Observing the isotopic evolution of snow meltwater helps in understanding the process of snow melting but remains a challenge to acquire in the field. In this study, we monitored the melting of two snowpacks near Baishui Glacier No. 1, a typical temperate glacier on the southeastern Tibetan Plateau. We employed a physically based isotope model (PBIM) to calculate the isotopic composition of meltwater draining from natural snowpacks. The initial condition of the PBIM was revised to account for natural conditions, i.e., the initial δ18O stratigraphy of snow layers before melting. Simulations revealed that the initial heterogeneity of δ18O in snow layers as well as ice-liquid isotopic exchange were responsible for most variations of δ18O in snow meltwater, whereas new snow and wind drift could result in sudden changes of the isotopic composition of the meltwater. The fraction of ice involved in the isotopic exchange (f) was the most sensitive parameter for the model output. The initial δ18O in the snowpack is mirrored in meltwater in case of small f and is smoothed with a large exchange fraction f. The other unknown parameter of the PBIM is the dimensionless rate constant of isotopic exchange, which depends on water percolation and initial snow depth. The successful application of the PBIM in the field might not only be useful for understanding snow melting process but might also provide the possibility of predicting the isotopic composition of snow meltwater and improve the accuracy of hydrograph separation.
Bibliographical noteFunding Information:
This research was supported by the National Natural Science Foundation of China (91647101 and 41705132), the State Key Laboratory of Cryospheric Sciences (SKLCS‐ZZ‐2020), and the China Postdoctoral Science Foundation (2016 T90964 and 2014 M552517). The authors greatly thank all the colleagues from Yulong Snow Mountain Glacier‐Environmental Observation and Research Station for their help in sampling and thank the reviewers for their constructive comments, which were greatly helpful for improving the quality of the paper.
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- Tibetan Plateau
- isotopic evolution
- isotopic exchange
- snow meltwater
- temperate glacier