Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps
Present-day activity of cold seeps in the ocean is evident from direct observations of methane emanating from the seafloor, the presence of chemosynthetic organisms, or the quantification of high gas concentrations in sediment pore waters and the water column. Verifying past cold seep activity and b...
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Frontiers Media S.A.
2021-02-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/feart.2020.570742/full |
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| author | Haoyi Yao Giuliana Panieri Moritz F. Lehmann Tobias Himmler Tobias Himmler Helge Niemann Helge Niemann Helge Niemann Helge Niemann |
| author_facet | Haoyi Yao Giuliana Panieri Moritz F. Lehmann Tobias Himmler Tobias Himmler Helge Niemann Helge Niemann Helge Niemann Helge Niemann |
| author_sort | Haoyi Yao |
| collection | DOAJ |
| description | Present-day activity of cold seeps in the ocean is evident from direct observations of methane emanating from the seafloor, the presence of chemosynthetic organisms, or the quantification of high gas concentrations in sediment pore waters and the water column. Verifying past cold seep activity and biogeochemical characteristics is more challenging but may be reconstructed from proxy records of authigenic seep carbonates. Here, we investigated the lipid-biomarker inventory, carbonate mineralogy, and stable carbon and oxygen isotope compositions of seep-associated carbonates from two active Arctic methane seeps, located to the northwest (Vestnesa Ridge; ∼1,200 m water depth) and south (Storfjordrenna; ∼380 m water depth) offshore Svalbard. The aragonite-dominated mineralogy of all but one carbonate sample indicate precipitation close to the seafloor in an environment characterized by high rates of sulfate-dependent anaerobic oxidation of methane (AOM). In contrast, Mg-calcite rich nodules sampled in sediments of Storfjordrenna appear to have formed at the sulfate-methane-transition zone deeper within the sediment at lower rates of AOM. AOM activity at the time of carbonate precipitation is indicated by the 13C-depleted isotope signature of the carbonates [−20 to −30‰ Vienna Pee Dee Belemnite (VPDB)], as well as high concentrations of 13C-depleted lipid biomarkers diagnostic for anaerobic methanotrophic archaea (archaeol and sn2-hydroxyarchaeol) and sulfate-reducing bacteria (iso and anteiso-C15:0 fatty acids) in the carbonates. We also found 13C-depleted lipid biomarkers (diploptene and a 4α-methyl sterol) that are diagnostic for bacteria mediating aerobic oxidation of methane (MOx). This suggests that the spatial separation between AOM and MOx zones was relatively narrow at the time of carbonate formation, as is typical for high methane-flux regimes. The seep-associated carbonates also displayed relatively high δ18O values (4.5–5‰ VPDB), indicating the presence of 18O-enriched fluids during precipitation, possibly derived from destabilized methane gas hydrates. Based on the combined isotopic evidence, we suggest that all the seep carbonates resulted from the anaerobic oxidation of methane during intense methane seepage. The seepage likely was associated to gas hydrates destabilization, which led to the methane ebullition from the seafloor into the water column. |
| first_indexed | 2024-12-21T12:36:08Z |
| format | Article |
| id | doaj.art-16f5c92376d44f728e42127083ede070 |
| institution | Directory Open Access Journal |
| issn | 2296-6463 |
| language | English |
| last_indexed | 2024-12-21T12:36:08Z |
| publishDate | 2021-02-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Earth Science |
| spelling | doaj.art-16f5c92376d44f728e42127083ede0702022-12-21T19:03:55ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632021-02-01810.3389/feart.2020.570742570742Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane SeepsHaoyi Yao0Giuliana Panieri1Moritz F. Lehmann2Tobias Himmler3Tobias Himmler4Helge Niemann5Helge Niemann6Helge Niemann7Helge Niemann8CAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, Tromsø, NorwayCAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, Tromsø, NorwayDepartment of Environmental Sciences, University of Basel, Basel, SwitzerlandCAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, Tromsø, NorwayGeological Survey of Norway, Trondheim, NorwayCAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, Tromsø, NorwayDepartment of Environmental Sciences, University of Basel, Basel, SwitzerlandDepartment of Marine Microbiology and Biogeochemistry, NIOZ Royal Institute for Sea Research, Texel, NetherlandsDepartment of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, NetherlandsPresent-day activity of cold seeps in the ocean is evident from direct observations of methane emanating from the seafloor, the presence of chemosynthetic organisms, or the quantification of high gas concentrations in sediment pore waters and the water column. Verifying past cold seep activity and biogeochemical characteristics is more challenging but may be reconstructed from proxy records of authigenic seep carbonates. Here, we investigated the lipid-biomarker inventory, carbonate mineralogy, and stable carbon and oxygen isotope compositions of seep-associated carbonates from two active Arctic methane seeps, located to the northwest (Vestnesa Ridge; ∼1,200 m water depth) and south (Storfjordrenna; ∼380 m water depth) offshore Svalbard. The aragonite-dominated mineralogy of all but one carbonate sample indicate precipitation close to the seafloor in an environment characterized by high rates of sulfate-dependent anaerobic oxidation of methane (AOM). In contrast, Mg-calcite rich nodules sampled in sediments of Storfjordrenna appear to have formed at the sulfate-methane-transition zone deeper within the sediment at lower rates of AOM. AOM activity at the time of carbonate precipitation is indicated by the 13C-depleted isotope signature of the carbonates [−20 to −30‰ Vienna Pee Dee Belemnite (VPDB)], as well as high concentrations of 13C-depleted lipid biomarkers diagnostic for anaerobic methanotrophic archaea (archaeol and sn2-hydroxyarchaeol) and sulfate-reducing bacteria (iso and anteiso-C15:0 fatty acids) in the carbonates. We also found 13C-depleted lipid biomarkers (diploptene and a 4α-methyl sterol) that are diagnostic for bacteria mediating aerobic oxidation of methane (MOx). This suggests that the spatial separation between AOM and MOx zones was relatively narrow at the time of carbonate formation, as is typical for high methane-flux regimes. The seep-associated carbonates also displayed relatively high δ18O values (4.5–5‰ VPDB), indicating the presence of 18O-enriched fluids during precipitation, possibly derived from destabilized methane gas hydrates. Based on the combined isotopic evidence, we suggest that all the seep carbonates resulted from the anaerobic oxidation of methane during intense methane seepage. The seepage likely was associated to gas hydrates destabilization, which led to the methane ebullition from the seafloor into the water column.https://www.frontiersin.org/articles/10.3389/feart.2020.570742/fullgas hydrateArcticseep carbonatemethane seeplipid biomarkers |
| spellingShingle | Haoyi Yao Giuliana Panieri Moritz F. Lehmann Tobias Himmler Tobias Himmler Helge Niemann Helge Niemann Helge Niemann Helge Niemann Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps Frontiers in Earth Science gas hydrate Arctic seep carbonate methane seep lipid biomarkers |
| title | Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps |
| title_full | Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps |
| title_fullStr | Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps |
| title_full_unstemmed | Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps |
| title_short | Biomarker and Isotopic Composition of Seep Carbonates Record Environmental Conditions in Two Arctic Methane Seeps |
| title_sort | biomarker and isotopic composition of seep carbonates record environmental conditions in two arctic methane seeps |
| topic | gas hydrate Arctic seep carbonate methane seep lipid biomarkers |
| url | https://www.frontiersin.org/articles/10.3389/feart.2020.570742/full |
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