Research ArticleGEOCHEMISTRY

A 160,000-year-old history of tectonically controlled methane seepage in the Arctic

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Science Advances  07 Aug 2019:
Vol. 5, no. 8, eaaw1450
DOI: 10.1126/sciadv.aaw1450
  • Fig. 1 Location and bathymetry of the sampling area.

    (A) Vestnesa Ridge (VR; white box) located in eastern Fram Strait, North Atlantic, northeast of the Molloy transform fault (MTF); KR, Knipovich Ridge; Gr, Greenland. Bathymetry from (54). (B) High-resolution bathymetry maps of the two sampled pockmarks over a low-resolution map, revealing multiple depressions and mounds within Lunde and Lomvi pockmarks. Stars indicate seabed samples (P1606001, P1606002, P1606005, P1606010, P1606011, P1606012, and P1606023). Triangles indicate drill sites of MeBo cores 127 (core GeoB21616-1) and 138 (core GeoB21637-1). The dashed line indicates seismic profile shown in (C). (C) Seismic profile across the SW sector of Lunde. Triangles indicate MeBo cores. The white vertical bar represents the maximum drilling depth of 23.95 m below seafloor, modified from (21). Note that the high-amplitude reflectors correspond to seep carbonates.

  • Fig. 2 Core lithology and representative seep carbonate samples with detailed U-Th ages (in ka ± 2σ).

    (A) Splice of adjacent MeBo cores 127 (core GeoB21616-1) and 138 (core GeoB21637-1) showing seabed and core samples and respective range of U-Th ages. Carbonate vertical scale is exaggerated for better visibility. (B) Scan of cut surface of seabed sample P1606001. (C and D) Scans of representative core samples. White arrows point to bivalve shells. Mic, microcrystalline carbonate cemented sediment; Vfc, void-filling cement.

  • Fig. 3 Timing of seep carbonate formation (U-Th ages ± 2σ) relative to regional paleoclimate (vertical shaded bars) and glacial tectonics.

    U-Th ages obtained from seabed samples indicate multiple post-LGM methane seepage and associated carbonate formation. Ages obtained from core samples [samples 127 (GeoB21616-1) and 138 (GeoB21637-1)] reveal two pre-LGM seepage periods between ~160 to 133 ka and ~50 to 40 ka. Timing of seep carbonate formation and paleoclimate variations suggest glacial tectonics, i.e., forebulge movement and post-glacial isostatic adjustment as main geological drivers of episodic methane release from Vestnesa Ridge. H4 and H5, Heinrich stadials (cold); HE1, Heinrich event 1 (cold); B-A, Bølling-Allerød interstadial (warm); YD, Younger Dryas (cold).

  • Fig. 4 Sketch illustrating the impact of glacial tectonics resulting from the waxing and waning of the Svalbard ice sheet on the subsurface fluid system of Vestnesa Ridge adapted from (20).

    (A) During ice sheet growth, horizontal mass transfer within the viscous asthenosphere (open arrows) facilitates migration of a glacial forebulge underneath Vestnesa Ridge. Sediment compaction due to vertical crustal adjustment (black arrows) causes reservoir overpressure. Reactivation of subvertical faults, connecting the gas reservoir to the seabed, provides migration pathways for deep-sourced fluids with methane (CH4) through the GHSZ. (B) Post-glacial relaxation and associated mass transfer in the asthenosphere (open arrows) result in isostatic adjustment (black arrows) and fault reactivation, providing fluid migration pathways (not to scale). BSR, bottom simulating reflector, indicating the lower boundary of the GHSZ; MTF, Molly transform fault.

  • Table 1 Detailed seabed sample locations and core sections containing seep carbonates.

    mbsf, meters below seafloor; R, rotary drilling; P, push coring; CC, core catcher; n.a., not applicable.

