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[1] 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 8 (l)], nonalgal particles [a NAP (l)], and colored dissolved organic matter [a CDOM (l)] 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* 8 (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* 8 (440) was due to a strong package effect that overwhelmed the influence of the pigment composition. A decrease in the a NAP (l) values from spring and summer to autumn likely originated from a decrease in the concentration of phytoplanktonic detritus. The a CDOM (l) 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 8 (l), a NAP (l), and a CDOM (l) should be taken into account in bio-optical models.

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[1] Recent observations show visible light attenuation in the Arctic Ocean to be greater than previously assumed. High attenuation observed during the period prior to ice melt and increased phytoplankton production, was attributed primarily to the high levels of absorption by chromophoric dissolved organic material (CDOM) present in these waters. Preliminary evidence suggests this material is produced by ice algae in the early spring. Optical data from the Chukchi shelf system collected in the spring and summer of 2002, were used to model energy absorption in the mixed layer by both dissolved and particulate material. In the spring, absorption by CDOM was responsible for increasing the energy absorbed in the mixed layer by 40% over pure seawater. Thus CDOM absorption represents a significant factor in the heating budget of Arctic surface waters. The energy absorbed by CDOM has the potential to account for 48% of the springtime ice melt driven by water column heating. With continued warming, negative feedback due to loss of ice algae habitat could slow down heating effects in the spring. However, terrestrial input of CDOM to the Arctic is postulated to increase due to the release of organic carbon from thawing permafrost. Coupled with the loss of the highly reflective sea ice cover during the spring and summer, CDOM absorption may become increasingly influential in the heating budget of Arctic surface waters.