Muted orbital-scale monsoon variability over the Korean Peninsula

A recent study identified an east-west dipole pattern in Asian Summer Monsoon precipitation and in its oxygen-isotope composition variability in response to orbital forcing (Wen et al., 2024). The Korean Peninsula (KP) is situated near the nodal line of this dipole and should therefore exhibit muted precessional variability in both. So far, this conjecture has not been tested using paleoclimatic data. Here, we present speleothem oxygen isotope ( δ ¹⁸ O) 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 (iCESM1.2) covering the past 130 000 years, along with tagging experiments for low and high insolation conditions, we show that, on precessional timescales, isotopic contributions from oceanic and continental moisture sources compensate each other over the KP, resulting in only a weak regional signal in precipitation δ ¹⁸ O. 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. We propose that, given the region's strong sensitivity to changes in moisture sources, paleo-water d-excess reconstructions from East Asia speleothems could provide valuable additional constraints on the drivers of regional monsoon systems. This study offers new insights into the spatiotemporal variability of Pan-Asian hydroclimates and its links to changes in moisture source.