[M-IS34] 古気候・古海洋変動

[MIS34-P14] 過去400年間の日本の初夏降水量とENSOの関係

*坂下 渉¹、横山 祐典¹、宮原 ひろ子²、山口 保彦³、阿瀬 貴博¹、オブラクタ スティーブン⁴、中塚 武⁵ (1.東京大学大気海洋研究所、2.武蔵野美術大学造形学部、3.東京大学大学院理学系研究科、4.秋田大学国際資源学部、5.総合地球環境学研究所)

The El Niňo-Southern Oscillation (ENSO) potentially influences East Asian Summer Monsoon (EASM) rainfall, but the relatively short instrumental rainfall record hinders the progress of a longer-term understanding of this relationship. To partially overcome this issue, we reconstruct precipitation from tree-ring oxygen isotopes (δ¹⁸O) in central Japan from AD 1612 to 1935. Our results show that tree-ring cellulose δ¹⁸O is significantly correlated with May-June (MJ) rainfall in central Japan, allowing us to examine the relation between the EASM summer rainfall and ENSO during the past 400 years. Time- and frequency-domain comparison of the tree-ring δ¹⁸O record and recent ENSO reconstructions show a common high-frequency (3-8 year) variability that characterized the mid-17th, late 18th and late 19th centuries. Similar analyses of instrumental MJ precipitation and several ENSO indexes during the 20th century reveal that this high-frequency oscillation reappeared from AD 1980. Comparison of ENSO and Pacific Decadal Oscillation (PDO) indexes reveals that the ENSO-EASM relationship is strong when ENSO variance is high, and the PDO phase may modulate the ENSO-EASM relationship over the past four centuries.