Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the s... more Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the source of CH 4 in Gulf of Cadiz mud volcanoes (MV) is a mixture of deep sourced thermo-genic CH 4 and shallow biogenic CH 4. We directly investigated this possibility by comparing porewater CH 4 concentrations and their δ 13 C values with the potential for Archaeal methanogenesis in Gulf of Cadiz mud volcano (MV) sediments (Captain Arutyunov, Bon-jardim, Ginsburg and Porto) using 14 Crate measurements. The CH 4 has a deep sourced thermogenic origin (δ 13 C ∼ −49‰) but becomes 13 C-depleted in and beneath the zone of anaerobic oxidation of methane (AOM) where the rates of hydrogenotrophic methanogenesis increase. Thus we infer that a portion of AOM-produced CO 2 is being recycled to CH 4 by methanogens yielding further 13 C-depleted CH 4 , which might be misinterpreted as indicative of a fully shallow biogenic origin for this gas. Production of H 2 is related to compositional changes in sedimentary organic matter, or to upward flux of substrate-enriched fluids. In contrast to other MVs in the Gulf of Cadiz, Ginsburg MV fluids are enriched in SO 2− 4 and contain very high concentrations of acetate (2478 µM below 150 cmbsf); however, the high levels of acetate did not stimulate methanogenesis but instead were oxidized to CO 2 coupled to sulphate reduction. Both anaerobic oxidation of thermogenic CH 4 linked to shallow methanogenesis and fluid geochemistry control the recycling of deep-sourced carbon at Gulf of Cadiz MVs, im-pacting near-surface δ 13 C-CH 4 values.
... spanning a range of European climate zones. Neither ether lipid was present in the aerobic ac... more ... spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal ...
Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the s... more Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the source of CH 4 in Gulf of Cadiz mud volcanoes (MV) is a mixture of deep sourced thermo-genic CH 4 and shallow biogenic CH 4. We directly investigated this possibility by comparing porewater CH 4 concentrations and their δ 13 C values with the potential for Archaeal methanogenesis in Gulf of Cadiz mud volcano (MV) sediments (Captain Arutyunov, Bon-jardim, Ginsburg and Porto) using 14 Crate measurements. The CH 4 has a deep sourced thermogenic origin (δ 13 C ∼ −49‰) but becomes 13 C-depleted in and beneath the zone of anaerobic oxidation of methane (AOM) where the rates of hydrogenotrophic methanogenesis increase. Thus we infer that a portion of AOM-produced CO 2 is being recycled to CH 4 by methanogens yielding further 13 C-depleted CH 4 , which might be misinterpreted as indicative of a fully shallow biogenic origin for this gas. Production of H 2 is related to compositional changes in sedimentary organic matter, or to upward flux of substrate-enriched fluids. In contrast to other MVs in the Gulf of Cadiz, Ginsburg MV fluids are enriched in SO 2− 4 and contain very high concentrations of acetate (2478 µM below 150 cmbsf); however, the high levels of acetate did not stimulate methanogenesis but instead were oxidized to CO 2 coupled to sulphate reduction. Both anaerobic oxidation of thermogenic CH 4 linked to shallow methanogenesis and fluid geochemistry control the recycling of deep-sourced carbon at Gulf of Cadiz MVs, im-pacting near-surface δ 13 C-CH 4 values.
... spanning a range of European climate zones. Neither ether lipid was present in the aerobic ac... more ... spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal ...
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