    Sample/coreLatitude (°N)Longitude (°E)PockmarkWater depth (m)Max. coring depth
    (mbsf)
    Core sections with
    seep carbonates
    (depth mbsf)
    P160600179°0.1445′06°55.308′Lomvi1206n.a.n.a.
    P160600279°0.156′06°55.278′Lomvi1204n.a.n.a.
    P160600579°0.15′06°55.386′Lomvi1203n.a.n.a.
    P160601079°0.45′06°54.47398′Lunde1210n.a.n.a.
    P160601179°0.456′06°53.958′Lunde1207n.a.n.a.
    P160601279°0.462′06°53.952′Lunde1207n.a.n.a.
    P160602379°0.414′06°54.07′Lunde1204n.a.n.a.
    GeoB21616-179°0.418′06°54.245′Lunde121013.902R (5.75 to 6.02);
    4P–CC (10.16 to
    10.27)
    GeoB21637-179°0.426′06°54.246′Lunde120923.9510R–CC (16.95 to
    17.09); 11R–CC
    (19.25 to 19.34);
    12R–1 (21.60 to
    21.73); 12R–2 (21.73
    to 22.53)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaaw1450/DC1

    Fig. S1. Area seabed photographs at Lomvi and Lunde pockmarks.

    Fig. S2. Scanned images of archive half sections and description of core GeoB21616-1.

    Fig. S3. Scanned images of archive half sections and description of core GeoB21637-1.

    Fig. S4. Scans of cut slabs from seabed carbonates with detailed U-Th sample locations and ages (ka BP ± 2σ).

    Fig. S5. Scans of thin-section slabs impregnated in epoxy resin with detailed U-Th sample locations and ages in ka BP ± 2σ.

    Fig. S6. Scans of thin-section slabs impregnated in epoxy resin with detailed U-Th sample locations and ages in ka BP ± 2σ.

    Fig. S7. Thin-section micrographs of seabed samples.

    Fig. S8. Thin-section micrographs of core samples (all cross-polarized light; pore space appears black).

    Fig. S9. Range of (230Th/232Th) versus (238U/232Th) from this study compared to other seep carbonate literature.

    Fig. S10. Calculated U-Th ages without dates excluded based on screening criteria plotted against sampling depth.

    Fig. S11. Seep carbonate ages and respective relative sea level.

    Fig. S12. Cross plots of carbonate carbon and oxygen stable isotope compositions (in ‰ VPDB).

    Fig. S13. Breakdown of the uncertainty budget of calculated seep carbonate ages.

    Fig. S14. Alternative interpretation of U-Th data.

    Table S1. Mineralogical compositions (weight %) of seabed sampled carbonates.

    Table S2. Mineralogical compositions (weight %) of core carbonates.

    Data file S1. Spreadsheet containing U-Th isotopic data of seep carbonates and seep carbonate-free sediment, as well as calculated U-Th ages and carbonate δ13C and δ18O values.

    References (5557)

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Area seabed photographs at Lomvi and Lunde pockmarks.
    • Fig. S2. Scanned images of archive half sections and description of core GeoB21616-1.
    • Fig. S3. Scanned images of archive half sections and description of core GeoB21637-1.
    • Fig. S4. Scans of cut slabs from seabed carbonates with detailed U-Th sample locations and ages (ka BP ± 2σ).
    • Fig. S5. Scans of thin-section slabs impregnated in epoxy resin with detailed U-Th sample locations and ages in ka BP ± 2σ.
    • Fig. S6. Scans of thin-section slabs impregnated in epoxy resin with detailed U-Th sample locations and ages in ka BP ± 2σ.
    • Fig. S7. Thin-section micrographs of seabed samples.
    • Fig. S8. Thin-section micrographs of core samples (all cross-polarized light; pore space appears black).
    • Fig. S9. Range of (230Th/232Th) versus (238U/232Th) from this study compared to other seep carbonate literature.
    • Fig. S10. Calculated U-Th ages without dates excluded based on screening criteria plotted against sampling depth.
    • Fig. S11. Seep carbonate ages and respective relative sea level.
    • Fig. S12. Cross plots of carbonate carbon and oxygen stable isotope compositions (in ‰ VPDB).
    • Fig. S13. Breakdown of the uncertainty budget of calculated seep carbonate ages.
    • Fig. S14. Alternative interpretation of U-Th data.
    • Table S1. Mineralogical compositions (weight %) of seabed sampled carbonates.
    • Table S2. Mineralogical compositions (weight %) of core carbonates.
    • Legend for data file S1
    • References (5557)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Data file S1 (Microsoft Excel format). Spreadsheet containing U-Th isotopic data of seep carbonates and seep carbonate-free sediment, as well as calculated U-Th ages and carbonate δ13C and δ18O values.

    Files in this Data Supplement:

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