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In calcareous parent material, pedogenic carbonate formation mostly involves dissolution and recrystallization of lithogenic carbonates with CO(2) of soil air, leading to a complete exchange of lithogenic carbon with soil-derived carbon. Interest in pedogenic carbonates has increased in recent decades because they are a useful tool for reconstructing paleoclimatic conditions (delta(13)C and delta(18)O) and past atmospheric CO(2) concentrations as well as for radiocarbon dating of soils. For such investigations, the recrystallization rate of primary CaCO(3) by pedogenic carbonate formation and the dependence of the recrystallization rate on environmental factors are essential, but still unquantified factors.

The recrystallization rate of primary CaCO(3) of loess at three CO(2) concentrations was estimated by isotopic exchange between primary CaCO(3) and the (14)C of artificially labeled CO(2). Loess was used for the study as a parent substrate for soil formation to simulate initial rates of CaCO(3) recrystallization. CO(2) concentrations of 380 ppm, 5000 ppm and 50,000 ppm lead to recrystallization rates of 4.1.10(-7) day(-1), 8.1.10(-7) day(-1) and 16.9.10(-7) day(-1), respectively. The relation between CO(2) concentrations and recrystallization rates was described by a saturation Curve. Under the tested experimental conditions, complete (95%) recrystallization of loess carbonate and formation of pedogenic carbonate would take 4.9-20.0.10(3) years, strongly depending on CO(2) concentration. We expect faster recrystallization rates under field conditions because of permanent CO(2) supply by root and rhizomicrobial respiration. This impedes the equilibrium between the inorganic C pools in solid, liquid and gaseous phases. (C) 2009 Elsevier B.V. All rights reserved.