Source: Global Biogeochemical Cycles

Melting glaciers release more than just water. Organic matter once trapped in ice can run into streams and rivers, where it becomes food for microbes. These organisms respire the organic matter back to the atmosphere in the form of carbon dioxide, with potential implications for climate change.

Despite its importance in the carbon cycle, glacial organic matter is not well understood. Holt et al. addressed this gap by using ultrahigh-resolution mass spectrometry to characterize the organic matter in 136 glacial meltwater rivers across six continents. They focused specifically on dissolved organic matter less than 0.7 micrometer across.

The team’s analysis revealed a vast array of organic molecules with more than 35,000 distinct chemical formulas—each of which may be broken down to different extents and at different rates—with no two glaciers carrying exactly the same suite of molecules. Human activity around glaciers often affected the kinds of organic matter they released, the researchers noted. Some in places including Alaska and Nepal contained signatures of fossil fuel combustion because they receive material from industrial centers. Others, such as those in remote regions of Greenland and New Zealand, appeared to carry mostly organic matter made by microbes living within the glacier’s ecosystem.

Glacial melting is accelerating around the world, creating a growing source of greenhouse gases in the atmosphere. But this work demonstrates that the contributions from glaciers are not all the same. When assessing how glaciers will influence climate and ecosystem change, scientists must consider different glaciers independently, the authors suggest. (Global Biogeochemical Cycles, https://doi.org/10.1029/2024GB008212, 2024)

—Saima May Sidik (@saimamaysidik), Science Writer

Citation: Sidik, S. M. (2024), Each glacier has a unique organic matter composition, Eos, 105, https://doi.org/10.1029/2024EO240456. Published on 15 October 2024.

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