Optical and Gravimetric Partitioning of Coastal Ocean Suspended Particulate Inorganic Matter (PIM)

Robert H Stavn, University of North Carolina Greensboro, Greensboro, NC, United States; Stennis Space Center, Visiting Scientist, Code 7330, Oceanography Division, Naval Research Laboratory, Stennis, MS, United States, Xiaodong Zhang, University of North Dakota, Grand Forks, ND, United States, Alexander U Falster, Maine Mineral and Gem Museum, Bethel, ME, United States, Deric Gray, US Naval Research Laboratory, Washington, DC, United States, Johannes J Rick, Alfred Wegener Institut, Biologisches Anstalt, Sylt, Germany and Richard W Gould Jr, Naval Research Lab., Ocenography, Stennis Space Center, MS, United States
Abstract:
Recent work on the composition of suspended particulates of estuarine and coastal waters increases our capabilities to investigate the biogeochemal processes occurring in these waters. The biogeochemical properties associated with the particulates involve primarily sorption/desorption of dissolved matter onto the particle surfaces, which vary with the types of particulates. Therefore, the breakdown into chemical components of suspended matter will greatly expand the biogeochemistry of the coastal ocean region. The gravimetric techniques for these studies are here expanded and refined. In addition, new optical inversions greatly expand our capabilities to study spatial extent of the components of suspended particulate matter. The partitioning of a gravimetric PIM determination into clay minerals and amorphous silica is aided by electron microprobe analysis. The amorphous silica is further partitioned into contributions by detrital material and by the tests of living diatoms based on an empirical formula relating the chlorophyll content of cultured living diatoms in log phase growth to their frustules determined after gravimetric analysis of the ashed diatom residue. The optical inversion of composition of suspended particulates is based on the entire volume scattering function (VSF) measured in the field with a Multispectral Volume Scattering Meter and a LISST 100 meter. The VSF is partitioned into an optimal combination of contributions by particle subpopulations, each of which is uniquely represented by a refractive index and a log-normal size distribution. These subpopulations are aggregated to represent the two components of PIM using the corresponding refractive indices and sizes which also yield a particle size distribution for the two components. The gravimetric results of partitioning PIM into clay minerals and amorphous silica confirm the optical inversions from the VSF.
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