SPATIALLY-COMPLEX RESPONSE OF REGIONAL WET-DRY CLIMATE TO HOLOCENE LARGE-SCALE CLIMATE FORCING ON THE NORTHEASTERN TIBETAN PLATEAU

Recent paleoclimate records from China have increased our understanding of Holocene monsoon dynamics, with increased monsoon activities during the early Holocene and continued weakening after the mid-Holocene. Further inland in central Asia, however, it is poorly known how monsoon system influenced regional climate. Here we analyze multiple sedimentary parameters from a freshwater lake (Hurleg Lake) located in a dry desert climate in NE Qaidam Basin to track effective moisture change during the Holocene. The chronology of the 688-cm core (HL05-2) taken at 2.7 m water was controlled by seven AMS dates on plant macrofossils. Loss-on-ignition analysis indicates that organic matter ranges 4-10%, while carbonate content oscillates greatly between <20% and >70%. Most low carbonate intervals correspond with clay-rich, “soil-textured” sediments containing abundant plant remains and roots, likely deposited in shallow water wetland environments, while high carbonate intervals indicate relatively deep and open water environments. Pollen analysis indicates that dry periods are dominated by desert pollen types including Chenopodiaceae (up to 80%) and Ephedra, while wet periods by Poaceae (~30%), Artemisia (20%) and Chenopodiaceae (~35%). The Artemisia-to-Chenopodiaceae ratio, an index of relative steppe and desert plant dominance, is <0.1 during dry periods but >0.6 in wet periods. Oxygen isotopes of both precipitated carbonates and ostracode (Plesiocypridopsis newtoni) shells show a decrease of ~4 per mil from the mid- to late Holocene, corresponding with decreasing Mg/Ca ratios in ostracode shells. Multiple magnetic parameters show the highest variability at 7-4 ka and low and stable values at 4-0 ka. The climate history from our site shows variable and drier climate from 11-4 ka, with millennial-scale variability (~1200-yr spacing) at 11-7 ka and increased variability (~500-yr) at 7-4 ka. During the last 4 ka the climate has been stable and wet. Our results are in sharp contrast with the records from Lake Qinghai and other sites east and south, indicating spatially complex responses of regional climate to large-scale climate forcing. The contrasting pattern suggests the importance of interaction between subtropical and mid-latitude atmospheric circulation systems in determining regional climate.