East Sound, Washington-1996 Field Season
 

Beam C, (particulate matter). Note the aggregation between 2 and 6 m,  whose shape mimics that of the 21.2 isopycnal (above).

Thin–layers 1996 – Time series data of light attenuation (beam-C, 412 nm) showed a persistent layer in the upper 6 m of East Sound during the 24-hour study in 1996.  The attenuation data indicated that particles were initially located between sigma-t of 20.6 to 21 kg m-3. Twenty four hours later, the particles were located in waters with sigma-t ranging from 21.2 to 21.6 kg m-3.  While the maximum in light attenuation varied between 3 and 5 m depth and did track density fluctuations to a degree, the maximum tended to be between 3 and 4 m depth.  These results suggest that some of the particles were not accumulating in waters of comparable density but may have been motile and seeking a particular irradiance level in the water column.  Largest accumulations of marine snow were always below the maximum in beam–C and were either above or below water with sigma–t of 21 kg m-3.  That layers of marine snow were below the maximum in beam-C suggests that beam-C was indicative of phytoplankton or detrital particles smaller than 500 µm.

            The layer of marine snow was likely being augmented continuously by settling particles.  As no large accumulations of marine snow occurred below 8 m  depth, either the sinking rate of the marine snow was reduced because of similarities of the density of the aggregates and the surrounding water, or marine snow that sank further was disaggregated.  Observations by divers indicated that marine snow deeper in the water column was older and was disaggregated. Rates of turbulent kinetic energy dissipation at depths with accumulations of marine snow and at depths deeper in the water column rarely exceeded 10^-8 m²s^-3.  Consequently, it is unlikely that small scale shears due to turbulence caused disaggregation of layers of marine snow while we sampled.  While infrequent, rates of turbulent kinetic energy at depths where phytoplankton abundances were higher did exceed 10^-6 m²s^-3.  Consequently, small scale shears due to turbulence may have contributed to aggregation of marine snow.
 

Return to the East Sound home page	click here
Return to the Biogeophysical Processes Page

last updated: October 27, 1999
Comments: brice@icess.ucsb.edu