『Abstract
　Laboratory experiments on reagent-grade calcium carbonate ad carbonate rich glacial sediments demonstrate previously unreported kinetic fractionation of carbon isotopes during the initial hydrolysis and early stages of carbonate dissolution driven by atmospheric CO2. There is preferential dissolution of Ca¹²CO3 during hydrolysis, resulting in δ¹³C-DIC values that are significantly higher isotopically than the bulk carbonate. The fractionation factor for this kinetic isotopic effect is defined as εcarb. εcarb is greater on average for glacial sediments (-17.4‰) than for calcium carbonate (-7.8‰) for the ＜63 μm size fraction, a sediment concentration of 5 g L^-1 and closed system conditions at 5℃. This difference is most likely due to the preferential dissolution of highly reactive ultra-fine particles with damaged surfaces that are common in subglacial sediments. The kinetic isotopic fractionation has a greater impact on δ¹³C-DIC at higher CaCO3 : water ratios and is significant during at least the first 6 h of carbonate dissolution driven by atmospheric CO2 at sediment concentrations of 5 g L^-1. Atmospheric CO2 dissolving into solution following carbonate hydrolysis does not exhibit any significant equilibrium isotopic fractionation for at least 〜6 h after the start of the experiment at 5℃. This is considerably longer than previously reported in the literature. Thus, kinetic fractionation processes will likely dominate the δ¹³C-DIC signal in natural environments where rock : water contact times are short ＜6-24 h (e.g., glacial systems, headwaters in fluvial catchments) and there is an excess of carbonate in the sediments. It will be difficult apply conventional isotope mass balance techniques in these types of environment to identify microbial CO2 signatures in DIC from δ¹³C-DIC data.』

1. Introduction
　1.1. Isotopic fractionation and carbonate equilibria
　　1.1.1. Chemical equilibria in the carbonate system
　　1.1.2. Equilibrium isotope fractionations in the carbonate system
　　1.1.3. Kinetic fractionations in the carbonate system
2. Materials and methods
3. Results and discussion
　3.1. Geochemical properties
　　3.1.1. The 5 g L^-1 closed system experiments
　　3.1.2. The 5 g L^-1 open system experiments
　　3.1.3. The 0.01 g L^-1 open system experiments
　3.2. Chemical and isotope equilibrium
　3.3. Isotopic fractionation
　3.4. δ¹³C variations in relation to weathering reactions
　　3.4.1. carbonate hydrolysis
　　3.4.2. Carbonation of carbonates
　3.5. Effect of carbonate concentration on kinetic isotopic fractionation
4. Conclusions
Acknowledgments
References