Influence Of Sea Ice And Sea Ice Biota On Downwelling Irradiance And Spectral Composition Of Light In McMurdo Sound

A dense population of microalgae grows in the lower layers of annual sea ice in McMurdo Sound, Antarctica. The attenuation of light by surface snow, congelation and platelet sea ice, and ice microalgae was measured using an underwater spectroradiometer with a cosine collector. The in vivo absorption spectrum derived from in situ light measurements was com-parable to the in vivo absorption spectrum measured in the laboratory. Microalgae demonstrated an absorption peak at about 675 nm and a broad peak between 450 and 550 nm. Absorption of light by ice microalgae affects not only the total photosynthetically active radiation (PAR) but also the spectral composition of radiation available to under-ice phytoplankton. Thus biological as well as physical properties of sea ice determine the under-ice light field in polar oceans.