No abstract

Arid northwestern China is considered to be a major source of atmospheric dust supply to the Northern Hemisphere. However, dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region. Hydrologically closed lakes in dust source areas act as a trap, providing the opportunity to trace the history of dust emission or eolian activity. Here we present the results of dust storm proxies and a dust storm history from Lake Sugan in the Qaidam Basin, a dust source area, on the northern Qinghai‐Tibetan Plateau. Grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred. In combination with a sediment chronology generated by counting annual laminations, a 2000‐year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments. Frequent and/or intensive dust storms occurred during the intervals AD 300–500, AD 1180–1240, and AD 1500–1700. The occurrence of dust storms largely coincided with the strengthening of the Siberian High with colder air masses from high latitudes, such as during the Little Ice Age, frequently encroaching into the dust source areas in northwestern China. Our results suggest that wind strength plays an important role in dust emissions in arid source areas. However, dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the Qaidam Basin.

The Sistan region in southeast Iran is considered as one of the most active dust source regions in South west Asia. The strong "Levar" winds in summer favor the uplift of large quantities of dust from the Hamoun basin, which is located in the northern part of Sistan. After a dry period at the end of the 1999s, and due to land-use change and desiccation of the Hamoun lakes, the frequency and severity of dust storms have been significantly increased. Within this framework, this study analyses the aerosol characteristics, dust loading and air quality over the Sistan region. The dust loading was measured using dust traps up to four and eight meters height (with a one meter distance between the traps) at two locations near the Hamoun basin during the period August 2009 to July 2010. The results show large quantities of transported dust that strongly dependent on the duration of the dust events, and secondarily, on the wind 2 speed and distance from the source region. The grain size distribution of the dusts reveals that the coarser calibers are found at the station nearer to Hamoun, while the large differences in the grain-size distribution found between the two stations indicate significant spatio-temporal variation in dust characteristics. Furthermore, to assess the air quality, Particulate Matter (PM 10 ) concentrations were measured over Zabol city during September 2010 to July 2011, and the Air Quality Index (AQI) was obtained. Daily PM 10 levels during intense dust storms rise up to 2000 gm -3 , even reaching to 3094 gm -3 , while the monthly mean PM 10 variationshows extreme values (>500 gm -3 ) for the period June to October. Analysis of the AQI shows that 61% of the days are associated with a high health risk, while 30.1% are even identified as hazardous.

No abstract

The Asian monsoon (AM) played an important role in the dynastic history of China, yet it remains unknown whether AM-mediated shifts in Chinese societies affect earth surface processes to the point of exceeding natural variability. Here, we present a dust storm intensity record dating back to the first unified dynasty of China (the Qin Dynasty, 221–207 B.C.E.). Marked increases in dust storm activity coincided with unified dynasties with large populations during strong AM periods. By contrast, reduced dust storm activity corresponded to decreased population sizes and periods of civil unrest, which was co-eval with a weakened AM. The strengthened AM may have facilitated the development of Chinese civilizations, destabilizing the topsoil and thereby increasing the dust storm frequency. Beginning at least 2000 years ago, human activities might have started to overtake natural climatic variability as the dominant controls of dust storm activity in eastern China.