CROSS-EURASIAN MOISTURE TRANSPORT AND CENOZOIC HYDROCLIMATE IN CENTRAL ASIA (Invited Presentation)

For much of the Cenozoic, Central Asia has received much of its moisture from the mid-latitude westerlies, which transport moisture across the Eurasian continent. Reconstructions of climate-tectonic interactions in Central Asia thus require knowledge of the cross-Eurasian moisture flux during prior greenhouse epochs. However, the response of the terrestrial hydrologic cycle to higher atmospheric CO₂ remains poorly constrained. To interrogate how the terrestrial hydrologic cycle may change with warming and higher CO₂, we utilize the Cenozoic geologic record of terrestrial stable oxygen isotopes (δ¹⁸O) as recorded in authigenic minerals, which reflect precipitation δ¹⁸O (δ¹⁸O_p). Values of δ¹⁸O_p are sensitive to changes in terrestrial hydroclimate, including to the ratio of precipitation (P) to evapotranspiration (ET) and to precipitable water. In short, decreasing P/ET or higher precipitable water produces shallower δ¹⁸O_p gradients inland, whereas increasing P/ET or lower precipitable water results in steeper δ¹⁸O_p continental gradients. We compile nearly 15,000 samples of authigenic carbonate and tooth enamel across Eurasia—the largest continental landmass—that span the Cenozoic Era to reconstruct the past spatial distribution and zonal (i.e. east-to-west) gradients of δ¹⁸O_p. We find that, in epochs with higher CO₂, zonal δ¹⁸O_p gradients increase, suggesting an increase in P/ET across Eurasia despite the expected increase in precipitable water in greenhouse climates. We compare these results to δ¹⁸O_p gradients simulated by an isotope-enabled climate model (iCESM) forced with both pre-industrial (PI) and 4xPI CO₂ mixing ratios. Simulated δ¹⁸O_p gradients shallow as CO₂ rises, in contrast to the reconstructed δ¹⁸O_p gradients. This data-model mismatch suggests either that Earth system feedbacks not represented in our iCESM simulations, such as changes in Northern Hemisphere ice extent and vegetation, may have fundamentally changed Northern Hemisphere hydroclimate or that land-surface processes under high CO₂ climates may be mis-represented in iCESM. In either case, the moisture flux into Central Asia during greenhouse epochs may have been lower and more highly distilled (i.e., lower δ¹⁸O) than predicted by theory.