The sources of supra-permafrost water and its hydrological effect based on stable isotopes in the third pole region

The sources of supra-permafrost water and its hydrological effects were studied, based on the presence of stable isotopes in 562 samples collected in different ablation periods from the source regions of the Yangtze River. The δ¹⁸O (δD and d-excess) values for the initial ablation, ablation, and end ablation periods were -10.18‰ (-71.39‰ and 10.08‰), -12.14‰ (-85.58‰ and 11.51‰) and -11.50‰ (-78.75‰ and 13.23‰), respectively. The order of the slopes for the supra-permafrost water evaporation lines from the different ablation periods was initial ablation (IA) > ablation (A) > end ablation (EA). An anti-altitude effect is documented here, for a specific altitude range, in what is believed to be the first record of such an occurrence. Outside of that range, clear altitude effects were apparent. We have been able to show that supra-permafrost water was mainly recharged by atmospheric precipitation, ground ice, and glacier and snow meltwater, in the initial ablation and end ablation periods, and contributions from glacier and snow meltwater were mainly concentrated in higher altitude regions. In contrast, in the ablation period, supra-permafrost water was mainly recharged by atmospheric precipitation and ground ice. The contributions of precipitation to supra-permafrost water were 78.79%, 85.47%, and 82.99% in the initial ablation, ablation, and end ablation periods, respectively. The contributions of ground ice to the supra-permafrost water were 14.05%, 14.53%, and 11.94%, respectively, while contributions of glacier and snow meltwater were 7.15% and 5.07% in the initial and end ablation period. For the initial ablation, ablation, and end ablation periods, contributions from atmospheric precipitation to the supra-permafrost water were 85.47%, 86.86%, and 86.84%, while contributions from ground ice were 14.53%, 13.14% and 13.16%, respectively.