A regional comparison of particle size distributions and the power law approximation in oceanic and estuarine surface waters

The particle size distribution (PSD) is commonly used in studies of sediment fluxes, phytoplankton dynamics, and optical scattering from particulates, but little is known about the spatial and temporal variability of this parameter. Here, we analyze in situ laser diffraction measurements of the PSD from a variety of estuarine and open ocean systems. The power law or Junge-type distribution provided a good fit to surface ocean particle size distributions measured from 6 to 250 mu m. PSD slopes ranged from 2.7 to 4.7 with a mean of 3.63. Consistent with theory, high particle slopes (3.78) and low particle concentrations characterized the open ocean waters of the Atlantic and the Southern Ocean. Lower PSD slopes (3.63) and high concentrations were characteristic of estuarine waters. River plumes consistently showed the lowest PSD slopes (3.30) and highest particle concentrations characteristic of larger bloom-forming phytoplankton and production of particle aggregates. In the North Atlantic, an inverse relationship was found between PSD slope and chlorophyll concentration. Such results follow the biological paradigm that larger phytoplankton are prevalent in bloom conditions and smaller phytoplankton dominate in oligotrophic water. Large temporal variability in PSD was observed in near coastal regions prone to sediment resuspension from storms and tidal flow. Dense sea grass beds consistently had lower particle concentrations compared to surrounding waters due to reductions in current flow and sediment resuspension. Simple power law approximations of particle size distributions can be successfully used to describe and assess particle distributions in a wide array of oceanic and estuarine water types.