LAUSR

This study explores second-order variability of inherent optical properties (IOPs) of particles caused by particle intrinsic attributes, including the mean particle size (DA) calculated by a LISST measurement restricted to a size range of 2.5–500 μm, mean apparent density (ρa), bulk refractive index (np), and composition (using a ratio of chlorophyll a to total suspended matter concentrations, Chl a/TSM, as the delegate), obtained from five field cruise observations collected from 2013 to 2015 in Bohai Sea (BS) and Yellow Sea (YS). Large variations in magnitude were observed in terms of mass-specific beam attenuation ( cp∗), scattering ( bp∗), and backscattering ( bbp∗), indicative of optically complex water conditions. cp∗ and bp∗ showed similarities in their change and driving mechanisms, in which DA explained the majority (35%), both np and ρa separately contributed variability levels of approximately 25%, and Chl a/TSM accounted for the lowest proportion (15%). Most (approximately 38%) of the variability in bbp∗ was found to be attributed to np when the other factors were responsible for the rest of the variation to different degrees of 9–29%. We also model cp∗, bp∗, and bbp∗ with direct linkages to DA, ρa, np, and Chl a/TSM using a multivariate linear regression method. The established cp∗, bp∗, and bbp∗ models generated very high goodness of fit results, with determination coefficients (R2) of above 0.970 (p < 0.001) and with favorable predictive errors (a mean absolute percentage error, MAPE, of approximately 30% for the cp∗ and bp∗ models and of approximately 40% for the bbp∗ model). Overall, the findings of this study further knowledge on the nature of the inherent optical properties in BS and YS, and are very helpful for understanding many marine biogeochemical processes.