11:15 〜 11:30
[ACC29-09] Stratigraphic observations of SE-Dome II ice core from southeastern Greenland drilled in 2021
キーワード：アイスコア、グリーンランド
During May and June 2021, a 250-meter-long ice core (SE-Dome II core) was drilled from the Southeastern Greenland Dome (SE-Dome; 67°11′30.14328″N, 36°28′12.77075″W, 3160.7 m a.s.l.), where is one of the highest accumulation areas in Greenland. The age of the ice core at 250 m in depth is estimated as AD 1827 based on the rough estimate from timescale of previous 90-meter-long ice core1). The high accumulation allows us to reconstruct paleo climate with high time-resolution and causes rapid densification of snow and ice. Hence, the stratigraphy of SE-Dome II core preserves unique densification processes such as packing and thermodynamic metamorphisms of firn and ice.
We conducted stratigraphic observations under the transmitted light, and bulk density, high resolution density, near infrared-ray (NIR), and electrical-conductivity (DEP) measurements in a cold room (-20 °C). We also measured H2O2 concentrations with depth intervals about 5 cm.
As a result, the close-off density of 830 kg m-3 was reached at about 87.14 m depth. From stratigraphic observations, three types of layers were observed: melt layers, high transmitted layers, and low transmitted layers. The snow-pit observation at the SE-Dome site indicated that the high transmitted layers tended to consist of large grains, and the low transmitted layers were small grains. The depths with melt layers and high transmitted layers corresponded to summer layers (of the ice core) determined by H2O2 concentrations. The low transmitted layers were observed regardless of seasons.
The observed number of melt layers is 90, with an average thickness of 1.7 ± 5.7 cm. The frequency and the thickness of melt layers have increased since 2000 (26 layers with an average thickness of 3.3 ± 10.4 cm). The high transmitted layers exhibit a similar tendency with the melt layers. On the other hand, the frequency and thickness of the low transmitted layers concentrate at 80-160 m depth (around 1940s). We consider that a recent warming trend in the Arctic causes snow melting and increases of melt layers and high transmitted layers.
References
1 Iizuka, Y. et al., 2021, BGR, 39, pp.1-12.
We conducted stratigraphic observations under the transmitted light, and bulk density, high resolution density, near infrared-ray (NIR), and electrical-conductivity (DEP) measurements in a cold room (-20 °C). We also measured H2O2 concentrations with depth intervals about 5 cm.
As a result, the close-off density of 830 kg m-3 was reached at about 87.14 m depth. From stratigraphic observations, three types of layers were observed: melt layers, high transmitted layers, and low transmitted layers. The snow-pit observation at the SE-Dome site indicated that the high transmitted layers tended to consist of large grains, and the low transmitted layers were small grains. The depths with melt layers and high transmitted layers corresponded to summer layers (of the ice core) determined by H2O2 concentrations. The low transmitted layers were observed regardless of seasons.
The observed number of melt layers is 90, with an average thickness of 1.7 ± 5.7 cm. The frequency and the thickness of melt layers have increased since 2000 (26 layers with an average thickness of 3.3 ± 10.4 cm). The high transmitted layers exhibit a similar tendency with the melt layers. On the other hand, the frequency and thickness of the low transmitted layers concentrate at 80-160 m depth (around 1940s). We consider that a recent warming trend in the Arctic causes snow melting and increases of melt layers and high transmitted layers.
References
1 Iizuka, Y. et al., 2021, BGR, 39, pp.1-12.