DUST STORM HISTORY OVER THE LAST 2000 YEARS DOCUMENTED BY LAMINATED LAKE SEDIMENTS IN ARID CENTRAL ASIA

Arid central Asia is one of the main dust and eolian silt source regions in the world. Here we use lake sediments in Sugan Lake to document dust history over the last 2000 years. Sugan Lake is a hydrologically closed lake in the Qaidam Basin of northwestern China, one of the two driest regions in central Asian. The annual precipitation around the lake is only 18.5 mm, but increases with altitude in the lake basin. Mean annual air temperature is 2.75„a C. Rivers formed by glacial melt and snow water in surrounding mountains form ground water in the fluvial plain and there is no surface river flow into the lake. Rather, the lake is directly recharged by springs around the lake margin. Therefore, the terrestrial detritus can only be transported into the lake through dust storm winds. The lake surface is frozen from mid-October to April, making it possible to deposit coarse dust-storm sand and silt in the lake. We collected aeolian samples on the frozen lake surface and measured grain size to understand the process of detritus deposition in the lake sediments. We found that both aeolian samples on the frozen lake ice surface and from the lake floor have the same grain-size distribution, and match samples from sediment cores. An 8.52m long core and several short cores from 1.0 m to 3.0 m long were drilled in Sugan Lake. Lake sediments in the cores have very clearly laminated features. Chronology was established using 210Pb and 137Cs for the most recent 200 years, together with 10 AMS 14C dates on plant remains in the cores. Dust history was reconstructed for the last 2000 years at a 5-10 year resolution, and shows quite clearly an increased trend in dust storm events over the last 20 years and strong dust storms during the middle of the Little Ice Age.