We use a global three-dimensional chemical transport model to quantify the influence of anthropogenic emissions on atmospheric sulfate production mechanisms and oxidant concentrations constrained by observations of the oxygen isotopic composition (Δ<sup>17</sup>O = &delta<sup>17</sup>O–0.52 × &delta<sup>18</sup>O) of sulfate in Greenland and Antarctic ice cores and aerosols. The oxygen isotopic composition of non-sea salt sulfate (Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>)) is a function of the relative importance of each oxidant (e.g. O<sub>3</sub>, OH, H<sub>2</sub>O<sub>2</sub>, and O<sub>2</sub>) during sulfate formation, and can be used to quantify sulfate production pathways. Due to its dependence on oxidant concentrations, Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) has been suggested as a proxy for paleo-oxidant levels. However, the oxygen isotopic composition of sulfate from both Greenland and Antarctic ice cores shows a trend opposite to that expected from the known increase in the concentration of tropospheric O<sub>3</sub> since the preindustrial period. The model simulates a significant increase in the fraction of sulfate formed via oxidation by O<sub>2</sub> catalyzed by transition metals in the present-day Northern Hemisphere troposphere (from 11% to 22%), offset by decreases in the fractions of sulfate formed by O<sub>3</sub> and H<sub>2</sub>O<sub>2</sub>. There is little change, globally, in the fraction of tropospheric sulfate produced by gas-phase oxidation (from 23% to 27%). The model-calculated change in Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) since preindustrial times (1850 CE) is consistent with Arctic and Antarctic observations. The model simulates a 42% increase in the concentration of global mean tropospheric O<sub>3</sub>, a 10% decrease in OH, and a 58% increase in H<sub>2</sub>O<sub>2</sub> between the preindustrial period and present. Model results indicate that the observed decrease in the Arctic Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) – in spite of increasing tropospheric O<sub>3</sub> concentrations – can be explained by the combined effects of increased sulfate formation by O<sub>2</sub> catalyzed by anthropogenic transition metals and increased cloud water acidity, rendering Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) insensitive to changing oxidant concentrations in the Arctic on this timescale. In Antarctica, the Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) is sensitive to relative changes of oxidant concentrations because cloud pH and metal emissions have not varied significantly in the Southern Hemisphere on this timescale, although the response of Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) to the modeled changes in oxidants is small. There is little net change in the Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) in Antarctica, in spite of increased O<sub>3</sub>, which can be explained by a compensatory effect from an even larger increase in H<sub>2</sub>O<sub>2</sub>. In the model, decreased oxidation by OH (due to lower OH concentrations) and O<sub>3</sub> (due to higher H<sub>2</sub>O<sub>2</sub> concentrations) results in little net change in Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>) due to offsetting effects of Δ<sup>17</sup>O(OH) and Δ<sup>17</sup>O(O<sub>3</sub>). Additional model simulations are conducted to explore the sensitivity of the oxygen isotopic composition of sulfate to uncertainties in the preindustrial emissions of oxidant precursors.