YOUNG SCIENTIST AWARD (DONATH MEDAL): TRACKING AND MODELING THE DEVELOPMENT OF THE SEDIMENTARY MIXED LAYER

Bioturbation—sediment mixing and ventilation by burrowing animals—shapes seafloor ecology, sediment properties and global marine biogeochemical cycling. Well-mixed sediments have long been assumed to appear at the Ediacaran-Cambrian boundary. However, field-based stratigraphic analyses, synthesizing sedimentological, ichnological and taphonomic data from a range of shallow marine facies, indicate that sediment mixing in shallow marine environments lagged significantly behind other early Paleozoic advances in benthic ecology, and that the development of bioturbation was a protracted process.

An equally critical question is when and how in Earth’s history bioturbators began to substantially influence marine biogeochemistry. Recent modeling work has suggested that even limited early Paleozoic bioturbation could have driven productivity crises and ocean-wide deoxygenation—in striking contrast to macroevolutionary and macroecological predictions. In order to move forward this debate, I will present new diagenetic modeling data exploring, in a quantitative and process-based manner, the relationship between bioturbation and global nutrient cycling—focusing on phosphorus (the ultimate limiting nutrient on geological timescales). In contrast to previous modeling work, I find that bioturbation does not uniformly or unidirectionally mediate increased phosphorus burial. Bioturbation does, however, appear to have enhanced the sensitivity of carbon and oxygen cycling to environmental perturbations.