: The effect of temperature on the carbon dioxide equilibrium pressure over seawater at steady-state with homogenious phases. The average temperature is assumed to be 15 °C and the CO2 content 383 ppm in the atmosphere. The difference between the equilibrium curve and 383 ppm level creates the driving force of CO2 absorbtion.

Fig 7: Seawater may effectively buffer temporal CO2 variations in the atmosphere. The calculations have been carried out by changing the amount of CO2 in the atmosphere.

Fig 8: Effect of sea depth on the partial pressures of carbon dioxide and water vapor. The CO2 absorption potential of seawater increases rapidly when total pressure increases. CO2 dissolution to seawater increases along with pressure. However, at very high pressure also calcite starts to dissolve also into seawater and this prevents the precipitation of the limestone. Usually this happens when the depth is more than 4500 m.

The primary reasons for the global temperature changes are the solar activity changes and variations in Earth's orbit, rotation and axis. See, for example:

http://www.gao.spb.ru/english/astrometr ... j_2009.pdf
http://myweb.wwu.edu/dbunny/research/gl ... idence.pdf

These very preliminary and brief chemical equilibrium calculations show that carbon dioxide may not be the only reason for the increase in the temperature of the Earth’s climate. In fact, it seems that a temperature increase may be the cause and the carbon dioxide content increase in the atmosphere is the natural effect of the climate change processes. Most likely, carbon dioxide contributes to global warming, but it is hardly the primary reason for global warming.

These preliminary and simple equilibrium calculations prove that we should invest much more effort on atmosphere and ocean chemistry research. We have to improve basic data of the equilibrium calculations and take into account also kinetics, temperature, pressure and concentration gradients, as well as validate the calculation models experimentally.

We have also to remember that we must find sustainable, low cost, new energy sources and solve the extensive environmental and emission problems, because energy costs and recycling are the key issues if we want to improve worldwide welfare. This is a fact, whether climate change is due to human activity or not.

The basic ideas of this paper may be summarised in the following conclusions:

1) The ozeans are and has been the most important and pre-eminent carbon sinks, Fig. 3.

2) The effect of humans is much less than 5% of the natural carbon cycle.

3) Huge amounts of CO2 are released from the sea, when sun heats up the thin surface layer of seawater, Fig 6. There are delays in this process due to diffusion and convection.

4) In cold areas ozeans absorb huge amounts of CO2, Fig. 6. There are delays in this process due to diffusion and convection.

5) Deep ozeans contain gigantic amounts of carbon, because carbon dissolution into seawater increases along with the pressure, Fig. 8.

Fig 9: Annual mean sea surface dissolved inorganic carbon. The cold red areas absorb much more carbon than the blue hot ones, ie. the arctic seas are CO2 absorbers. This experimental result is in nice agreement with current calculated results given in Fig. 6.

Fig 10: Annual CO2 Flux Estimated from Air-Sea Difference in CO2 Partial Pressure. The red areas may emit and the blue ones absorb CO2.


Fig 11: Partial pressure of CO2 may be very high at sea surface at higher temperatures like 26 °C. In these conditions seawater cannot absorb CO2 at all. The average CO2 partial pressure in homogenious seawater is some 150 - 200 ppm, Fig. 6, but on sea surface it may be much higher due to slowness of the diffusion and convection.

Fig 12: Experience curve relating actual atmospheric carbon dioxide levels with actual global average sea surface temperature. It is not a time scale, just the simple relation between two physical parameters independent of time. The line shown is just the sequence of actual plotted points for each end month of the two moving averages. References (prof. Lance Endersbee):

Some References:
http://en.wikipedia.org/wiki/File:WOA05 ... _AYool.png
http://www.geol.ucsb.edu/faculty/lea/pd ... 0Paleo.pdf
http://www.ldeo.columbia.edu/res/pi/CO2 ... _2000.html
http://www.ldeo.columbia.edu/res/pi/CO2 ... indmap.pdf
http://www.ldeo.columbia.edu/res/pi/CO2 ... luxmap.pdf

Antti Roine, 15 October 2009