Deep chlorophyll maximum

The deep chlorophyll maximum (DCM), also called the subsurface chlorophyll maximum,^[1][2] is the region below the surface of water with the maximum concentration of chlorophyll. The DCM generally exists at the same depth as the nutricline, the region of the ocean where the greatest change in the nutrient concentration occurs with depth.^[3]

A DCM is not always present - sometimes there is more chlorophyll at the surface than at any greater depth - but it is a common feature of most aquatic ecosystems, especially in regions of strong thermal stratification.^[4] The depth, thickness, intensity, composition, and persistence of DCMs vary widely.^[2][5]

A common way of determining the DCM is through the use of a CTD rosette, an underwater instrument that measures various parameters of water at specific depths.^[4] The location and formation of the DCM depends on multiple factors, such as the resident organisms' nutritional needs and light availability. Some organisms have adapted to lower levels of light through increasing its cellular chlorophyll amounts,^[6] and others have adapted by migrating vertically with varying nutrient and light levels.^[7] The DCM species composition vary with water chemistry, location, seasonality, and depth.^[3][8] Not only is there a difference in DCM species composition between oceans and lakes, variation is also present within different oceans and lakes. Because the DCM holds much of the world's primary productivity, it plays a significant role in nutrient cycling,^[9] the flow of energy, and biogeochemical cycles.^[10]