Increase in elemental carbon values between 1970 and 2004 observed in a 300-year ice core from Holtedahlfonna (Svalbard)

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.

Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?

“…The high-elevation Greenland records indicate a BC deposition peak around 1910 followed by rapidly decreasing deposition until 1950 and more or less stable, almost preindustrial values until the present (McConnell, 2010). The Svalbard ice core clearly concurs with the Greenland records for the early 20th century but unexpectedly shows a pronounced increase in BC concentrations and deposition from 1970 to the top of the core in 2004 (Ruppel et al, 2014). The reasons for the observed post-1970 BC deposition increase in Svalbard -while at the same time Greenland ice cores, atmospheric measurements (e.g.…”

“…The increasing BC deposition on the Svalbard glacier has significant effects on the radiative budget of this site and concurs with substantially increased summer melting of the glacier since the 1980s (Ruppel et al, 2014). The increased melt of the glacier is better explained by the combination of observed increasing summer temperatures and the increasing BC concentrations than by increasing temperatures alone.…”

“…Four continuous BC ice core records covering ca. 1750 to 2013 have been published from Greenland (McConnell et al, 2007;McConnell and Edwards, 2008;McConnell, 2010;Keegan et al, 2014) and one 300-year record (1700 to 2004) from Svalbard (Ruppel et al, 2014). The high-elevation Greenland records indicate a BC deposition peak around 1910 followed by rapidly decreasing deposition until 1950 and more or less stable, almost preindustrial values until the present (McConnell, 2010).…”

“…Sharma et al, 2013) and model results (e.g. Koch et al, 2011) suggest decreasing BC values -was left partly unresolved (Ruppel et al, 2014). Increasing flaring emissions from northern Russia in the Barents Sea area that do not reach the Greenland ice coring sites due to restricted isentropic uplift in the Arctic, and potentially increasing wetscavenging efficiency due to increasing temperatures particularly around Svalbard, were the leading hypotheses (Ruppel et al, 2014).…”

“…The increased melt of the glacier is better explained by the combination of observed increasing summer temperatures and the increasing BC concentrations than by increasing temperatures alone. To estimate the extent of the climatic implications suggested in Ruppel et al (2014) it is essential to solve whether the observed increasing BC deposition trend in Svalbard since 1970 can be corroborated with other data. Furthermore, it is necessary to thoroughly assess the BC sources responsible and the deposition processes associated to the observed increase because these may affect also other parts of the Arctic.…”