Hydroclimatic significance of stable isotopes in precipitation from glaciers of Garhwal Himalaya, Upper Ganga Basin (UGB), India

Abstract

Stable isotopic composition of precipitation as preserved in continental proxy climate archives (e.g., ice cores, lacustrine sediments, tree rings, groundwater, and organic matter) can sensitively record fluctuations in local meteorological variables. These are important natural climatic tracers to understand the atmospheric circulation patterns and hydrological cycle and to reconstruct past climate from archives. Precipitation was collected at Dokriani Glacier to understand the response of glaciers to climate change in the Garhwal Central Himalaya, Upper Ganga Basin. The local meteoric water line deviates from the global meteoric water line and is useful for the identification of moisture source in the region. The data suggest different clusters of isotopic signals, that is, summer (June–September) and winter (November–April); the mean values of δ18O, δD, and d ‰ during summer are −13.03‰, −84.49‰, and 19.78 ‰, respectively, whereas during winter, the mean values of δ18O, δD, and d ‰ are −7.59‰, −36.28‰, and 24.46 ‰, respectively. Backward wind trajectory analysis ascertains that the major source of precipitation during summer is from the Indian Summer Monsoon and during winter from the westerlies. Regression analysis has been carried out in order to establish interrelationship between the precipitation isotopic signatures and meteorological variables such as air temperature, relative humidity, and precipitation. Temperature and precipitation have good correlation with the isotopic signatures of precipitation with R2 values >.5, suggesting that both temperature and amount effects prevail in the study region. Multiple regression analysis found strong relationships for both the seasons. The relationship of deuterium excess with δ18O, relative humidity, and precipitation are significant for the winter season. No significant relationships of deuterium excess were found with other meteorological variables such as temperature and radiation. The correlation and regression analysis performed are significant and valuable for interpretation of processes in the hydrological cycle as well as for interpretation of palaeoclimate records from the region.

Moisture Sources for Precipitation and Hydrograph Components of the Sutri Dhaka Glacier Basin, Western Himalayas

“…The Sutri Dhaka stream showed a slope of (7.1 ± 0.2) with an intercept of (5 ± 2.7). The slopes of the regression lines of all components (snow, ice, rain, stream) are similar within their uncertainty, which confirms that they have common moisture sources [20]. However, the intercepts of all components are highly variable, suggesting the effect of secondary isotope fractionation processes during precipitation events and melting processes.…”

“…Stable water isotope ratios of oxygen (δ 18 O) and hydrogen (δ 2 H), along with second order parameter, deuterium excess d − excess = δ 2 H − 8δ 18 O , have been widely used to trace moisture sources for precipitation, identify mixing water from various sources and to quantify their relative contributions [10,11]. Several isotope-based studies have been conducted in the Himalayan and polar regions to trace moisture sources and estimate the hydrograph components [12][13][14][15][16][17][18][19][20][21][22][23]. Moisture sources for precipitation over the central and eastern Himalayas are primarily derived from the Indian Summer Monsoon (ISM) during June-September, while moisture sources to the western Himalayas are predominantly derived from the Mediterranean region due to Western Disturbances (WDs) during winter (October-May) [6,24].…”

Study of isotopic seasonality to assess the water source of proglacial stream in Chhota Shigri Glaciated Basin, Western Himalaya

“…It is established that June end and late September act as the transitional months where onset and retreat of ISM take place, respectively in UCB. Seasonal variability in moisture source in UCB holds the analogous pattern with that of UGB (Verma et al, ). Moisture source variation in both basins is well corroborated with isotopic evolution of precipitated water (Sections 5.2 and 5.3) in the region.…”

“…Rainwater shows isotopic enrichment (δ 18 O/δD: −4.82‰/−16.96‰ and δ 18 O/δD: −8.57‰/−28.8‰) during either end of ablation season (June and October), respectively, whereas with the onset and influence of peak ISM during July (δ 18 O/δD: −10.59‰/−66.92‰), August (δ 18 O/ δD: −14.35‰/−95.57‰) and September (δ 18 O/δD: −16.01‰/−99.88‰) values are evident of being progressive depletion (Figure ). Rainwater over Chhota Shigri glacier catchment shows analogous and consistent pattern of isotopic seasonality with Chorabari glacier (Kumar et al, 2018), Dokriani glacier (Verma et al, ), and Gangotri glacier catchments (Rai et al, ) in the UGB during summer monsoon period (June–October). The glacier melt components (snow and glacier ice) obtained from winter deposited snowpack and shallow ice core (on the basis of their active melt layers involved in runoff generation) showed distinct isotopic characteristics.…”

“…Isotopic composition (δ 18 O/δD) of rainwater showed enrichment during either end of ablation season or non‐ISM period (June and October). In contrary, during peak ablation and influence of ISM (July end to September), progressive isotopic depletion is observed, attributed to the nature of climatic set‐up at moisture source, that is, Indian Ocean, rain out effect, and amount effect (Verma et al, ; Wei & Lin, ). Isotopic enrichment and depletion in rainwater reflecting the specific source conditions during water vapour formation driven by westerly (isotopic enriched) and ISM (isotopic depleted), respectively, in the Chhota Shigri glacierized catchment (Kumar et al, 2018).…”