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Vertically migrating swimmers generate aggregation-scale eddies in a stratified column
Isabel A Houghton1, Jeffrey R Koseff1, Stephen G Monismith1
1Bob and Norma Street Environmental Fluid Mechanics Laboratory, Civil and Environmental Engineering, Stanford University, Stanford, CA, USA.
Nature
|April 20, 2018
Summary
Marine zooplankton, like brine shrimp, create large eddies during vertical migration, significantly enhancing ocean mixing. Their collective movement drives turbulence, impacting ocean physics and nutrient transport.
Area of Science:
- Oceanography
- Biological Oceanography
- Fluid Dynamics
Background:
- Biologically generated turbulence is crucial for ocean mixing and nutrient transport.
- Previous studies suggested animal-generated turbulence is too small-scale to impact ocean mixing.
- Zooplankton aggregations during migration introduce new length scales relevant to ocean mixing.
Purpose of the Study:
- To investigate if collective zooplankton behavior can generate large-scale turbulence.
- To quantify the mixing efficiency of zooplankton-induced turbulence.
- To assess the impact of zooplankton on ocean stratification and mixing.
Main Methods:
- Experimentally simulating centimeter-scale zooplankton (Artemia salina) migration.
- Measuring the generation of eddies and mixing in a stratified fluid.
- Analyzing the scale of turbulence relative to density stratification.
Main Results:
- Collective migration of brine shrimp generates aggregation-scale eddies.
- These eddies effectively mix stable density stratification.
- Turbulent diffusivity was observed to be up to three orders of magnitude greater than molecular diffusivity.
Conclusions:
- Marine zooplankton aggregations can significantly alter water column physics.
- Zooplankton-driven turbulence has the potential to impact ocean biogeochemical cycles.
- The findings challenge previous assumptions about the scale limitations of biologically generated turbulence.
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