From ice to flow: Tracing the transformation of glacial dissolved organic matter across a typical Tibetan Plateau glacier-lake-stream continuum

Mountain glaciers are melting at an accelerated rate due to global warming, thereby significantly altering proglacial and downstream hydrology. However, the biogeochemical transformation of dissolved organic matter (DOM) along the glacier-lake-stream continuum remains unclear. We investigated DOM dynamics within a typical continuum on the Dagu Glacier (eastern Tibetan Plateau) by analyzing samples from supraglacial snow, surface ice, a proglacial lake, and downstream glacier-fed stream during the mid- (July) and late-melting (October) seasons of 2021, coupled with <i>in situ</i> incubation experiments at the glacier terminus. Optical spectroscopy revealed that protein-like components dominated the supraglacial snow, ice, and proglacial lake samples (≥62.8%), whereas stream samples exhibited higher proportions of humic-like components (20.6–37.2%), indicating an increasing terrestrial influence downstream. Ultrahigh-resolution mass spectrometry (FT-ICR MS) analysis further revealed a 12.8–35.8% decrease in aliphatic and peptide-like compounds, alongside a 12.7–36.2% increase in lignin, polyphenolic compounds, and polycyclic aromatic compounds along the continuum. The bio-incubation experiment confirmed that microbial degradation was the key driver of DOM transformation, demonstrating a 26.3% loss of aliphatic and peptide-like compounds over 30 days.<b> </b>These findings advance our understanding of glacial DOM biogeochemistry and its seasonal evolution.