Inherent optical properties and optical mass classification of the waters of the Strait of Georgia, British Columbia, Canada

Bio-physical and in situ hyperspectral optical data were measured during April and July, 2006, in the euphotic waters of central and southern Strait of Georgia, British Columbia, Canada. Particulate absorption and scattering were derived from the optical measurements of beam attenuation and chromophoric dissolved organic matter (CDOM) absorption. The concentration of CDOM was measured with a fluorometer, and water samples were collected for total suspended material (TSM) and chlorophyll a (chl a). The results showed that waters closer to the Fraser River discharge presented the highest concentrations of TSM (18.2 mg L−1) and CDOM (32.1 ppb Quinine Sulphate Dihydrate Equivalent (QSDE)), whereas in deeper waters and waters farther from the plume, both TSM (0.2 mg L−1) and CDOM (6.0 ppb QSDE) were relatively lower, and chl a relatively higher (11.3 μg L−1), reaching the lowest values at the bottom of the euphotic layer (0.3 μg L−1). The waters of the Strait of Georgia’s euphotic zone showed well-defined attenuation coefficients and absorption-to-scattering ratios, which allowed for the optical classification of riverine plume (OM1), estuarine (OM2), and northern and deeper (OM3) waters. Generally, particulate scattering dominated the attenuation of light in these waters. The particulate scattering was mostly influenced by inorganic particles, especially in OM1. High loads of inorganic particulate scatterers possibly increased the diffuse light into OM2. Conversely, the relatively higher absorption by CDOM in deeper waters indicates the possibility of competition with phytoplankton for short wavelength radiation. The data and analyses in this study provide important baseline optical information for the waters of the Strait of Georgia.