Abstract
The characterization of particulate and phytoplankton community composition is crucial to our understanding of the interactions amongst ecological, biogeochemical, and physical processes in the ocean. Relationships between seawater constituents and their optical properties can be used to understand their composition in various oceanic conditions. By validating and using hyperspectral remote sensing reflectance measurements and derived estimates of phytoplankton absorption, this thesis first addresses the influence of physical and biogeochemical gradients on sub-km scale phytoplankton community composition across the river plume–ocean mixing zone in the northern Gulf of Mexico. Our observations reveal the existence of localized regions of dominant picophytoplankton communities in an area of the coastal margin, which are otherwise characteristically dominated by larger microphytoplankton. Secondly, this thesis examines relationships of backscattering and other inherent optical properties to particle composition, including chlorophyll concentrations and associated pigment proxies for phytoplankton size classes and total suspended matter. Optical measurements across horizontal and vertical spatial scales included those acquired from in situ instrumentation and analyses of discrete water samples as well as values retrieved from hyperspectral radiometry. We demonstrate that the relationship between backscattering measurements, such as particulate backscattering and the backscattering ratio, and chlorophyll provide empirical support for the optical retrieval of particulate and phytoplankton community composition. Absorption and backscattering measurements are of primary significance to applications of optical remote sensing in the ocean, and the use of such information along with in situ particulate and phytoplankton composition and pigment concentration data is crucial to our understanding of oceanic biogeochemical processes. Our findings and the novel data set presented here add to a growing body of literature on the use of inherent optical properties to discern characteristics of various biogeochemical constituents in optically complex coastal and open ocean waters.