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

摘要

The first record of dust deposition events on Mt. Elbrus, Caucasus Mountainsderived from a snow pit and a shallow firn core is presented for the2009–2012 period. A combination of isotopic analysis, SEVIRI red-green-bluecomposite imagery, MODIS atmospheric optical depth fields derived using theDeep Blue algorithm, air mass trajectories derived using the HYSPLIT modeland analyses of meteorological data enabled identification of dust sourceregions with high temporal (hours) and spatial (ca. 20–100 km) resolution.Seventeen dust deposition events were detected; fourteen occurred inMarch–June, one in February and two in October. Four events originated inthe Sahara, predominantly in northeastern Libya and eastern Algeria.Thirteen events originated in the Middle East, in the Syrian Desert andnorthern Mesopotamia, from a mixture of natural and anthropogenic sources.Dust transportation from Sahara was associated with vigorous Saharandepressions, strong surface winds in the source region and mid-troposphericsouthwesterly flow with daily winds speeds of 20–30 m s?1 at700 hPa level. Although these events were less frequent than thoseoriginating in the Middle East, they resulted in higher dust concentrationsin snow. Dust transportation from the Middle East was associated with weakerdepressions forming over the source region, high pressure centred over orextending towards the Caspian Sea and a weaker southerly or southeasterlyflow towards the Caucasus Mountains with daily wind speeds of12–18 m s?1 at 700 hPa level. Higher concentrations of nitrates andammonium characterised dust from the Middle East deposited on Mt. Elbrus in2009 indicating contribution of anthropogenic sources. The modal values ofparticle size distributions ranged between 1.98 μm and4.16 μm. Most samples were characterised by modal values of2.0–2.8 μm with an average of 2.6 μm and there was nosignificant difference between dust from the Sahara and the Middle East.