The Mediterranean biogeochemical reanalysis of the Copernicus Marine Service has been recently published in Frontiers in Marine Science and provides information on changes and variability in the Mediterranean Sea over the past decades. The reanalysis integrates several novel elements: ERA5 atmospheric forcing, coupling with the new 1/24° physical reanalysis, updated versions of the BFM model and biogeochemical variational assimilation scheme, and several updated observational datasets for assimilation and validation purposes. As a result of the developed three-level validation framework, robust skill assessment of the 12 considered variables offers CMEMS users a measure of accuracy at different spatial and temporal scales. The estimated accuracy of the reanalysis is high for all variables, except ammonium, and the validation is successfully extended to certain emerging properties describing ecosystem processes (e.g., DCM and the depth of the nitracline and subsurface oxygen maximum) using the BGC-Argo dataset. The reanalysis represents a consistent reconstruction of the Mediterranean Sea biogeochemical state and its multiscale variability over the last two decades, quantifying the impact of external and atmospheric forcing on basin-scale tendencies toward surface deoxygenation and acidification, in agreement with previous works. The manuscript is available at the following link https://www.frontiersin.org/articles/10.3389/fmars.2021.741486/full Multidecadal and multivariate data of the biogeochemical reanalysis are available at https://resources.marine.copernicus.eu/?option=com_csw&view=details&prod....
