Bioturbation feedbacks on the phosphorus cycle

Bioturbation—sediment mixing and ventilation by burrowing animals—provides one of the most prominent examples of how animals shape their surroundings. A critical but longstanding question is when and how in Earth's history bioturbators began to similarly influence marine biogeochemistry. Recent work has proposed that even though the development of well-mixed sediments was a protracted process, the initial rise of bioturbators led to a decrease in marine phosphate levels, global productivity crises and ultimately deoxygenation events in the early Cambrian oceans. Herein, using a diagenetic model, we provide a new view of how bioturbators impact the global phosphorus cycle. Our work focuses on incorporating more realistic representation of bioturbation with a more complete and mechanistic parameterization of benthic phosphorus cycling than has previously been used to explore the early Paleozoic. We find, in contrast to previous modeling studies, that bioturbation does not uniformly or unidirectionally mediate increased phosphorus burial. Enhanced biodiffusion of sedimentary particles can mediate enhanced phosphorus burial. In contrast, bioirrigation—nonlocal transport of solutes via burrows—enhances phosphorus recycling and may therefore stimulate rather than stymy productivity. Given evidence from the geologic record that bioirrigation rather than biodiffusion was predominant during the ramping up of bioturbation (through the early Paleozoic), the emergence of bioturbation is unlikely to have driven deoxygenation events.