High-resolution provenance of desert dust deposited on Mt. Elbrus, Caucasus in 2009–2012 using snow pit and firn core records

S Kutuzov,V Mikhalenko,P Ginot,I Lavrentiev,S Kemp,M Shahgedanova

doi:10.5194/tc-7-1481-2013

Abstract

Abstract. The first record of dust deposition events on Mt. Elbrus, Caucasus Mountains derived from a snow pit and a shallow firn core is presented for the 2009–2012 period. A combination of isotopic analysis, SEVIRI red-green-blue composite imagery, MODIS atmospheric optical depth fields derived using the Deep Blue algorithm, air mass trajectories derived using the HYSPLIT model and analyses of meteorological data enabled identification of dust source regions with high temporal (hours) and spatial (ca. 20–100 km) resolution. Seventeen dust deposition events were detected; fourteen occurred in March–June, one in February and two in October. Four events originated in the Sahara, predominantly in northeastern Libya and eastern Algeria. Thirteen events originated in the Middle East, in the Syrian Desert and northern Mesopotamia, from a mixture of natural and anthropogenic sources. Dust transportation from Sahara was associated with vigorous Saharan depressions, strong surface winds in the source region and mid-tropospheric southwesterly flow with daily winds speeds of 20–30 m s−1 at 700 hPa level. Although these events were less frequent than those originating in the Middle East, they resulted in higher dust concentrations in snow. Dust transportation from the Middle East was associated with weaker depressions forming over the source region, high pressure centred over or extending towards the Caspian Sea and a weaker southerly or southeasterly flow towards the Caucasus Mountains with daily wind speeds of 12–18 m s−1 at 700 hPa level. Higher concentrations of nitrates and ammonium characterised dust from the Middle East deposited on Mt. Elbrus in 2009 indicating contribution of anthropogenic sources. The modal values of particle size distributions ranged between 1.98 μm and 4.16 μm. Most samples were characterised by modal values of 2.0–2.8 μm with an average of 2.6 μm and there was no significant difference between dust from the Sahara and the Middle East.

Highlights

Ice and firn cores provide a valuable proxy data on climatic and environmental changes including changes in aridity as documented by mineral dust deposited on glacier surface and trapped in ice (Legrand and Mayewski, 1997; Thompson et al, 2006)
The snow pit record began 7 September 2009, when the pit was excavated and extended to the winter of 2009–2008. It is not clear whether the shallow core and the snow pit isotopic records overlap and it is possible that a short period at the end to middle of September 2009 is not represented
While deposition of the Saharan dust on glaciers was detected in many studies (e.g. Schwikowski et al, 1995; Sodemann et al, 2006; Wagenbach and Geis, 1989), so far the Caucasus is the only region where deposition of dust originating in the Middle East was researched in detail

Summary

Introduction

Ice and firn cores provide a valuable proxy data on climatic and environmental changes including changes in aridity as documented by mineral dust deposited on glacier surface and trapped in ice (Legrand and Mayewski, 1997; Thompson et al, 2006). Present and past records of dust, stored in glacier ice, provide valuable information on frequency of deposition events, sources and atmospheric pathways of mineral dust which can be used to assess changes in atmospheric circulation, environments in source regions and validate climate models (Xu et al, 2010; Wu et al, 2013). Delmonte et al, 2002; Petit et al, 1999; Ruth, 2003) These records characterise global and long-range dust transportation patterns and changes on the millennial time scales. A number of studies examined variability in mineral dust transportation and deposition on glaciers of Central Asia (Dong et al, 2009; Kreutz et al, 2001; Thompson et al, 1989; Wake et al, 1994; Yang et al, 2006), Himalayas and Tibetan Plateau (Kaspari et al, 2009; Wu et al, 2009, 2013; Xu et al, 2010) and the Altai (Olivier et al 2003; 2006)

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