Predicting the response of O₂ dynamics in intertidal sediments to changing environmental conditions is essential for understanding and forecasting the impacts of climate change on coastal biogeochemical functioning. However, key environmental controls such as light, temperature and tidal regime (immersion vs. emersion) are only partially integrated into existing sediment biogeochemical models. Additionally, inversion-based approaches, which infer reaction rates from measured O₂ profiles without explicitly representing the underlying diagenetic mechanisms, cannot be used predictively. We developed a reaction-transport model for simulating O₂ dynamics in MPB-inhabited intertidal sediments at high spatial and temporal resolution under variable environmental forcing. The model was constrained and evaluated using laboratory microsensor measurements of O₂ concentrations and gross photosynthesis in muddy sediments from the Oosterschelde tidal bay (the Netherlands). Our analysis indicates that the studied MPB community is adapted to low irradiance and responds to changing light conditions through vertical migration. Reoxidation of reduced inorganic substances dominates sediment O₂ consumption at low irradiance, whereas aerobic mineralization becomes increasingly important at higher irradiance, with photorespiration representing an additional relevant O₂ sink under high-irradiance conditions. Additionally, both the O₂ producing and consuming processes show strong immersion-emersion and temperature response. Overall, the model is released as an open-source tool, providing a framework that can be adapted and refined for interpreting and predicting O₂ dynamics in intertidal systems under a broad range of environmental conditions.