We develop and produce reanalyses of physical, chemical and biological variables that go back several decades, for example for ocean currents, temperature, salinity, nutrient salts, as well as the movement and extent of sea ice. The reanalyses supplement the observation-based datasets with simulated meteorological, oceanographic, and biogeochemical variables, which are as close to reality as possible. The information is freely available through the Copernicus Marine Service, and can be used in climate studies and environmental monitoring, among other things.