HNLC regions cover 20% of the world’s oceans and are characterized by varying physical, chemical, and biological patterns. These surface waters have annually varying, yet relatively abundant macronutrient concentrations compared to other oceanic provinces. While HNLC broadly describes the biogeochemical trends of these large ocean regions, all three zones experience seasonal phytoplankton blooms in response to global atmospheric patterns. On average, HNLC regions tend to be growth-limited by iron and variably, zinc. This trace metal limitation leads to communities of smaller sized phytoplankton. Compared to more productive regions of the ocean, HNLC zones have higher ratios of silicic acid to nitrate because larger diatoms, that require silicic acid to make their opal silica shells, are less prevalent. Unlike the Southern Ocean and the North Pacific, the Equatorial Pacific experiences temporal silicate availability which leads to large seasonal diatom blooms.