Slowing planetary rotation influences ocean nutrient cycling and oxygenation.

Abstract

Marine habitability for complex life on Earth and Earth-like planets requires bioavailable nutrients and dissolved oxygen. The cycling of nutrients and oxygen is controlled by physical ocean circulation. However, our understanding of how circulation has varied through time and space is incomplete for Earth and unconstrained for Earth-like exoplanets. Earth's rotation has slowed over time, affecting ocean circulation by modifying the Coriolis effect. We use a three-dimensional Earth system model to explore how slowing planetary rotation influences ocean circulation and biogeochemistry. We show that slower rotation enhances wind-driven upwelling and global circulation. Nutrient recycling is consequently more efficient, increasing photosynthetic productivity. Additionally, enhanced ocean oxygenation improves habitability for aerobic life under a well-oxygenated atmosphere. However, under a poorly oxygenated atmosphere, slowing rotation increases oxygen fluxes from the ocean to the atmosphere. Therefore, Earth's rotational history may have been a long-term background control on surface oxygenation and the evolution of animals.