Tropospheric Ozone During the Last Interglacial

The history of tropospheric O3, an important atmospheric oxidant, is poorly constrained because of uncertainties in its historical budget and a dearth of independent records. Here, we estimate the mean tropospheric O3 burden during the Last Interglacial period (LIG; 115 to 130 thousand years ago) using a record of the clumped isotopic composition of O2 (i.e., Δ36 values) preserved in Antarctic ice. The measured LIG Δ36 value is 0.03 ± 0.02‰ (95% CI) higher than the late pre‐industrial Holocene (PI; 1,590–1,850 CE) value and corresponds to a modeled 9% reduction in LIG tropospheric O3 burden (95% CI: 3%–15%), caused in part by a substantial reduction in biomass burning emissions during the LIG relative to the PI. These results are consistent with the hypothesis that late‐Pleistocene megafaunal extinctions caused woody and grassy fuels to accumulate on land, leading to enhanced biomass burning in the preindustrial Holocene.