Seasonal variability of light absorption properties and water optical constituents in Hudson Bay, Canada

Previous studies have shown that the properties of optically significant water constituents (phytoplankton, suspended matter, and colored dissolved organic matter (CDOM)) in Hudson Bay are different from other Arctic regions. A new bio‐optical data set collected in summer 2010 shows that this region also presents seasonal variability of the light absorption coefficients by the different constituents, with a higher relative proportion of CDOM absorption in summer than in the fall as a result of decreased phytoplankton absorption in summer. The slope of the exponential function describing nonalgal particles and CDOM spectral absorption shows little variability between fall and summer. Seasonal variability of light absorption coefficients and water optical constituents is more pronounced near the coast, while less variability is observed in the central part of the bay. Very low summertime chlorophyll‐specific absorption coefficients by phytoplankton, among the lowest reported in the literature, are attributed to the high proportion of large size phytoplankton (microphytoplankton) and important packaging effect. There is also a smaller contribution of accessory pigments to total pigments in the summer than in the fall, resulting in a lower blue‐to‐red phytoplankton absorption ratio. These results emphasize that it is necessary to take into account the seasonal variability of light absorption properties in bio‐optical models for further remote sensing applications in Hudson Bay.