Thin Layers are structures of the water column which were discovered when advances in instrumentation and deployment technologies allowed us to sample at the temporal and spatial scales where patterns were revealed. Although they may extend for kilometers, Thin Layers are only a few 10's of centimeters in vertical thickness. They have distinct physical, biological, chemical, optical and acoustical signatures. Thin Layers of phytoplankton or zooplankton may contain densities of organisms ranging up to 1000 times those found just above, or below the structure. These extraordinary concentrations of living material must have important implications for many aspects of marine ecology (e.g.phytoplankton growth dynamics, micro- and macrozooplankton grazing, behaviour, life histories, predation, harmful algal blooms), as well as for ocean optics and acoustics.

A Brief Example

There are many different kinds of Thin Layers. Below is an example of a Thin Layer of zooplankton, as visualized with acoustical scattering. Thus, this biological Thin Layer is also an acoustical layer. The figure shows the persistence of a thin layer of zooplankton (green line, about 65 dB) over a 48 hour period. Further interpretation of this data can be found on the Acoustical Layers page (below).

Sv at 265 KHz: TAPS Mooring Z in East Sound, WA., 24-26 June 1998
© D.V. Holliday

X axis = time, 24 - 26 June 1998
Y axis = depth, in meters, bottom referenced

Volume Scattering Strength (dB)