[A-CC29] アイスコアと古環境モデリング

[ACC29-02] グリーンランド南東部、高涵養量ドームにおける浅層アイスコアプロジェクトの概要と研究成果

★招待講演

*飯塚 芳徳¹、的場 澄人¹、古川 崚仁¹、安藤 卓人¹、斉藤 健¹、Parvin Fahmida¹、網野 智美¹、柴田 麻衣¹、門田 萌¹、関 宰¹、杉山 慎¹、植村 立²、藤田 耕史³、鶴田 明日香⁴、服部 祥平⁴、藤田 秀二⁵、本山 秀明⁵、永塚 尚子⁵、大藪 幾美⁵、山口 悟⁶、安達 聖⁶、大野 宏⁷、堀 彰⁷、宮本 千尋⁸、高橋 嘉夫⁸、佐々木 千晶⁹、鈴木 利孝⁹、Bautista VII Angel^10,11、松崎 浩之¹⁰、堀内 一穂¹²、宮本 淳¹³、芳村 圭¹⁴、Sjolte Jesper¹⁵、庭野 匡思¹⁶、大島 長¹⁶、橋本 明弘¹⁶、山崎 哲秀¹⁷、青木 輝夫¹⁸ (1.北海道大学低温科学研究所、2.琉球大学理学部、3.名古屋大学環境学研究科、4.東京工業大学物質理工学院応用化学系、5.国立極地研究所、6.防災科学技術研究所、7.北見工業大学社会環境工学科、8.東京大学大学院理学系研究科、9.山形大学大学院理工学研究科、10.東京大学 大学院工学系研究科、11.フィリピン核研究所、12.弘前大学理工学研究科、13.北海道大学高等教育推進機構、14.東京大学生産技術研究所、15.ルンド大学第四紀地理学教室、16.気象庁気象研究所、17.アバンナック、18.岡山大学自然科学研究科)

キーワード：アイスコア、グリーンランド、高涵養

On May 2015, we drilled a 90.45 m ice core in a high accumulation area of the southeastern Greenland Ice Sheet. The drilling site (SE-Dome; 67.18°N, 36.37°W, 3170 m a.s.l.) is located 185 km north of the town of Tasiilaq in southeastern Greenland [1]. Then we measure physical and chemical properties of the SE-Dome ice core. Based on the measurements, we show the general characteristics of the SE-Dome ice core. I) As for dating of the ice core [2], we propose a dating method based on matching the δ¹⁸O variations between ice-core records and records simulated by isotope-enabled climate models. We applied this method to a δ¹⁸O record from the SE-Dome ice core. The close similarity between the δ¹⁸O records from the ice core and models enables correlation and the production of a precise age scale, with an accuracy of a few months. II) As for physical property [3], the ice was –20.9 ºC at 20-m depth. The close-off density of 830 kg m^-3 occurs at 83.4–86.8-m depth, which is about 20-m shallower than that obtained from empirical models, indicating that the firn with a higher density is softer than that from empirical result. We interpret that the high accumulation rate creates a high overburden pressure in a short time. The relative softness of the firn may arise from 1) there being not enough time to form bonds between grains as strong as those in a lower accumulation-rate area, and similarly, 2) the dislocation density in the firn being relatively high. III) As for chemical property [4], we measured the major ion fluxes, and obtained records of annual ion fluxes from 1957 to 2014. We find a high average NO₃^- flux (1.13 mmol m^-2 yr^-1) in the ice core, which suggests a negligible effect from post-depositional NO₃^- loss, indicating the SE-Dome region is an excellent location for reconstructing nitrate fluxes. For the non-sea-salt (nss) SO₄^2- and NH₄⁺ fluxes, a decreasing and increasing trend from 1970 to 2010, respectively, tracks well with the anthropogenic SO_x and NH₃ emissions. In contrast, the decadal trend of NO₃^- flux differs from the decreasing trend of anthropogenic NO_x emissions. We continue to investigate the paleoenvironment with multi proxies from several analyses (e.g. [5]) of the high-time-resolution and chemicals-well-preserved ice core.

References
[1] Iizuka et al., (2016). Bulletin of Glaciological Research, 34, 1–10. https://doi.org/10.5331/bgr.15R03
[2] Furukawa et al., (2017). Journal of Geophysical Research: Atmospheres, 122, 10,873–10,887. https://doi.org/10.1002/2017JD026716
[3] Iizuka et al., (2017). Arctic, Antarctic, and Alpine Research, 49, 13–27. https://doi.org/10.1657/AAAR0016-034
[4] Iizuka et al., (2018). Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1002/2017JD026733
[5] Bautista et al., (2018) Journal of Environmental Radioactivity 184–185, 14–21, https://doi.org/10.1016/j.jenvrad.2017.12.015