RECONSTRUCTION OF HOLOCENE VEGETATION, CLIMATE, AND LAND USE CHANGES BASED ON POLLEN ANALYSIS OF CORES FROM LAKE KHARGAL MONGOLIA

Analysis of palynomorphs in sediment cores from Lake Khargal (49.9°N, 102.77°E), located in the semi-arid forest-steppe ecotone of northern Mongolia, allows reconstruction of vegetation, climate, and land use changes in the watershed throughout the Holocene. AMS radiocarbon dates of a 2.1 m percussion core from the central basin indicate a nearly constant sedimentation rate and a basal age of ~5.4 cal kyr BP. Dated archaeological sites provide evidence of human habitation in the area beginning ~3.5 cal kyr BP. Increases in abundance and co-occurrence of pollen taxa such as Cerealia-type, Plantago sp., Cichorioideae, Urtica, and Liliaceae are indicative of human agriculture at ~3.1 cal kyr BP and again at ~1.2 cal kyr BP. Abundance of the coprophilous fungal spore Sporormiella sp., found only in the dung of herbivores, is a proxy for numbers of grazers in the watershed. Increases in Sporormiella are recorded between 3.3 and 2.5 cal kyr BP and again from 2.1 cal kyr BP to the present. Co-occurrence of agricultural indicators and Sporomiella provides evidence for pastoralism after ~3.3 cal kyr BP. Decreases in arboreal Betula pollen at ~3.5 cal kyr BP and again at ~1.6 cal yr BP and coeval peaks in Sporormiella abundance may indicate increased clearing to create more rangeland for livestock. Comparison with a 4.3 m Livingstone core with a basal age of 11.5 cal kyr BP extends the record throughout the Holocene. Appearances of anthropogenic indicator taxa are coeval in the two cores, reinforcing the timing of land use changes in the watershed. Changes in ratios of pollen taxa from five distinct modern moisture regimes indicate relatively humid conditions between 11.0 and 10.0 cal kyr BP, followed by increasing aridity until 7.8 cal kyr BP. Humidity subsequently increases to a peak at 2.1 cal kyr BP and then declines to the present. These data point to a climate influenced by North Atlantic Westerlies rather than South or East Asian monsoon flow.