[M-IS16] Paleoclimatology and paleoceanography

[MIS16-12] Characteristic of radiocarbon dates in response to sea-level changes in the Bonaparte Gulf, Northwestern Australia

*Takeshige Ishiwa^1,2,3, Yusuke Yokoyama^2,3,4, Stephen Obrochta⁵, Katsuto Uehara⁶, Jun'ichi Okuno^1,7, Minoru Ikehara⁸, Yosuke Miyairi² (1.National Institute of Polar Research, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 4.Japan Agency for Marine-Earth Science and Technology, 5.Graduate School of International Resource Science, Akita University, 6.Research Institute for Applied Mechanics, Kyushu University, 7.Department of Polar Research Science, School of Multidisciplinary Science, The Graduate University for Advanced Studies (SOKENDAI), 8.Center for Advanced Marine Core Research, Kochi University)

Keywords:Radiocarbon dating, Sea-level change, Paleotidal modeling

Radiocarbon dating is an essential method for constraining Late Quaternary age models and applied to carbon-containing materials. Past climate and sea-level changes influence depositional process so that paleoenvironmental reconstruction is needed to select an appropriate dating material. We present radiocarbon dates variation performed on macrofossils, foraminifers, and acid-insoluble carbon (AIC), as well as paleo-tidal modeling results from the Bonaparte Gulf in northwestern Australia. The varied topography and large tidal range of this gulf are the dominant factors of the past depositional process in response to sea-level change. We will reveal the variation of radiocarbon dates in response to sea-level changes, which appear as changes in paleowater depth and paleotide. Carbonate fossil material reveals a more reliable depositional age than acid insoluble carbon at sea level below -70 m because of little lateral transport caused by reduced tidal activity. On the other hand, acid insoluble carbon ages are more reliable at sea level above – 70 m because redeposition of old fossil influences carbonate fossils ages due to enhanced tidal activity. Our results indicate that the age models' reliability has changed over time, especially on the continental shelf, where environmental changes due to sea-level fluctuations are significant.