Spectral distribution of light under a subarctic winter lake cover

This study examines the spectral distribution of light penetrating the snow and ice cover of a lake in subarctic Labrador. Using a large sample under a range of cover conditions, the role of distinct layers, (snow, white or snow ice, black or clear ice) commonly found in subartic and temperate lake winter covers, was investigated. Measurement and analysis were restricted to wavelengths between 450 nm and 720 nm. Snow and white ice light transmittance was greatest at 450 and 470 to 500 nm respectively. Absorption was greatest in the red portion of the measured spectrum; white ice showing greater red absorption than snow. Black ice light transmittance showed only a slight wavelength dependence. The differential spectral absorption of light by snow and white ice layers produced a marked spectral distribution of the light that reaches the lake water surface. The importance of a spectral, rather than polychromatic, approach to the study of light, in winter biological limnology studies, is stressed.