A HIGH RESOLUTION RECORD OF HOLOCENE LAKE SEDIMENTS FROM THE ALASHAN DESERT, NW CHINA

Short term fluctuations of lake level changes during the early to middle Holocene lake history of Juyan Lake (Alashan desert, Inner Mongolia) has been determined from geomorphological, geochemical, XRD, and pollen analyses. Morphologically disconnected from hydrological influences of the Hei River catchment, eastern Juyan Lake seems to reflect the local Holocene climatic evolution. Well preserved palaeoshorelines indicate a maximum lake extension of the recently dry basin of about 350 km². The catchment covers an area of about 3,400 km², mainly located in the southern foothills of Gobi Altay mountain ranges.

An 8.25 m long sediment core from the northwestern part of eastern Juyan lake provides detailed information about changes in sedimentation processes, e.g. variations in salt contents and hydrology between 10 cal ka and 240 cal AD. The age model is based on 5 AMS-datings on organic compounds: 9420±110 (10,626), 7013±41 (7800), 4605±30 (5315), 3127±29 (3358), 1786±22 BP (1709 cal BP). Grain-size analyses indicate short term variations of lake phases were interrupted by aeolian deposition during early Holocene time, while a long term stable lake phase prevailed from middle Holocene to historical time. High aragonite, hydromagnesite and halite content indicates extremely saline conditions due to the ion supply from the nearby catchment. Hence, the water budget was mainly controlled by local runoff and precipitation. Pollen spectra match sedimentological and mineralogical results. Due to the varying Artemisia/Chenopodiaceae ratio and the similarly changing abundance of some desert taxa (Nitraria, Calligonum, Reaumuria), it is possible to distinguish between periods with steppe vegetation, mainly indicating wetter conditions, and with desert vegetation, mainly suggesting drier conditions. According to the age model, wetter conditions prevailed between about 8.2-7.5, 6.6-6.2, 5.6-4.8, 4.3-4.0 and 3.2-2.8 cal ka BP.