A novel in-situ C-14 extraction system for surface exposure dating to reconstruct the past Antarctic ice sheet
Mr Yusuke Shimizu1, Dr. Yusuke Yokoyama1, Dr. Yosuke Miyairi1, Dr. Masako Yamane2
1Atmosphere and Ocean Research Institute, The University of Tokyo , Kashiwa, Japan, 2Institute for Space-Earth Environmental Research, Nagoya University, Chikusa-ku, Japan
In-situ carbon-14 (C-14) surface exposure dating is a powerful tool to understand the Earth surface processes including reconstruction of past Antarctic ice sheets behavior during the late Quaternary (Hippe et al., 2017). However, the markedly small amounts of in-situ C-14 in quartz hampered the advance of study using this technique until recently (Lifton et al., 2001).
This study developed in-situ C-14 extraction system which heats samples to 1650 ℃ for extracting in-situ C-14 from quartz at Atmosphere and Ocean Research Institute, The University of Tokyo (Yokoyama et al., 2004; Fülöp et al., 2019). Our newly developed in-situ C-14 extraction system consists of three parts: the extraction furnace, the gas cleaning line, and the graphitization port. The new system employed novel heating furnace that requires dramatically short time to raise the target temperature for the experiment.
To test the extraction system performance, we prepared two types of granite samples, namely in-situ C-14 free samples and in-situ C-14 saturated samples. The initial experiments showed the high blank level (1.6 x 10^8 C-14 atoms) and the low extraction efficiency (5.6%).
Each procedural step required the blank test to understand the cause of high background, and the results suggested that several components of the extraction systems were identified as the source of C-14 contamination. After the revision of the apparatus design was made, the new system showed sufficiently low blank level (4.6 x 10^4 C-14 atoms).
The initial extraction system circulated Oxygen-Helium mixed gas during extraction heating to convert released carbon to carbon dioxide. This gas circulation possibly cooled the quartz sample and prevented quartz grains from releasing in-situ C-14. Thus, we improved our heating procedure to increase the extraction efficiency. The extraction furnace was filled with Oxygen-Helium gas before the heated extraction and was kept closed during the heating. The extraction efficiency ranged from 98% to 105% with this new procedure.
These results indicates that the novel system is successfully able to extract in-situ C-14 from sample for surface exposure dating.
Fülöp, R. H., Fink, D., Yang, B., Codilean, A. T., Smith, A., Wacker, L., … & Dunai, T. J. (2019). The ANSTO–University of Wollongong in-situ 14C extraction laboratory. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 438, 207-213.
Hippe, K. (2017). Constraining processes of landscape change with combined in situ cosmogenic 14C-10Be analysis. Quaternary Science Reviews, 173, 1-19.
Lifton, N. A., Jull, A. T., & Quade, J. (2001). A new extraction technique and production rate estimate for in situ cosmogenic 14C in quartz. Geochimica et Cosmochimica Acta, 65(12), 1953-1969.
Yokoyama, Y., Caffee, M. W., Southon, J. R., & Nishiizumi, K. (2004). Measurements of in situ produced 14C in terrestrial rocks. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 223, 253-258.
Yusuke Shimizu received his BS in Earth and planetary science from the University of Tokyo in 2019, and his MS from the University of Tokyo in 2021.