It has been suggested that much of the observed glacial-interglacial variability in the atmospheric mixing ratio of CO2 (xCO2) could potentially be driven by a perturbation of the marine Si cycle. To date, only relatively simple steady-state analysis has been made of this hypothesis. In this study, we develop a description of the ocean carbon cycle, incorporating novel descriptions for the recycling of Si, both within the water column and in deep-sea sediments. A high degree of computational efficiency enables model integrations over multiple glacial-interglacial cycles, driven by a time-varying input of dissolved Si to the ocean. Due to the long time constant (~23 ka) of atmospheric xCO2 response to perturbation in Si supply and the highly nonlinear nature of opal preservation in deep-sea sediments, we find that reduction in the deposition rate of aeolian silicates at the surface ocean can explain little (<3 ppm) of the rapid ~90 ppm rise in atmospheric xCO2 observed at glacial termination. However, increased Si supply has the potential to make an important contribution to the decline in atmospheric xCO2 associated with the much slower transition from interglacial to full glacial conditions.