Dataset Information

Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

ABSTRACT: Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

SUBMITTER: Loyd SJ

PROVIDER: S-EPMC4961868 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

Loyd S J SJ Sample J J Tripati R E RE Defliese W F WF Brooks K K Hovland M M Torres M M Marlow J J Hancock L G LG Martin R R Lyons T T Tripati A E AE

Nature communications 20160722

Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various m ...[more]

PMID: 27447820

Similar Datasets

Project description:UnlabelledMarine methane seeps are globally distributed geologic features in which reduced fluids, including methane, are advected upward from the subsurface. As a result of alkalinity generation during sulfate-coupled methane oxidation, authigenic carbonates form slabs, nodules, and extensive pavements. These carbonates shape the landscape within methane seeps, persist long after methane flux is diminished, and in some cases are incorporated into the geologic record. In this study, microbial assemblages from 134 native and experimental samples across 5,500 km, representing a range of habitat substrates (carbonate nodules and slabs, sediment, bottom water, and wood) and seepage conditions (active and low activity), were analyzed to address two fundamental questions of seep microbial ecology: (i) whether carbonates host distinct microbial assemblages and (ii) how sensitive microbial assemblages are to habitat substrate type and temporal shifts in methane seepage flux. Through massively parallel 16S rRNA gene sequencing and statistical analysis, native carbonates are shown to be reservoirs of distinct and highly diverse seep microbial assemblages. Unique coupled transplantation and colonization experiments on the seafloor demonstrated that carbonate-associated microbial assemblages are resilient to seep quiescence and reactive to seep activation over 13 months. Various rates of response to simulated seep quiescence and activation are observed among similar phylogenies (e.g., Chloroflexi operational taxonomic units) and similar metabolisms (e.g., putative S oxidizers), demonstrating the wide range of microbial sensitivity to changes in seepage flux. These results imply that carbonates do not passively record a time-integrated history of seep microorganisms but rather host distinct, diverse, and dynamic microbial assemblages.ImportanceSince their discovery in 1984, the global distribution and importance of marine methane seeps have become increasingly clear. Much of our understanding of methane seep microorganisms-from metabolisms to community ecology-has stemmed from detailed studies of seep sediments. However, it has become apparent that carbonates represent a volumetrically significant habitat substrate at methane seeps. Through combined in situ characterization and incubation experiments, this study demonstrates that carbonates host microbial assemblages distinct from and more diverse than those of other seep habitats. This emphasizes the importance of seep carbonates as biodiversity locales. Furthermore, we demonstrate that carbonate-associated microbial assemblages are well adapted to withstand fluctuations in methane seepage, and we gain novel insight into particular taxa that are responsive (or recalcitrant) to changes in seep conditions.

Project description:Methane emissions from vehicle exhaust, as a source of methane, are often overlooked. However, in areas with high vehicle activity, the emissions can be substantial. There is a notable lack of characterization regarding the variable concentrations and isotopic signatures of methane in vehicle exhaust. This gap in knowledge limits our understanding of the mechanisms of methane production in vehicles and the factors controlling concentration variations and isotopic fractionation, which also makes it difficult to identify and reduce methane emissions from vehicle exhaust. This study characterized the methane concentration ([CH4]), methane-to-ethane ratio (C2:C1), methane carbon and hydrogen isotopes (δ13C and δD), and methane clumped isotopologues (Δ13CH3D and Δ12CH2D2) of the vehicle exhaust methane endmember. [CH4] varied widely from below 1 ppm to more than 3000 ppm, potentially influenced by vehicle maintenance and operational phases. Ethane concentrations ([C2H6]) correlated with [CH4], yet C2:C1 varied significantly from 0.1% to 18.3%. The δ13C and δD values of exhaust methane were less negative than those of natural gas. A large portion of samples showed a positive linear relationship between [CH4], δ13C from -22‰ to -11‰, and δD values from -170‰ to -120‰, while their clumped isotopologues exhibit ~0.8‰ clumping in Δ13CH3D and ~-2.4‰ anti-clumping in Δ12CH2D2. A small portion of the samples exhibited distinct isotopic characteristics, with their δ13C and δD values either becoming significantly more positive or aligning closer to the composition of ambient air, while their Δ12CH2D2 values showed a marked increase, reaching between +25‰ to +33‰. These concentration and isotope characteristics show trends that can be explained by a combination of processes, including 1) methane formation in the engine, 2) methane combustion in the engine, 3) methane oxidation by the catalytic converter, and 4) mixing with air. The observed isotopic fractionation can be explained by thermo equilibrium and Rayleigh fractionations. These processes, elucidated through isotopic and clumped isotopologue analyses, underscore the intricate dynamics and controls of vehicular methane emissions.

Dataset Information

Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

Publications

Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets