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Rain water combines with CO2 to form H2CO3 carbonic acid. More CO2 is scrubbed out by weathering of rocks forming bicarbonates and carbonate ions. This is washed down to the ocean floor.
combustion of fossil fuels releases about 5.4 billion tons of carbon a year as CO2 into atmosphere. In addition, deforestation practices contribute about 1.6 billion tons of carbon a year to atmospheric CO2. So, the total input of CO2 from human activities is about 7.0 billion tons of carbon a year. However, only about 3.4 billion tons of carbon a year accumulates in the atmosphere. That means there is an atmospheric CO2 sink of about 3.6 billion tons of carbon a year.
biggest carbon reservoir, carbonate rocks contain about 6.1x107 billion tons of carbon, which is 1694 times and 1.1x105 times larger than those of oceans and world vegetation respectively (Houghton & Woodwell, 1989). Carbonate rocks occupy an area of about 22 million square kilometers in the world (Yuan, 1997).The basic reactions for carbonate rocks weathering can be expressed by: CaCO3+CO2+H2O <----> Ca2++2HCO3- for limestone CaMg(CO3)2 +2CO2+2H2O <---> Ca2++Mg2++4HCO3- for dolomite.