Holocene stalagmite oxygen isotopic record from the Japan Sea side of the Japanese Islands, as a new proxy of the East Asian winter monsoon

Stalagmite oxygen stable isotopic records from Chinese and Japanese caves have described the intensity of the East Asian summer monsoon (EASM) in the late Quaternary. In this study, we present a stalagmite δ18O record over the past 10,000 years from Fukugaguchi Cave, Itoigawa, Honshu, Japan, facing the Japan Sea. The regional climate is characteristically wet in winter and nearly 60% of the annual precipitation occurs from November to March when the East Asian winter monsoon (EAWM) brings moisture from the Japan Sea warmed by the Tsushima Warm Current. Rainwater δ18O values near the cave generally decrease with the precipitation amount, indicating an amount effect. The stalagmite δ18O profile has had a concurrent trend with winter precipitation observed near the cave since 1924 in addition to high-resolution records of the eolian fraction observed in China. These agreements suggest that the Fukugaguchi stalagmite δ18O record reflects the EAWM intensity. In comparison of our profile with the EASM record obtained from Chinese stalagmites, inverse correlation was recognized only in the earlier interval of 10.0-5.2 ka, suggesting that the southward migration of the intertropical convergence zone intensified the EAWM. From a peak at 5.2 ka, the EAWM intensity quickly decreased and remained at a lower level between 4.5 and 3.0 ka. Since 3.0 ka, the Fukugaguchi record has high-amplitude changes of millennial time scales, including two peak intervals in 2.9-2.5 ka and 1.3-0.7 ka. EAWM-related winter precipitation might have been amplified with intensification of the Tsushima Warm Current that enhanced the land-sea thermal contrast during winter season. A co-variation presumed between the Fukugaguchi δ18O record and the Chinese EAWM records implies that the thermal contrast between East Asia and NW Pacific may have influenced the winter monsoon in throughout the East Asian climate system.