Potential glacial‐interglacial changes in stable carbon isotope ratios of methane sources and sink fractionation

Schaefer, H. Martin; Whiticar, Michael J.

doi:10.1029/2006gb002889

Cited by 23 publications

(61 citation statements)

References 100 publications

(231 reference statements)

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“…However, tropical wetland emissions are higher in the southern hemisphere (19), whereas remote sensing shows that [CH4] increased mainly in the northern tropics and subtropics (13). Also, tropical wetlands are relatively 13 C-enriched (-52‰ to -60‰) and match our post-2006 perturbation not as well as rice cultivation (-59 to -65‰) and C3-fed ruminants (-60‰ to -74‰) (3,24,26). This isotopic evidence against tropical wetlands is not strong, given the ranges of reported δ 13 C(So) for various sources.…”

supporting

confidence: 72%

“…S8 to S12). δ 13 C(So) ~ -59‰ is characteristic for biogenic sources (3,24,26). Thermogenic or pyrogenic emissions would require compensating changes in other sources or sinks.…”

mentioning

confidence: 99%

“…S4 to S7). δ 13 C(So) ~ -35‰ is characteristic for thermogenic CH4 (3,24,26), which is mainly emitted from the production of oil, natural gas, and coal (21,22). Simultaneous biogenic and pyrogenic reductions could produce the same signal as thermogenic reductions.…”

mentioning

confidence: 99%

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A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

Schaefer

Fletcher

Veidt

et al. 2016

Science

397

462

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Between 1999 and 2006, a plateau interrupted the otherwise continuous increase of atmospheric methane concentration [CH4] since preindustrial times. Causes could be sink variability or a temporary reduction in industrial or climate-sensitive sources. We reconstructed the global history of [CH4] and its stable carbon isotopes from ice cores, archived air, and a global network of monitoring stations. A box-model analysis suggests that diminishing thermogenic emissions, probably from the fossil-fuel industry, and/or variations in the hydroxyl CH4 sink caused the [CH4] plateau. Thermogenic emissions did not resume to cause the renewed [CH4] rise after 2006, which contradicts emission inventories. Post-2006 source increases are predominantly biogenic, outside the Arctic, and arguably more consistent with agriculture than wetlands. If so, mitigating CH4 emissions must be balanced with the need for food production.

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supporting

confidence: 72%

“…S8 to S12). δ 13 C(So) ~ -59‰ is characteristic for biogenic sources (3,24,26). Thermogenic or pyrogenic emissions would require compensating changes in other sources or sinks.…”

mentioning

confidence: 99%

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A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

Schaefer

Fletcher

Veidt

et al. 2016

Science

397

462

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“…Another, more likely, explanation for the δ 13 CH 4 shift during the MIS 5-4 transition involves changes in the characteristic isotope values of individual sources themselves 33 , controlled by climate and CO 2 -induced changes in ecosystem composition. As the primary process of CH 4 production is the anaerobic decomposition of plant material, atmospheric CO 2 affects δ 13 CH 4 in many ways.…”

Section: Climate and Co 2 -Induced Changes In Wetland Ecosystemsmentioning

confidence: 99%

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

et al. 2013

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During the last glacial cycle, greenhouse gas concentrations fluctuated on decadal and longer timescales. Concentrations of methane, as measured in polar ice cores, show a close connection with Northern Hemisphere temperature variability, but the contribution of the various methane sources and sinks to changes in concentration is still a matter of debate. Here we assess changes in methane cycling over the past 160,000 years by measurements of the carbon isotopic composition δ 13 C of methane in Antarctic ice cores from Dronning Maud Land and Vostok. We find that variations in the δ 13 C of methane are not generally correlated with changes in atmospheric methane concentration, but instead more closely correlated to atmospheric CO 2 concentrations. We interpret this to reflect a climatic and CO 2 -related control on the isotopic signature of methane source material, such as ecosystem shifts in the seasonally inundated tropical wetlands that produce methane. In contrast, relatively stable δ 13C values occurred during intervals of large changes in the atmospheric loading of methane. We suggest that most methane sources-most notably tropical wetlands-must have responded simultaneously to climate changes across these periods.C limate variations over the past glacial cycle are characterized by global temperature changes 1,2 , sea-level fluctuations 3,4 and substantial changes in atmospheric greenhouse gas concentrations 5 . Abrupt climate shifts, for example DansgaardOeschger events, characterize much of the glacial records in the Northern Hemisphere and are mirrored in the icecore CH 4 record 6,7 . The nature of the CH 4 -climate coupling on glacial-interglacial and millennial timescales is still a matter of debate 7,8 . Studies of the interpolar CH 4 concentration difference using ice cores from both polar regions are interpreted as a constraint of the latitudinal distribution of CH 4 emission sources 9,10 . Furthermore, most CH 4 sources/sinks have characteristic isotope signatures. Accordingly, atmospheric CH 4 isotope records provide refined boundary conditions to constrain changes in individual sources or sinks over time [11][12][13] . Here we present CH 4 isotope data from ice cores covering the past 160,000 years (160 kyr; Fig. 1), thereby extending the atmospheric δ 13 CH 4 record to a full glacial-interglacial cycle. Generally, our record confirms increased δ 13 CH 4 values under full glacial conditions 11 , decreasing δ 13 CH 4 during terminations (except during the unique Younger Dryas cold reversal) and the continuation of this declining trend over the following interglacial 13 , irrespective of the CH 4 evolution. Although an unambiguous alignment of termination I and II is not possible owing to the Younger Dryas event, δ 13 CH 4 values of the two deglaciations seem to be offset by ∼2 (Fig. 2) Fig. 3). In stark contrast to the MIS 5-4 transition, rapid CH 4 changes during Dansgaard-Oeschger events are not imprinted in the δ 13 CH 4 record. Comparing the full δ 13 CH 4 record with other global climate reco...

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“…However, biogenic sources (such as wetlands and BB) may change their isotopic signatures in parallel to changing climate and environmental conditions (25,34). For the last glacial, Möller et al (25) showed that the 13 C content of CH 4 (δ 13 CH 4 ) is higher at low CO 2 levels and concluded that biome changes play a major role in this isotopic change.…”

mentioning

confidence: 99%

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH₄ice core records

Bock

Schmitt

Beck

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Atmospheric methane (CH 4 ) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ 13 CH 4 and δD(CH 4 )] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH 4 ) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH 4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.atmosphere | methane | megafauna | ice core | stable isotopes

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Potential glacial‐interglacial changes in stable carbon isotope ratios of methane sources and sink fractionation

Cited by 23 publications

References 100 publications

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH₄ice core records

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Potential glacial‐interglacial changes in stable carbon isotope ratios of methane sources and sink fractionation

Cited by 23 publications

References 100 publications

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by 13 CH 4

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by 13 CH 4

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4ice core records

Contact Info

Product

Resources

About

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by ¹³ CH ₄

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH₄ice core records