Abstract
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.
Highlights
During the last century the Arctic has warmed twice as fast as the rest of the world, which is likely partly explained by changes in albedo and related feedbacks in the Arctic, a region covered with high reflectivity snow and ice (ACIA, 2005)
Atmospheric Black carbon (BC) measurements from the Arctic only go back to 1989, but the stations at Alert (Ellesmere Island, Canada), Barrow (Alaska, USA) and Zeppelin (Ny-Ålesund, Svalbard, Norway) record an overall 40 % decline in atmospheric BC concentrations between 1990 and 2009 (Sharma et al, 2013)
The atmospheric trend is explained by a general decrease in BC emissions in northern latitudes since the 1990s, in particular associated with the collapse of the Soviet Union (Hirdman et al, 2010a; Sharma et al, 2013)
Summary
During the last century the Arctic has warmed twice as fast as the rest of the world, which is likely partly explained by changes in albedo and related feedbacks in the Arctic, a region covered with high reflectivity snow and ice (ACIA, 2005). The climate effects of BC are intensified in snow and ice, where it lowers their reflectivity, leading to earlier spring melt BC has been estimated to be the second most important climate warming agent globally after carbon dioxide, and in the Arctic it is even more important than greenhouse gases (Jacobson, 2001; Hansen and Nazarenko, 2004; Bond et al, 2013). The BC-albedo effect has been suggested to have caused 20 % of the warming and snow- and ice-cover loss in Published by Copernicus Publications on behalf of the European Geosciences Union
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