Fig. 4: Reconstructed lake water CO₂ concentrations and pH values over the past 26 kyr based on δ¹³C data from Tibetan Plateau lakes (4 newly sampled lakes and 9 previously reported lakes).

Solid black lines represent mean CO₂ concentrations and pH values calculated at 300-year intervals and grey shadings indicate standard deviation. a Reconstructed CO₂ concentrations in lake water. The red line indicates atmospheric equilibrium CO₂ concentrations (derived from ice core data⁸). Values above this line represent lakes acting as CO₂ sources to the atmosphere, while values below indicate CO₂ sinks. b Calculated CO₂ concentration changes relative to modern lake water. For lakes with data extending to ~4 ka, we used the youngest data point as the modern reference. For lakes without data after 4 ka (Lake Qinghai, Zhari Namco, Pumoyum Co, and Heihai), we used contemporary measured CO₂ concentrations as the baseline. c Reconstructed pH values of lake water.