The 18OCD (18O Carbonate-DIC) Excel macro is a tool to investigate mechanisms of isotopic fractionation between CaCO3 minerals (inorganic or biogenic) and water. The macro calculates the oxygen isotope ratio (18O/16O and δ18O) of CaCO3 and the fractionation factor between CaCO3 and water (α_c/w) as a function of the solution temperature, mineral growth rate and the solution chemistry (i.e. pH, salinity, [DIC], [Ca2+] and the activity of the enzyme carbonic anhydrase). The mathematical model behind these calculations is presented in details in the following paper:
Devriendt L. S., Watkins J. M. and McGregor H. V. (2017) Oxygen isotope fractionation in the CaCO3-DIC-H2O system. Geochimica Cosmochimica Acta 214, 115-142. https://doi.org/10.1016/j.gca.2017.06.022
Please contact me (laurent.devriendt#nioz.nl) if you would like an access to the BASIC code and equations of the Excel macro.