Beam attenuation, scattering and backscattering of marine particles in relation to particle size distribution and composition in Hudson Bay (Canada)

Abstract

This study investigated the relationships between the concentration of biogeochemical parameters and particulate beam attenuation (c p ), scattering (b p ), and backscattering (b bp ) in Hudson Bay. Results showed that most of the variability resulted from the presence of a deep chlorophyll maximum. c p , b p , and b bp were all adequate proxies to estimate total suspended matter (TSM) but were mostly sensitive to particulate inorganic matter (PIM) in the surface layer, and particulate organic matter (POM) at the chlorophyll maximum depth. The backscattering ratiob bp varied in the range of 0.005-0.05 and was inversely related to the POM : TSM ratio. According to the Twardowski et al. (2001) model, the PSD slope n well representedb bp and bulk refractive index n p in relation to particulate composition. For inorganic particulate dominated waters, bothb bp and n p had a larger range and a higher mean value than at organic particulate dominated waters. This knowledge on the optical properties related to the PSD and particulate composition provides valuable information for further investigation and broadens our understanding of ocean optics in high latitude waters leading to potential improvements of regional scale remote sensing algorithms.

Particulate Backscattering Ratio as an Indicator of Changing Particle Composition in Coastal Waters: Observations From Great Barrier Reef Waters

“…At LJCO our observations of type 2 waters are similar, while type 1 waters show values lower than these theoretical predictions (Figure ). However, lower than 0.02 values of backscattering ratio are theoretically predicted (Duforêt‐Gaurier et al, ; Twardowski et al, ) and observed (Boss et al, ; Loisel et al, ; McKee & Cunningham, ; Snyder et al, ; Whitmire et al, ; Xi et al, ) in regions dominated by phytoplankton and organic detritus and recently also found in the waters of Yellow and East China Seas dominated on average by 80% of inorganic particles (Sun et al, ). Microscopic imaging of mineral/organic flocs in our study area (Bainbridge et al, ) shows complex particle geometries, which may explain the difference from idealized theoretical prediction based on more regular geometry and no organic matter.…”

Variability of Particle Size Distributions in the Bohai Sea and the Yellow Sea

“…For instance, phytoplankton functional types usually vary with size, a finding that has been incorporated into global biogeochemical models and used to assess the ecological feedback to the ocean's carbon In this study, we investigate the variability in PSD in two typically shallow and semi-enclosed seas, the Bohai Sea (BS) and the Yellow Sea (YS), with the following two objectives: (1) to model the PSD of the surface waters; and (2) to characterize the spatial variability and vertical distributions of the PSD. The potential findings by this study are very significant for understanding and documenting the particle size distributions in the BS and the YS, which have been regarded as important factors influencing water inherent optical properties [11,[40][41][42][43], and further changing water color remote sensing signals [44].…”

Bio-optical variability at a Vancouver Island aquaculture site

“…A Wetlabs ac‐s was used to collect profiles of total nonwater beam attenuation, c pg ( ), absorption, a pg ( ), and dissolved absorption, a g ( ), at 86 spectral channels between 400 nm and 737 nm with a spectral resolution of 4 nm and a measurement accuracy ± 0.01 m −1 . Di‐ionized water and air calibrations were performed on this instrument before, during and after data collection periods to ensure instrument precision remained within factory specifications (Xi et al ). On each sampling day, approximately every fourth cast was performed with a 0.2 μm filter attached to the absorption tube of the ac‐s to measure a g ( ).…”

“…The reported precision error of the calibrated ac‐s is ± 0.005 m −1 (Wetlabs 2015), which we ensured was maintained through water and air calibrations (section Optical profile data analysis). Under low scattering conditions, b p error can be as high as 18% (Piskozub et al ; Martinez‐Vincente et al ; Xi et al ). Error should be lower in our study due to relatively large b p magnitudes.…”