Abstract
Abstract. The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.
Highlights
Black carbon (BC) is a carbonaceous fine particle with strong light-absorbing ability
The elemental carbon (EC) concentrations ranged between 4.7 and 20.3 μg L−1, which is in the same range as EC concentrations of 1.4, 9.4 and 11.6 μg L−1 previously measured at the same site in spring surface snow of 2007, 2008 and 2009, respectively (Forsström et al, 2009, 2013; Fig. 4b)
There is a notable drop of a factor of 2.5 in the EC deposition values from the last data point in the 300-year ice core to the first sample in the firn core (9.3 mg m−2 yr−1 deposited between ca. mid2005 and early 2006) (Fig. 8)
Summary
Black carbon (BC) is a carbonaceous fine particle with strong light-absorbing ability. It is produced by natural and anthropogenic incomplete combustion of biomass and fossil fuels and may be transported with prevailing winds over thousands of kilometres from its emission sources Ramanathan and Carmichael, 2008; Bond et al, 2013). It poses a global environmental threat by warming the atmosphere, but the climate impacts of BC are amplified in the Arctic, where its deposition on snow and ice decreases surface reflectance and hastens snow and ice melt, which further decreases the re-. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
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