The University of Maine Maine In-situ Sound & Color Lab
School of Marine Sciences
Observations of Particle Dynamics During OASIS 2004 and 2005

Processes controlling the vertical distribution of particles in the ocean are not fully understood, partly because particles in aquatic systems are predominantly packaged as flocs, which have markedly different transport properties than single-grain particles. Despite the importance of flocs, understanding of the controls on their size and packaging within the water column is poor, in part due to the difficulty of sampling and characterizing the often delicate particles in situ. Less-intrusive in-water methods such as optical and acoustical backscatter, laser particle sizing, and microphotography combined with image processing techniques are able provide estimates of single grain and floc size spectra and abundance, as well as proxies for their composition. Here we present coincident measurements of particle size spectra (using laser particle sizing and microphotography), bulk optical and acoustical properties, waves, currents, and estimates of shear stress, that were measured in September 2004 and 2005, at ~1.25 meters above bottom in shallow waters (12m) south of Martha's Vineyard, Massachusetts during the ONR Optics, Acoustics, and Stress In Situ (OASIS) project. During resuspension events, decoupling of particle concentration and size distribution is illustrative of processes such as particle flocculation and de-flocculation within the water column. Time series of particle size distributions, combined with in situ estimates of stress, are used to assess flocculation rates and mechanisms near the ocean bottom.

Slade, W.H., E. Boss, T.G. Milligan, P.S. Hill, and J.H. Trowbridge, 2006. Observations of Particle Dynamics During OASIS 2004 and 2005. 2006 Spring Ocean Sciences Meeting.

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