OSL chronology and paleoclimatic implications of paleodunes in the middle and southwestern Qaidam Basin, Qinghai-Tibetan Plateau

Aeolian sediments are widely distributed in the Qaidam Basin, northeastern Qinghai-Ti^tan Plateau （QTP）. The pale（xiunes are mainly located at the southeastern, middle and southwestem Qaidam Basin. However, ages ofpaleodunes in the middle and southwestern Qaidam Basin have not been well studied, although they are close to and might connect to the evolution of salt lakes in the cenWal basin. In this study, we use single aliquot regeneration （SAR） protocol of Optically Stimulated Luminescence （OSL） to date the dune sand in these two regions. The results show that： （1） Sand accumulation in these regions started at ca. 4-3 ka and lasted to ca. 0.5 ka when they were stabilized, due to the arid climate in the late Holocene. （2） The underlying fluvial sand was fomaed during deghcialion at 12.6±0.8 ka. （3） The stabilization pe- riods of the paleodunes correspond to stages of glacier advance in the northeastem QTP, during which lower temperatures caused the decrease of evapomlion and increase of the effective moisttwe, leading to an increase of vegetation cover and stabilizalion of the dunes.

Five decades of glacier changes in the Hulugou Basin of central Qilian Mountains, Northwest China

The Heihe River Basin is the second largest inland river basin in the arid regions of Northwest China. Glaciers provide a large proportion of water resources for human production and living. Studies of glacier changes and their impact on water resources in the arid lands are of vital importance. A joint expedition was carried out in 2010 for investigating glaciers in the Hulugou Basin, which is located in the upper reaches of Heihe River. There- fore, glacier changes in the Hulugou Basin of central Qilian Mountains during the past 50 years were analyzed in this study by comparing topographic maps, satellite images, digital elevation models and field observation data from different periods. Results showed that the total area of the 6 glaciers in the Hulugou Basin decreased by 0.590±0.005 km^2 during the period 1956-2011, corresponding to a loss of 40.7% over the total area in 1956. The average area reduction rate of the 6 glaciers is 0.011 km^2/a. During the past five decades, the glacier shrinkage was accelerated. The changes in glacier ice surface elevation ranged from -15 to 3 m with an average thinning of 10±8 m or an annual decrease of 0.23±0.18 m （0.20±0.15 m/a water equivalent） for the period 1956-2000. The area of Shiyi Glacier in the Hulugou Basin decreased from 0.64 km^2 in 1956 to 0.53 km2 in 2011 with a reduction rate of 17.2%. The Shiyi Glacier had been divided into two separated glaciers because of severe melting. Comparative analysis showed that glacier shrinkage in the Hulugou Basin is more serious than that in the other regions of Qilian Mountains.

Co-occurrence of nitrite-dependent anaerobic methane oxidizing and anaerobic ammonia oxidizing bacteria in two Qinghai-Tibetan saline lakes

Nitrite-dependent anaerobic methane-oxidiz- ing （n-damo） bacteria and anaerobic ammonia oxidizing （anammox） bacteria are two groups of microorganisms involved in global carbon and nitrogen cycling. In order to test whether the n-damo and anammox bacteria co-occur in natural saline environments, the DNA and cDNA samples obtained from the surficial sediments of two saline lakes （with salinity of 32 and 84 g/L, respectively） on the Tibetan Plateau were PCR-amplified with the use of anammox- and n-damo-specific primer sets, followed by clone library construction and phylogenetic analysis. DNA and cDNA- based clones affiliated with n-damo and anammox bacteria were successfully retrieved from the two samples, indicating that these two groups of bacteria can co-occur in natural saline environments with salinity as high as 84g/L. Our finding has great implications for our understanding of the global carbon and nitrogen cycle in nature.

Luminescence Chronology and Radiocarbon Reservoir Age Determination of Lacustrine Sediments from the Heihai Lake,NE Qinghai-Tibetan Plateau and Its Paleoclimate Implications

The accurately determining the lake ^14C reservoir age has a crucial significance for climatic reconstruction. In this study, the optically stimulated luminescence （OSL） dating method is employed to date samples from highstand lacustrine sediments, palaeoshoreline, fluvial terrace, and the alluvial fan of the Heihai Lake catchment. Accelerator mass spectrometry （AMS） 14C dating was also used to date fossil plants from highstand lacustrine sediments. Based on the calculations of linear regression with OSL against radiocarbon ages for same layers of two sections, the quantitative ^14C reservoir ages were estimated to lie between 3 353 and 3 464 yr during the 1.8 to 2.4 ka, which showed temporal variation. The sources of old carbon are the dissolution of carbonate bedrocks distributed along the Kunlun Mountain. The OSL ages of the different members of the hydatogen sedimentary system at Heihai Lake catchment indicate that a stronger hydrologic condition occurred from 3.0±0.2 to 1.8±0.2 ka, with a maximum lake level of 9 m higher than present. This humid stage was widely recorded in different sediments on the QTP and Chinese Loess Plateau （CLP）, indicating its broad synchronicity across the Asian Summer Monsoon region. The enhanced East Asian Summer Monsoon （EASM） and the Indian Summer Monsoon （ISM） resulted in the increase of moisture availability for the Heihai Lake area during this stage.