page_title: Thin layers (oceanography)
section_title: Eddies, Filaments, and Fronts
hierarchical_section_title: Thin layers (oceanography) / Formation / Eddies, Filaments, and Fronts
caption_attribution_description: English: Gyrotactic trapping of swimming plankton due to sharp changes in flow velocities in the ocean. The fluid mechanics of this is also called gyrotaxis.
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: Another obvious cause of thin layers is the horizontal transport of waters with high plankton concentration into waters with lower concentrations. In this case, upwelled intrusions of nutrient-rich slope water are suggested to be the cause of algal blooms and some thin layers. However, thin layers have been observed to form at the boundaries of more complex fluid mechanisms such as eddies, filaments, and fronts. These thin layers were located at the transition layer, a region of maximum shear and stratification at the base of the mixed layer.
caption: Gyrotactic trapping of swimming plankton due to sharp changes in flow velocities in the ocean.
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