Distribution and isotopic compositions of n-alkanes and n-alkenes in the cryoconites from the Tibetan Plateau glaciers

In the current study, cryoconite samples were collected from six glaciers on the Tibetan Plateau to analyze n -alkanes and n -alkenes. The findings revealed that the concentrations of n -alkanes and n -alkenes varied from 40.1 to 496.1 μg g −1 and from 4.6 to 13.8 μg g −1 , respectively. The carbon preference index of the long-chain n -alkanes ranged from 3.3 to 8.4, and the average chain length ranged from 28.7 to 29.3. Moreover, the δ 13 C of the n -alkanes in cryoconites were within the range of C 3 plants, demonstrating that the n -alkanes in cryoconites were only derived from vascular plants. However, the δD mean were more negative than that of C 3 plants, which could be caused by dry and humid conditions of glaciers. Unlike n -alkanes, n -alkenes ranged from C 17:1 to C 30:1 and showed a weak even-over-odd carbon number preference in the Dongkemadi, Yuzhufeng, Laohugou and Tianshan glacier, but a weak odd carbon preference in the Qiyi glacier. The n -alkenes in the YL Snow Mountains showed an obvious odd-over-even carbon number predominance from C 17:1 to C 22:1 with C max at C 19:1 , and the even-over-odd carbon number preference from C 23:1 to C 30:1 with C max at C 28:1 . This demonstrated that the n -alkenes of cryoconites may be mainly derived from in situ production in glaciers.