Anthropogenic pollution can be entrained from the atmosphere into snow and sea ice where it causes increased absorption of solar radiation. Black carbon accounts for 85% of absorption by impurities in snow and sea ice. Increased absorption causes decreased snow and sea ice albedo, which has climatic consequences, and decreased light penetration, which affects photobiology and photochemistry of snow and sea ice. To investigate the effects of black carbon on sea ice two methods are utilised; radiative-transfer modelling and laboratory experiments with artificial sea ice. Firstly, radiative-transfer calculations are undertaken using the TUV (tropospheric ultraviolet- visible)-snow model, showing black carbon is most influential when concentrated in a surface 5 cm layer of a snow-free melting sea ice, which could exacerbate sea ice melting rates. A thin snow layer over sea ice (<5 cm) will “disguise” black carbon in sea ice, although times of year when sea ice is snow-free correspond with times of largest solar radiation, further exacerbating melt rates. Secondly, to validate the TUV-snow model, a sea ice simulator has been developed which creates sea ice in 2 tonne tanks, replicating polar temperatures, illumination conditions, seawater salinity, fabric of sea ice and ocean energy balance. Results from the response of the simulated sea ice to black carbon are compared to radiative-transfer calculations in order to validate the model. To recreate measurements of the artificial sea ice reflectance, using the TUV-snow model, the black carbon mass-ratio in the top layer of sea ice must be reduced by a factor of three in the model, compared to that added to the artificial ice. Two reasons are suggested for this; different absorption cross-section of black carbon added to the ice or mobilisation of black carbon from the artificial sea ice surface. The results presented in this thesis greatly improve understanding of the effects of black carbon in sea ice on albedo and light penetration depths, and are of use to climate modellers investigating global climatic effects of black carbon.
|1 Nov 2014
|Unpublished - 2014