Extended Data Fig. 6: Bayesian isotope mixing model of carbon sources to river emissions.

The proportional contribution of different aged carbon sources to river carbon emissions using a Bayesian isotope mixing model^52,72. We use three endmembers to define the potential carbon sources available in global river catchments: decadal-aged carbon representing atmospheric CO₂ fixed in vegetation and soil carbon between 1950 and 2023 (Fig. 1c), millennial-aged carbon representing carbon in the top 30 cm of soils, globally (1,390 ± 310 years (ref. ²⁷)), and petrogenic carbon representing carbonate minerals and rock organic matter. The line in the middle of the boxes represents the median, the box limits represent the upper and lower quartiles and the whiskers extend to 1.5 times the interquartile range for the possible solutions in the mixing model. We modelled the contribution of these sources to river carbon F¹⁴C observations (duplicates removed) grouped by biome (a) and lithology (b), following Fig. 2.