Climate shapes the oxygenation of Earth's atmosphere across the Great Oxidation Event

Abstract

We use a one-dimensional atmospheric photochemical model to investigate the effect of temperature and humidity variations on the evolution of O2 and O3 across the Great Oxidation Event (GOE), and find that changes to the atmospheric temperature profile can change O2 and O3 levels by up to three orders of magnitude. Cold temperatures (<280 K) result in stable low O2 levels (mixing ratio of 10−4), whereas temperate (280 K−310 K) and hot (>310 K) temperatures result in stable high O2 levels (mixing ratio of 10−2) after the GOE. Warm and wet climates lead to an increased atmospheric oxidation power through the increased production of hydrogen oxide (HOx) radicals, catalyzing the oxidation and depletion of the principal reduced species (CH4, CO and H2). Consequently, warmer temperatures lead to less O2 lost through the oxidation of reduced species, resulting in higher O2 and O3 levels relative to colder temperatures.The GOE occurred around the same period as the onset of the Snowball Earth Huronian glaciations. Cold climates during the glaciations were eventually terminated by the build-up of volcanic greenhouse gases in the atmosphere, leading to Hot-Moist Greenhouse climates. Temperature and humidity likely varied extensively from Snowball Earth climates during the glaciations to Hot-Moist Greenhouse climates. However, current photochemical models of the GOE do not consider the effect of this climate variability on the evolution of O2 and O3 across the GOE. Our results show that temperature and humidity exert a strong control on atmospheric chemistry through O2, O3, and HOx feedbacks, which has important implications for our understanding of the climate-redox evolution of the GOE.