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Long-period astronomical forcing of westerlies' strength in Central Asia during Miocene climate cooling

Abstract : The continental expression of global cooling during the Miocene Climate Transition (MCT) in Central Asia is poorly documented, as the tectonically active setting complicates the correlation of Neogene regional and global climatic developments. This study presents new geochemical data (CaSO4 content, carbonate δ13C and δ18O) from the endorheic alluvial‐lacustrine Aktau succession (Ili Basin, south‐east Kazakhstan) combined with findings from the previously published facies evolution. Time series analysis revealed long eccentricity forcing of the paleohydrology throughout the entire succession, split into several facies‐dependent segments. Orbital tuning, constrained by new laser ablation U‐Pb dates and a pre‐existing magnetostratigraphy, places the succession in a 5.0 Ma long interval in the Middle to Late Miocene (15.6 to 10.6 Ma). The long‐term water accumulation in the Ili Basin followed the timing of the MCT, suggesting increased precipitation in the catchment area in response to climate cooling and stronger westerly winds. This was paced by minima of the 2.4 Ma eccentricity cycle, that favoured the establishment of a discharge playa (~14.3 Ma) and a perennial lake (12.6 to 11.8 Ma). Furthermore, low obliquity amplitudes (nodes) caused a transient weakening of the westerlies at ~13.7 to 13.5 Ma and at ~12.7 Ma, resulting in negative hydrological budgets and salinization. Flooding of the windward Ili Basin coeval with aridification in the leeward basins suggests that the Tian Shan was a climate boundary already in the Middle Miocene. Our results emphasize the impact of climate fluctuations on the westerlies' strength and thus on Central Asian hydrology.
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Konstantin Frisch, Silke Voigt, Verestek Verena, Erwin Appel, Richard Albert, et al.. Long-period astronomical forcing of westerlies' strength in Central Asia during Miocene climate cooling. Paleoceanography and Paleoclimatology, American Geophysical Union, 2019, 34 (11), pp.1784-180. ⟨10.1029/2019PA003642⟩. ⟨insu-02369864⟩



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