Particulate Scattering and Backscattering in Relation to the Nature of Particles in the Red Sea

Abstract

The ocean contains a large variety of suspended particles that cover a broad size range, from 0.1 nm to 1 mm, and vary in origin (i.e., biogenic or terrestrial), shape and internal composition (i.e., refractive index; Stramski et al., 2004). The pool of suspended particles is often divided into non-algal particles and phytoplankton. Non-algal particles include: (1) heterotrophs (i.e., bacteria, viruses and zooplankton), (2) non-living organic detritus produced by zoo-and phyto-plankton (i.e., fecal pellets, dead cells), and (3) mineral particles (e.g., silicate shells, dusts, clay, etc.). The phytoplankton pool is often divided according to cell size (Sieburth et al., 1978), into pico-phytoplankton (0.2-2 µm), nano-phytoplankton (2-20 µm) and micro-phytoplankton

A Conceptual Approach to Partitioning a Vertical Profile of Phytoplankton Biomass Into Contributions From Two Communities

“…Our values of were found to vary over the season, with a median value of 0.00035 m −1 (see Supplementary Figure S6 ), consistent with the ranges reported in Kheireddine et al. ( 2021 ) and globally by Bellacicco et al. ( 2019 ) at 700 nm.…”

“…Using a large dataset of scattering and absorption measurements collected in the Red Sea, Kheireddine et al (2021) recently demonstrated that the background backscattering coefficient 𝐴𝐴 (𝑏𝑏 𝑘𝑘 𝑏𝑏𝑏𝑏 ) is likely dominated by non-algal particles. Our values of 𝐴𝐴 𝐴𝐴 𝑘𝑘 𝐴𝐴𝑏𝑏 were found to vary over the season, with a median value of 0.00035 m −1 (see Supplementary Figure S6), consistent with the ranges reported in Kheireddine et al (2021) and globally by Bellacicco et al (2019) at 700 nm. Higher 𝐴𝐴 𝐴𝐴 𝑘𝑘 𝐴𝐴𝑏𝑏 values were found during the winter period (Figure 5 and Supplementary Figure S6), possibly reflecting seasonal variation in the concentrations of non-algal particles (Bellacicco et al, 2019(Bellacicco et al, , 2020.…”

“…Using a large dataset of scattering and absorption measurements collected in the Red Sea, Kheireddine et al. (2021) recently demonstrated that the background backscattering coefficient $$({b}_{bp}^{k})$$ is likely dominated by non‐algal particles. Our values of $${b}_{bp}^{k}$$ were found to vary over the season, with a median value of 0.00035 m −1 (see Supplementary Figure ), consistent with the ranges reported in Kheireddine et al.…”

“…Finally, $${b}_{bp}^{k}$$, a constant background particle backscattering coefficient, thought to be dominated by non‐algal particles in the region (Brewin et al., 2015; Kheireddine et al., 2021), can be computed as $$${b}_{bp}^{k}={b}_{bp,k}^{\ast }{b}_{bp,s}.$$$ The total backscattering coefficient can therefore be reconstructed as $$${b}_{bp}(z)={b}_{bp,1}^{B}{B}_{1}(z)+{b}_{bp,2}^{B}{B}_{2}(z)+{b}_{bp}^{k}.$$$ …”

“…Finally, , a constant background particle backscattering coefficient, thought to be dominated by non‐algal particles in the region (Brewin et al., 2015 ; Kheireddine et al., 2021 ), can be computed as The total backscattering coefficient can therefore be reconstructed as …”