Tropospheric Ozone During the Last Interglacial

The history of tropospheric O-3, 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 O-3 burden during the Last Interglacial period (LIG; 115 to 130 thousand years ago) using a record of the clumped isotopic composition of O-2 (i.e., Delta(36) values) preserved in Antarctic ice. The measured LIG Delta(36) value is 0.03 +/- 0.02 parts per thousand (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 O-3 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.