Marine phytoplankton bloom. Satellite image of a large green bloom of phytoplankton in the Gulf of Finland, Baltic Sea. Every summer, the nutrient-rich, cooler waters of the northern basins of the North Atlantic and Arctic Oceans promote more growth among marine plants and phytoplankton than is found in tropical waters. This produces massive blooms of phytoplankton that spread across hundreds and sometimes thousands of kilometres. Blooms off Scandinavia in the summer of 2018 were particularly intense. Imaged by the Operational Land Imager (OLI) on NASA's Landsat 8 satellite, on 18th July 2018.