A generalizable box model for kinetic clumped isotope effects in the
CaCO3 -DIC-H2O system
Abstract
Most Earth surface carbonates precipitate out of isotopic equilibrium
with their host solution, complicating the use of stable isotopes in
paleoenvironment reconstructions. Disequilibrium can arise from exchange
reactions in the DIC-H2O system as well as during crystal growth
reactions in the DIC-CaCO3 system. Existing models account for kinetic
isotope effects in these systems separately but the models have yet to
be combined in a general framework. Here, a box model is developed for
describing disequilibrium carbon, oxygen, and clumped isotope effects in
the CaCO3-DIC-H2O system. The model is applied to inorganic calcite
precipitation experiments where there is a known CO2 influx and CaCO3
outflux. The example provided can be adapted to other situations
involving CO2 absorption (e.g., corals, foraminifera, high-pH
travertines) or degassing (e.g., speleothems, low-pH travertines,
cryogenic carbonates) and/or mixing with other DIC sources.