[M-IS23] [JJ] Paleoclimatology and paleoceanography

[MIS23-09] High-resolution reconstruction of climates under the three great famines in the Edo period based on intra-ring oxygen isotope ratio of tree rings and historical daily weather record

★Invited papers

*Kenjiro Sho¹, Yuta Kojin², Ikumi Hamada¹, Kaoru Kamatani³, Masaki Sano³, Akane Tsushima³, Takeshi Nakatsuka³ (1.Nagoya Institute of Technology, 2.Taisei Corporation, 3.Research Institute for Humanity and Nature)

Keywords:Tree-ring cellulose, Stable oxygen isotope ratio, Intra-ring fluctuation, Relative humidity, The three great famines in the Edo period, Historical daily weather record

Stable oxygen isotope ratio (δ¹⁸O) of tree-ring cellulose is known to reflect well relative humidity at the time of ring formation. In this study we attempt high-resolution reconstruction of climates under the three great famines (Kyoho, Tenmei, Tempo) in the Edo period (1603-1867) by analyzing intra-ring data of oxygen isotope ratio of tree-rings. Tree-ring samples used in this study were taken from two hinoki (Chamaecyparis obtusa) trees growing at the Mt.Tanakami site, Shiga Prefecture, central Japan. We extracted cellulose from the wood samples by the “cross-section” method and divided into 12 (or 2, 6, 24, depending on the ring width) segments for each ring using a scalpel. Isotopic measurement was carried out using a continuous flow system with a pyrolysis-type elemental analyzer and an isotope ratio mass spectrometer (TCEA-Delta V Advantage). By comparing measured intra-ring data of cellulose δ¹⁸O and observational data of relative humidity at the adjacent meteorological station for the mid- to late 20th century, intra-ring δ¹⁸O was found to reflect variation of humidity at sub-seasonal (monthly or finer) temporal resolution in the growth season of the tree (May-Jul. or May-Sep. for our samples). According to this result, we reconstructed variations of humidity for the pre- to early Baiu rainy season (May-Jun.) and the mid- to late Baiu season (Jun.-Jul) usingδ¹⁸O chronologies of early part and middle or late part of each ring (Figure). For the pre- to early Baiu season, highly variable δ¹⁸O was found in the Kyoho period (1716-1736), implying periodical occurrence of dry early summer caused by delayed onset of the Baiu season. We can also recognize significant decrease in δ¹⁸O (increase in humidity) in the Tempo period (1831-1845), probably due to abnormally early onset of the Baiu season. Contrarily, variability of δ¹⁸O is relatively small for the mid- to late Baiu season.