page_title: Thin layers (oceanography)
section_title: Vertical Migration
hierarchical_section_title: Thin layers (oceanography) / Formation / Vertical Migration
caption_attribution_description: English: A plankton patch in the ocean being dispersed horizontally due to velocity shear
context_page_description: Thin layers are concentrated aggregations of phytoplankton and zooplankton in coastal and offshore waters that are vertically compressed to thicknesses ranging from several centimeters up to a few meters and are horizontally extensive, sometimes for kilometers. Generally, thin layers have three basic criteria: 1) they must be horizontally and temporally persistent; 2) they must not exceed a critical threshold of vertical thickness; and 3) they must exceed a critical threshold of maximum concentration. The precise values for critical thresholds of thin layers has been debated for a long time due to the vast diversity of plankton, instrumentation, and environmental conditions. Thin layers have distinct biological, chemical, optical, and acoustical signatures which are difficult to measure with traditional sampling techniques such as nets and bottles. However, there has been a surge in studies of thin layers within the past two decades due to major advances in technology and instrumentation.
context_section_description: Many phytoplankton normally exhibit a diel vertical migration (DVM) pattern that dictates their depth in the water column based on the time of day. Phytoplankton require sunlight for photosynthesis and protein production, but they are not primarily attracted to light. This is evident by their single move up near the surface prior to sunrise and single move down into deeper waters prior to sunset. Their collective movements may result in the aggregation that form thin layers. These regular movements are thought to be governed by an internal clock in normal nutrient concentrations However, they have also been observed to migrate irregularly when nutrient concentrations are higher or lower than normal.
caption: A plankton patch in the ocean being dispersed horizontally due to velocity shear
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