Moving 6-year analysis of Water body chlorophyll-a in Black Sea for each season: winter (December-February), spring (March-May), summer (June-August), autumn (September-November). Every year of the time dimension corresponds to the 6-year centered average of the season. 6-years periods span from 1990-1995 until 2016-2021. Data Sources: observational data from SeaDataNet/EMODNet Chemistry Data Network. Units: mg/m^3. DIVA analysis: The computation was done with the DIVAnd (Data-Interpolating Variational Analysis in n dimensions), version 2.7.9, using GEBCO 30sec topography for the spatial connectivity of water masses. The horizontal resolution of the produced DIVAnd maps grids is 0.05 degrees. The vertical resolution is 7 depth levels: 0, 5, 10, 20, 30, 40, 50m. The horizontal correlation length: 80km. The vertical correlation length (in meters): twice the vertical resolution (10, 10, 20, 20, 20, 20, 20). The error variance (epsilon2): 1 An anamorphosis transformation was applied to the data: threshold value=200. Background field: not used. Quality control of the observations was applied using the interpolated field: QCMETHOD=3 and visual inspection (Observations with residuals outside the minimum and maximum values of the 99% quantile were discarded from the analysis after thoroughly visual inspection).