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Seep-carbonate lamination controlled by cyclic particle flux

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ABSTRACT

Authigenic carbonate build-ups develop at seafloor methane-seeps, where microbially mediated sulphate-dependent anaerobic oxidation of methane facilitates carbonate precipitation. Despite being valuable recorders of past methane seepage events, their role as archives of atmospheric processes has not been examined. Here we show that cyclic sedimentation pulses related to the Indian monsoon in concert with authigenic precipitation of methane-derived aragonite gave rise to a well-laminated carbonate build-up within the oxygen minimum zone off Pakistan (northern Arabian Sea). U–Th dating indicates that the build-up grew during past ~1,130 years, creating an exceptional high-resolution archive of the Indian monsoon system. Monsoon-controlled formation of seep-carbonates extends the known environmental processes recorded by seep-carbonates, revealing a new relationship between atmospheric and seafloor processes.

No MeSH data available.


Related in: MedlinePlus

Laminae counting and elemental composition analysed with LA-ICP-MS.(a) Scan of epoxy impregnated, polished slab, highlighting individual 204 laminae and spots of isotope samples (1–10; see Supplementary Table S1); note mottled intervals (black arrows) sometimes lack distinct lamination; white arrow indicate overlapping of lamina #101; epoxy resin and unfilled porosity appear dark grey to black. (b) Thin-section scan of the build-up top displaying the relative position of the thin section used for LA-ICP-MS (inlet) and the actual ablation spots (black rectangle in the upper right of the blown-up section). (c) Thin section micrograph (plane-polarized light) displaying the LA-ICP-MS ablation craters within clotted and fibrous aragonite (Cfa) and fossilised biofilms (see also Supplementary Fig. S1); craters that yielded high aluminium (Al) contents are associated with biofilms (purple circles); arrow points towards the top. (d,e) bar diagrams showing element contents of LA-ICP-MS analyses; high strontium (Sr) contents agree with aragonite as dominant carbonate cement; spots with relative high contents of terrigenous aluminium (Al) are highlighted (grey bands); note that high silicon (Si) and magnesium (Mg) contents correlate with high Al contents.
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f2: Laminae counting and elemental composition analysed with LA-ICP-MS.(a) Scan of epoxy impregnated, polished slab, highlighting individual 204 laminae and spots of isotope samples (1–10; see Supplementary Table S1); note mottled intervals (black arrows) sometimes lack distinct lamination; white arrow indicate overlapping of lamina #101; epoxy resin and unfilled porosity appear dark grey to black. (b) Thin-section scan of the build-up top displaying the relative position of the thin section used for LA-ICP-MS (inlet) and the actual ablation spots (black rectangle in the upper right of the blown-up section). (c) Thin section micrograph (plane-polarized light) displaying the LA-ICP-MS ablation craters within clotted and fibrous aragonite (Cfa) and fossilised biofilms (see also Supplementary Fig. S1); craters that yielded high aluminium (Al) contents are associated with biofilms (purple circles); arrow points towards the top. (d,e) bar diagrams showing element contents of LA-ICP-MS analyses; high strontium (Sr) contents agree with aragonite as dominant carbonate cement; spots with relative high contents of terrigenous aluminium (Al) are highlighted (grey bands); note that high silicon (Si) and magnesium (Mg) contents correlate with high Al contents.

Mentions: To gather evidence for the impact of seasonal sedimentation on the Makran OMZ seeps, a well-laminated, columnar authigenic carbonate build-up was examined. It is 47 cm long and varies between 12 and 17 cm in diameter, and was sampled from the seafloor in an area of active methane seepage (sample GeoB12353-11; N24° 48.44′, E63° 59.64′; 734 m water depth; Fig. 1). Such well-laminated carbonate build-ups have only been sampled within the Makran OMZ, whereas numerous methane seeps located in water depths below 1100 m are characterized by widespread carbonate crusts15. Carbonate fabrics were described macroscopically, by optical, and secondary electron microscopy (Fig. 2; see also Supplementary Fig. S1). Semi-quantitative X-ray diffraction, stable isotope analyses (δ13C, δ18O; Supplementary Table S1), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to reveal compositional variations (Fig. 2b,c,d; see Supplementary Table S2). Insights about structural properties were gained through X-ray computer tomography and results were used for a fluid flow simulation (Fig. 3; Supplementary Fig. S2). The timing of build-up growth was determined by U–Th dating, using an isochron approach (Table 1; Supplementary Fig. S3; e.g., refs 2, 16).


