High-Resolution Evidence for Middle Holocene East Asian Winter and Summer Monsoon Variations: Snapshots of Fossil Coral Records

We first generated 53-, 4-, 10-, and 9-year-long bimonthly time series of oxygen isotopes (δ¹⁸O), Sr/Ca, and U/Ca from 4.4 and 4.9 ka corals in Okinawa, Japan. Results indicate that the mid-Holocene sea surface temperature (SST) and seawater δ¹⁸O were <1°C lower and 0.1–0.2‰ higher than today. Spectral analyses of reconstructed SST and seawater δ¹⁸O time series revealed East Asia monsoon (EAM) and El Niño/Southern Oscillation (ENSO) variations. Moreover, the latter had a dominant component of decade-scale hydrologic variations. The Sr/Ca and U/Ca variations with removal of the ENSO component showed larger fluctuations by ~2°C in winter and ~0.6°C in summer at 4.4 ka relative to today, demonstrating (slightly) greater influences of the EAM variation on the northwestern subtropical Pacific in winter (summer) at that time, which are probably caused by enhancement of the EAM intensity and/or a southward migration of the latitudinal circulation.