Aeolian dust dynamics in the Fergana Valley, Central Asia, since ～30 ka inferred from loess deposits

Knowledge of the interactions among atmospheric dynamics, dust emissions and climate system is essential to understand the physical mechanisms for the dust lifecycle, their role in loess formation as well as the predictions of future dust concentration. However, these issues still remain relatively poorly known in Central Asia(CA). The extensive loess deposits on the CA pediments provide a promising archive to explore atmospheric dust dynamics and climatic conditions in the past and their association with loess formation. This study investigates the granulometric and magnetic properties of a loess section(named Osh section) in the Fergana Valley, which provides a sensitive record of atmospheric dust dynamics since 30 ka based on radiometric(AMSC) dating. The frequency-dependent magnetic susceptibility(χfd) and the mean grain size are used to reconstruct the broadscale effective moisture and summer atmospheric dynamics pattern in CA, respectively. The results show that the precession forcing exerts a huge influence on the wind-regime variabilities in CA, but with different physical processes under the impact of the Northern Hemisphere ice sheet(NHIS) before and after 15 ka. The origin of the sedimentation rate variations in the Osh loess is also linked to the NHIS-modulated changes of the atmospheric circulation patterns. Either the strengthened westerlies or the increased surface roughness from higher vegetation cover in loess-deposition areas have significantly accelerated the loess accumulation. As a result, these complicated influence factors of sedimentation rate change in the Osh loess section, especially during the Holocene epoch, may hamper accessibility of the authentic dust emission flux and atmospheric dust concentration in CA.