The effects of additional black carbon on the albedo of Arctic sea ice: variation with sea ice type and snow cover
Other literature type, Article
Marks, A. A.
King, M. D.
- Publisher: Copernicus Publications
(issn: 1994-0424, eissn: 1994-0424)
GE1-350 | QE1-996.5 | Environmental sciences | Geology
The response of the albedo of bare sea ice and snow-covered sea ice to the addition of black carbon is calculated.
Visible light absorption and light-scattering cross-sections are derived for a typical first-year and multi-year sea ice
with both "dry" and "wet" snow types. The cross-sections are derived using data from a 1970s field study that
recorded both reflectivity and light penetration in Arctic sea ice and snow overlying sea ice. The variation of
absorption cross-section over the visible wavelengths suggests black carbon is the dominating light-absorbing
impurity. The response of first-year and multi-year sea ice albedo to increasing black carbon, from 1 to 1024 ng g<sup>−1</sup>,
in a top 5 cm layer of a 155 cm-thick sea ice was calculated using a radiative-transfer model. The albedo of the
first-year sea ice is more sensitive to additional loadings of black carbon than the multi-year sea ice. An addition
of 8 ng g<sup>−1</sup> of black carbon causes a decrease to 98.7% of the original albedo for first-year sea
ice compared to a decrease to 99.7% for the albedo of multi-year sea ice, at a wavelength of 500 nm. The
albedo of sea ice is surprisingly unresponsive to additional black carbon up to 100 ng g<sup>−1</sup> . Snow layers
on sea ice may mitigate the effects of black carbon in sea ice. Wet and dry snow layers of 0.5, 1, 2, 5 and 10 cm
depth were added onto the sea ice surface. The albedo of the snow surface was calculated whilst the black carbon
in the underlying sea ice was increased. A layer of snow 0.5 cm thick greatly diminishes the effect of black carbon
in sea ice on the surface albedo. The albedo of a 2–5 cm snow layer (less than the <i>e</i>-folding depth of snow)
is still influenced by the underlying sea ice, but the effect of additional black carbon in the sea ice is masked.