MID-PROTEROZOIC OXYGEN AND METHANE (Invited Presentation)

High concentrations of the greenhouse gases CO₂ and CH₄ have long been invoked to explain the observation of a largely ice-free climate despite lower solar luminosity during the Precambrian. However, recently a ‘methane paradox’ has emerged, wherein the atmospheric CH₄ abundances required to buffer the Proterozoic climate system are difficult to reproduce in global biogeochemical models. Here, we use a biogeochemical model of a microbial mat ecosystem to examine whether terrestrial cyanobacterial rich sediments (‘mats’) could have released significant amounts of CH₄ to the atmosphere under the low pO₂ conditions characteristic of most of Precambrian time. We then use these fluxes to inform an Earth system model inversion of the extent of microbial mat coverage on Earth’s land surface that would be required to buffer mid-Proterozoic climate. Terrestrial mats on as little ~8-10% of the exposed land surface can strongly buffer climate, depending on atmospheric pO₂ level. Further, although the photochemical stability of CH₄ in the atmosphere increases as atmospheric oxygen levels rise methane fluxes from mat ecosystems drop dramatically, suggesting novel links between planetary oxygenation and catastrophic climate instability during the Proterozoic.