Seasonal variability in the light absorption properties of western Arctic waters: Parameterization of the individual components of absorption for ocean color applications

The light absorption properties of particulate and dissolved materials strongly influence the propagation of visible light in oceanic waters and therefore the accuracy of ocean color algorithms. While the general absorption properties of these materials have been reported for Arctic waters, their seasonal variability remains unknown. We investigated the light absorption coefficients of phytoplankton [a ϕ ( λ )], nonalgal particles [a NAP ( λ )], and colored dissolved organic matter [a CDOM ( λ )] in both coastal and oceanic waters of the western Arctic Ocean from spring to autumn. Values for the chlorophyll a –specific absorption coefficient of phytoplankton [a* ϕ (440)] declined significantly from the ice melt period in the early spring to the summer. Using high‐performance liquid chromatography, we show that the decrease in a* ϕ (440) was due to a strong package effect that overwhelmed the influence of the pigment composition. A decrease in the a NAP ( λ ) values from spring and summer to autumn likely originated from a decrease in the concentration of phytoplanktonic detritus. The a CDOM ( λ ) near the surface decreased by 34% from spring to summer as a result of photobleaching by solar radiation. The colored dissolved organic matter (CDOM) absorption values then increased significantly during autumn, resulting from the cumulative injection of Alaskan Coastal Waters into the Arctic as well as CDOM generated in situ. Our results suggest that all of the absorption components are tightly linked to biogeochemical processes, and thus the seasonal variability in a ϕ ( λ ), a NAP ( λ ), and a CDOM ( λ ) should be taken into account in bio‐optical models.