Different dissolved organic matter composition between central and southern glaciers on the Tibetan Plateau

A large amount of dissolved organic matter (DOM) is stored in glacier ecosystems, which is crucial for downstream oligotrophic aquatic ecosystems during glacier melting. However, knowledge about their spatial differences in glacier ecosystems on the Tibetan Plateau (TP) is limited. We qualitatively and quantitatively analyzed the DOM in snow, ice, cryoconite, and glacier-fed streams in five glaciers in the central and southern TP using ultra-high-resolution mass spectrometry. Our results revealed that there were no significant differences in DOM concentrations or composition between the central and southern TP glaciers in snow and ice samples. However, the southern cryoconite contained significantly higher relative intensities of carbohydrate-, lignin-, tannin-, and condensed aromatic-like compounds and lower intensities of lipid-like compounds than the central cryoconite. In addition, the DOM molecules sustained in the cryoconite of the southern glacier were predominantly classified as condensed aromatic-like compounds, whereas those of the central TP glaciers were classified as lignin-like compounds. Except different terrestrial input, the network analysis and backward trajectory revealed that different bacterial composition and anthropogenic inputs caused this difference. Higher forest cover leaded to higher relative intensities of lignin- and tannin- DOM in the southern cryoconite than the central cryoconite. Sixty-six operational taxonomic units (OTUs) were associated with the degradation of lipid-, proteins/amino sugar- and lignin-like components which showed significantly higher relative abundance in the southern cryoconite than the central cryoconite. More anthropogenic inputs brought by the India monsoon affect the carbohydrate- and condensed aromatic-like compounds in the southern cryoconite. DOM exported into glacial streams of the central TP glaciers was dominated by tannin- and condensed aromatic-like compounds, whereas more labile components were discharged from the southern TP glacier. Our study provides new insights on the glacier DOM composition in and exported from different glaciers in the face of changing climate.