N2O and CH4 variations during the last glacial epoch: Insight into global processes

Flückiger, Jacqueline; Blunier, Thomas; Stauffer, B.; Chappellaz, J.; Spahni, Renato; Kawamura, Kenji; Schwander, Jakob; Stocker, Thomas F.; Dahl-Jensen, Dorthe

doi:10.1029/2003gb002122

Cited by 192 publications

(214 citation statements)

References 72 publications

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“…The land model is defined on the same horizontal grid as the atmosphere and includes components for biogeophysics, biogeochemistry, the hydrologic cycle as well as a dynamic global vegetation model 71,72 . In order to improve the simulation of the land surface hydrology and vegetation cover, new parameterizations for canopy interception and soil evaporation have been implemented into the land component 73 [78][79][80] . In addition, the 38 ka BP ICE-5G continental ice-sheet distribution has been implemented 76 .…”

Section: Numerical Experimentsmentioning

confidence: 99%

North Atlantic forcing of tropical Indian Ocean climate

Mohtadi

Prange

Oppo

et al. 2014

Nature

246

228

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The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells 1-5 , but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.In the North Atlantic, the most recent glacial and deglacial periods are characterized by a series of abrupt and severe cold snaps of millennial duration associated with either iceberg instabilities and surges (Heinrich events) or freshwater input from the Arctic Ocean 6 (the Younger Dryas). These abrupt events are of particular interest because they were rapidly communicated through the ocean by a slowdown, or potentially a shutdown, of the Atlantic meridional overturning circulation 7 (AMOC) and through the atmospheric circulation 8 causing climate anomalies worldwide. Climate archives document a significant tropical hydrologic response to these events. Dry Younger Dryas and Heinrich stadials have been reported from various marine and terrestrial archives across the tropical Indian Ocean 4,9-14 .However, a few records suggest wet Younger Dryas or Heinrich stadials over northeast Australia 15 , southern Indonesia 5,16 and southeast Africa 12,17 . Although there seems to be strong evidence that the intertropical convergence zone (ITCZ) moved southwards in the tropical Atlantic 2 , a wide range of mechanisms have been offered to explain the connection between the cooling of the North Atlantic and tropical Indian Ocean hydroclimates: a weakening of the rainfall system in response to regional sea surface cooling 13,14 ; and changes in the monsoon intensity 4,10,16 associated with a southward shift in the mean 1 or winter 4,5,15 position of the ITCZ or in the position of oceanic fronts 18 .How...

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Section: Numerical Experimentsmentioning

confidence: 99%

North Atlantic forcing of tropical Indian Ocean climate

Mohtadi

Prange

Oppo

et al. 2014

Nature

246

228

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“…Oceanic processes are thought to drive carbon dioxide variations [Flückiger et al, 2004], but the drive on methane variations is still a matter of conjecture. The expansion and contraction of northern and tropical wetlands may be a key control [Brook et al, 2000;Delmotte et al, 2004;Flückiger et al, 2004;MacDonald et al, 2006], as may the stability of marine and terrestrial clathrates [MacDonald, 1983[MacDonald, , 1990Nisbet, 1989Nisbet, , 1990Paull et al, 1991Paull et al, , 1994Kennett et al, 2003]. There is debate, in particular, regarding the contribution of these sources to the rapid rises in methane observed during deglaciation [Brook et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

Subglacial methanogenesis: A potential climatic amplifier?

Wadham

Tranter

Tulaczyk

et al. 2008

Global Biogeochemical Cycles

114

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[1] Subglacial environments are a previously neglected component of the Earth's global carbon cycle, a reflection of the view held until recently that they are dominated by abiotic and oxic conditions. Here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over North America and Europe during glaciations were host to significant populations of anaerobic microorganisms, including methanogens, able to metabolize organic carbon sequestered during interglacials and overridden during Quaternary glacials. In doing so, we review the current evidence for subglacial methane release during deglaciation, estimate the size of the subglacial reservoir of organic carbon (SOC), and assess the amount of SOC available to subglacial microbes and the likely pathways and rates of carbon turnover. We then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations. We calculate that the SOC equates to 418-610 Pg C and includes carbon from terrestrial soils/vegetation, peatlands, lake, and marine sediments. The SOC that is potentially available for microbial conversion to methane is smaller than this estimate due to (1) glacial erosion, (2) accumulation of recalcitrant organic carbon compounds over time, (3) conversion to carbon dioxide by aerobic/anaerobic respiration, and (4) incomplete conversion of labile organic matter to methane. We estimate that the total SOC available for conversion to methane is 63 Pg C. Our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates. We believe, however, that there is a strong likelihood that subglacial microbes could convert 63 Pg of SOC to methane during a glacial cycle. If this were the case, release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations. Our findings suggest that it may well be important to consider subglacial environments as active components of the Earth's carbon cycle. Conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation, however, awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions.

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“…Especially CH 4 records have been used as proxy on the extension of wetlands on the stability of marine clathrates as CH 4 source. On glacial timescales, periods of warmer climate in the Northern Hemisphere correlated with increased concentrations of CH 4 and N 2 O in the atmosphere (Flückiger et al, 2004;Loulergue et al, 2008;Schilt et al, 2010). Moreover, the mixing Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

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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N₂O and CH₄ variations during the last glacial epoch: Insight into global processes

Abstract: [1] Greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere, its natural variations, and the responses to fast climatic changes in the past. We present high-resolution nitrous oxide (N 2 O) and methane (CH 4

Cited by 192 publications

References 72 publications

North Atlantic forcing of tropical Indian Ocean climate

North Atlantic forcing of tropical Indian Ocean climate

Subglacial methanogenesis: A potential climatic amplifier?

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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N2O and CH4 variations during the last glacial epoch: Insight into global processes

Abstract: [1] Greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere, its natural variations, and the responses to fast climatic changes in the past. We present high-resolution nitrous oxide (N 2 O) and methane (CH 4

Cited by 192 publications

References 72 publications

North Atlantic forcing of tropical Indian Ocean climate

North Atlantic forcing of tropical Indian Ocean climate

Subglacial methanogenesis: A potential climatic amplifier?

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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About

N₂O and CH₄ variations during the last glacial epoch: Insight into global processes

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