Towards a holistic sulfate-water-O2 triple oxygen isotope systematics

Triple oxygen isotope (∆17O with δ18O) signals of H2O and O2 found in sulfate oxidative weathering origin offer promising constraints on modern ancient weathering, hydrology, atmospheric gas concentrations, bioproductivity. However, interpretations the sulfate-water-O2 system rely assuming fixed oxygen-isotope fractionations between water, which, contrastingly, are shown to vary widely sign amplitude. Instead, here we anchor triple systematics homogeneous composition empirical modeling. Our resulting framework does not require a priori assumptions O2- versus H2O‑oxygen ratio accounts for mass-dependent mass-independent fractionation ∆17O δ18O sulfate's O2‑oxygen source. Within this framework, new measurements constrain ~2.3 Ga Paleoproterozoic gross primary productivity 6 160 times present-day levels, important implications biological carbon cycle response high CO2 concentrations prevalent early Earth.