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
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, and that of the NEEM ice core measured by a CFA system between 9500 and 14500 yr BP.
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.
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