Martin Werner

Dansgaard-Oeschger (DO) events during the last ice age are thought to reflect rapid shifts in the Atlantic Meridional Overturning Circulation (AMOC). Greenland ice cores suggest warming transitions within only a few decades—or even just over 10 years. Using precisely dated speleothem oxygen-isotope records from the Asian monsoon region, we have shown that the same DO warmings unfolded over more than a century. Isotope modeling revealed that Greenland records primarily capture a rapid atmospheric reorganization triggered by the initial sea-ice retreat in the northeastern North Atlantic, whereas the parallel AMOC recovery and hemispheric thermal adjustment proceeded much more slowly. These findings reveal that natural AMOC transitions evolved more slowly than the rapid North Greenland oxygen-isotope shifts would imply, thereby refining our understanding of “abruptness” during DO events.

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.

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.

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.

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.

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.

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.

Water stable isotopologues, particularly H₂¹⁸O and HD¹⁶O, are valuable tracers of physical and dynamical processes within the hydrological cycle. These isotopologues have been widely incorporated into isotope-enabled atmospheric general circulation models to constrain moisture sources and transport pathways. However, comprehensive evaluations of such models over the Tibetan Plateau (TP), a region whose complex orography substantially modulates South Asian monsoon dynamics, remain scarce. Here, we systematically evaluate simulations of water vapor isotopic composition (δ¹⁸O_v) from the ECHAM6-wiso model against daily in-situ observations from four high‐altitude stations (Kathmandu, Lulang, Namco, and Muztag) on the Tibetan Plateau, spanning January 2020 to November 2021. The model successfully reproduces the spatial distribution and seasonal cycle of δ¹⁸O_v; however, probability density functions reveal a systematic underestimation of isotopic depletion. Through a multi‐scale temporal decomposition of the daily δ¹⁸O_v time series, we attribute over 50% of the simulation error to deficiencies in representing large-scale atmospheric circulations (periods ≥ 30 days), while the remaining error is linked to synoptic-scale processes (3–7 days) associated with fractionation, including cloud microphysics, post‐condensation effects, and surface evaporation. The model's inability to accurately simulate terrain-induced atmospheric moisture blocking over the TP results in bias in atmospheric circulation variations, thereby amplifying the contribution of circulation-related processes to the overall error. These findings underscore the significance of atmospheric circulation in water vapor isotopic simulations and highlight the value of high‐resolution water vapor isotopic datasets for improving our understanding of moisture source attribution and water‐cycle dynamics in regions of complex topography.