Seep-carbonate lamination controlled by cyclic particle flux
Laminae counting and elemental composition analysed with LA-ICP-MS.(a) Scan of epoxy impregnated, polished slab, highlighting individual 204 laminae and spots of isotope samples (1–10; see Supplementary Table S1); note mottled intervals (black arrows) sometimes lack distinct lamination; white arrow indicate overlapping of lamina #101; epoxy resin and unfilled porosity appear dark grey to black. (b) Thin-section scan of the build-up top displaying the relative position of the thin section used for LA-ICP-MS (inlet) and the actual ablation spots (black rectangle in the upper right of the blown-up section). (c) Thin section micrograph (plane-polarized light) displaying the LA-ICP-MS ablation craters within clotted and fibrous aragonite (Cfa) and fossilised biofilms (see also Supplementary Fig. S1); craters that yielded high aluminium (Al) contents are associated with biofilms (purple circles); arrow points towards the top. (d,e) bar diagrams showing element contents of LA-ICP-MS analyses; high strontium (Sr) contents agree with aragonite as dominant carbonate cement; spots with relative high contents of terrigenous aluminium (Al) are highlighted (grey bands); note that high silicon (Si) and magnesium (Mg) contents correlate with high Al contents.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5120270&req=5

f2: Laminae counting and elemental composition analysed with LA-ICP-MS.(a) Scan of epoxy impregnated, polished slab, highlighting individual 204 laminae and spots of isotope samples (1–10; see Supplementary Table S1); note mottled intervals (black arrows) sometimes lack distinct lamination; white arrow indicate overlapping of lamina #101; epoxy resin and unfilled porosity appear dark grey to black. (b) Thin-section scan of the build-up top displaying the relative position of the thin section used for LA-ICP-MS (inlet) and the actual ablation spots (black rectangle in the upper right of the blown-up section). (c) Thin section micrograph (plane-polarized light) displaying the LA-ICP-MS ablation craters within clotted and fibrous aragonite (Cfa) and fossilised biofilms (see also Supplementary Fig. S1); craters that yielded high aluminium (Al) contents are associated with biofilms (purple circles); arrow points towards the top. (d,e) bar diagrams showing element contents of LA-ICP-MS analyses; high strontium (Sr) contents agree with aragonite as dominant carbonate cement; spots with relative high contents of terrigenous aluminium (Al) are highlighted (grey bands); note that high silicon (Si) and magnesium (Mg) contents correlate with high Al contents.
Mentions: To gather evidence for the impact of seasonal sedimentation on the Makran OMZ seeps, a well-laminated, columnar authigenic carbonate build-up was examined. It is 47 cm long and varies between 12 and 17 cm in diameter, and was sampled from the seafloor in an area of active methane seepage (sample GeoB12353-11; N24° 48.44′, E63° 59.64′; 734 m water depth; Fig. 1). Such well-laminated carbonate build-ups have only been sampled within the Makran OMZ, whereas numerous methane seeps located in water depths below 1100 m are characterized by widespread carbonate crusts15. Carbonate fabrics were described macroscopically, by optical, and secondary electron microscopy (Fig. 2; see also Supplementary Fig. S1). Semi-quantitative X-ray diffraction, stable isotope analyses (δ13C, δ18O; Supplementary Table S1), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to reveal compositional variations (Fig. 2b,c,d; see Supplementary Table S2). Insights about structural properties were gained through X-ray computer tomography and results were used for a fluid flow simulation (Fig. 3; Supplementary Fig. S2). The timing of build-up growth was determined by U–Th dating, using an isochron approach (Table 1; Supplementary Fig. S3; e.g., refs 2, 16).

View Article: PubMed Central - PubMed

ABSTRACT

Authigenic carbonate build-ups develop at seafloor methane-seeps, where microbially mediated sulphate-dependent anaerobic oxidation of methane facilitates carbonate precipitation. Despite being valuable recorders of past methane seepage events, their role as archives of atmospheric processes has not been examined. Here we show that cyclic sedimentation pulses related to the Indian monsoon in concert with authigenic precipitation of methane-derived aragonite gave rise to a well-laminated carbonate build-up within the oxygen minimum zone off Pakistan (northern Arabian Sea). U–Th dating indicates that the build-up grew during past ~1,130 years, creating an exceptional high-resolution archive of the Indian monsoon system. Monsoon-controlled formation of seep-carbonates extends the known environmental processes recorded by seep-carbonates, revealing a new relationship between atmospheric and seafloor processes.

No MeSH data available.


Related in: MedlinePlus