[M-IS14] Paleoclimatology and paleoceanography

[MIS14-P31] Intra-annual tree-ring oxygen isotope variation of Thujopsis dolabrata in Tsugaru, northern Japan, and its correlation with ocean-atmosphere climate indices

*Kenjiro Sho¹, Fuhito Asai¹, Kanta Nakane¹, Motonari Ohyama², Zhen Li³, Takeshi Nakatsuka³ (1.Nagoya Institute of Technology, 2.Tohoku University, 3.Nagoya University)

Keywords:Intra-annual tree-ring oxygen isotope analysis, Thujopsis dolabrata in Tsugaru region, northern Japan, PDO index

Oxygen stable isotope ratios (δ¹⁸O) in tree-ring cellulose have been used to reconstruct hydroclimatic environments (mainly relative humidity and isotope ratios in soil water) in the past. The authors have been conducting research on hydroclimatic reconstruction for recent several centuries using intra-ring oxygen isotope data to obtain high temporal resolution of reconstruction. In this study, we analyzed intra-ring variation of oxygen isotope ratios for the period 1840-2001 using two Aomori cypress (Thujopsis dolabrata) trees collected at Kanagi town in Tsugaru region, Aomori Prefecture, northern Japan (40°54'N, 140°28'E). After the wood samples were cut into thin cross-sectional plates and the cellulose was isolated, each annual ring was divided into six segments in the direction of growth under a microscope, and the oxygen isotope ratios were measured using an on-line system of elemental analyzer and isotope ratio mass spectrometer. The obtained intra-ring oxygen isotope variation showed maximum values in segment 1, the earliest part of an annual ring, and minimum values in segment 6, the latest part, for most of the measured annual rings. According to the correlation analysis between the oxygen isotope ratios of each segment and the monthly relative humidity observation data at the nearest meteorological station (Aomori) for 1882-2001, the highest negative correlation was found in May for segment 1, in later seasons gradually for later segments, and in August-September for segment 6 for both sample trees. Therefore, the growth period of these trees can be estimated as May to September. Moreover, to examine the relationship between the intra-ring oxygen isotope data and large-scale climatic and oceanic conditions, we analyzed the correlations between the oxygen isotope ratios of each segment and various ocean-atmosphere climate indices. As a result, strong correlation was found between the oxygen isotope ratios of segments 3-4 (corresponding to June to early July) and the PDO indices in fall to winter in the previous several years. Spatial correlations of the oxygen isotope ratios of segments 3-4 and the PDO indices with the gridded SST data in the North Pacific showed similar spatial correlation patterns for both. Therefore, PDO variability may affects the hydroclimatic environment in the Tsugaru region in June to early July with substantial time lags through some mechanisms such as the variability of Aleutian low.