Distinct glacial-interglacial amplitudes of Asian monsoon water isotopes during the last deglaciation

Understanding Asian summer monsoon changes during the last deglaciation through the oxygen isotope offers insights into future hydroclimate. However, the cause of limited glacial-interglacial shifts in oxygen isotope over eastern China remains unknown. Here, combining oxygen isotope records with isotope-enabled climate simulations, we identify a pronounced east-west contrast in glacial-interglacial oxygen isotope amplitudes between South Asia (larger changes) and eastern China (muted signal), despite comparable precipitation changes. This contrast is driven primarily by ice-sheet forcing, with opposing effects from orbital and greenhouse-gas further damping the isotope response in eastern China. Water-tagging experiments reveal that the weaker eastern China signal reflects competing processes: depletion primarily driven by increased Pacific-sourced moisture from a strengthened northwestward-shifted Western Pacific Subtropical High, alongside enrichment resulting from reduced rainout and enhanced local recycling over the marginal seas. These findings mechanistically reconcile puzzling differences between water isotope and other hydrological proxies across monsoon region on glacial-interglacial variability. A weak glacial-interglacial isotopic signal in eastern China reflects compensatory processes in atmospheric moisture routing and local recycling, primarily orchestrated by ice-sheet forcing, according to speleothem records, climate simulations, and water-tagging experiments.