Japan Geoscience Union Meeting 2014

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Symbol H (Human Geosciences) » H-TT Technology & Techniques

[H-TT35_1AM2] Developments and applications of AMS techniques for earth and human environmental research

Thu. May 1, 2014 11:00 AM - 12:45 PM 311 (3F)

Convener:*Toshio Nakamura(Center for Chronological Research, Nagoya University), Hiroyuki Matsuzaki(School of Engineering, The University of Tokyo), Kimikazu Sasa(Research Facility Center for Science and Technology, University of Tsukuba), Hisao Nagai(Faculty of humanities and Sciences, Nihon University), Masayo Minami(Center for Chronological Resarch, Nagoya University), Chair:Toshio Nakamura(Center for Chronological Research, Nagoya University)

12:00 PM - 12:15 PM

[HTT35-12] Cosmogenic 36Cl/10Be ratio in the Antarctic ice core during the last deglaciation and early Holocene

*Kimikazu SASA1, Kazuna KUROSUMI1, Keisuke SUEKI1, Tsutomu TAKAHASHI1, Yuki MATSUSHI2, Yuki TOSAKI3, Kazuho HORIUCHI4, Tomoko UCHIDA5, Hiroyuki MATSUZAKI6, Hideaki MOTOYAMA7 (1.University of Tsukuba, 2.Kyoto University, 3.National Institute of Advanced Industrial Science and Technology, 4.Hirosaki University, 5.Tohoku University, 6.The University of Tokyo, 7.National Institute of Polar Research)

Keywords:36Cl/10Be, Cosmogenic nuclide, Accelerator Mass Spectrometry, Radiometric age determination, Ice core

36Cl is cosmogenic nuclide (half-life:301 kyr) produced mainly by a reaction of 40Ar(p, nα)36Cl in the upper atmosphere. Cosmogenic nuclides fall on the Earth's surface at a rate depending on the nuclide production rates and hence reflecting the cosmic ray intensity. Therefore we can reconstruct fluctuations of cosmic ray intensity, by determining the past 36Cl depositional flux. Such fluctuations of cosmic ray intensity may indicate paleo solar activity and/or variations in the Earth's geomagnetic field. In this presentation, we report the results of cosmogenic 36Cl measurements during 10.55 - 18.42 kyr b2k in the ice core drilled at the Dome Fuji station, Antarctica (Motoyama et al., 2007). 36Cl in the ice was measured with the accelerator mass spectrometry (AMS) system at the University of Tsukuba (Sasa et al., 2010). The results show that 36Cl conc. is 0.21 - 1.80 × 104 atoms g-1 and 36Cl flux is 0.54 - 3.25 × 104 atoms cm-2 yr-1. The variation of 36Cl flux in early Holocene shows similar fluctuations of 10Be flux in the same ice core. 36Cl/10Be is constant at 0.10 ± 0.01 in early Holocene. This means that this value can be used for radioactive age dating of the old ice core. 36Cl/10Be varies in the last deglaciation. It suggests that the decrease in 36Cl/10Be ratio is linked to climate change.