5:15 PM - 6:45 PM
[ACC27-P06] Dating of an ice core drilled in the blue ice area in the southern Yamato Mountains, Antarctica
Keywords:Antarctica, Yamato Mountains, Blue ice area, Ice core, Chronology, Methane
In blue ice areas, ice sheet flow is interrupted by mountains and older ice is exposed on the surface. Ice cores drilled in blue ice areas can more easily reconstruct older environments. For this reason, many studies have been conducted on ice cores obtained in blue ice areas (e.g., in Antarctica, Allan Hills (Spaulding et al., 2013), Taylor Glacier (Baggentos et al., 2017), and Larsen BIA (Lee et al., 2022), and in Greenland, Pakitsoq (Petrenko et al., 2006)).
The 24th Japanese Antarctic Research Expedition drilled an ice core approximately 100 m long in the blue ice area in the southern Yamato Mountains, Antarctica (referred as the South Yamato core). In previous studies, various methods such as ice sheet flow models and measurements of the composition in trapped air have been used to determine the age of the South Yamato core (e.g., Nakawo et al., 1988; Machida et al., 1996; Moore et al., 2006), however, they have not been able to determine the age of the core accurately. In this study, we determined the gas age of the South Yamato core by comparing the variations of methane concentration and atmospheric oxygen isotope ratio of trapped air in the South Yamato core with those from the Dome Fuji core (Kawamura et al., 2007; Oyabu et al., 2022) and WAIS Divide core (Rhodes et al., 2015; Seltzer et al., 2017). We extracted trapped air from the South Yamato core at depths of 35-65 m by wet extraction method and analyzed them for the methane concentration and atmospheric oxygen isotope ratio at National Institute of Polar Research (NIPR). The methane and oxygen isotope data were analyzed in combination with previously unpublished data. We note that the data shallower than 6 m was excluded from the analysis because of the contamination by cracks.
As a result, three peaks of the methane concentration that correspond to the Dansgaard-Oeschger (D-O) event were observed at depths of 10 m, 50 m, and 70-80 m of the South Yamato core, and a characteristic small peak was observed around 90 m. By comparing with the methane variations of the Dome Fuji core and WAIS Divide core, we found that the gas age of the South Yamato core is likely to be between 41 and 49 kyr BP.
As for the oxygen isotope ratios of the trapped air, it was found that the core was greatly affected by gas loss fractionation, in which lighter isotopes preferentially escape, leaving the remaining gas in the core enriched in the heavy isotope. It is because the South Yamato core had been stored at a relatively high temperature, -20℃, for 40 years after drilling. By applying the correction proposed by Severeinghaus et al. (2009), we obtained the oxygen isotope ratio variations consistent with those at 41-49 kyr BP of the Dome Fuji core and WAIS Divide core.
We try to measure the South Yamato core with a continuous flow analysis system at NIPR to obtain high-resolution methane concentration, which may allow us to construct a precise gas age scale. In addition, we will measure the stable isotope ratio of methane to understand the cause of the methane variations for the period of 41-49 kyr BP which corresponds to the D-O events 10, 11, 12.
Reference:
Baggenstos, D. et al., Climate of the Past, 13, 943–958, 2017.
Kawamura, K. et al., Nature, 448, 912-916, 2007.
Lee, G. et al., The Cryosphere, 16, 2301–2324, 2022.
Machida, T. et al., Proceedings NIPR Symposium Polar Meteorology Glaciology, 10, 55-65, 1996.
Moore, J. C. et al., Journal of Geophysical Research, 111, D16302, 2006
Nakawo, M. et al., Annals of Glaciology, 10, 126-129, 1988.
Oyabu, I. et al., Quaternary Science Reviews, 294, 107754, 2022.
Petrenko, V. V. et al., Quaternary Science Reviews, 25, 865–875, 2006.
Rhodes, R. H. et al., Science, 348(6238), 1016-1019, 2015.
Seltzer, A. M. et al., Climate of the Past, 12, 1323-1338, 2017.
Severinghaus, J. P. et al., Science, 324, 1431-1434, 2009.
Spaulding, N. E. et al., Quaternary Research, 80, 562–574, 2013.
The 24th Japanese Antarctic Research Expedition drilled an ice core approximately 100 m long in the blue ice area in the southern Yamato Mountains, Antarctica (referred as the South Yamato core). In previous studies, various methods such as ice sheet flow models and measurements of the composition in trapped air have been used to determine the age of the South Yamato core (e.g., Nakawo et al., 1988; Machida et al., 1996; Moore et al., 2006), however, they have not been able to determine the age of the core accurately. In this study, we determined the gas age of the South Yamato core by comparing the variations of methane concentration and atmospheric oxygen isotope ratio of trapped air in the South Yamato core with those from the Dome Fuji core (Kawamura et al., 2007; Oyabu et al., 2022) and WAIS Divide core (Rhodes et al., 2015; Seltzer et al., 2017). We extracted trapped air from the South Yamato core at depths of 35-65 m by wet extraction method and analyzed them for the methane concentration and atmospheric oxygen isotope ratio at National Institute of Polar Research (NIPR). The methane and oxygen isotope data were analyzed in combination with previously unpublished data. We note that the data shallower than 6 m was excluded from the analysis because of the contamination by cracks.
As a result, three peaks of the methane concentration that correspond to the Dansgaard-Oeschger (D-O) event were observed at depths of 10 m, 50 m, and 70-80 m of the South Yamato core, and a characteristic small peak was observed around 90 m. By comparing with the methane variations of the Dome Fuji core and WAIS Divide core, we found that the gas age of the South Yamato core is likely to be between 41 and 49 kyr BP.
As for the oxygen isotope ratios of the trapped air, it was found that the core was greatly affected by gas loss fractionation, in which lighter isotopes preferentially escape, leaving the remaining gas in the core enriched in the heavy isotope. It is because the South Yamato core had been stored at a relatively high temperature, -20℃, for 40 years after drilling. By applying the correction proposed by Severeinghaus et al. (2009), we obtained the oxygen isotope ratio variations consistent with those at 41-49 kyr BP of the Dome Fuji core and WAIS Divide core.
We try to measure the South Yamato core with a continuous flow analysis system at NIPR to obtain high-resolution methane concentration, which may allow us to construct a precise gas age scale. In addition, we will measure the stable isotope ratio of methane to understand the cause of the methane variations for the period of 41-49 kyr BP which corresponds to the D-O events 10, 11, 12.
Reference:
Baggenstos, D. et al., Climate of the Past, 13, 943–958, 2017.
Kawamura, K. et al., Nature, 448, 912-916, 2007.
Lee, G. et al., The Cryosphere, 16, 2301–2324, 2022.
Machida, T. et al., Proceedings NIPR Symposium Polar Meteorology Glaciology, 10, 55-65, 1996.
Moore, J. C. et al., Journal of Geophysical Research, 111, D16302, 2006
Nakawo, M. et al., Annals of Glaciology, 10, 126-129, 1988.
Oyabu, I. et al., Quaternary Science Reviews, 294, 107754, 2022.
Petrenko, V. V. et al., Quaternary Science Reviews, 25, 865–875, 2006.
Rhodes, R. H. et al., Science, 348(6238), 1016-1019, 2015.
Seltzer, A. M. et al., Climate of the Past, 12, 1323-1338, 2017.
Severinghaus, J. P. et al., Science, 324, 1431-1434, 2009.
Spaulding, N. E. et al., Quaternary Research, 80, 562–574, 2013.