Heling Jin

Geochemical weathering of aeolian sand and its palaeoclimatic implications in the Mu Us Desert, northern China, since the Late Holocene

In the semi-arid and arid regions of northern China, geochemical behavior of the aeolian deposit is closely related to climatic and environmental changes, which was used to reconstruct the past history of environmental evolution and possibly forcing mechanisms. However, the related result was still scarce due to the lack of detailed geochemical analysis results in the desert sediments. In the present study, we systematically analyzed the geochemical components and parameters of the paleo-aeolian sand dune and modern mobile sand deposits in the Mu Us Desert and discuss the climatic variation inferred from the paleo-aeolian sand dune during the past 4.2 ka BP. The results indicated that (1) geochemical composition of the sandy deposits were dominated by SiO2, Al2O3 and Na2O and the deposits probably originated from the widespread upper continental crust (UCC) and were formed by long-term weathering, transport and re-deposition; (2) these sandy deposits were subjected to weaker weathering or uneven weathering under cold and dry conditions, and had highly similar material sources and degrees of weathering and leaching in general; and (3) the direct OSL (Optically Stimulated Luminescence) dating ages and geochemical parameters from the palaeosol-aeolian sand dune indicated that the regional climate change experienced several typically cold and warm intervals. These intervals are 4.2, 2.8 ka BP and Little Ice Age and Medieval Warm Period, which probably attributed to periodic variations of the Asian summer monsoonal strength and cold events of the northern Atlantic Ocean in low and high latitudes of the Northern Hemisphere. Our results suggest that the development of the sand dune in the Mu Us Desert provided a suitable archive for understanding the past local climatic change, which is linked to the global climatic change.

EXTRACTION OF SENSITIVE GRAIN-SIZE COMPONENT FROM THE KE PEAT DEPOSIT OF THE GONGHE BASIN AND ITS IMPLICATION FOR HOLOCENE CLIMATIC AND ENVIRONMENTAL CHANGE

Grain size versus standard deviation was applied to extract sensitive grain size from the grain size distribution data of the Holocene KE peat deposit of the Gonghe Basin,northeastern Qinghai-Tibetan Plateau.We found that the sensitive grain size component of 63~252 μm(63~112 μm and112~252 μm)can reflect the intensity variation of the regional winter monsoon,upon which we reconstructed the history of the regional winter monsoonal evolution.Our results suggest that the intensity of winter monsoon declined in the period of 10.0~8.5 cal.kaBP,and obviously increased in 8.5~7.1 cal.kaBP.The weakest winter monsoon emerged in 7.1~ 3.8 cal.kaBP,and it became stronger in the period between 3.8 cal.kaBP and 0.5 cal.kaBP.Afterwards,the winter monsoon rapidly weakened.Comparative study demonstrates that the evolution of regional winter monsoon is correlated well with the climatic change records of the Qinghai-Tibetan Plateau and the marginal monsoonal zone and monsoonal zone in eastern China from different research sources.We also found seven phases of the stronger winter monsoon,which are apparently coincident with the cold events found in the polar ice core and North Atlantic Ocean,probably indicating the inherent relationship of the dynamic mechanism between the regional and the global climatic changes.