Formation of 13C/12C Isotope Ratios in Speleothems: A Semi-Dynamic Model

Abstract

A theoretical approach towards predicting the carbon isotope composition of carbonate cave deposits is presented. The proposed model simulates time variations of both the chemical and isotopic composition of the carbonate solution and deposited calcite in the course of CaCO₃ precipitation. Two phases of the precipitation process are distinguished and treated separately: initial outgassing of the solution until a certain degree of supersaturation of CO₃^2- ions is reached and subsequent precipitation of CaCO₃ related to further outgassing. Precipitation rates of CaCO₃ predicted by the model agree fairly well with literature data. The model predicts δ¹³C values of deposited calcite within a range of ca −16 to +3‰ depending on temperature, chemical and isotope parameters of the initial solution and actual degree of the precipitation process.