14C dating correction method for tectonically active complex deep marine environments at cold seep vents off Eastern Japan: Seawater DIC acquisition by Calpyptogena sp. bivalves

Mr Kazuhiro Yagasaki1, Dr. Juichiro Ashi1, Prof. Yusuke  Yokoyama1, Dr. Stephen Obrochta2, Dr. Yosuke Miyairi1, Dr. Shin’ichi Kuramoto3

1Atmosphere And Ocean Research Institute, The University of Tokyo, Tokyo, Japan, 2Department of Earth Science, Akita University, Akita, Japan, 3Japan Agency for Marine Earth-Science and Technology (JAMSTEC), Yokohama, Japan

Shells and corals are often used as proxies for sea surface temperature reconstructions in paleoclimatology. These species utilise the dissolved inorganic carbon (DIC) in seawater making it suitable for analysing ocean circulation through the measurement of radiocarbon 14C. It is also possible to estimate the age of the shell through analysing the growth increments within the shells and radiocarbon 14C dating. Yet correction models in deeper marine environment remains complicated due to the multiple variables that must be considered, which include problems such as carbon sinks, ocean current flux and dead carbon effect from seafloor vents.

This study proposes a correction method at a depth of 600m at the Daini Tenryu Knoll off Tokai, Japan, which is a renowned region for recurrent M8 class earthquakes that occur very 100-150 years. Due to the regular tectonic activity and the presence for rich methane hydrate layers below the seafloor (Ashi et al., 2002, Otsuka et al., 2015), the fault regions are common with cold seep vents, which accommodate various sized colonies of Calyptogena sp. bivalves. We propose a novel method towards developing such a correction model in this complex environment and to determine if the Calyptogena sp. is affected by the methane from beneath the seafloor or from biogenic origins. Radiocarbon age of seawater DIC depth profiles and bivalve shell measurements conducted using a Single-Stage Accelerated Mass Spectrometer (AMS) (Yokoyama et al., 2007).

Reference

Ashi, J., H. Tokuyama and A. Taira, 2002. Distribution of methane hydrate BSRs and its implication for the prism growth in the Nankai Trough, Marine Geology, 187, 177-191.
Otsuka, H., Morita, S., Tanahashi, M., and Ashi, J., 2015, Foldback reflectors near methane hydrate bottom-simulating reflectors: Indicators of gas distribution from 3D seismic images in the eastern Nankai Trough. Island Arc, 24 145-158.
Yokoyama, Y., Miyairi, Y., Matsuzaki, H. and Tsunomori, F. (2007): Relation between acid dissolution time in the vacuum test tube and time required for graphization for AMS target preparation. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259: 330-334.


Biography:

I am a PhD candidate at the AORI, The University of Tokyo. I am also currently working for The Nippon Foundation on global environmental projects and SEABED 2030 as well.
I am a marine geologist, focusing around studying past active fault movements off the Tokai region in Eastern Japan. My interest has been around the interaction between active fault movements and bivalve communities at methane seeps in the region that are thought to hold detailed active fault movement records.
I look forward to discussing this interesting finding with you all, and hope to find other possible unexplored ideas.

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Date

Nov 08 - 19 2021