10:15 AM - 10:30 AM
[ACC21-06] CH4 concentrations during the Holocene reconstructed from the NEEM (Greenland) and Dome Fuji (East Antarctica) ice cores
Keywords:Ice core, methane, Holocene, Greenland, Antarctica
Methane (CH4), the second most important anthropogenic greenhouse gas, has increased in the atmosphere by a factor 2.5 since the onset of the Industrial Revolution, which account for ~20% of the total increase in radiative forcing over that time[1]. Ice cores from both polar regions preserve the past atmospheric CH4, and thus have the potential to constrain the changes in CH4 concentration difference between the polar regions. The inter polar difference of CH4 is one of the approaches to understand the evolution of CH4 budget and its relationship with climate. To reconstruct the CH4 inter polar difference during the Holocene, we have been measuring CH4 concentrations in the NEEM (Greenland) and Dome Fuji (Antarctica) ice cores over the period from 200 to 14500 years before present (yr BP), with a mean time resolution of ~50 years. Since most of this time period is overlapping with the brittle zone in the Greenland core, it is challenging to reconstruct accurate CH4 concentration during the Holocene from the NEEM ice core.
Ice samples without visible cracks were carefully selected from the NEEM and Dome Fuji ice cores. We employed a newly established wet extraction system (an improved version of ref. 2) the National Institute of Polar Research, with a typical sample size of ~80 g (ice). The air released from ice was first collected into a sample tube (electropolished stainless steel tube with a metal-seal valve), and then it was split into two aliquots. One aliquot was measured by a gas chromatograph (Agilent Technologies 7890A) for CO2, CH4 and N2O concentrations, and the other was measured by a mass spectrometer (Thermo DELTA V Plus) for δ15N of N2, δ18O of O2, δ(O2/N2), δ(Ar/N2) and total air content. We have measured 181 samples for the NEEM ice core. Analytical precision of CH4 concentration was estimated to be ±2.4 ppb from the pooled standard deviation from duplicate measurements (n=53).
Before the Holocene, the NEEM CH4 concentration is relatively high (620-705 ppb) during the Bølling-Allerød, and it rapidly decreases to <500 ppb during the Younger Dryas, and then increases to ~750 ppb at the beginning of the Holocene. During the Holocene, CH4 concentration first decreases to the minimum of ~610 ppb around 5000 yr BP, and it increases afterwards. Our record agrees well with a high resolution CH4 concentration record from the GISP2 ice core for last 2000 years[3], and that of the NEEM ice core measured by a CFA system between 9500 and 14500 yr BP[4].
We completed the NEEM measurements and started the Dome Fuji measurements, and the resulting CH4 inter polar difference will be deduced and discussed in the presentation.
References
[1] P. Forster et al., in Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al., Eds. (Cambridge Univ. Press, Cambridge, 2007), pp. 131–234.
[2] Kawamura et al. (2003). Atmospheric CO2 variations over the last three glacial-interglacial climatic cycles deduced from the Dome Fuji deep ice core, Antarctica using a wet extraction technique. Tellus B, 55(2), 126–137.
[3] Mitchell et al. (2013). Constraints on the Late Holocene Anthropogenic Contribution to the Atmospheric Methane Budget. Science, 342(6161), 964–966.
[4] Chappellaz et al. (2013). High-resolution glacial and deglacial record of atmospheric methane by continuous-flow and laser spectrometer analysis along the NEEM ice core. Clim. Past, 9(6), 2579–2593.
Ice samples without visible cracks were carefully selected from the NEEM and Dome Fuji ice cores. We employed a newly established wet extraction system (an improved version of ref. 2) the National Institute of Polar Research, with a typical sample size of ~80 g (ice). The air released from ice was first collected into a sample tube (electropolished stainless steel tube with a metal-seal valve), and then it was split into two aliquots. One aliquot was measured by a gas chromatograph (Agilent Technologies 7890A) for CO2, CH4 and N2O concentrations, and the other was measured by a mass spectrometer (Thermo DELTA V Plus) for δ15N of N2, δ18O of O2, δ(O2/N2), δ(Ar/N2) and total air content. We have measured 181 samples for the NEEM ice core. Analytical precision of CH4 concentration was estimated to be ±2.4 ppb from the pooled standard deviation from duplicate measurements (n=53).
Before the Holocene, the NEEM CH4 concentration is relatively high (620-705 ppb) during the Bølling-Allerød, and it rapidly decreases to <500 ppb during the Younger Dryas, and then increases to ~750 ppb at the beginning of the Holocene. During the Holocene, CH4 concentration first decreases to the minimum of ~610 ppb around 5000 yr BP, and it increases afterwards. Our record agrees well with a high resolution CH4 concentration record from the GISP2 ice core for last 2000 years[3], and that of the NEEM ice core measured by a CFA system between 9500 and 14500 yr BP[4].
We completed the NEEM measurements and started the Dome Fuji measurements, and the resulting CH4 inter polar difference will be deduced and discussed in the presentation.
References
[1] P. Forster et al., in Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al., Eds. (Cambridge Univ. Press, Cambridge, 2007), pp. 131–234.
[2] Kawamura et al. (2003). Atmospheric CO2 variations over the last three glacial-interglacial climatic cycles deduced from the Dome Fuji deep ice core, Antarctica using a wet extraction technique. Tellus B, 55(2), 126–137.
[3] Mitchell et al. (2013). Constraints on the Late Holocene Anthropogenic Contribution to the Atmospheric Methane Budget. Science, 342(6161), 964–966.
[4] Chappellaz et al. (2013). High-resolution glacial and deglacial record of atmospheric methane by continuous-flow and laser spectrometer analysis along the NEEM ice core. Clim. Past, 9(6), 2579–2593.