IN-SITU CHARACTERISTICS OF PARTICLES SETTLING WITHIN A DEEP-WATER ESTUARY

A Floc Camera Assembly is used to obtain the in-situ size, shape, conc entration and settling velocity of marine particles, providing insight into the in-situ excess-density, porosity and mass of flocs, their po pulation characteristics, and aggregation and sedimentation rate. Data high-light the time-dependent character of marine snow, including nea r-instantaneous, daily and seasonal influences for a mid-latitude estu ary, Halifax Inlet. Methods are developed for estimating the mean size of the constituent particles comprising flocs, for determining the nu mber spectra of non-flocculated and flocculated particles, and for det ermining the mass concentration and mass flux spectra for suspended fl ocs. The most active aggregation level is just below the estuarine sur face layer. The largest aggregation rates involve the finest (<10 mu m ) suspended particles colliding by both differential settling and turb ulent shear. During plankton blooms, large flocs become attached to th e mucoid stringers. The settling velocity of stringers is, in turn, co ntrolled by these large flocs attached to their base. Floc settling ve locity varies with flee size, and as a seasonally-variable power funct ion. A floc's excess density also varies with flee size, but the relat ionship changes daily. Flocs account for between 36% and 100% of the t otal suspended mass within Halifax Inlet, and >90% of the mass below t he surface layer. Flee concentrations may change by a factor of four i n just a few minutes, affected by the flux of larger flocs. When river input of suspended load is high, hoc concentration is also high, but the portion of total particulate matter composed of floc is low. Mean flee size varies considerably between seasons and sometimes between es tuarine location. Small flocs form when primary production is low and river input is high. Large flocs form when river input is very low. Su spended stringers are highest during the spring freshet and associated plankton bloom.