Pierre Cartigny Justin A. Hayles Christophe Thomazo Pierre Sansjofre Virgil Pasquier Stefan V. Lalonde Pascal Philippot Bryan Alan Killingsworth 2022 <p><span>Triple&nbsp;oxygen isotope&nbsp;(∆</span>¹⁷<span>O with δ</span>¹⁸<span>O) signals of H</span>₂<span>O and O</span>₂<span>&nbsp;found in&nbsp;sulfate&nbsp;of oxidative weathering origin offer promising constraints on modern and ancient weathering, hydrology,&nbsp;atmospheric gas&nbsp;concentrations, and bioproductivity. However, interpretations of the sulfate-water-O</span>₂<span>&nbsp;system rely on assuming fixed oxygen-isotope fractionations between sulfate and water, which, contrastingly, are shown to vary widely in sign and amplitude. Instead, here we anchor sulfate-water-O</span>₂<span>&nbsp;triple oxygen isotope systematics on the homogeneous composition of atmospheric O</span>₂<span>&nbsp;with empirical constraints and modeling. Our resulting framework does not require a priori assumptions of the O</span>₂<span>- versus H</span>₂<span>O‑oxygen ratio in sulfate and accounts for the signals of mass-dependent and mass-independent fractionation in the ∆</span>¹⁷<span>O and δ</span>¹⁸<span>O of sulfate's O</span>₂<span>‑oxygen source. Within this framework, new ∆</span>¹⁷<span>O measurements of sulfate constrain ~2.3&nbsp;Ga Paleoproterozoic gross primary productivity to between 6 and 160 times present-day levels, with important implications for the biological&nbsp;carbon cycle&nbsp;response to high CO</span>₂<span>&nbsp;concentrations prevalent on the early Earth.</span></p> application/pdf 10.1016/j.chemgeo.2021.120678 en Elsevier Towards a holistic sulfate-water-O2 triple oxygen isotope systematics article