Muted orbital-scale Monsoon Variability over the Korean Peninsula

Abstract. A recent study identified an east-west dipole pattern in East Asian Summer Monsoon (EASM) variability in response to precessional-scale forcing (Wen et al., 2024). The Korean Peninsula (KP) is situated near the nodal line of this dipole. It should therefore exhibit muted precessional variability in precipitation and its oxygen isotope composition (δ¹⁸O_p). So far, this conjecture has not been tested using paleoclimatic data. Here, we present speleothem δ¹⁸O (δ¹⁸O_sp) records from the KP, which support the notion of suppressed orbital-scale hydroclimate variability. Conducting a transient model simulation with the isotope-enabled Community Earth System Model (iCESM) covering the past 130,000 years, along with tagging experiments for low and high insolation conditions, we show that, on precessional scales, isotopic contributions from oceanic and continental moisture sources compensate each other over the KP, resulting in only a weak regional signal in δ¹⁸O_p. Based on iCESM1.2 simulations, we further demonstrate that deuterium excess (d-excess) variability over the KP would still capture the moisture source region’s zonal seesaw response to precessional forcing, indicating that the reconstruction of paleo water d-excess values from eastern Asian speleothem fluid inclusions could provide new valuable insights into the drivers of regional monsoon systems. This study provides new insights into the spatiotemporal variability of Pan-Asian hydroclimates and its links to changes in moisture source.