OxyPOM: A biogeochemical model for Oxygen and Particulate Organic Matter dynamics with process-specific temperature sensitivity

Periods of low dissolved oxygen concentration — hypoxia and anoxia — threaten the health of aquatic ecosystems and the services they provide. Hypoxia is strongly influenced by temperature, but the different sensitivities and response functions of oxygen removal and production processes to temperature are not regarded in most models. Here we present OxyPOM—Oxygen and Particulate Organic Matter, a temperature-aware process-based biogeochemical model. OxyPOM incorporates process-specific temperature sensitivities for the key oxygen-related processes: photosynthesis, re-aeration, respiration, mineralization, and nitrification. Other temperature-sensitive variables, such as optimal light intensity, winter grazing inhibition, and pathogenesis, are also represented. Our model was tested in an idealized water-column experiment that represents a typical estuary with a seasonal low-oxygen environment. Differences between process-specific and uniform temperature sensitivities affect seasonal patterns, resulting in higher divergence between the two scenarios, particularly in summer months. While these changes may balance in the overall annual oxygen budget, uniform sensitivities may underestimate particulate organic carbon production by up to a factor of four over the year and overestimate nutrient concentrations. This nuanced approach to temperature sensitivity allows us to explore and test new hypotheses related to climate warming and heatwaves, addressing the ecosystem changes required by climate change models.