Aeolian dust history since 14.4 cal. ka B.P. indicated by grain-size end members of Shayan loess in the southern Kazakhstan

The arid Central Asia is not only the main dust source area in the world, is also the sensitive area to climate change. It is very important to reconstruct the past history of aeolian dust and investigate its driving mechanism in the arid Central Asia in order to govern modern dust and improve human living environment. However, there are still three different views on the driving mechanism of aeolian dust in the arid Central Asia. In this study, we obtain the Shayan loess profile(SY profile: 42.86°N, 69.07°E; 200m a.s.l.; 650cm in thickness)which is located on the bank of Shayan River in the Southern Kazakhstan. The SY profile is homogeneous and massive without obvious stratification and light yellow in appearance, indicating that there is no obvious soil formation. Six AMS 14C samples were collected at 98cm, 200cm, 302cm, 402cm, 502cm and 602cm in the SY profile, and total 162 samples were sampled at 4cm intervals for particle size analysis. Based on the six AMS 14C dates in the Bacon program, we established the depth-date model of SY profile and the age at the bottom of SY profile is 14.4cal.ka B.P. The parametric grain size end-member analysis was used to investigate the aeolian dust history since 14.4cal.ka B.P. inferred from the Shayan profile and four end-member components were extracted to reflect the sedimentary dynamic characteristics. The results indicated that: (1)The grain size compositions can be divided into four components(EM1, EM2, EM3 and EM4), EM1(modal grain size is 1.59μm) is the clay component transported over long distances by the strong westerlies winds and carried by the coarse particles in the form of aggregates, EM2(modal grain size is 14.16μm) represents the background of atmospheric dust in the deposition period and the fine silt component in the form of floating dust, EM3(modal grain size is 39.91μm) indicates the near-source coarse silt component transported at low altitude and short distance, EM4(modal grain size is 89.34μm) shows local sand components resulted from strong wind conditions. (2)The aeolian dust history indicated by the EM3+EM4 content shows that the wind force in the study area was strong from 14.4cal.ka B.P. to the Early Holocene(14.4~8.2cal.ka B.P.), weak in the Middle Holocene(8.2~4.2cal.ka B.P.), and increased again in the Late Holocene(4.2~0cal.ka B.P.). (3)The intensity of Siberian high was the main driving force of the past aeolian dust in the arid Central Asia.