BIOPERIANT12: a mesoscale-resolving coupled physics–biogeochemical model for the Southern Ocean

Abstract. We present BIOPERIANT12, a regional 1/12° ocean–ice–biogeochemical model configuration of the Southern Ocean (SO) based on the Nucleus for European Modelling of the Ocean platform. It is designed to investigate mean state, seasonal cycle, and upper ocean (< 500 m) dynamics, with a particular focus on processes influencing carbon, heat exchange, biogeochemical mechanisms, and the assumptions underlying physical–biogeochemical model parameterisations within the SO. Over the analysis period 2000–2009, the model demonstrates a stable and realistic upper ocean mean state compared to observation-based products. We use ocean biomes to delineate the major subregions and evaluate the biogeochemical properties of the model, including surface chlorophyll and partial pressure of carbon dioxide. BIOPERIANT12 captures key spatial and temporal features of SO biogeochemistry (BGC), though it tends to overestimate biological biomass and underrepresents high-frequency variability. The model shows skill in reproducing large-scale patterns and seasonal cycles across biomes, offering insights into regional dynamics that are often obscured in coarser models. Despite its limitations, BIOPERIANT12 provides a valuable high-resolution framework for process studies, model–data intercomparisons, and future investigations into mesoscale influences on carbon and heat dynamics. It offers a useful tool for addressing long-standing uncertainties in air–sea exchange and ecosystem variability in the SO.