Particles in the bottom boundary layer: Concentration and size dynamics through events

The dynamics of particles is examined using two laser diffraction instrumen ts, LISST-100, mounted on a tripod. These sensors measured optical transmis sion and the area and volume distribution of particles. Particle size and c oncentration data from these instruments are examined together with the mea n stress estimates obtained from a nearby tripod using a Benthic Acoustic S tress Sensors array velocimeter. The following three significant results ar e presented: (1) the size distribution of particles varies widely in respon se to forcing conditions; (2) in a surprise observation during Hurricane Ed ouard, despite a decrease in optical transmission that would ordinarily be interpreted as an increasing sediment load, a dramatic decrease in suspende d sizes revealed an actual reduction in suspended volume; and (3) there is a positive correlation between median particle size in the current boundary layer and mean current stress during combined wave current storm events. T his final result indicates that after the initial breakup of flocculates du ring a storm event the size dynamics of the boundary layer is no longer con trolled by aggregation/disaggregation processes but is controlled by a bala nce between gravitational settling and upward diffusion.