Fig. 3

The trends of the calcite saturation state and Ca isotopes with time during the carbon injection phase from monitoring borehole HN-4. a Ca isotope ratios (blue line) and calcite saturation index (dotted black line). The blue shaded area represents the 2 s.e. analytical uncertainty on the isotope measurements. b shows the evolution of pH (dotted black line) and the calculated CO₂ precipitation rate based on Ca isotopes (red line). The red shaded area represents the 2σ propagated uncertainty on the individual precipitation rates. The grey shaded areas represent the carbon injection periods