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The North Pacific Gyre Oscillation (NPGO) significantly imprints on hydrological fluctuations of the East Asian summer monsoon (EASM) region, but this has not yet been observed in proxy-based hydroclimate reconstructions. This study reports a tree-ring cellulose oxygen isotope (δ 18 O) record from northeastern Japan spanning A.D. 1927-2010, overlapping with instrumental data, which we analyzed to determine if tree-ring δ 18 O in northeastern Japan records a signal consistent with the NPGO. Our results indicate that the tree-ring δ 18 O has a significant negative correlation with May-June (MJ) precipitation, as well as with short-term MJ relative humidity variation. Time-lagged temporal-domain comparisons indicate that the tree-ring δ 18 O is significantly correlated with the following year March-April (MA) and MJ NPGO index before the North Pacific climate transition in the late 1980s, particularly on decadal timescales. These relationships between our tree-ring δ 18 O and the climate patterns in the North Pacific are consistent with the actual early-summer precipitation. Spatial spring and early-summer sea-surface temperature anomalies exhibit a NPGO-like pattern in the following year. Spatial early-summer sea-level pressure anomalies also indicate North Pacific Oscillation (NPO) like patterns in the western North Pacific. These results suggest a lagged response of the NPGO to the EASM climate changes, and tree-ring δ 18 O in northeast Japan has a potential linkage with NPGO index from winter to early summer of the following year.

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