skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps

Authors:
; ; ; ; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1398679
Grant/Contract Number:
FE000291; 0023495
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 449; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-08 20:22:41; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
Netherlands
Language:
English

Citation Formats

Prouty, N. G., Sahy, D., Ruppel, C. D., Roark, E. B., Condon, D., Brooke, S., Ross, S. W., and Demopoulos, A. W. J. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps. Netherlands: N. p., 2016. Web. doi:10.1016/j.epsl.2016.05.023.
Prouty, N. G., Sahy, D., Ruppel, C. D., Roark, E. B., Condon, D., Brooke, S., Ross, S. W., & Demopoulos, A. W. J. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps. Netherlands. doi:10.1016/j.epsl.2016.05.023.
Prouty, N. G., Sahy, D., Ruppel, C. D., Roark, E. B., Condon, D., Brooke, S., Ross, S. W., and Demopoulos, A. W. J. 2016. "Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps". Netherlands. doi:10.1016/j.epsl.2016.05.023.
@article{osti_1398679,
title = {Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps},
author = {Prouty, N. G. and Sahy, D. and Ruppel, C. D. and Roark, E. B. and Condon, D. and Brooke, S. and Ross, S. W. and Demopoulos, A. W. J.},
abstractNote = {},
doi = {10.1016/j.epsl.2016.05.023},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 449,
place = {Netherlands},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.epsl.2016.05.023

