Phytoplankton “Missing” Absorption in Marine Waters: A Novel Pigment Compensation Model for the Packaging Effect

The packaging effect (Q_a^*) of phytoplankton pigments can account for over half of the variability in the phytoplankton absorption coefficient (a_ph) in oceanic waters. Given the significance of a_ph in many marine biogeochemical and environmental processes, exploring the packaging effect on absorption properties is a crucial task. In the present study, two pigment compensation models for quantifying the packaging effect are developed for Case I and Case II waters using high-performance liquid chromatography (HPLC) derived pigments and a_ph data. The Case I model is based on data from the NOMAD data set from the Atlantic Ocean, and the Case II model is based on data taken in the marginal seas of China. Phytoplankton “missing” absorption is derived by subtracting the reconstructed a_ph without the packaging effect from the measured a_ph. Our proposed models use the established relationships between “missing” absorption and specific absorption coefficients of pigment groups without the packaging effect to quantify pigment group concentrations. Validation using independent in situ data sets demonstrates that significant improvements are achieved to quantify the packaging effect, especially for waters under abnormal packaging effect conditions (Q_a^* > 1), where the mean ratio of normal Q_a^* increasing largest from 40% to 90% in 455 nm in Case I water and from 70% to 100% in 520 nm in Case II water. Applying the proposed models to satellite data displays the spatial distributions of the packaging effect in the Atlantic Ocean and the marginal seas of China, as delegates of Case I and II waters, respectively. The Q_a^* intensity negatively covaries with the chlorophyll-a distribution. This study shows the spatial variability of the packaging effect from satellite observations for the first time.