Archaean oxygen oases driven by pulses of enhanced phosphorus recycling in the ocean.

Earth's first rise in atmospheric oxygen between about 2.43 billion and 2.1 billion years ago fundamentally transformed the atmosphere and oceans, setting the foundation for the evolution of complex life. However, geochemical evidence reveals intermittent oceanic oxygen oases before the rise of atmospheric oxygen, although the mechanisms that drove the production and accumulation of oxygen remain poorly constrained. Here we present redox-sensitive trace metal and iron speciation data, and phosphorus phase partitioning results, for a 2.93-billion-year-old drill core from the Red Lake area, Canada, to reconstruct oceanic phosphorus cycling and links to oxygen production in the dominantly anoxic, iron-rich Archaean ocean. Our data document one of the earliest known intervals of surface water oxygen accumulation, predating the first accumulation of atmospheric oxygen by about 500 Ma. These intervals were preceded by ferruginous intervals and intervals of enhanced sulfide availability, which led to pulsed increases in oceanic phosphorus bioavailability via anoxic recycling from sediments. Enhanced phosphorus bioavailability would have helped stimulate photosynthetic primary productivity and organic carbon burial, probably exerting a major control on the episodic development of oxygen oases in the late Archaean ocean. This, in turn, led to a critical transitional phase in the development of an oxygenated surface environment.