Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 4 2009 10.5194/os-5-635-2009 http://www.ocean-sci.net/5/635/2009/ http://www.ocean-sci.net/5/635/2009/os-5-635-2009.html http://www.ocean-sci.net/5/635/2009/os-5-635-2009.pdf 635 647 2009-12-07 Impact of data assimilation of physical variables on the spring bloom from TOPAZ operational runs in the North Atlantic A. Samuelsen annette.samuelsen@nersc.no L. Bertino C. Hansen Nansen Environmental and Remote Sensing Center, Bergen, Norway A reanalysis of the North Atlantic spring bloom in 2007 was produced using the real-time analysis from the TOPAZ North Atlantic and Arctic forecasting system. The TOPAZ system uses a hybrid coordinate general circulation ocean model and assimilates physical observations: sea surface anomalies, sea surface temperatures, and sea-ice concentrations using the Ensemble Kalman Filter. This ocean model was coupled to an ecosystem model, NORWECOM (Norwegian Ecological Model System), and the TOPAZ-NORWECOM coupled model was run throughout the spring and summer of 2007. The ecosystem model was run online, restarting from analyzed physical fields (result after data assimilation) every 7 days. Biological variables were not assimilated in the model. The main purpose of the study was to investigate the impact of physical data assimilation on the ecosystem model. This was determined by comparing the results to those from a model without assimilation of physical data. The regions of focus are the North Atlantic and the Arctic Ocean. Assimilation of physical variables does not affect the results from the ecosystem model significantly. The differences between the weekly mean values of chlorophyll are normally within 5–10% during the summer months, and the maximum difference of ~20% occurs in the Arctic, also during summer. 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