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Oxygen and deuterium isotope characteristics of Teesta river catchment from Sikkim Himalaya, India: Implications of different moisture sources

Sheikh Nawaz Ali, Anupam Sharma, Shailesh Agrawal, M. G. Yadava, R. A. Jani, Jyotsna Dubey, P. Morthekai
Geochemical Journal, Vol. 54, No. 5, P. 327-336, 2020

ABSTRACT

The present investigations of δ18O and δD values of Teesta river system (glacier fed; Eastern Indian Himalaya) along a steep altitudinal gradient has helped to better understand the spatial variability of the isotopic composition in water and moisture sources. We have used the stable isotope composition of the main Teesta River, its major tributaries, glacial melt streams (nallah) and few high altitude lakes. As the region is dominated by Indian Summer Monsoon precipitation brought by the Bay of Bengal Branch, the δ18O values ranges from ~–11 to –15‰ and δD from ~–41 to –128‰ in the main Teesta River. We propose that as the monsoonal moisture penetrates along the river valleys towards higher Himalaya, a progressive depletion in 18O and D isotopes take place during orographic lifting, resultant cooling and progressive rainout. It is observed that d-excess values range between –1 to 18 and suggests mixed moisture source having contributions from moisture originating in Bay of Bengal and mid-latitude westerlies.

KEYWORDS

Indian summer monsoon, water isotopes, Bay of Bengal, Eastern Himalaya, mid-latitude westerlies

Supplementary Materials(file)

https://www.jstage.jst.go.jp/article/geochemj/54/5/54_2.0604/_supplement/_download/54_2.0604_1.pdf

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