An eddy-permitting simulation of the Southern Ocean ecosystem and biogeochemistry

The Southern Ocean is a major region of the oceanic uptake of anthropogenic CO2, however it is also the region where ocean carbon cycle models show the largest disagreements partly due to the poor representation of physical circulation at the scale of ocean fronts and eddies. To improve the realism and quantification the regional ocean carbon fluxes, we developed a high-resolution ocean carbon cycle model of the Southern Ocean. The model employs circulation fields that are determined by the Southern Ocean State Estimate in which the circulation fields are assimilated with a suite of satellite and in-situ physical observation for the late 2000s. The model's transport scheme is realistic and computationally efficient, allowing biogeochemical and ecological parameterizations to be implemented at eddy-permitting spatial resolution. The model fields are tested against in-situ tracer and satellite ocean color data, demonstrating that the model can reproduce the spatial and temporal variability of large-scale biogeochemical and ecological parameters. The energetic mesoscale eddies dominate local fluxes of nutrients and carbon, but the large-scale tracer budget highlights the compensation between wind-driven and eddy-induced tracer fluxes. Sensitivity experiments are performed to investigate the importance of iron sources in regulating the biological productivity by purposefully suppressing (i) atmospheric dust deposition, (ii) continental shelf sediment, and (iii) deep water iron sources. Each source makes a distinct imprint on the spatial pattern of dissolved iron, and the model better reproduces the observed chlorophyll when all the sources are included in the simulation. Diagnoses of limiting nutrients and tracer budgets guide our understanding in the factors controlling the regional biological productivity and carbon balance.