Keywords:peat, cellulose, oxygen isotopes
The oxygen isotopic composition of rainfall water has climate signals such as temperature and precipitation. Therefore, we can use the δ18O values of plant cellulose which preserves the δ18O values of rainfall water for paleoclimate reconstruction. At the Hani peat mire in northeastern China, paleoclimate reconstruction was attempted using the δ18O values of cellulose in the peat core, and the variation of the δ18O values in bulk samples was interpreted that it reflects the variation of temperature (Hong et al., 2009). On the other hands, the analysis of δ18O in different plant tissues in the same sample from the Rhishiri Minamihama high mire showed that the δ18O values of sphagnum is lower than the other species (Yamamoto and Seki, unpublished data), suggesting that bulk cellulose δ18O values may have reflected fractional variation in different tissues. In this study, we separated sphagnum and plant tissues and measured their cellulose δ18O for peat core samples retrieved from the Bekanbeushi high mire. The δ18O values of sphagnum were always lower than those of Vaccinium oxycoccos and Calamagrostis neglecta var. aculeolata. Temporal variation in the δ18O of sphagnum indicated that the value was lower around 1500 years ago and higher around 1100 years ago, corresponding to Dark Age Cold Period and Medieval Warm Period, respectively. The difference of the δ18O values between plant tisuues and sphagnum has a negative correlation with the δ18O values of sphagnum. This suggests that relative humidity was higher in warmer periods, which is analogous to modern summer climate in Bekanbeushi area..