Abstract
Abstract. A shallow ice core was extracted at the summit of Mera Peak at 6376 m a.s.l. in the southern flank of the Nepalese Himalaya range. From this core, we reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on a monsoonal precipitation pattern. According to the seasonal precipitation regime in which 80% of annual precipitation falls between June and September, we estimated changes in the concentrations of these aerosols in surface snow. The analyses revealed that mass fluxes are a few orders of magnitude higher for dust (10.4 ± 2.8 g m−2 yr−1 than for rBC (7.9 ± 2.8 mg m−2 yr−1). The relative lack of seasonality in the dust record may reflect a high background level of dust inputs, whether from local or regional sources. Over the 10-year record, no deposition flux trends were detected for any of the species of interest. The data were then used to simulate changes in the surface snow albedo over time and the potential melting caused by these impurities. Mean potential melting caused by dust and rBC combined was 713 kg m−2 yr−1, and for rBC alone, 342 kg m−2 yr−1 for rBC under certain assumptions. Compared to the melting rate measured using the mass and energy balance at 5360 m a.s.l. on Mera Glacier between November 2009 and October 2010, i.e. 3000 kg m−2 yr−1 and 3690 kg m−2 yr−1 respectively, the impact of rBC represents less than 16% of annual potential melting while the contribution of dust and rBC combined to surface melting represents a maximum of 26%. Over the 10-year period, rBC variability in the ice core signal primarily reflected variability of the monsoon signal rather than variations in the intensity of emissions.
Highlights
We investigated the impact of refractory black carbon and dust on seasonal changes in surface albedo and the melting it may have caused over the last decade
Like water stable isotopes, refractory black carbon (rBC), ammonium or fluoride deposition are consistent with the precipitation patterns related to the monsoon, with higher or spiking concentrations during the dry season. rBC concentrations were compared with black carbon (BC) atmospheric measurements made at the Nepal Climate Observatory Pyramid (NCO-P) site
With this study using aerosol fluxes reconstructed from Mera Glacier firn core analyses combined with atmospheric measurements made at the Nepal Climate Observatory – Pyramid site, we estimated their impact on glacier melting
Summary
Quantifying emissions is one of the major challenges for the development of air quality and climate policies (Fowler et al, 2009; Isaksen et al, 2009) and quantification should account for different changes in human-related emissions and natural emissions over time as well as changes in their geographical distribution. Major uncertainties in past and current global inventories of anthropogenic and natural emissions limit the establishment of a reliable framework of emission inventories that is required for realistic emission scenarios. This is especially true for the Indian subcontinent where reliable estimates of past and current emissions are crucially lacking. India on its own contributes 10 to 20 % of all current aerosol emissions worldwide (Bond et al, 2007) and has received the greatest attention from compilers of emission inventories
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