EOLIAN LANDSCAPE EVOLUTION CONTROLLED BY SEDIMENT AVAILABILITY SINCE THE LGM IN THE HULUNBUIR SANDY LAND, NORTHEAST CHINA

The Hulunbuir Sandy Land is the highest latitude eolian depositional system in China. This semi-stabilized dune field is at the northern limit of the East Asian summer monsoon (EASM), thus sensitive to climate variability. Previous studies speculated that this dune system expanded in area by ~3 to 10-fold during the Last Glacial Maximum (LGM), and there are four eolian depositional phases separated by soil development during the Holocene. However, the relationship between dune construction and sediment supply, and the responses of eolian processes to the fluctuation of the EASM are largely unknown. The earliest evidence to date for eolian activity is from the lowest exposed white sand beneath a thick paleosol which yielded an age of ~17 ka, as revealed from the study of 12 sedimentary sections with 29 optically stimulated luminescence (OSL) ages. Our stratigraphic evidence indicates that there was a cold climate sand sheet landscape, instead of sand dunes, prior to ~15 ka because sediment availability may have been limited by the ubiquitously distributed permafrost during the LGM. The cumulative probability density function of 71 published OSL ages from eolian units of the dune field places pervasive eolian accumulation between ~15 and 9 ka. Meanwhile, the development of paleosols in two sections appears to span this period, reflecting the co-occurrence of pedogenesis and eolian accretion during the last deglaciation. This partial landscape stability was associated with a rise in summer temperature and precipitation recorded by pollen spectra in nearby lake records. This increased temperature also has the potential to release loose sediments from the frozen ground. Widespread paleosols and modest eolian deposition between 9 and 3.5 ka indicate that the Hulunbuir Sandy Land was mostly stabilized during the middle Holocene, which appears concurrent with an increase in EASM precipitation, similar to other dune fields in eastern China. During the past 200 years, there was widespread sand dune reactivation, reflecting human disturbances, particularly grazing and cultivation since the late Qing Dynasty (A.D. 1644-1912). The geomorphologic and stratigraphic and inferences on sediment availability collectively suggest that the extent of the dune field during the LGM is similar to present limits.