page_title: Deep chlorophyll maximum
section_title: Measurements
hierarchical_section_title: Deep chlorophyll maximum / Measurements
caption_attribution_description: CTD probe (Conductivity, Temperature, Depth) to be deployed from research vessels (height: 1.50 m). The probe is used to measure physical oceanographic parameters (inner part); surrounded by Niskin-Bottles to take water samples from selected depth levels.
context_page_description: The deep chlorophyll maximum, also called the subsurface chlorophyll maximum, is the region below the surface of water with the maximum concentration of chlorophyll. 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. The depth, thickness, intensity, composition, and persistence of DCMs vary widely. 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.
  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. 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, and others have adapted by migrating vertically with varying nutrient and light levels.
context_section_description: The DCM is often located tens of meters below the surface, and cannot be observed by using traditional satellite remote sensing methods. Estimates of primary productivity are often made via these remote sensing methods coupled with statistical models, though these statistical calculations may not have accurately included production in the DCM. The DCM of a study area can be determined in-situ through the use of an underwater instrument (CTD rosette with niskin bottles) to measure various parameters such as salinity (including dissolved nutrients), temperature, pressure, and chlorophyll fluorescence. Collected water samples can be used to determine phytoplankton cell counts. These measurements can then be converted into chlorophyll concentrations, phytoplankton biomass, and phytoplankton productivity. Another way to estimate primary productivity in the DCM is to create a simulation of the DCM formation in a region by making a 3D model of the region. This can be done if sufficient hydrodynamic and biogeochemical data exists for that ocean region.
caption: Fig. 1 Field photo of a CTD rosette, which measures the conductivity, temperature, and pressure of water samples.
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