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 2 Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada, B2Y 4A2

2. Conventional wisdom 1.Small particles in suspension affect the optical and acoustical properties of the water column. 2.Large particles in suspension determine the mass flux of sediment to the seabed.

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

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

5. Emerging views 1.Flocs interact strongly with small particles in suspension. 2.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 1.Measure the suspended size distribution of particles 1 µm to 1 cm in diameter in the bottom boundary layer. 2.Link the suspended particle size distribution to optics, acoustics, and stress.

9. Preliminary results

10. September 16, 2004 at 0800 (UTC) LISST DFC D 25 = 435 µm

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

12. Plans for 2005 1.Alter the digital floc camera orientation to prevent accumulation of sediment on the camera housing. 2.Deploy optics, acoustics, particle sizing and flow velocity instruments simultaneously. 3.Deploy INSSECT?

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

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

15. Transmission imageFlorescence image 300 µm CLSM floc images 300 µm EuroSTRATAFORM - Gulf of Lions, 2005