Variability of scattering and backscattering of marine particles in relation to particle concentration, size distribution, and composition off the eastern hainan coast in the south China sea

The light scattering and backscattering coefficients of particles (bp(λ) and bbp(λ)) and their association with particle concentration, size distribution, and composition off the eastern Hainan coast in the South China Sea (SCS) were analyzed between August and September 2013. Variations in bp(532) and bbp(532) were correlated to changes in the LISST-based total cross-sectional area and volume concentration of particles (AC and VC). Two significantly different covariations between bbp(λ) and bp(λ) and chlorophyll a concentration (Chla) were observed, and all samples were clearly separated into two groups (Group A and Group B) using the threshold relationship between bbp and Chla. Samples in Group B, most of which were collected in the nepheloid layer, showed higher bp/AC and bbp/AC than those in Group A. This indicates the presence of inorganic particles with higher np in Group B than in Group A. The relationship between bbp and Chla for Group A could be well fitted by a published model involving a constant backscattering background independent of Chla. A significant relationship (R2 = 0.85) was observed between bbp and Chla in the Chla maximum layer, which was different from that in other layers. This finding might imply that both an increase in the micro-phytoplankton community and a decrease in the contribution of background backscattering to bbp at the Chla maximum layer. Understanding this variability of beam-scattering properties off the eastern Hainan coast can improve our understanding of marine biogeochemical processes at a regional scale, and can also promote the application of these regional bio-optical relationships for ocean color.