{"id":442779,"date":"2026-05-06T04:22:31","date_gmt":"2026-05-06T11:22:31","guid":{"rendered":"https:\/\/climatescience.press\/?p=442779"},"modified":"2026-05-06T04:22:33","modified_gmt":"2026-05-06T11:22:33","slug":"ancient-subglacial-methane-reveals-major-mid-holocene-retreat-of-the-greenland-ice-sheet","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=442779","title":{"rendered":"Ancient Subglacial Methane Reveals Major Mid-Holocene Retreat of the Greenland Ice Sheet"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

Researchers sampled 26 meltwater streams<\/strong> across the entire western margin of the Greenland Ice Sheet (GrIS). They found pervasive, biogenic methane (CH\u2084)<\/strong> dissolved in supersaturated subglacial meltwater. Radiocarbon dating showed the CH\u2084 is 1.5\u20134.4 thousand years old<\/strong> (roughly 1500\u20134500 years before present).<\/p>\n\n\n\n

This methane was produced by methanogenic archaea (microbes) <\/strong>breaking down organic matter under anoxic (oxygen-poor) conditions beneath the ice. The ages align with the Holocene Thermal Maximum <\/strong>(roughly 11\u20135 ka BP), a warmer period when the Greenland Ice Sheet was smaller than today. Proglacial areas accumulated organic matter (soils, vegetation), which later advancing ice overrode, providing the substrate for subglacial methanogenesis.<\/p>\n\n\n\n

Methanogenic archaea<\/strong> (also called methanogens) are a specialized group of anaerobic archaea<\/strong> that produce methane (CH\u2084)<\/strong> as a byproduct of their energy metabolism. They are the only known organisms capable of methanogenesis and play a critical role in the global carbon cycle, especially in oxygen-free (anoxic) environments.<\/p>\n\n\n\n

Domain:<\/strong> Archaea (not bacteria). They have distinct cell membranes (ether lipids), ribosomes, and metabolic pathways that differ from bacteria.<\/p>\n\n\n\n

Strict anaerobes:<\/strong> Oxygen is toxic to them. They thrive in environments with no or very low oxygen, such as wetlands, rice paddies, ruminant digestive tracts, marine sediments, landfills, and subglacial sediments<\/strong>.<\/p>\n\n\n\n

Energy metabolism: <\/strong>They are chemolithotrophs or chemoorganotrophs that generate energy by converting simple carbon compounds into CH\u2084. This process is their primary (often only) way to obtain energy.<\/p>\n\n\n\n

Main Methanogenesis Pathways<\/strong> <\/p>\n\n\n\n

    \n
  1. Hydrogenotrophic (CO\u2082-reducing):<\/strong> The most widespread.
    CO\u2082 + 4H\u2082 \u2192 CH\u2084 + 2H\u2082O
    Uses hydrogen (H\u2082) or formate as electron donors.<\/li>\n\n\n\n
  2. Acetoclastic (acetate-splitting):<\/strong> Common in freshwater sediments.
    CH\u2083COOH (acetate) \u2192 CH\u2084 + CO\u2082<\/li>\n\n\n\n
  3. Methylotrophic:<\/strong> Uses methylated compounds (methanol, methylamines, dimethyl sulfide, etc.).
    Example: 4CH\u2083OH \u2192 3CH\u2084 + CO\u2082 + 2H\u2082O<\/li>\n<\/ol>\n\n\n\n

    Some methanogens can also use other substrates like alcohols or even methoxylated aromatic compounds from lignin.<\/p>\n\n\n\n

    They use unique coenzymes such as coenzyme M (CoM)<\/strong>, coenzyme B<\/strong>, tetrahydromethanopterin (H\u2084MPT)<\/strong>, and factor F\u2084\u2082\u2080<\/strong> (which gives some a greenish fluorescence).<\/p>\n\n\n\n

    In the Greenland Ice Sheet <\/strong>studies (including the recent 2026 Nature Geoscience paper), sequences from Methanosarcinales<\/strong> and Methanomicrobiales<\/strong> are frequently detected in subglacial meltwater.<\/p>\n\n\n\n

    _____________________________________________________________________________________<\/p>\n\n\n\n

    Mid-Holocene retreat of the Greenland Ice Sheet indicated by subglacial methane release<\/strong><\/p>\n\n\n\n

    Mid-Holocene retreat of the Greenland Ice Sheet indicated by subglacial methane release<\/strong> is the title of a research article published on May 5, 2026, in Nature Geoscience.<\/p>\n\n\n\n

    Methane (CH\u2084) emissions occur at glacier margins globally, with subglacial CH\u2084 production identified beneath the Greenland Ice Sheet (GrIS). Researchers extensively sampled 26 meltwater streams<\/strong> across the entire western margin of the GrIS. They found pervasive, biogenic CH\u2084<\/strong> (produced by microbes) dissolved in supersaturated subglacial meltwater. Radiocarbon dating revealed the methane’s age as 1.5\u20134.4 thousand years before present <\/strong>(ka BP).<\/p>\n\n\n\n

    These ages indicate that the organic matter fueling subglacial methanogenesis (by methanogenic archaea under anoxic conditions) accumulated in proglacial areas (soils, tundra vegetation) when the ice sheet was smaller than today during the Holocene Thermal Maximum<\/strong> (~11\u20135 ka BP). Subsequent ice readvances overrode this carbon-rich material, enabling ongoing microbial CH\u2084 production.<\/p>\n\n\n\n

    Ice sheet dynamics:<\/strong> The findings support greater mid-Holocene retreat (and subsequent readvance) of the GrIS than some models previously suggested. This points to higher sensitivity to climate warming.<\/p>\n\n\n\n

    Current and future CH\u2084 flux:<\/strong> A continuum degradation model estimates that western Greenland\u2019s subglacial organic matter could sustain CH\u2084 production for another 200 years<\/strong>. The lateral flux from land-terminating sectors is estimated at **715 tonnes per year** (range 481\u20131,020 t\/yr).<\/p>\n\n\n\n

    Broader context: <\/strong>Subglacial carbon cycling and CH\u2084 release are relevant to glacial environments worldwide. Increased melting could enhance subglacial connectivity and methane transport in the future<\/p>\n\n\n\n

    The team (led by researchers including J.E. Hatton, A. Stehrer-Pol\u00e1\u0161kov\u00e1, and M. Stibal from Charles University, Czechia, with international collaborators) used:<\/p>\n\n\n\n