Bioturbation—sediment mixing by burrowing animals—critically shapes seafloor ecology and sediment properties, as well as global marine biogeochemical cycling. Geologic archives indicate that the appearance of intensively and deeply mixed sediments lagged significantly behind relatively early advances in the colonization of the seafloor. However, the biogeochemical impact of early bioturbation has remained extensively debated. Similarly, understanding of how bioturbation—and bioturbation-biogeochemical feedbacks—will respond to ongoing and future climatic change is severely limited. To address this question, I will present diagenetic model data exploring the relationship between bioturbation and biogeochemical cycling. This approach indicates that these relationships are complex and non-linear, and that differences in both intensity and style of bioturbation—in conjunction with varying environmental boundary conditions—can promote highly variable biogeochemical responses.