Friday, 9 September 2005 - 9:30 AM

This presentation is part of: Reservoir Age Variability in the Marine Environment

Radiocarbon marine reservoir ages in the western North Pacific estimated by pre-bomb molluscan shells

Minoru Yoneda1, Hikaru Uno1, Yasuyuki Shibata1, Ryo Suzuki2, Yuichiro Kumamoto3, Kunio Yoshida4, and Takenori Sasaki4. (1) Environmental Chemistry Division, National Institute for Environmental Studies, Onogawa16-2, Tsukuba, 305-8506, Japan, (2) Environmental Research Center, Ltd., Tsukuba, 305-0857, Japan, (3) Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan, (4) University Museum, University of Tokyo, Tokyo, 113-0033, Japan

The reservoir ages in the western North Pacific are estimated based on apparent 14C ages of pre-bomb molluscan shells in this study. We have reported some investigations on the temporal and spatial variability in the marine reservoir ages of this area using both modern shells [1] and faunal remains from prehistoric shellmiddens in Hokkaido [2,3]. However, that is still not fully understood because of complicated ocean dynamics and the lack of accessibility to proper modern samples.

Although the shells housed at Kyoto University Museum are exceptionally well-organized collection of pre-bomb molluscan shell, our pilot study showed unexpected discrepancy among samples from the same location and some exceptional anomalies [1]. In this previous study, however, the apparently large marine reservoir effect as large as 800 14C years in the northern part Japan, especially in Hokkaido, suggests the difference in 14C contents between the Oyashio current in the north and Kuroshio current in the south. But the rigorous selection of samples should be done in the light of their living circumstance, water depth, diet, evidence of catch alive, and accurate information of sampling location and date, in order to obtain more detailed map of reservoir ages in this area.

For this study, we selected a series of plankton-feeding bivalves and limpet (including a few gastropods), which had kept paired shells and/or soft tissue on their surface, from the biological shell collection of the University Museum of the University of Tokyo. Around one hundred samples were measured for radiocarbon ages at NIES-TERRA in order to estimate the variability of marine reservoir ages in the western North Pacific, including the Japanese archipelago, Taiwan, and the Philippines. Some preliminary estimations and oceanographic interpretations will be discussed.

[1] Yoneda et al., Nucl. Instrum. Meth. B 172, 377 (2000).

[2] Yoneda et al., Radiocarbon 43, 465 (2001).

[3] Yoneda et al., Nucl. Istrum. Meth. B 223-224, 376 (2004).


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