Measuring the Influence of Animals on Turbulence in the Sea
1997
Zhou, Meng | Powell, Thomas M. | Huntley, Mark E.
We intend to answer whether marine animals can produce significant turbulent mixing. Two cruises were conducted in Norwegian fjords in winter, 1995 and spring, 1996. We used a microstructure CTD to measure the turbulent dissipation rate epsilon in euphausiid swarms directly. We also used ADCP spectral broadening measurements to estimate kinetic energy produced by euphausiid swimming. We revealed that euphausiid swarms have horizontal scales of 10(exp -1)-10 1km and vertical scales of 10(exp 1)-10(exp 2) m. The abundance can reach to 10(exp 2)-1000 individuals m-3. Within a swarm, the turbulence mixing can be significantly increased by their swimming up to the same order as wind induced mixing. This mixing produced by animal aggregations is very important to the local turbulence, acoustic, and optical fields, especially in coastal regions where zooplankton swarms are often found. We learnt that euphausiids may therefore be acting as farmers in the sea.' They can create enough turbulent mixing to bring continuous supply of nutrients from deep water into surface water for phytoplankton growth. We also demonstrated that the spectral broadening measurements of an ADCP can be used to estimate the swimming velocities of marine macro-zooplankton. This new technology has opened a door to study in situ swimming behaviors of zooplankton.
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