Japan Geoscience Union Meeting 2015

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS34] Paleoclimatology and paleoceanography

Thu. May 28, 2015 2:15 PM - 4:00 PM 301A (3F)

Convener:*Kazuyoshi Yamada(Museum of Natural and Environmental history, Shizuoka), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Ikuko Kitaba(Research Centre for Palaleoclimatology, Ritsumeikan University), Akihisa Kitamura(Institute of Geosciences, Faculty of Science, Shizuoka University), Masaki Sano(Research Institute for Humanity and Nature), Takeshi Nakagawa(Ritsumeikan University), Akira Hayashida(Department of Environmental Systems Science, Doshisha University), Chair:Ikuko Kitaba(Research Centre for Palaleoclimatology, Ritsumeikan University)

3:15 PM - 3:30 PM

[MIS34-14] Hydroclimate variations in southwestern Japan over the past 1500 years inferred from oxygen isotope ratios in tree rings

*Masaki SANO1, Katsuhiko KIMURA2, Koh YASUE3, Takeshi NAKATSUKA1 (1.Research Institute for Humanity and Nature, 2.Fukushima University, 3.Shinshu University)

Keywords:Tree rings, Oxygen isotope, Yakushima Island, Monsoon

Oxygen isotope ratios (δ18O) in tree-ring cellulose have been widely used to reconstruct hydroclimate variations and atmospheric circulations over monsoon Asia. However, most of previous reconstructions based on tree-ring δ18O cover only the past several hundred years, and therefore millennium-scale reconstructions are yet to be developed. Here we present a well-replicated 1500-year tree-ring δ18O chronology that was constructed using living and fallen dead trees (Cryptomeria japonia) in Yakushima Island, southwestern Japan. First of all, core or disk samples were absolutely dated by matching ring-width patterns among different trees. Then a total of 14 trees were selected for isotopic analysis. We employed the 'plate method' to isolate cellulose component directly from a 1.0-mm wood plate. Each annual ring of cellulose was separated using a razor blade. Finally δ18O of individual ring was determined using a continuous flow isotope ratio mass spectrometer coupled to an elemental analyzer. The δ18O time series were highly correlated with one another, suggesting that common climatic signals are preserved in all the sampled trees. Because the δ18O series did not show prominent age-related trends, all the series were simply normalized to have the same mean during the overlapping segments. The normalized series were then averaged to construct the final chronology. Response analysis using ambient climate records for the last 50 years indicates that tree-ring δ18O is mainly governed by summer relative humidity. We therefore interpret this record as a proxy of hydroclimate related to East Asian summer monsoon. Low-frequency variations in our chronology are similar to those of a Northern Hemisphere temperature reconstruction. More specifically our reconstruction shows a relatively dry (wet) condition during the Medieval Warm Period (the Little Ice Age). Centennial-scale fluctuations of sea surface temperatures in the equatorial Pacific may play a role in modulating long-term hydroclimate changes in southwestern Japan.