Optical properties of sea ice doped with black carbon – an experimental and radiative-transfer modelling comparison

Radiative-transfer calculations of the light reflec- tivity and extinction coefficient in laboratory-generated sea ice doped with and without black carbon demonstrate that the radiative-transfer model TUV-snow can be used to pre- dict the light reflectance and extinction coefficient as a func- tion of wavelength. The sea ice is representative of first-year sea ice containing typical amounts of black carbon and other light-absorbing impurities. The experiments give confidence in the application of the model to predict albedo of other sea ice fabrics.
Sea ices, ∼ 30 cm thick, were generated in the Royal Hol- loway Sea Ice Simulator (∼ 2000 L tanks) with scattering cross sections measured between 0.012 and 0.032 m2 kg−1 for four ices. Sea ices were generated with and without ∼ 5 cm upper layers containing particulate black carbon. Nadir reflectances between 0.60 and 0.78 were measured along with extinction coefficients of 0.1 to 0.03cm−1 (e- folding depths of 10–30 cm) at a wavelength of 500 nm. Val- ues were measured between light wavelengths of 350 and 650 nm. The sea ices generated in the Royal Holloway Sea Ice Simulator were found to be representative of natural sea ices.
Particulate black carbon at mass ratios of ∼ 75, ∼ 150 and ∼300ngg−1 in a 5cm ice layer lowers the albedo to 97, 90 and 79 % of the reflectivity of an undoped “clean” sea ice (at a wavelength of 500 nm).