PRINCIPAL 



INVESTIGATOR(S) Yogesh C. Agrawal 



Northwest Research Associates, Inc. 



P.O. Box 3027 



Bellevue, WA 98009-3027 



PROJECT TITLE THE SIZE DISTRIBUTION AND CONCENTRATION OF 



SEDIMENTS NEAR THE SEABED: A SPECIFICATION OF 

 THE BOTTOM BOUNDARY CONDITION 



AMOUNT OF FUNDrNG FY 1994: $84 K 



SUMMARY OF GOALS 



To the extent that organics are sequestered or derived from bottom sediments, it is 

 important to determine this flux. Our interest is in the estimation of sediment related input/output 

 at the seafloor. The sediments, stirred by the wave-induced near-bed oscillatory motion, produce 

 a strong nepheloid layer of the order of 5-10 cm thick in a region termed the 'wave boundary 

 layer'. This layer contains all that material which is either of high density, large, or both so that 

 the net result is that it has a high settling rate. Significant mass transport of such large material 

 can occur in the wave boundary layer. To date, no precise measurements of the sediment have 

 been made; single parameter data such as optical backscatter are subject to enormous errors due 

 to a spatially and temporally varying size distribution - to which these sensors are highly 

 sensitive. Our approach employs a new sensor system, developed as a follow up of one used on 

 the California shelf in the experiment STRESS. The instrument is based on laser diffraction by 

 a particle ensemble. The angular scattering pattern is recorded and subsequently mathematically 

 inverted to obtain size spectra and concentration. 



The present effort involves development of a sensor which can make these measurements 

 close to bed, unlike its predecessor used in STRESS. We have used fiber-optics to create a 

 remote sensor head. The instrument is called LISST-3. 



Special goals include: 



(1) Development and test of the new instrument; 



(2) Field deployment from a cruise in July, 1994; 



(3) Analysis of data recovered in August; 



(4) Interpretation of carbon content with the fluorescence data of Dr. Steve Lohrenz 

 of University of S. Mississippi. 



