Hydrogen Isotopes Preclude Marine Hydrate CH
 4
 Emissions at the Onset of Dansgaard-Oeschger Events

Bock, Michael; Schmitt, Jochen; Möller, Lars; Spahni, Renato; Blunier, Thomas; Fischer, Hubertus

doi:10.1126/science.1187651

Cited by 72 publications

(88 citation statements)

References 30 publications

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“…To date, the 2000 M. Bock et al: Improving accuracy and precision of δD(CH 4 ) analyses few published ice core δD(CH 4 ) studies required from 0.5 kg (Bock et al, 2010b) to more than 1 kg (Sowers, 2006(Sowers, , 2010Mischler et al, 2009) of ice from multi-parameter deep ice cores with a typical precision of around 3 to 4 ‰. This error bar is still large in view of the observed natural variability, which is rather small: about 30 ‰ for glacial-interglacial and 20 ‰ for rapid changes during the last glacial (Sowers, 2006;Bock et al, 2010b). This study presents new developments based on Bock et al (2010a) to improve precision and accuracy and significantly reduce the sample size for (ice core) δD(CH 4 ) measurements.…”

Section: Introductionmentioning

confidence: 99%

“…Ferretti et al, 2005;Fischer et al, 2008;Sowers, 2010;Sapart et al, 2012;Möller et al, 2013) provide further insight into processes and sources controlling the global methane cycle. For instance, knowledge of the temporal evolution of the hydrogen isotopic composition of methane (δD(CH 4 ) or δ 2 H(CH 4 )) over the termination of the last ice age (14 000-18 000 years before present) (Sowers, 2006) as well as during rapid warming events between 32 000-42 000 years before present (Bock et al, 2010b) made it possible to reject the "clathrate gun hypothesis" proposed by Kennett et al (2003) as the trigger for the steep atmospheric methane increases.…”

Section: Introductionmentioning

confidence: 99%

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Improving accuracy and precision of ice core δD(CH4) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

et al. 2014

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Abstract. Firn and polar ice cores offer the only direct palaeoatmospheric archive. Analyses of past greenhouse gas concentrations and their isotopic compositions in air bubbles in the ice can help to constrain changes in global biogeochemical cycles in the past. For the analysis of the hydrogen isotopic composition of methane (δD(CH 4 ) or δ 2 H(CH 4 )) 0.5 to 1.5 kg of ice was hitherto used. Here we present a method to improve precision and reduce the sample amount for δD(CH 4 ) measurements in (ice core) air. Preconcentrated methane is focused in front of a high temperature oven (pre-pyrolysis trapping), and molecular hydrogen formed by pyrolysis is trapped afterwards (post-pyrolysis trapping), both on a carbon-PLOT capillary at −196 • C. Argon, oxygen, nitrogen, carbon monoxide, unpyrolysed methane and krypton are trapped together with H 2 and must be separated using a second short, cooled chromatographic column to ensure accurate results. Pre-and post-pyrolysis trapping largely removes the isotopic fractionation induced during chromatographic separation and results in a narrow peak in the mass spectrometer. Air standards can be measured with a precision better than 1 ‰. For polar ice samples from glacial periods, we estimate a precision of 2.3 ‰ for 350 g of ice (or roughly 30 mL -at standard temperature and pressure (STP) -of air) with 350 ppb of methane. This corresponds to recent tropospheric air samples (about 1900 ppb CH 4 ) of about 6 mL (STP) or about 500 pmol of pure CH 4 .

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving accuracy and precision of ice core δD(CH4) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

et al. 2014

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“…In contrast, δD CH4 (Sowers, 2006;Bock et al, 2010) and 14 CH 4 (Petrenko et al, 2009) data from ice cores, suggest that marine methane hydrate degassing may not be the cause of atmospheric methane enrichment intervals through late Quaternary.…”

Section: Introductionmentioning

confidence: 89%

Gas hydrate destabilization and methane release events in the Krishna–Godavari Basin, Bay of Bengal

Joshi¹,

Mazumdar²,

Peketi³

et al. 2014

Marine and Petroleum Geology

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Methane release events have been linked to global warming, alteration of the carbon cycle and influence on biota. However, unequivocal evidence of paleomethane release events are limited. We report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core (MD161-8) from the Krishna-Godavari (K-G) Basin, Bay of Bengal. The most negative δ 13 C spikes are recorded during the marine isotope stages MIS-4 and at the transition of MIS-5 to 4. Occurrence of highly 13 C depleted (average δ 13 C = -48±2.4 ‰ VPDB) authigenic high magnesian calcite are also reported within this time window from the core MD161-8. In the present work an unequivocal explanation for the observed 13 C depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical/ electron microscopy or C-O stable isotope ratio analyses due to possible influence of diagenetic alteration. We attribute the observed episodic methane expulsion events, as inferred from the negative δ 13 C excursions and earlier reports on the occurrence chemosynthetic bivalves and Mo concentration anomaly to the destabilization of the base of gas hydrate stability zone (BGHSZ). Sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here. Shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage. Shale and salt tectonics in the passive continental margins being a globally observed phenomenon, its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time. Additional evidence of methane emission from site MD161-15 further supports the link between shale tectonics and methane emission.

