Area containing species, populations or communities with comparatively higher natural biological productivity.
- Frontal areas
- Upwelling zones
- Hydrothermal vents
- Seamounts, polynyas
Case study: Equatorial High Productivity Zone
At the beginning of many marine food chains are single-celled, microscopic plants called phytoplankton. Through the process of photosynthesis, phytoplankton use chlorophyll and the sun’s energy to convert carbon dioxide and water to organic compounds for growth and reproduction. The generation of new plant material by photosynthesis is called primary production, which is available as a resource for consumers and subsequently their predators all the way up the food chain.
Scientists use estimates of primary production as the most basic measure of the biological productivity of the ocean. Primary production does not occur uniformly throughout the ocean. The rate of production depends mainly on the quantity of phytoplankton already in the water, the availability of light and required nutrients such as nitrogen and phosphorus, and the water temperature. Geographic location and physical processes such as currents and climate all influence the availability of light and nutrients.
Phytoplankton are most abundant (yellow, high chlorophyll) in high latitudes and in upwelling zones along the equator and near coastlines. They are scarce in remote oceans (dark blue), where nutrient levels are low. This map shows the average chlorophyll concentration in the global oceans from July 2002–May 2010. Image courtesy NASA Earth Observatory.
The central Pacific Ocean receives a large amount of light throughout the year and sustains a high level of primary productivity due to an oceanographic phenomenon called the equatorial divergence. In this phenomenon, physical processes caused by winds, currents, and the rotation of the Earth force water near the surface to flow away from the equator. To replace it, nutrient-rich water is drawn up from the ocean depths, bringing a steady supply of nutrients to the sunlit surface and producing a band of consistently high primary productivity at the equator. Historically high sperm whale abundance has been recorded in this area.
The Equatorial High Productivity Zone was described by participants at the Regional EBSA Workshop for the Eastern Tropical and Temperate Pacific, and designated as a EBSA at COP12 (Decision XII/22, October 2014).