Observations of ultraviolet light reflection and transmission by first‐year sea ice

Abstract

As part of a comprehensive program investigating the electromagnetic properties of sea ice, measurements were made of the optical properties of young ice and first‐year sea ice at ultraviolet wavelengths. Young sea ice observations were made in a specially designed sea ice pond at the Cold Regions Research and Engineering Laboratory (Hanover, NH), while first‐year sea ice was examined in the Chukchi Sea and Beaufort Sea near Barrow, Alaska. The results indicated that, in general, albedo increased with increasing wavelength from 305 to 380 nm, with values for first‐year ice in the 0.4 to 0.6 range. Transmittance through bare first‐year ice was roughly 0.5 to 2 percent. Extinction coefficients for bare sea ice were between 2 and 4 m−1 and decreased with increasing wavelength. The presence of a snow cover had a profound impact on ultraviolet light levels under sea ice, with even a thin (0.1‐m‐thick) snow cover reducing transmitted ultraviolet light by more than an order of magnitude. Observed transmittances indicated that the attenuation of ultraviolet light by sea ice and snow was greater than that of the photosynthetically active radiation.