Recent Increase in Elemental Carbon Concentration and Deposition in a Svalbard Ice Core

Black carbon (BC) is an aerosol produced by incomplete combustion of biomass and fossil fuels. Due to its strong light absorption it warms the atmosphere. Climate effects of BC are intensified in the Arctic where its deposition on snow and ice decreases surface albedo, causing earlier spring melt and associated feedbacks. Despite the significant role of BC in Arctic climate warming, there is little information on its concentrations and climate effects in the Arctic in time periods preceding direct observational data. Here we present first results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard (European Arctic) glacier (Holtedahlfonna) from 1700 to 2004. The inner part of a 125 m deep ice core was melted, filtered and analyzed for apparent elemental carbon using a thermal optical method. EC concentrations (μg L^-1) and the deposition (mg m^-2 yr^-1) were generally low in the pre-industrial era. Concentrations peaked around 1910 and again around 1950, whereas only the 1910 peak was recorded in the EC deposition, followed by decreasing deposition values. Strikingly, both EC concentration and deposition started to increase rapidly from the 1970s until 2004. This rise is not seen in any thus far published European or Arctic ice core, and it seems to contradict atmospheric BC measurements from the Arctic which indicate decreasing atmospheric BC concentrations since the beginning of the observations at the end of 1980s. However, the magnitude of the measured concentrations is in accordance with previous ice core EC measurements from the European Alps and a BC concentration and deposition peak around 1910 has also been recorded in Greenland ice cores. Work is continuing to disentangle the cause of the increasing EC values in the recent decades suggested by the present ice core. Contribution from any local sources has been ruled out. Back trajectory modeling is carried out to establish the EC source areas. The present results might indicate some long-range transport of EC to Svalbard, since BC emissions have decreased or stayed constant in Europe and North America for the last decades, whereas the emissions from China, India and parts of the former USSR have increased at the same time. Regardless of the cause of the increasing EC values, these results have significant implications to the past radiative transfer at the coring site. This project will continue with modeling of the past EC surface radiative forcing in the Holtedahlfonna area based on the present results.