17:15 〜 18:30
[U13-P02] Radiocarbon Variability Recorded in Coral from Kikai Island to Understand Oceanography in the North Pacific Region
★Invited Papers
Atmospheric radiocarbon (14C) rapidly increased after 1955 because of the nuclear test. This artificial 14C called bomb-14C is diffused into the surface ocean and taken up by coral skeletons from ambient seawater. However, the deep ocean is isolated from direct CO2 exchange from the atmosphere. Therefore, bomb-14C in coral can be used as a very sensitive indicator of vertical and horizontal advection of water masses, which contributes to the understanding of ocean circulation [1].
In this study, a challenge has made with a high vacuum gas treatment line that specially designed for small quantity of samples (ca.100 μg C). This experiment is aiming at obtaining seasonal-resolution 14C data between 1940 and 1990 using the coral obtained from Kikai Island and revealing physical oceanographic information around Kuroshio region. The age model was based on high resolution Sr/Ca data determined by Kawakubo et al. (2017) [2].
At present, the contamination level during experimental steps of our method has been confirmed to be relatively low and constant by several repeated tests using standard samples distributed from International Atomic Energy Agency (IAEA). Besides, samples from the top part of coral corresponding to summer and winter shown by peaks of Sr/Ca data after 1975 has been measured. The trend and value of current bomb curve are similar to previous studies in Kikai Island and at other sampling sites in the Pacific, which proves the reliability of our data in high confidence. In this presentation, we will show the 14C results and discuss the oceanographic implications inferred from the data.
[1] Hirabayashi, S., Yokoyama, Y., Suzuki, A., Miyairi, Y., Aze, T., Siringan, F., & Maeda, Y. (2019). Insight into Western Pacific Circulation from South China Sea Coral Skeletal Radiocarbon. Radiocarbon, 61(6), 1923-1937.
[2] Kawakubo, Y., Alibert, C., & Yokoyama, Y. (2017). A reconstruction of subtropical western North Pacific SST variability back to 1578, based on a Porites Coral Sr/Ca record from the northern Ryukyus, Japan. Paleoceanography, 32, 1352– 1370.
In this study, a challenge has made with a high vacuum gas treatment line that specially designed for small quantity of samples (ca.100 μg C). This experiment is aiming at obtaining seasonal-resolution 14C data between 1940 and 1990 using the coral obtained from Kikai Island and revealing physical oceanographic information around Kuroshio region. The age model was based on high resolution Sr/Ca data determined by Kawakubo et al. (2017) [2].
At present, the contamination level during experimental steps of our method has been confirmed to be relatively low and constant by several repeated tests using standard samples distributed from International Atomic Energy Agency (IAEA). Besides, samples from the top part of coral corresponding to summer and winter shown by peaks of Sr/Ca data after 1975 has been measured. The trend and value of current bomb curve are similar to previous studies in Kikai Island and at other sampling sites in the Pacific, which proves the reliability of our data in high confidence. In this presentation, we will show the 14C results and discuss the oceanographic implications inferred from the data.
[1] Hirabayashi, S., Yokoyama, Y., Suzuki, A., Miyairi, Y., Aze, T., Siringan, F., & Maeda, Y. (2019). Insight into Western Pacific Circulation from South China Sea Coral Skeletal Radiocarbon. Radiocarbon, 61(6), 1923-1937.
[2] Kawakubo, Y., Alibert, C., & Yokoyama, Y. (2017). A reconstruction of subtropical western North Pacific SST variability back to 1578, based on a Porites Coral Sr/Ca record from the northern Ryukyus, Japan. Paleoceanography, 32, 1352– 1370.