Presentation Information
[AAS08-P04]Variations in atmospheric CH4 concentration since the Industrial Revolution from the SE-Dome II ice core, southeastern Greenland
*Mai Suzuki1, Ikumi Oyabu2,1, Kenji Kawamura2,1, Satoshi Sugawara3, Taku Umezawa4, Yoshinori Iizuka5 (1.The Graduate University for Advanced Studies, 2.National Institute of Polar Research, Research Organization of Information, 3.Miyagi University of Education, 4.Graduate School of Science, Tohoku University, 5.Institute of Low Temperature Science, Hokkaido University)
Keywords:
ice core,methane,firn,Greenland
Methane (CH4) is one of the most important greenhouse gases and is emitted from both natural and anthropogenic sources. Direct observation of atmospheric CH4 in the Arctic and Antarctica started in the 1980s; thus, the concentration histories before this period need to be reconstructed from the analyses of polar ice cores. In Antarctica, high-resolution and high-precision CH4 data during the industrial period is available from the Law Dome ice core (Rubino et al., 2019), which was drilled at a high-accumulation site (about 1 m w.e. year-1). However, there have been no high-quality data from Greenland ice cores because of several problems such as in-situ CH4production in high-impurity layers in the ice sheet and the lack of Greenland cores from very high accumulation sites (Rhodes et al., 2013; Umezawa et al., 2022). In this study, we analyzed the SE-Dome II core (67°19’17” N, 36°47’03” W, 3,161m a.s.l; Iizuka et al., 2021), which was drilled at a high-accumulation site in southeastern Greenland (about 1 m w.e. year-1; Kawakami et al., 2023) to reconstruct the CH4 concentration between the 1840s and 2000s. To generate a continuous and high-resolution record while minimizing possible age reversal or age discontinuity due to inhomogeneous gas trapping at the bottom of firn, we cut the ice core at the boundaries of annual layers, so that each sample contains one year of accumulation (~1 m).
The atmospheric gases are enclosed as air bubbles at the bottom of firn, so the age of gas is always younger than the age of ice at the same depth (the difference is called Δage).
Gas age = Ice age - Δage
The ice age of the SE-Dome II core covers from 1799 to 2020. The time scale was established by counting the seasonal variations in H2O2 concentration (Kawakami et al., 2023). To estimate the gas age along the core, we first calculated the average Δage by comparing the CH4 data of the SE-Dome II core with that of direct observation at Point Barrow in Alaska (Lan et al., 2025). Next, we estimated the temporal variation of Δage by combining a firn densification model (Herron and Langway, 1980), a firn gas transport model (Sugawara et al., 2003) and a parameterization of gas age at close-off (Buizert et al., 2013).
Our new reconstruction shows that the CH4 concentration increased from ~830 ppb to ~1800 ppb between the 1840s and the 2000s, with particularly rapid increase after the 1940s. We did not find anomalous (non-atmospheric) CH4 values as previously found in other Greenland ice cores (e.g., Rhodes et al., 2013), possibly because of low impurity concentrations in the core due to the extremely high accumulation rate.
The CH4 growth rate was ~10 ppb year-1 since the 1840s and increased since the late 1940s. The maximum growth rate for the past 200 years (~20 ppb year-1) occurred in the late 1970s, just before the establishment of direct atmospheric observations.
We calculated the Inter-Polar Difference (IPD) in CH4 concentration deduced from the SE-Dome II and Law Dome core. Micthell et al. (2013) showed the IPD was ~40 ppb from 1600 to 1800. Our data shows that the IPD increased ~50 ppb to 1840s and reached ~80 ppb in 1940s. After the late 1940s, the IPD increased with major fluctuations and exceeded 160 ppb in the 1980s just before the direct observation. The growth rate and IPD in this study suggest that the CH4 emission strongly increased in the Northern Hemisphere after the 1940s.
The atmospheric gases are enclosed as air bubbles at the bottom of firn, so the age of gas is always younger than the age of ice at the same depth (the difference is called Δage).
Gas age = Ice age - Δage
The ice age of the SE-Dome II core covers from 1799 to 2020. The time scale was established by counting the seasonal variations in H2O2 concentration (Kawakami et al., 2023). To estimate the gas age along the core, we first calculated the average Δage by comparing the CH4 data of the SE-Dome II core with that of direct observation at Point Barrow in Alaska (Lan et al., 2025). Next, we estimated the temporal variation of Δage by combining a firn densification model (Herron and Langway, 1980), a firn gas transport model (Sugawara et al., 2003) and a parameterization of gas age at close-off (Buizert et al., 2013).
Our new reconstruction shows that the CH4 concentration increased from ~830 ppb to ~1800 ppb between the 1840s and the 2000s, with particularly rapid increase after the 1940s. We did not find anomalous (non-atmospheric) CH4 values as previously found in other Greenland ice cores (e.g., Rhodes et al., 2013), possibly because of low impurity concentrations in the core due to the extremely high accumulation rate.
The CH4 growth rate was ~10 ppb year-1 since the 1840s and increased since the late 1940s. The maximum growth rate for the past 200 years (~20 ppb year-1) occurred in the late 1970s, just before the establishment of direct atmospheric observations.
We calculated the Inter-Polar Difference (IPD) in CH4 concentration deduced from the SE-Dome II and Law Dome core. Micthell et al. (2013) showed the IPD was ~40 ppb from 1600 to 1800. Our data shows that the IPD increased ~50 ppb to 1840s and reached ~80 ppb in 1940s. After the late 1940s, the IPD increased with major fluctuations and exceeded 160 ppb in the 1980s just before the direct observation. The growth rate and IPD in this study suggest that the CH4 emission strongly increased in the Northern Hemisphere after the 1940s.