The Spatial Distribution of Dissolved Organic Matter and Its Molecular Fingerprints in Seasonal Snow Over Northeastern China.

Dissolved organic matter in seasonal snow (DOMsnow) has a noticeable effect on the carbon cycle, carbon reserve, and ecosystems globally, but its regional characteristics remain unclear owing to a lack of surface measurements. The molecular compositions, potential sources, and degrees of oxidation of DOMsnow were investigated over northeastern China. The results of quantitative analysis for DOMsnow reflect the importance of anthropogenic influence. Fourier transform‐ion cyclotron resonance‐mass spectrometry analyses indicate that most (∼71%) identified molecular formulas are consistent with terrestrial compounds and derive from underlying soil and atmospheric deposition. Microbe‐derived compounds are also important contributors (∼34%) to the DOMsnow pool. The heterogeneous distribution of DOMsnow molecules is a complex process caused by many kinds of factors. Sulfate ions, organic aerosols, longitude, and altitude explain 76.2% of the regional difference in organic components. High levels of oxidation DOMsnow molecules are found, and such high reactive molecules indicate the presence of secondary organic matter and aging processes within the snowpack. The objective of this study is to investigate the characteristics of DOMsnow in high‐latitude regions of China so that we can further understand the impacts of changes in regional processes. Plain Language Summary: Dissolved organic matter in seasonal snow (DOMsnow) has significantly influenced ecosystems in cryospheric regions globally. The purpose of this study was to investigate the molecular compositions, potential sources, and influence factors of DOMsnow in northeastern (NE) China. We found that DOMsnow content in NE China was significantly influenced by anthropogenic factors. Molecules from the terrestrial environment contributed significantly to DOMsnow through atmospheric deposition and snow‐soil exchange. In addition, we identified a significant number of molecules with high oxidation, which are critical indicators of secondary organic products in snow. Sulfate ions, organic aerosols, longitude, and altitude may also play an important role in determining the regional heterogeneity of DOMsnow molecules. The proportion of DOMsnow compounds was not significantly different, but environmental differences could explain the difference in molecular weight. [ABSTRACT FROM AUTHOR]