Ocean redox evolution past and present

The availability and spatial landscape of marine oxygen and related redox-sensitive elemental cycles has changed dramatically over the last 4 billion years. This chapter uses a database framework to synthesize recent quantitative and conceptual advances in this story, emphasizing an integrated view of modern and ancient processes. We highlight three main timescales of marine redox evolution: modern and anthropogenic, glacial-interglacial, and geologic. On modern and anthropogenic timescales, the discussion focuses on defining redox thresholds and physical and biogeochemical mechanisms driving spatiotemporal variations. For ancient timescales, we synthesize proxy constraints on coupled ocean-atmosphere redox dynamics and feedbacks with biological and geologic evolution.