Influence of snow cover and algae on the spectral dependence of transmitted irradiance through Arctic landfast first-year sea ice

Extensive spatial and temporal observations of sea ice algae remain limited due in part to current destructive and time intensive sampling techniques. In this paper we examine the influence of snow cover and ice algal biomass on the spectral dependence of photosynthetically available radiation transmitted through the snow-ice matrix using a data set collected in Resolute Passage, Canada, from 3 to 21 May 2003. The relationships between a normalized difference index (NDI) of transmitted irradiance with ice algal biomass and with snow cover provided a means to examine and compare observational and modeled data. In contrast to the dominant scattering properties of snow, absorption largely controls the spectral diffuse attenuation coefficient of algae. Our results show that snow has little effect on the distribution of transmitted spectral irradiance at wavelengths between 400 and 550 nm, whereas algae have a strong absorption peak near 440 nm that dominates changes in spectral transmission across this wavelength range. Up to 89% of the total variation in algae biomass was accounted for with a single NDI wavelength combination. Therefore the blue wavelength peak in algal spectral absorption lends particularly well to the remote estimation of algae biomass using transmitted irradiance. Deviations between observed and modeled data highlight the need for improvements to model inputs and therefore more detailed observations of processes controlling snow, ice, and algae in situ optical properties.