Figure 2

Mineral weathering end-member mixing. (a) Mineral unit-normalised sulphate versus bicarbonate abundance. The Gaoping River data collected over multiple years in relation to the quaternary end-member mixing line. Literature data points where ionic compositions reflect incursion of seawater plot away from the quaternary mixing line. One data point from this study (datapoint with highest mineral unit normalised sulphate) deviated from the mixing line due to high ammonium amounts that are attributed to anthropogenic inputs and therefore wasn’t considered further in this study. Removing these anomalies, the data from this study correlates with R² = 0.99, and for all studies with R² = 0.99. (b) Mineral unit-normalised sulphate versus pMC of DIC. The three mineral weathering reactions producing bicarbonate span a ternary mixing triangle. All of the data lie outside of this mixing ternary due to the addition of sulphate from sulphuric acid weathering of silicates. The latter process, which leaves DI¹⁴C on the x-axis unaffected, adds sulphate until a theoretical maximum of one mole per weathered mineral unit, representing 100% silicate weathering by sulphuric acid.