Light-absorbing impurities can reduce the density of melting snow

Climatic effects of black carbon (BC) deposition on snow have been proposed to result from reduced snow albedo and increased melt due to light-absorbing particles. In this study, we hypothesize that BC may decrease the liquid-water retention capacity of melting snow, and present our first data, where both the snow density and elemental carbon content were measured.

In our experiments, artificially added light-absorbing impurities decreased the density of seasonally melting natural snow. No relationship was found in case of natural non-melting snow.We also suggest three possible processes that might lead to lower snow density. These include: 1. Semi-direct effect of absorbing impurities, where absorbing impurities would cause melt and/or evaporation from the liquid phase and sublimation from the solid phase of the surrounding snow, resulting in air pockets around the impurities, and thus lower snow density; 2. BC affecting the adhesion between liquid water and snow grains, i.e., if BC reduces adhesion, the liquid-water holding capacity decreases; 3. BC affecting the snow grain size. In this case, absorbing impurities would increase the melting and metamorphosis processes, resulting in larger snow grains, which would lower the water retention capacity.The results are significant because snow density is an important snow parameter found to correlate with factors affecting the snow melt (such as snow age and liquid-water holding capacity), and because snow density multiplied by snow depth equals the important climate model parameter of snow water equivalent (SWE). Our results may also have potential in reducing the uncertainties identified by the IPCC, related to the effect of black carbon on snow melt and climate change.For the paper, we used data from Sodankylä Arctic Research Center field campaigns of SoS-2013, SNORTEX-2010, SNORTEX-2009 and SR-2009. Filters from the 2010 snow samples were analyzed for BC by our co-operative partner S. Doherty, University of Washington. The work was supported by the Academy of Finland project "Arctic Absorbing Aerosols and Albedo of Snow", and the Nordic Center of Excellence (NCoE), Nordic Top Research Initiative "Cryosphere-atmosphere interactions in a changing Arctic climate" (CRAICC), and the EU Life+ project Mitigation of Arctic warming by controlling European black carbon emissions, MACEB.

More information:

Researcher Outi Meinander, outi.meinander@fmi.fi

Citation: Meinander O, A. Kontu, A. Virkkula, A. Arola, L. Backman, P. Dagsson-Waldhauserová, O. Järvinen, T. Manninen, J. Svensson, G. de Leeuw, and M. LeppärantaBrief communication: Light-absorbing impurities can reduce the density of melting snow. The Cryosphere, 8, 991-995, 2014http://www.the-cryosphere.net/8/991/2014/tc-8-991-2014.html