Global phytoplankton concentrations change seasonally, as revealed by these three-month "climatological" composites for all months between November 1978-June 1986 during which the CZCS collected data: January-March (upper left), April-June (upper right), July-September (lower left), and October-December (lower right).Note the "blooming" of phytoplankton over the entire North Atlantic with advent of northern hemisphere spring, and seasonal increases in equatorial phytoplankton concentrations in both Atlantic and Pacific Oceans, and off the western coasts of Africa and Peru.