Phytoplankton data from the cruise number AFR-258 with research vessel "AFRICANA" from 2.12.-15.12.2009 in front of Namibia. Phytoplankton samples taken by CTD- rosette sampler from different depths within the upper mixed layer. Date are mean values of the depth range given.Phytoplankton counted by means of inverted microscope according to the classical UTERMÖHL method. Counts converted to biomass (wet weight) according to the method described by HELCOM (2010, http://www.helcom.fi/groups/monas/CombineManual/AnnexesC/en_GB/). Principle of the method also described by Olenina et al. (2006, hdl:10013/epic.39031.d001).