Modeling the evolving interplay of the carbon and silica cycles through Earth's history

The chemical weathering of silicate rocks removes CO₂ from the atmosphere while delivering dissolved silica to the oceans, thus inexorably linking the geochemical cycles of carbon and silicon with global climate. Today, this relationship is moderated by pelagic biomineralizing organisms which facilitate the majority of sedimentary burial of carbon and silicon as carbonate and opal (the Cretan ocean). However, modern calcifiers and silicifiers only evolved and reached ecological prominence relatively recently in Earth's history. Throughout most of the Phanerozoic, such burial was accomplished by shallow-water dwelling calcifiers and relatively less efficient silicifiers (the Neritan ocean), and by inorganic SiO₂ and CaCO₃ precipitation in supersaturated seawater throughout much of the Precambrian (the Strangelove ocean). We have developed a new model to explore the effects of the increasing level of biological participation in the carbon and silica cycles over Earth's history. Running each combination of Strangelove/Neritan/Cretan C- and Si-cycles to steady state demonstrates the effects of the presence of relatively low versus high efficiency biomineralizers on equilibrium conditions (particularly the mineral saturation of CaCO₃ and SiO₂ in seawater). A further set of experiments explores how the presence of biomineralizers affects the sensitivities and response time of both cycles to perturbation by carbon release. A final set of experiments examines the response of the response of the Strangelove ocean to the termination of Neoproterozoic glacial intervals, which, if accurately described by the Snowball Earth hypothesis, likely represents the largest perturbation of the coupled C- and Si-cycles in Earth History.