Thanks to NASA’s Coastal Zone Color Scanner (CZCS, 1978-1986), nearly ocean-wide coverage of the distribution of phytoplankton pigment in the upper part of the euphotic zone and, in effect, in the mixed layer of the open ocean, is now available. This coverage includes seasonality and interannual variability. The CZCS observations confirm that the physics of the ocean provide the backbone of the geographic and temporal patterns of pigment distribution and, by inference, of primary production rate. For example, phytoplankton concentrations and production are enhanced where upwelling or seasonal overturn of the water column replenishes nutrient concentrations in the mixed layer, whereas the timing of this enhancement may be controlled by upwelling, seasonal overturn, or the mixed layer becoming shallower than the critical depth.

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