11:00 〜 13:00
[ACC29-P02] Reconstruction of atmospheric CH4 concentration during the penultimate glacial period from the Dome Fuji ice core
キーワード：アイスコア、メタン、CFA、氷期、D/O
Ice cores and other paleoclimate records (e.g., stalagmites and marine sediment cores) have revealed that the last glacial period was characterized by the repetition of Dansgaard-Oeschger (D/O) events, which are abrupt warming events in Greenland, and associated climate changes in the Northern Hemisphere. The counterpart to the D/O event is seen in Antarctic temperatures, which is thought to be caused by changes in the Atlantic meridional overturning circulation (AMOC). The number and timing of D/O and associated events are consistent among various paleoclimate records from around the globe during the last glacial period. However, for the periods older than the last glacial period, the number, timing, and frequency of D/O events are inconsistent among paleoclimate records. Because rapid changes in atmospheric methane (CH4) for the last glacial period are mostly synchronous with D/O events, the D/O events before the last glacial period (where continuous Greenland ice cores do not exist) may be reconstructed from analyses of CH4 concentration in Antarctic deep ice cores. However, the CH4 reconstruction in the older glacial periods has been limited to the analyses of discrete samples with a typical temporal resolution of about 500 years, which is insufficient to capture short and small D/O events. Here, we present a nearly continuous CH4 record during the penultimate glacial period (Marine Isotope Stage 6) from the continuous flow analysis (CFA) of the Dome Fuji ice core.
We analyzed the second Dome Fuji deep ice core from 1869 to 2076 m (207-m long) using the CFA system at National Institute of Polar Research, which continuously melt the ice and measure multiple components simultaneously. For the CH4 measurements, the air with small portion of meltwater was separated from the bulk of meltwater with a debubbler, and then extracted with a membrane degasser. The air was then dried with a Nafion drier and measured with a cavity ringdown spectrometer (Picarro G2301), which was customized to operate at low cavity pressure (40 Torr).
We reconstructed CH4 concentrations during the penultimate glacial period (~145,000 – 195,000 years ago). The amplitude and shape of relatively large D/O-like peaks (several tens of ppb) found in our record are in good agreement with the results of discrete measurements of the Dome Fuji and EDC cores (e.g., Loulergue et al., 2008, Nature and our preliminary data), indicating the validity of the CFA results. Furthermore, the CFA data exhibit previously unidentified variations with small amplitudes (about 10 ppb) and short durations (several hundred years). During the studied period, 26 peaks were detected. 23 peaks were detected during MIS3 (~20,000 – 70,000 years ago) in the last glacial period when applying the same detection threshold on the first derivative of the CH4 time series. The number of the D/O-like events (with abrupt increase and gradual decrease) during the penultimate glacial period is larger than previously proposed based on the analyses of water isotope and dust records of the DF and EDC cores (DF Project Members, 2017, Sci. Adv.) as well as the discrete CH4 data from the EDC core (Loulergue et al., 2008). By comparing the CFA records of water isotopic ratio and CH4 concentration on the respective age scales (for ice and gas), most of the D/O-like CH4 increases appear to have corresponding peaks in the water isotopic record (so-called Antarctic Isotopic Maxima). The amplitudes of the D/O-like events in the penultimate glacial period are generally smaller than those in the last glacial period (even after considering the signal smoothing in the DF core by the slow bubble trapping process). These results suggest that the D/O-like events repeatedly occurred during the penultimate glacial period, but with some differences from those in the last glacial period.
We analyzed the second Dome Fuji deep ice core from 1869 to 2076 m (207-m long) using the CFA system at National Institute of Polar Research, which continuously melt the ice and measure multiple components simultaneously. For the CH4 measurements, the air with small portion of meltwater was separated from the bulk of meltwater with a debubbler, and then extracted with a membrane degasser. The air was then dried with a Nafion drier and measured with a cavity ringdown spectrometer (Picarro G2301), which was customized to operate at low cavity pressure (40 Torr).
We reconstructed CH4 concentrations during the penultimate glacial period (~145,000 – 195,000 years ago). The amplitude and shape of relatively large D/O-like peaks (several tens of ppb) found in our record are in good agreement with the results of discrete measurements of the Dome Fuji and EDC cores (e.g., Loulergue et al., 2008, Nature and our preliminary data), indicating the validity of the CFA results. Furthermore, the CFA data exhibit previously unidentified variations with small amplitudes (about 10 ppb) and short durations (several hundred years). During the studied period, 26 peaks were detected. 23 peaks were detected during MIS3 (~20,000 – 70,000 years ago) in the last glacial period when applying the same detection threshold on the first derivative of the CH4 time series. The number of the D/O-like events (with abrupt increase and gradual decrease) during the penultimate glacial period is larger than previously proposed based on the analyses of water isotope and dust records of the DF and EDC cores (DF Project Members, 2017, Sci. Adv.) as well as the discrete CH4 data from the EDC core (Loulergue et al., 2008). By comparing the CFA records of water isotopic ratio and CH4 concentration on the respective age scales (for ice and gas), most of the D/O-like CH4 increases appear to have corresponding peaks in the water isotopic record (so-called Antarctic Isotopic Maxima). The amplitudes of the D/O-like events in the penultimate glacial period are generally smaller than those in the last glacial period (even after considering the signal smoothing in the DF core by the slow bubble trapping process). These results suggest that the D/O-like events repeatedly occurred during the penultimate glacial period, but with some differences from those in the last glacial period.