Abstract. The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65 • N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m −2 and for the snow-albedo effect 0.016 W m −2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.

[1] The concentration of apparent elemental carbon (EC a , based on a thermal-optical method) in the snow was investigated in Svalbard (European Arctic) during spring 2007. The median EC a concentration of 81 samples was 4.1 mg l À1 and the values ranged from 0 to 80.8 mg l À1 of melt water. The median concentration is nearly an order of magnitude lower than the previously published data of equivalent black carbon (BC e , based on an optical method), obtained from Svalbard snow in the 1980s. A systematic regional difference was evident: EC a concentrations were higher in east Svalbard compared to west Svalbard. The observations of snow EC a cover spatial scales up to several hundred kilometers, which is comparable to the resolution of many climate models. Measurements of atmospheric carbonaceous aerosol (2002)(2003)(2004)(2005)(2006)(2007)(2008) at Zeppelin station in Ny-Å lesund, Svalbard, were divided to air mass sectors based on calculated back trajectories. The results show that air originating from the eastern sector contains more than two and half times higher levels of soot than air arriving from south to west. The observed east-west gradient of EC a concentrations in snow may be because of a combination of the atmospheric concentration gradient, the orographic effect of the archipelago, and the efficient scavenging of the carbonaceous particles through precipitation.

[1] Black carbon (BC) and other light-absorbing particles deposited on snow and ice are known to perturb the surface radiative balance. There are few published observations of the concentration of these particles in the snow in Scandinavia and the European Arctic. We measured BC concentrations in snow samples collected in this region from 2007 to 2009, and we present the results here. The data set includes 484 surface samples and 24 column samples (covering the accumulation season) from snow on land, glaciers, and sea ice. Concentrations up to 88 ng of carbon per gram of snow (ng/g) were found in Scandinavia, while lower values were observed at higher latitudes: 11-14 ng/g in Svalbard, 7-42 ng/g in the Fram Strait, and 9 ng/g in Barrow. Values compare well with other observations but are generally found to be a factor of 2-3 higher than modeled BC concentrations in snow in the chemical transport model Oslo CTM2. This model underestimation comes in spite of potentially significant undercatch in the observations. The spring melt period enhanced BC levels in surface snow at the four sites where the BC concentrations were monitored from March to May in 2008 and 2009. A data set of replicate samples is used to establish a concentration-dependent estimate of the meter-scale variability of BC concentration in snow, found to be around ±30% of the average concentration.

Abstract. Black carbon (BC) is a light-absorbing particle that warms the atmosphere–Earth system. The climate effects of BC are amplified in the Arctic, where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming, there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal–optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004 after a temporary low point around 1970, reaching unprecedented values in the 1990s. This rise is not seen in Greenland ice cores, and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. For example, changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere are discussed for the differences between the Svalbard and Greenland ice core records, as well as the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values between 1970 and 2004, the results have significant implications for the past radiative energy balance at the coring site.

[1] Today we experience an accelerated melting of sea ice in the Arctic which global circulation models are inadequate to predict. We believe one of the reasons is the shortcomings in the sea ice albedo schemes for these models. This paper investigates a physically based sea ice albedo scheme for ECHAM5 GCM, which separates between snow-covered sea ice, bare sea ice, melt ponds, and open water (separately for the albedos and albedo fractions). The new albedo scheme includes important components such as albedo decay due to snow aging, bare sea ice albedo dependent on the ice thickness, and a melt pond albedo dependent on the melt pond depth. The explicit treatment of melt pond albedos has, to our knowledge, not been included in general circulation models before and represents a substantial improvement when simulating the annual cycle of sea ice albedo. The new albedo scheme overall reduces the sea ice albedo both in winter, because of snow aging, and in summer, because of melt ponds. The reduced sea ice albedo leads to overall reduced sea ice thickness, concentration, and volume, with large temporal and spatial variations. In the Northern Hemisphere in March, some areas experience increased albedo, resulting in thicker sea ice and higher ice concentration, but in August the pattern is spatially homogeneous, with reduced albedo, thickness, and concentrations for all areas where the new scheme has a significant effect.