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“…Brenninkmeijer et al (2003) describe how the isotope fractionation of specific source and sink processes affect the integrated isotopic composition of the respective trace gases in the atmosphere. In an inverse approach, ice core isotope records of CH 4 and N 2 O provide distinct constraints on biogeochemical processes that can be linked to the variability observed in the CH 4 and N 2 O mixing ratios on decadal to millennial timescales (Sowers et al, 2003(Sowers et al, , 2005Sowers, 2006Sowers, , 2009Ferretti et al, 2005;Schaefer et al, 2006;Bock et al, 2010b;Melton et al, 2011a;Sapart et al, 2012). Because ice core records of CH 4 and N 2 O isotopic composition indicate the natural response of specific greenhouse gas sinks and sources to palaeoclimate changes, this information is of great interest to global warming predictions.…”

Section: P Sperlich Et Al: Ch 4 and N 2 O Isotopes In Ice Core Samplesmentioning

confidence: 99%

An automated GC-C-GC-IRMS setup to measure palaeoatmospheric δ13C-CH4, δ15N-N2O and δ18O-N2O in one ice core sample

et al. 2013

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Abstract. Air bubbles in ice core samples represent the only opportunity to study the mixing ratio and isotopic variability of palaeoatmospheric CH4 and N2O. The highest possible precision in isotope measurements is required to maximize the resolving power for CH4 and N2O sink and source reconstructions. We present a new setup to measure δ13C-CH4, δ15N-N2O and δ18O-N2O isotope ratios in one ice core sample and with one single IRMS instrument, with a precision of 0.09, 0.6 and 0.7‰, respectively, as determined on 0.6–1.6 nmol CH4 and 0.25–0.6 nmol N2O. The isotope ratios are referenced to the VPDB scale (δ13C-CH4), the N2-air scale (δ15N-N2O) and the VSMOW scale (δ18O-N2O). Ice core samples of 200–500 g are melted while the air is constantly extracted to minimize gas dissolution. A helium carrier gas flow transports the sample through the analytical system. We introduce a new gold catalyst to oxidize CO to CO2 in the air sample. CH4 and N2O are then separated from N2, O2, Ar and CO2 before they get pre-concentrated and separated by gas chromatography. A combustion unit is required for δ13C-CH4 analysis, which is equipped with a constant oxygen supply as well as a post-combustion trap and a post-combustion GC column (GC-C-GC-IRMS). The post-combustion trap and the second GC column in the GC-C-GC-IRMS combination prevent Kr and N2O interferences during the isotopic analysis of CH4-derived CO2. These steps increase the time for δ13C-CH4 measurements, which is used to measure δ15N-N2O and δ18O-N2O first and then δ13C-CH4. The analytical time is adjusted to ensure stable conditions in the ion source before each sample gas enters the IRMS, thereby improving the precision achieved for measurements of CH4 and N2O on the same IRMS. The precision of our measurements is comparable to or better than that of recently published systems. Our setup is calibrated by analysing multiple reference gases that were injected over bubble-free ice samples. We show that our measurements of δ13C-CH4 in ice core samples are generally in good agreement with previously published data after the latter have been corrected for krypton interferences.

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Hydrogen Isotopes Preclude Marine Hydrate CH ₄ Emissions at the Onset of Dansgaard-Oeschger Events

Abstract: Events Emissions at the Onset of Dansgaard-OeschgerThe following resources related to this article are available online at www.sciencemag.org

Cited by 72 publications

References 30 publications

Improving accuracy and precision of ice core δD(CH<sub>4</sub>) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Improving accuracy and precision of ice core δD(CH<sub>4</sub>) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Gas hydrate destabilization and methane release events in the Krishna–Godavari Basin, Bay of Bengal

An automated GC-C-GC-IRMS setup to measure palaeoatmospheric δ<sup>13</sup>C-CH<sub>4</sub>, δ<sup>15</sup>N-N<sub>2</sub>O and δ<sup>18</sup>O-N<sub>2</sub>O in one ice core sample

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Hydrogen Isotopes Preclude Marine Hydrate CH 4 Emissions at the Onset of Dansgaard-Oeschger Events

Abstract: Events Emissions at the Onset of Dansgaard-OeschgerThe following resources related to this article are available online at www.sciencemag.org

Cited by 72 publications

References 30 publications

Improving accuracy and precision of ice core δD(CH&lt;sub&gt;4&lt;/sub&gt;) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Improving accuracy and precision of ice core δD(CH&lt;sub&gt;4&lt;/sub&gt;) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Gas hydrate destabilization and methane release events in the Krishna–Godavari Basin, Bay of Bengal

An automated GC-C-GC-IRMS setup to measure palaeoatmospheric δ&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt;, δ&lt;sup&gt;15&lt;/sup&gt;N-N&lt;sub&gt;2&lt;/sub&gt;O and δ&lt;sup&gt;18&lt;/sup&gt;O-N&lt;sub&gt;2&lt;/sub&gt;O in one ice core sample

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Hydrogen Isotopes Preclude Marine Hydrate CH ₄ Emissions at the Onset of Dansgaard-Oeschger Events

Improving accuracy and precision of ice core δD(CH<sub>4</sub>) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Improving accuracy and precision of ice core δD(CH<sub>4</sub>) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

An automated GC-C-GC-IRMS setup to measure palaeoatmospheric δ<sup>13</sup>C-CH<sub>4</sub>, δ<sup>15</sup>N-N<sub>2</sub>O and δ<sup>18</sup>O-N<sub>2</sub>O in one ice core sample