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Putative fossils of chemotrophic microbes preserved in seep carbonates from Vestnesa Ridge, off northwest Svalbard, Norway

Himmler, Tobias and Crémière, Antoine and Birgel, Daniel and Wirth, Richard and Orphan, Victoria J. and Kirsimäe, Kalle and Knies, Jochen and Peckmann, Jörn and Lepland, Aivo (2022) Putative fossils of chemotrophic microbes preserved in seep carbonates from Vestnesa Ridge, off northwest Svalbard, Norway. Geology, 50 (2). pp. 169-173. ISSN 0091-7613. doi:10.1130/g49620.1.

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The microbial key players at methane seeps are methanotrophic archaea and sulfate-reducing bacteria. They form spherical aggregates and jointly mediate the sulfate-dependent anaerobic oxidation of methane (SD–AOM: CH₄ + SO₄²⁻ → HCO₃⁻ + HS⁻ + H₂O), thereby inducing the precipitation of authigenic seep carbonates. While seep carbonates constitute valuable archives for molecular fossils of SD–AOM-mediating microbes, no microfossils have been identified as AOM aggregates to date. We report clustered spherical microstructures engulfed in ¹³C-depleted aragonite cement (δ¹³C values as low as –33‰) of Pleistocene seep carbonates. The clusters comprise Mg-calcite spheres between ~5 μm (single spheres) and ~30 μm (clusters) in diameter. Scanning and transmission electron microscopy revealed a porous nanocrystalline fabric in the core area of the spheres surrounded by one or two concentric layers of Mg-calcite crystals. In situ measured sphere δ¹³C values as low as –42‰ indicate that methane-derived carbon is the dominant carbon source. The size and concentric layering of the spheres resembles mineralized aggregates of natural anaerobic methanotrophic archaea (ANME) of the ANME-2 group surrounded by one or two layers of sulfate-reducing bacteria. Abundant carbonate-bound ¹³C-depleted lipid biomarkers of archaea and bacteria indicative of the ANME-2-Desulfosarcina/Desulfococcus consortium agree with SD–AOM-mediating microbes as critical agents of carbonate precipitation. Given the morphological resemblance, in concert with negative in situ δ¹³C values and abundant SD–AOM-diagnostic biomarkers, the clustered spheres likely represent fossils of SD–AOM-mediating microbes.

Item Type:Article
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URLURL TypeDescription
Himmler, Tobias0000-0001-8847-0266
Crémière, Antoine0000-0001-7382-2097
Orphan, Victoria J.0000-0002-5374-6178
Kirsimäe, Kalle0000-0002-1221-3623
Knies, Jochen0000-0002-0114-5629
Peckmann, Jörn0000-0002-8572-0060
Additional Information:© 2021 Geological Society of America. Manuscript received 25 September 2020; Revised manuscript received 24 August 2021; Manuscript accepted 25 August 2021; Published online 20 October 2021. Professional support at sea by the master and crew during expedition P1606 on R/V G.O. Sars and the skillful work of the ROV Ægir 6000 team (University of Bergen, Norway) are greatly acknowledged. Thanks go to Anja Schreiber (GeoForschungsZentrum, Potsdam, Germany) for meticulous focused ion beam work and Yunbin Guan (Caltech, Pasadena, California, USA) for nanoSIMS operations. Thoughtful comments by Russell S. Shapiro and two anonymous reviewers helped to improve the manuscript. This study was supported by the Research Council of Norway through the Petromaks2 NORCRUST project (grants 255150 and 223259).
Funding AgencyGrant Number
Research Council of Norway255150
Research Council of Norway223259
Issue or Number:2
Record Number:CaltechAUTHORS:20211201-180908972
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Official Citation:Tobias Himmler, Antoine Crémière, Daniel Birgel, Richard Wirth, Victoria J. Orphan, Kalle Kirsimäe, Jochen Knies, Jörn Peckmann, Aivo Lepland; Putative fossils of chemotrophic microbes preserved in seep carbonates from Vestnesa Ridge, off northwest Svalbard, Norway. Geology 2021; 50 (2): 169–173. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112143
Deposited By: Tony Diaz
Deposited On:01 Dec 2021 18:47
Last Modified:01 Feb 2022 18:32

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