Spatial variations of ¹⁰Be in surface snow along the inland traverse route of Japanese Antarctic Research Expedition

Dr Kazuho Horiuchi1, Shinji Kato2, Kou  Ohtani1, Dr Naoyuki  Kurita3, Shun  Tsutaki4, Fumio  Nakazawa4, Hideaki Motoyama4, Kenji Kawamura4, Hirofumi Tazoe5, Naofumi Akata5, Keisuke Yamagata6, Hiroyuki Matsuzaki6

1Graduate School of Science and Technology, Hirosaki University, Hirosaki, Japan, 2Hachinohe Office, National Tax Agency, Hachinohe, Japan, 3Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan, 4National Institute of Polar Research, Tachikawa, Japan, 5Institute of Radiation Emergency Medicine, Hirosaki, Japan, 6Micro Analysis Laboratory, Tandem accelerator (MALT), The University of Tokyo, Bunkyo-ku, Japam

Snow and ice layers in Antarctica have huge and diverse implications on global climatic and paleoclimatic phenomena. They not only are involved in global climate changes but also serve as cryo-archives providing a lot of key information for paleoclimate communities. Cosmogenic ¹⁰Be is probably one of such information. Cosmic-ray variations and events, which are of geomagnetic, solar and other celestial origins, have been intensively investigated using temporal ¹⁰Be variations analyzed in polar ice cores (e.g. Beer et al., 2012). Temporal ¹⁰Be records are also used to evaluate snow accumulation rates of ice cores from inland Antarctica by assuming a fairly constant fallout rate of the nuclide within relatively small fluctuations recording the production signals (e.g. Cauquoin et al., 2015). However, spatial distribution of ¹⁰Be in surface snow is scarcely investigated and it was reported only by a few studies (e.g. Berggren, et al., 2013). We here present a data set of ¹⁰Be in surface snow samples obtained along the inland traverse route of the 59th and 60th Japanese Antarctic Research Expedition (JARE). The traverse expeditions were conducted between the coastal S16 point (69°02’S, 40°03’E) and the vicinity of the inland Dome Fuji station (77°19’S, 39°42’E). The route is almost straight (precisely arc-like) from north to south and from the foot of the slope (0.6 km in altitude) to the high plateau (up to 3.8 km in altitude). We took fresh snow or fresh drift snow samples in early austral summer (Nov. 12th to Dec. 17th, 2017) in the 59th JARE and in mid-austral summer (Jan. 1st to Jan. 19th, 2019) in the 60th JARE. The samples were then transported in frozen form to Japan. Sample pretreatments were performed at Hirosaki University. Accelerator Mass Spectrometry was employed for the ¹⁰Be analysis at Micro Analysis Laboratory, Tandem accelerator (MALT), The University of Tokyo. The ¹⁰Be concentrations in the samples varied by an order of magnitude from 3.7 × 10³ to 8.6 × 10⁴ atoms/g. Plotted against the latitude, the concentrations show a clear southward increasing trend with an upward inflection point around 75° S (3.5 km in altitude) for the JARE 59th. On the other hand, for the JARE 60th, such a trend is less clear and the concentrations are sometimes significantly higher than those of the 59th JARE north of 75° S. We compared our results with a compiled data set of snow accumulation rates (SAR) from snow stake measurements along the traverse route during the last three decades (Kamiyama et al., 1994; Tsutaki et al., in preparation). The comparison suggests that the ¹⁰Be variations observed in the 59th JARE are largely accounted for by variations of the local mean SAR and a possible difference of the ¹⁰Be fallout rate between the high plateau and the other areas. On the other hand, higher ¹⁰Be concentrations sometimes found in the 60th JARE samples can be interpreted to reflect a seasonal variation of ¹⁰Be fallout, which is related to stratosphere–troposphere exchange that may cause a distinct ¹⁰Be enhancement in mid-austral summer.


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Date

Nov 08 - 19 2021