| 28 Jul 2026
Transient simulation of Holocene climatic and isotopic variations across global monsoon regions
Abstract. Speleothem oxygen isotopes provide key insights into Holocene monsoon variability, but the scale-dependent and regionally variable controls on precipitation δ18O remain poorly resolved. Here, we use a continuous 8.3 ka isotope-enabled transient simulation based on AWI-ESM2-wiso to investigate Holocene climatic and isotopic changes and quantify driving mechanisms for the isotopic variations via a four-predictor multiple linear regression (MLR) model. The simulation successfully reproduces the orbitally driven long-term weakening of Northern Hemisphere monsoons and the bipolar hydroclimatic response to the 8.2 ka freshwater perturbation, characterized by a southward Intertropical Convergence Zone (ITCZ) shift, Northern Hemisphere drying and isotopic enrichment, and Southern Hemisphere moistening and depletion. MLR results show that regional precipitation amount serves as the dominant and temporally stable control on monsoon δ18O. Secondary predictors including moisture transport, continental recycling, and source temperature exert regionally divergent and time-varying influences. Supplementary large-scale climate indices can improve model performance for specific monsoon domains. El Niño und die Southern Oscillation (ENSO) is the most widespread teleconnection affecting most monsoon domains, while Atlantic Meridional Overturning Circulation (AMOC) and South Atlantic Convergence Zone (SACZ) act as additional key controls over Southwestern South American Monsoon. Spatial correlation analyses further demonstrate that the precipitation amount effect is weak and spatially heterogeneous at local grid scales but becomes robust and uniform at the regional scale. This further indicates that individual speleothem records may misrepresent large-scale monsoon signals due to local spatial noise, while regional proxy ensembles effectively capture the dominant precipitation-isotope relationship.
General comments
Very good research on paleoclimate and stable isotopes. The specific comments can improve the manuscript.
Specific comments
Lines 18-20. Insert more recent literature on the use of oxygen (δ 18O) or hydrogen (δD) for hydrological and paleo-hydrological studies.
- Medici, G., Marianelli, D., Cornacchia, I., Gori, F., Brandano, M. 2026. Multi-disciplinary approach to paleokarst occurrence in the Eocene–Oligocene succession of the Apulia Carbonate Platform (Salento, Italy). Facies, 72(2), 17.
- Barbieri, M. 2019. Isotopes in hydrology and hydrogeology. Water, 11(2), 291.
Line 72. The general goal of your research is clear. But, what about the specific objectives? You can describe the 3 to 4 specific objectives of your research by using numbers (e.g., i, ii, and iii) at the end of your introduction.
Line 87. Provide more detail on the boundary conditions. You should at least describe the types.
Line 87. Provide reference for the types of boundary conditions of your model.
Line 104. Table 1 needs a link with a map?
Line 233. Some issues with the significant figures after the comma. Please, fit it.
Line 276. Here, I can see a paragraph with references and new concepts. I would keep it as a discussion creating a separate conclusion.
Figures and tables
Table 1. I would couple the table with a figure that shows the study regions.
Figure 3b. Add the associated equations.
Figure 3. Make the legends larger and readable.
Figure 4. Same here, make the legends larger and readable.
Figure 9. Enlarge font size for the content of the two axes.