Isotopic signature of snow and glacier water sources across the Annapurna Himalayas
Abstract
Himalayan rivers supply water to most of South-East Asia. It is important to understand sources contributions of these rivers, especially during the long lasting dry season when upland storages slowly drain. During summer months, monsoon rains dominate river discharge in the Himalayas; while during baseflow, river discharge is maintained by upland storage from groundwater, snow, and glacier ice. Yet, the role and dimensions of these different storage components in the Himalayan cycle are not well understood. Here, we investigate the melt contribution to river discharge during baseflow with stable isotope analysis prior to the emerging 2015 monsoon season. We sampled water end-members of both snow and glaciers as well as of rivers and tributaries from both sides of the mountain range. Sampling locations around Annapurna covered elevations from <1 to >5km asl. Our analysis shows a range of isotopic signature of river waters around δ18O -14.4+/- 1.7 ‰ n = 70, glacier samples around δ18O -17.7+/- 1.6‰ n =11, and snow samples around δ18O -14.5+/- 5.5‰ n = 35. Deuterium excess depicts local evaporation and condensation conditions of water vapor and appears to distinguish water storage compartments throughout the study area. We observe decreasing D-excess of our end-members across the orographic barrier, from the Modi Khola Catchment in the south (D-excess 17.2+/- 2.5‰ n =16) to the Marshyangdi Catchment in the north (D-excess 13.7 +/- 1.3‰ n = 29). The Kali Gandaki River cuts through the orographic barrier, connecting the wet south with the dry north. It integrates a mixing signal of western (D-excess 15.5 +/-0.7‰ n = 3) and eastern (D-excess 11.1 +/-0.2‰ n = 4) sources with steadily decreasing D-excess towards the north. These different signals are used in a mixing model to calculate water contributions of different landscapes and storage compartments to the river discharge across the orographic barrier. Our results demonstrate that glaciers along the southern edge of the Tibetan Plateau can be distinguished by their characteristic isotopic signature. Using this distinct signature enables us to unravel melt contributions across the Himalayan to the large rivers supplying the Himalayan foreland with water.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMPP31D2338H
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 1833 Hydroclimatology;
- HYDROLOGYDE: 4904 Atmospheric transport and circulation;
- PALEOCEANOGRAPHYDE: 4914 Continental climate records;
- PALEOCEANOGRAPHY