EARLY PALEOZOIC BIOTURBATION AND FEEDBACKS ON PHOSPHORUS CYCLING (Invited Presentation)

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 early rise of bioturbators led to a decrease in marine phosphate levels, global productivity crises and ultimately deoxygenation events in the early Cambrian oceans. However, a paucity of biogeochemical models with both realistic representation of bioturbation and full, mechanistic parameterization of benthic phosphorus cycling has hampered efforts to test these hypotheses. In order to address these issues, I used a modified version of the SedChem diagenetic model (cf. Zhao et al., 2020) to explore, in a quantitative and process-based manner, the relationship between bioturbation and global phosphorus cycling. In contrast to previous modeling studies, I find 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 advectional transport of solutes via open burrows—facilitates enhanced phosphorus recycling, stimulating rather than stymying productivity. Given evidence from the geologic record that bioirrigation rather than biodiffusion was predominant during the early Paleozoic ramping up of bioturbation, the emergence of bioturbation is unlikely to have driven deoxygenation events but may have enhanced the sensitivity of marine biogeochemical systems to environmental perturbation.