One size fits all? - Optimising ocean biogeochemistry for different circulations

Global biogeochemical ocean models are often tuned to match observed inorganic and organic quantities and fluxes. This tuning is typically carried out ``by hand'', and specific for a given circulation. However, this rather subjective approach might not yield the best fit to observations; it is also linked to the circulation, including its specific features and/or errors. Too investigate the interplay between circulation and biogeochemical model parameters we optimised a biogeochemical model coupled to five different offline circulations. Three of six optimal model parameters correlate significantly with specific features of the circulation model. The clear relationship between these parameters and circulation characteristics, which can be easily diagnosed from global models, can provide some guidance when tuning global biogeochemistry within a circulation model. Cross-validation experiments show that even when transferring these among the circulation the resulting variability of biogeochemical properties is lower than presented in earlier studies. The results suggest that optimisation and a careful analysis of the biogeochemical parameter space even in more simplified frameworks can guide biogeochemical model development, or help when deciding about the necessary level of model complexity.