Spatial and seasonal variation of major ions in Himalayan snow and ice: A source consideration

The spatial and temporal variation of major ions (Ca2+, Mg2+, Na+, K+ NH4+, SO42-, NO3- and Cl-) in Himalayan snow and ice is investigated by using two snow pits from the East Rongbuk glacier (28 degrees 01'N, 86 degrees 58'E, 6500 m a.s.l.), one snow pit from the Nangpai Gosum glacier (28 degrees 03'N, 86 degrees 39'E, 5700 m a.s.l.), one snow pit from the Gyabrag glacier (28 degrees 11N, 86 degrees 38'E, 6303 m a.s.l.), and three ice cores from the Sentik (35 degrees 59'N, 75 degrees 58'E, 4908 m a.s.l.), Dasuopu (28 degrees 33'N, 85 degrees 44'E, 7000 m a.s.l.), and East Rongbuk (27 degrees 59'N, 86 degrees 55'E, 6450 m a.s.l.) glaciers, respectively. In general, the major ions show a significant seasonal variation, with high concentrations during the non-monsoon (pre-monsoon and post-monsoon) season and relatively low concentrations during the monsoon season. Monsoon precipitation with high local/regional dust loading related to summer circulation is possibly responsible for the high concentrations occurring sporadically during the monsoon season. The crest of the Himalayas is an effective barrier to the spatial distribution of Na+ Cl- and NH4+ concentrations, but not to the major ions associated with dust influx (e.g. Ca2+ and Mg2+). Atmospheric backward trajectories from the HYSPLIT_4 model used in identifying chemical species sourcing suggest that the major ions in the Himalayan snow and ice come mainly from the Thar Desert located in the North India, as well as West Asia, or even the distant Sahara Desert in the North Africa during the winter and spring seasons. This is different from the conventionally assumed and and semi-arid regions of the central Asia. Factors, such as different vapor sources due to atmospheric circulation patterns and geographical features (e.g. altitude, topography), may contribute to the differences in major ionic concentrations between the western and eastern Himalayas. (C) 2009 Elsevier Ltd. All rights reserved.