Atmospheric dust dynamics in southern Central Asia: Implications for buildup of Tajikistan loess sediments

Abstract

Loess, as a terrestrial aeolian deposit, forms extensive landforms over several parts of the Central Asia, especially in southern Tajikistan. However, the dust dynamics for the loess formation over this region remain largely unknown. This study uses loess trace elements and meteorological reanalysis data to study the linkages between the atmospheric circulation patterns, aeolian dust transport and deposition and formation of loess sediments with emphasis in southern Tajikistan. Meteorological data indicates that the dust emissions and accumulation over southern Tajikistan maximize during the hot and dry summer season. The foothills in the north Afghanistan are the most likely dust sources, while the Central Asian deserts (e.g. Karakum) may also have a minor contribution. The prevailed near-surface air currents in the southern Central Asia run southward and then eastward when meeting the Hindu Kush Mountains. The dust-plume transport is mostly blocked by the towering Pamirs, and the deposits settle down forming thick and extensive loess sediments. Long-term trends in precipitation, wind speed and surface moisture affect the dust emissions, while there is a strong evidence of linkage between changes in the intensity of the Caspian Sea - Hindu Kush Index (CasHKI) and dust activity in the Afghan-Tajik Basin. It is recommended that the CasHKI modes can determine the dust activity, while precipitation affects most likely the interannual timescales, which have implications for interpretation of palaeoclimatic proxies of loess-paleosol sequences. However, further challenges come from the proper use of CasHKI in paleoclimatology and comprehensive research is needed.