Advances in Glacier Biogeochemistry: A Global Survey of Dissolved Organic Matter in Glacial Meltwater

Abstract In their 1999 paper “ Widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling ,” Sharp and co‐authors initiated a paradigm shift from glaciers viewed as abiotic systems to glacier environments hosting active microbial communities and corresponding biogeochemical cycling. Since then, the field of glacier biogeochemistry has sought to elucidate how these microbes function and the consequences of their activity in glacial and proglacial environments, and for global biogeochemical cycles. Subsequent research has supported the existence of active biogeochemical cycling by the “glacial microbiome.” Paradoxically, dissolved organic matter (DOM) exported in glacier meltwater is both ancient and a labile source of organic carbon that may be readily incorporated into downstream ecosystems. Further, DOM that has been characterized in glacier systems (using both fluorescence spectroscopy and ultrahigh resolution mass spectrometry) from different locations shares specific fluorescence and molecular formulae characteristics, hinting at a potential commonality in “glacial DOM.” The recent manuscript “ Gradients of Deposition and In Situ Production Drive Global Glacier Organic Matter Composition ” (Holt et al., 2024, https://doi.org/10.1029/2024gb008212 ) addresses these two observations by employing Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) to characterize DOM composition at the molecular level from glacier sites located around the globe. The use of both the powerful FT‐ICR MS technique and an unparalleled global glacier data set offers a unique insight into glacier DOM variability and commonality, and the source of ancient and/or labile DOM in glacier runoff. Further, the study provides an impetus for specific future lines of investigation.