Atmospheric Dynamics Patterns in Southern Central Asia Since 800 ka Revealed by Loess‐Paleosol Sequences in Tajikistan

The atmospheric mechanisms responsible for the loess grain‐size variations in central Asia are less clear, and an increasing number of studies have found that the coarse‐grained component is likely supplied by the surface circulation rather than by the westerlies (westerlies circulation). In this study, we attempt to determine the atmospheric dynamics patterns in the Afghan‐Tajik Basin during the past 800 kyr, based on the coarse grain‐size fraction of loess, combined with a study of modern dust transport processes. We suggest that the coarse grain‐size fraction can be used to indicate the intensity of near‐surface winds, while on glacial‐interglacial time scales, the variations of loess grain size in Tajikistan are dominated by Northern Hemisphere ice volume via its effect on the strength of the Siberian High. In addition, we suggest that atmospheric greenhouse gases concentration affected the loess grain size during interglacials via their influence on the temperature of southern high latitudes. Plain Language Summary Arid central Asia (ACA) is an important area of eolian dust emission and deposition. The Tajikistan loess sequences are the oldest loess deposits found so far in central Asia and are an important archive of information about the development of climate and atmospheric circulation in central Asia. However, the implications of grain‐size variations of the central Asian loess for climate change and atmospheric dust transport are controversial. Based on the coarse (>25 μm) grain‐size fraction of loess, combined with a study of modern dust transport, we find that the variations of the grain size of the Tajikistan loess on glacial‐interglacial time scales were dominated by changes in Northern Hemisphere ice volume (NHIV) during the last 800 kyr. However, atmospheric greenhouse gases (GHGs) concentrations may affect the loess grain size during interglacials via their influence on the temperature of southern high latitudes, which may help us understand dust activity against the background of global warming. Key Points The grain‐size distribution of loess in Tajikistan is mainly determined by changes in the dynamics of near‐surface winds Variations of the grain size on glacial‐interglacial time scales were dominated by changes in Northern Hemisphere ice volume Atmospheric greenhouse gases may have affected grain‐size variability during interglacials via control on southern high‐latitude temperature