image: Green and brown shading over land indicates decreases and increases in δ18Op, respectively, while blue and red shading over the oceans represents SST reductions and increases, based on iCESM-LME simulations. Purple arrows highlight dominant moisture transport pathways contributing to δ18Op variations over eastern China. Solid purple line boxes indicate the defined oceanic source regions used in the water-tagging experiment: the Northern North Atlantic (NNA), Northern North Pacific (NNP), Equatorial Indian (EQI), Subtropical Pacific (SNP), Western Equatorial Pacific (WEP), Eastern Equatorial Pacific (EEP), and Western Equatorial Pacific (WEP). Northern Pacific (SNP), Western Equatorial Pacific (WEP), Eastern Equatorial Pacific (EEP), Subtropical Indian Ocean (SSI), and the North Pacific (NNP). Subtropical Indian (SSI), and Subtropical South Pacific (SSP); The black dashed box indicates eastern China (100°E–120°E, 20°N–40°N).
Credit: ©Science China Press
Recently, a study led by Dr. Weiyi Sun and his team from the School of Geography at Nanjing Normal University was published in SCIENCE CHINA Earth Sciences. The team used simulations from the isotope-enabled Community Earth System Model-Last Millennium Ensemble (iCESM-LME), together with δ18O reconstructions to investigate decadal variability of the East Asian monsoon.
Earlier studies have emphasized local precipitation amount, seasonal effects, and moisture transport pathways have influenced on decadal variability of δ¹⁸Op. In particular, the mechanisms controlling δ¹⁸Op variability—especially related to moisture sources and transport pathways—remain insufficiently understood.
The study revealed that δ¹⁸Op share a quasi-11-year cycle as the leading mode of decadal variability across the monsoon region. Spatially, δ¹⁸Op exhibits a coherent regional pattern, while precipitation itself shows a tripolar wet–dry–wet mode. By comparing the solar-forcing-only experiment with the control experiment reflecting internal variability, the researchers confirmed that external solar forcing plays a dominant role in driving the quasi-11-year δ¹⁸Op cycle.
Water-tagging experiments further demonstrated that enhanced solar irradiance modulates a La Niña–like SST anomalies, which enhances the Walker Circulation. This leads to enhanced upstream convection over the Maritime Continent and a greater contribution of moisture from the equatorial Pacific, resulting in lower δ18Op values across the monsoon region. Our findings suggest that the quasi-11-year δ18Op cycle primarily reflects shifts in moisture sources driven by solar activity.
This study provides new insights into the decadal variability of δ18Op over the past millennium, promotes comparability between model simulations and proxy records, and holds important scientific value for understanding monsoon dynamics and projecting future changes in the East Asian monsoon.
See the article:
Da C, Wang X, Sun W, Liu J, Ning L, Chen G. 2025. Decadal variability in δ18O over the East Asian monsoon region responding to solar activity over the last millennium. Science China Earth Sciences, 68(9): 2853–2866, https://doi.org/10.1007/s11430-025-1644-0
Journal
Science China Earth Sciences
Method of Research
Computational simulation/modeling