MODELLING THE DYNAMIC INTERPLAY BETWEEN ECOLOGY AND REDOX DURING CRITICAL INTERVALS IN THE HISTORY OF LIFE

In times of major biosphere stress, rarely is there a single stressor and simple biotic response. Rather, there is a dynamic system of multi-scale feedbacks connecting local biological and environmental processes, such as biotic innovations or volcanic provinces, to system-level changes to the Earth system, such as changes to global temperature and atmospheric composition. Interaction between the levels may cause the complex ecosystem change implicated in many mass-extinction events, including ocean anoxia and food web collapse. Understanding these events requires constructing process models which can explore these interconnected life-environment feedbacks across scales. But connecting localized, short timescale matter and energy fluxes through ecosystem components to global Earth system cycles over geological timescales is a particular modelling challenge. We introduce a 1D biogeochemical column model of a shelf sea in the PALEOtoolkit modelling framework to explore the bidirectional interactions between biology and the physical and chemical environment. The model consists of a coupled ocean-sediment system with key components of early ecological networks, such as size-structured plankton communities, benthic microorganisms, early filter feeders and simple burrowers, represented by systems of ecological functions. Representing the biological populations explicitly presents an alternative to standard approaches in biogeochemical models, where the biological pump in the ocean or bioturbation in the sediment are parameterized from modern data, and the water column and sediment column are often explored separately, without the biological link between organic reservoirs and fluxes. Our approach allows the redox profile in the ocean and sediment to be formed directly by modeled biological activity, and nutrient cycling to be linked to this activity. The model is being used to explore hypotheses on the effects of filter feeders and burrowers on redox conditions and phosphorus cycling, and is particularly suited to studying extinction events where shelf sea anoxia and ecological community collapse are hypothesized to have played a major role.