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Paul Hill 1 , Timothy Milligan 2 , and Kristian Curran 1

OPTICS, ACOUSTICS, AND STRESS IN A NEARSHORE BOTTOM NEPHLOID LAYER The role of in situ particle size distribution. Paul Hill 1 , Timothy Milligan 2 , and Kristian Curran 1 1 Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1

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Paul Hill 1 , Timothy Milligan 2 , and Kristian Curran 1

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  1. OPTICS, ACOUSTICS, AND STRESS IN A NEARSHORE BOTTOM NEPHLOID LAYERThe role of in situ particle size distribution Paul Hill1, Timothy Milligan2, and Kristian Curran1 1Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1 2Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada, B2Y 4A2

  2. Conventional wisdom • Small particles in suspension affect the optical and acoustical properties of the water column. • Large particles in suspension determine the mass flux of sediment to the seabed.

  3. Concentration Diameter, m The Effects of Flocculation Chemically Dispersed Salt Water

  4. The Effects of Flocculation t < 0.2 Pa t > 0.2 Pa

  5. Emerging views • Flocs interact strongly with small particles in suspension. • Under some circumstances flocs themselves affect the optical and acoustical properties of the water column.

  6. The Effects of Flocculation (from Flory et al., 2004, DSR) Backscatter observed by the Hydroscat-6 vs. the sum of the area per unit volume of particles observed in corresponding in situ images

  7. Goals of the study • Measure the suspended size distribution of particles 1 µm to 1 cm in diameter in the bottom boundary layer. • Link the suspended particle size distribution to optics, acoustics, and stress.

  8. Preliminary results

  9. Preliminary results D25 = 435 µm LISST DFC September 16, 2004 at 0800 (UTC)

  10. Challenge to overcome September 14, 2004 at 1900 (UTC)

  11. Alter the digital floc camera orientation to prevent accumulation of sediment on the camera housing. Deploy optics, acoustics, particle sizing and flow velocity instruments simultaneously. Deploy INSSECT? Plans for 2005

  12. INSSECT Digital floc camera LISST Tilt/compass Settling column Digital video camera Carousel sediment trap Rotating base

  13. Floc settling velocities (from Mikkelsen et al., 2005, CSR)

  14. CLSM floc images EuroSTRATAFORM - Gulf of Lions, 2005 300 µm 300 µm Transmission image Florescence image

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