Spectral and Broadband Albedos of Antarctic Sea Ice Types: Snow, Nilas, Slush, Frost-flowers

The solar energy budget of the Antarctic Ocean is largely determined by fractional area covered by sea ice and the sea-ice albedo, which is highly variable depending on the surface type. The albedos of open water, nilas, nilas with frost-flowers, slush, and first-year ice with both thin and thick snow cover were measured in the East Antarctica sea ice zone during the Sea Ice Physics and Ecosystems Experiment II (SIPEX II) field campaign from September to November 2012, near 65S, 120E. This was a project of the Australian National Antarctic Research Expeditions (ANARE). These results augment a dataset from prior expeditions reported by Brandt et al. (2005), by extending the spectral coverage to longer wavelengths and by measuring some ice types that had not been encountered on the prior expeditions.

The spectral albedos were measured across the ultraviolet, visible, and near-infrared wavelengths using an ASD spectral radiometer. The albedo of snow on sea ice shows no evidence of light-absorbing particulate impurities (LAI) such as black carbon or organics, which is consistent with the extremely small quantities of LAI collected by filtering snow meltwater at the ice stations occupied during SIPEX-II. The albedo of snow depends on snow thickness as well as snow grain size. The albedo of bare nilas increases with nilas thickness, but the growth of frost-flowers causes the nilas albedo to increase dramatically by about 0.2 at the UV and visible wavelengths. Slush is formed when blowing snow falls into a lead of open water; its albedo increases with slush thickness. For all surface types except for open water, albedos are highest in the UV and visible and decrease while nilas has the most gradual decrease. The albedo of open water under diffuse illumination is constant at 0.07 for all wavelengths.

The spectral albedos are integrated over wavelength, using both clear-sky and cloudy-sky incident solar spectra, to obtain broadband albedos for wavelength bands commonly used in climate models.

Reference: Brandt, R.E., S.G. Warren, A.P. Worby, and T.C. Grenfell, 2005: Surface albedo of the Antarctic sea-ice zone. J. Climate, 18, 3606-3622.