Please click here to download the map associated with this article.Since the formation of satellite-borne visible spectral radiometry (ocean colour), oceanographers have developed techniques to map phytoplankton biomass on a global scale, with a major application being to model primary production and the ocean carbon cycle in the context of climate change. However, we now recognise that marine carbon cycling links specifically to the activity of particular phytoplankton functional groups. From the perspective of primary production and the global carbon cycle, cell size is thought to be sufficient for defining these functional groups. This has led to a variety of bio-optical methods that use satellite data to differentiate between phytoplankton size classes. Here we combine an established phytoplankton size class algorithm which is integrated into an available-light primary production model in order to partition and map primary production estimates from microplankton (>20μm) and combined nano-picoplankton (