Modelling of biogeochemical parameters in the Baltic Sea with a NEMO-ERGOM model system and ensemble based data assimilation

The current reanalysis and forecasting products provided by the Baltic Monitoring and Forecasting Centre (BAL-MFC) are based on an online one-way coupled NEMO-ERGOM system. Specifically, they use the 3D ocean-ice model NEMO v4.0 in combination with the sea ice and thermodynamic model SI3 and the biogeochemical model ERGOM in a version from 2015 developed at the Leibniz Institute for Baltic Sea Research (IOW). This contribution will highlight the status of the current system with respect to biogeochemical parameter modelling in the Baltic Sea. Furthermore, the advancements towards including biogeochemical ensemble based data assimilation into the products will be presented. For this, the Parallel Data Assimilation Framework PDAF v2.0 is used. The recent introduction of PDAF-OMI, the Observation Module Infrastructure, allows for a modular implementation of different observation types, thus ensuring that the data assimilation of both the physical parameters (satellite sea-surface temperature; temperature and salinity profiles) and the biogeochemical parameters (currently oxygen and nutrients profiles) can be done using the same code.

Validation results of the NEMO-ERGOM-PDAF system with profile assimilation of dissolved oxygen, nitrate and phosphate will be presented. The validation focusses on the influence of the biogeochemical data assimilation on the oxygen and nutrient conditions in the deep basins of the Baltic Sea, which are typically anoxic.