Save / Share:
  • Authigenic carbonates are intercalated with massive gas hydrates in sediments of the Cascadia margin. The deposits were recovered from the uppermost 50 cm of sediments on the southern summit of the Hydrate Ridge during the RV Sonne cruise SO110. Two carbonate lithologies that differ in chemistry, mineralogy, and fabric make up these deposits. Microcrystalline high-magnesium calcite (14 to 19 mol% MgCO{sub 3}) and aragonite are present in both semiconsolidated sediments and carbonate-cemented clasts. Aragonite occurs also as a pure phase without sediment impurities. It is formed by precipitation in cavities as botryoidal and isopachous aggregates within pure white, massive gasmore » hydrate. Variations in oxygen isotope values of the carbonates reflect the mineralogical composition and define two end members: a Mg-calcite with {delta}{sup 18}O = 4.86% PDB and an aragonite with {delta}{sup 18}O = 3.68% PDB. On the basis of the ambient bottom-water temperature and accepted equations for oxygen isotope fractionation, the authors show that the aragonite phase formed in equilibrium with its pore-water environment, and that the Mg-calcite appears to have precipitated from pore fluids enriched in {sup 18}O. Oxygen isotope enrichment probably originates from hydrate water released during gas-hydrate destabilization.« less
  • Evidence for precipitation of authigenic carbonate fluorapatite (CFA) in Long Island Sound and Mississippi Delta sediments suggests that formation of CFA is not restricted to environments of active coastal upwelling. The authors present porewater data suggestive of CFA formation in both these areas. Application of a sequential leaching procedure, designed specifically to separate authigenic carbonate fluorapatite from other phosphorus-containing phases, including detrital apatite of igneous or metamorphic origin, provides strong supporting evidence for authigenic apatite formation in these sediments. The size of the authigenic apatite reservoir increases with depth, indicating continued formation of CFA during early diagenesis. This depth increasemore » is mirrored by a decrease in solid-phase organic P at both sites, suggesting that CFA is forming at the expense of organic P. Mass balance considerations, application of diagenetic models to intersitital water nutrient data, and the saturation state of the interstitial water are consistent with this interpretation. Diagenetic redistribution of phosphorus among the different solid-phase reservoirs is observed at both sites, and results in near perfect retention of P by these sediments over the depth intervals sampled. Formation of CFA in continental margins which do not conform to the classically defined regions of phosphorite formation renders CFA a quantitatively more important sink than has previously been recognized. Including this reservoir as a newly identified sink for reactive P in the ocean, the residence time of P in the modern ocean must be revised downward. The implication for ancient oceans of CFA formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive P from the oceans than of localized concentration of CFA in phosphatic sediments by secondary physical processes. 90 refs., 5 figs., 2 tabs.« less
  • A recently discovered thermophilic bacterium, Geobacillus thermoglucosidasius M10EXG, ferments a range of C5 (e.g., xylose) and C6 sugars (e.g., glucose) and istolerant to high ethanol concentrations (10percent, v/v). We have investigated the central metabolism of this bacterium using both in vitro enzyme assays and 13C-based flux analysis to provide insights into the physiological properties of this extremophile and explore its metabolism for bio-ethanol or other bioprocess applications. Our findings show that glucose metabolism in G. thermoglucosidasius M10EXG proceeds via glycolysis, the pentose phosphate pathway, and the TCA cycle; the Entner?Doudoroff pathway and transhydrogenase activity were not detected. Anaplerotic reactions (includingmore » the glyoxylate shunt, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase) were active, but fluxes through those pathways could not be accuratelydetermined using amino acid labeling. When growth conditions were switched from aerobic to micro-aerobic conditions, fluxes (based on a normalized glucose uptake rate of 100 units (g DCW)-1 h-1) through the TCA cycle and oxidative pentose phosphate pathway were reduced from 64+-3 to 25+-2 and from 30+-2 to 19+-2, respectively. The carbon flux under micro-aerobic growth was directed formate. Under fully anerobic conditions, G. thermoglucosidasius M10EXG used a mixed acid fermentation process and exhibited a maximum ethanol yield of 0.38+-0.07 mol mol-1 glucose. In silico flux balance modeling demonstrates that lactate and acetate production from G. thermoglucosidasius M10EXG reduces the maximum ethanol yieldby approximately threefold, thus indicating that both pathways should be modified to maximize ethanol production.« less
  • Sulfate reduction rates (SRR) and concentrations of SO{sub 4}{sup 2{minus}}, H{sub 2}S, pyrite sulfur, total sulfur, CH{sub 4}, and organic carbon were measured with high depth resolution through the entire length of the SO{sub 4}{sup 2{minus}}-zone and well into the CH{sub 4}-xone at two continental slope stations in the eastern South Atlantic (Benguela upwelling area). The sediments were characterized by a high organic carbon content of approx. 7.5% at GeoB 3703 and 3.7% at GeoB 3714. At GeoB 3703 SO{sub 4}{sup 2{minus}} concentrations decreased linearly with depth to about 40 {micro}M at the sulfate-methane transition zone (SMT) at 3.5 m,more » while at GeoB 3714, SO{sub 4}{sup 2{minus}} remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 {micro}M at the SMT at 6 m. Direct rate measurements of SRR ({sup 35}SO{sub 4}{sup 2{minus}}) showed that the highest SRR occurred within the surface 3--5 cm with peak rates of up to 20 and 7 nmol SO{sub 4}{sup 2{minus}} cm{sup 3}/day at GeoB 3703 and GeoB 3714, respectively. SRR decreased quasi-exponentially with depth at GeoB 3703 and the cumulative SRR over the length of the SO{sub 4}{sup 2{minus}} zone resulted in an areal SRR of 1114--3493 {micro}mol/m{sup 2} day at GeoB 3703 with more than 80% of the total sulfate reduction proceeding in the top 30 cm sediment. Modeled SRR balanced both methane oxidation rates and measured SRR within the SMT, but severely underestimated by up to 89% the total SRR{sub area} that were obtained from direct measurements. Modeled and measured SRR were reconciled by including solute transport by irrigation described by a non-local pore water exchange function ({alpha}) which had values of up to 0.3 year{sup {minus}1} in the top sediment, and decreased exponentially to zero (i.e., no irrigation) at 2--3 meters (i.e., above SMT). These results suggested that co-existing sulfate reduction processes and linear SO{sub 4}{sup 2{minus}} gradients can be maintained by a non-local transport mechanism such as irrigation, by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube-dwelling animals, or some similar physical transport phenomenon (i.e., bubble ebullition).« less