Reorganisation of Earth’s biogeochemical cycles briefly oxygenated the oceans 520 Myr ago

Abstract

The Phanerozoic radiation of bilaterian animals has been linked to oxygenation of Earth’s oceans, due to the oxygen demand of the evolving animal ecosystems. However, how early animals may have regulated Earth’s surface oxygen budget via self-stabilizing feedbacks is poorly understood. Here, we report parallel positive uranium, carbon, and sulphur isotope excursions from carbonate successions in Siberia that document a brief global oxygenation episode 521–520 Myr ago, at the onset of diversification of larger arthropods known from the fossil record. Our data and model indicate that an abrupt increase in the sinking rate of marine organic matter expanded the oxygenated zone in the oceans and that reducing conditions returned 1.3 ± 0.8 Myr after the onset of this transient oxygenation episode, necessitating a strong negative feedback to the increasing levels of oxygen. We speculate that larger zooplankton could have sourced both oxygen and food to the seafloor, fueling bioturbation over wider areas and, thereby, stabilizing O2-rich habitats in the oceans. Thus, this reorganization exemplifies how animal ecosystems might have influenced oxygen availability in Earth’s surface environment soon after their establishment.