1228 Ocean Dynamics (2019) 69:1217–1237 Fig. 7 Comparison of the different model simulations with in situ data: experiments FREE (top), WEAK (middle) and STRONG-lin (bottom). The values for the coarse grid are shown in the left column and those for the fine mesh in the right column directly updated, together with the physical fields, by the LESTKF utilising the ensemble-estimated cross-covariances between the SST and the BGC fields. Thus, one expects a more directed and larger influence of the assimilation. If some BGC model field is not correlated with SST, the ensemble represents this relation (up to sampling error in