Fig. 2: pH, calcite saturation state and atmospheric CO₂ reconstructed from oyster δ¹¹B.

95% confidence intervals are shaded for all simulated evolutions (red envelope), with median values shown by central line. Calculations used to generate these curves are described in the methods. Results obtained using the minimum ΔpH method are shown by the grey lines, with uncertainty represented by the grey shaded window. The minimum pH method take the average δ¹¹B values pre and during the excursion, with the length of the grey bars indicating the time periods averaged. Atmospheric CO₂ is plotted as doublings, which is relatively robust to uncertainties in initial conditions, with indicative CO₂ concentrations using the minimum and mean estimate of initial CO₂ generated by our calcualtions shown in the additional axes. Relative timescale using astrochronology of Xu et al.¹³ by correlation with St Audrie’s Bay, converted to absolute time using an age of 201.564 Ma for the initial negative carbon isotope excursion^3,15.