Citation:

pnas.1613883114

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Abstract:

Atmospheric methane (CH4) records reconstructed from polar ice cores represent a integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here we present dual stable isotopic methane records (d13CH4 and dD(CH4)) 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 new dD(CH4) constraint, it appears that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 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 years compared to 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 due to biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.

Project(s):

European Project for Ice Coring in Antarctica (EPICA)

Funding:

Fifth Framework Programme (FP5), grant/award no. EVK2-CT-2000-00077 : European Project for Ice Coring in Antarctica

Fourth Framework Programme (FP4), grant/award no. ENV4980702 : European Project for Ice Coring in Antarctica

Coverage:

Median Latitude: -75.290050 * Median Longitude: 102.534478 * South-bound Latitude: -78.464420 * West-bound Longitude: 0.068400 * North-bound Latitude: -72.783330 * East-bound Longitude: 159.066670

Date/Time Start: 1980-01-01T00:00:00 * Date/Time End: 2008-12-31T00:00:00

Comment:

All methane isotope data are given as measured (d13C wrt VPDB, dD wrt VSMOW). All data are given corrected for gravitational settling in the firn. d13CH4 data are additionally given corrected for diffusional fractionation in the firn. All relevant information concerning data and corrections are given in the main article, the Materials and Methods section and in the Supporting Information (SI).

All data are free of krypton interference during the mass spectrometric analysis. For details see Schmitt et al. (2014, doi:10.5194/amt-7-2645-2014).

All data are given on a depth scale and the gas age according to AICC 2012: Veres et al. (2013, doi:10.5194/cp-9-1733-2013 and Bazin et al. (2013, doi:10.5194/cp-9-1715-2013).

License:

Creative Commons Attribution-NoDerivs 3.0 Unported (CC-BY-ND-3.0)

Size:

5 datasets

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Datasets listed in this publication series

Bock, M; Schmitt, J; Beck, J et al. (2017): Stable isotopic methane (δ¹³CH4) records of ice core EDC. https://doi.org/10.1594/PANGAEA.873913
Bock, M; Schmitt, J; Beck, J et al. (2017): Stable isotopic methane (dD(CH4)) records of ice core EDC. https://doi.org/10.1594/PANGAEA.873916
Bock, M; Schmitt, J; Beck, J et al. (2017): Stable isotopic methane (dD(CH4)) records of ice core EDML. https://doi.org/10.1594/PANGAEA.873917
Bock, M; Schmitt, J; Beck, J et al. (2017): Stable isotopic methane (δ¹³CH4) records of ice core TALDICE. https://doi.org/10.1594/PANGAEA.873914
Bock, M; Schmitt, J; Beck, J et al. (2017): Stable isotopic methane (δ¹³CH4) records of ice core Vostok. https://doi.org/10.1594/PANGAEA.873915