Xiaohao Wen

Pleniglacial millennium-scale climate variations in northern China based on records from the Salawusu River Valley

Situated in the Salawusu River Valley, southeast of Chinas Mu Us Desert, the MGS2 (Milanggouwan section) portion of the Milanggouwan stratigraphic section records 5.5 sedimentary cycles consisting of alternations between dune sand deposits and fluvial or lacustrine facies. We analyzed the grain-size and CaCO3 distributions in MGS2, and found that Mz (mean particle diameter) and a (standard deviation) displayed clear variations in peaks and valleys within different sedimentary facies. The CaCO3 content averaged 0.4% in the dune sand deposits, 1.43% in the fluvial facies, and 8.82% in the lacustrine facies. Both the grain-size distribution and CaCO3 contents, which equal the indicators for the alternation among the sedimentary fades, suggest the occurrence of 5.5 cycles. These results suggest that the observed cycles mainly resulted from fluctuations between a cold and dry winter monsoon climate and a warm and humid summer monsoon climate, and that the MGS2 portion experienced at least 5.5 fluctuations between these two extremes. This high-frequency climatic fluctuation indicates a strong influence of millennium-scale variations in the strength of the East Asian winter and summer monsoons in our study area during the Pleniglacial.

East Asian monsoon variations on millennial scale during 35,000–25,000 a BP from records of grain size, CaCO3 and organic matter in the Badain Jaran Desert, China

The CGS3a segment of the Chagelebulu section in the southeastern Badain Jaran Desert in China records five and a half sedimentary cycles consisting of aeolian dune sands or loess alternating with overlying fluviolacustrine during 35,000–25,000 a BP. Based on the analyses of grain size, calcium carbonate (CaCO3) and organic matter (OM) for 139 samples in the CGS3a segment, we found that the values of mean particle size (Mz) (ϕ) and standard deviation (σ), CaCO3, and OM from the lacustrine facies generally tended to be higher than those of the underlying dune sands or loess. These data indicate that the grain size was fine and poorly sorted with high values of CaCO3 and OM in the lacustrine facies, and grain size was coarse and well sorted with low values of CaCO3 and OM in the dune sands and loess. A graph of these values showed five and a half oscillations between layers, which were generally similar to the sedimentary cycles. A sedimentary cycle between the dune sands or loess and lacustrine facies in the CGS3a segment represents a cold–dry and warm–humid climate cycle. Therefore, we suggest that the CGS3a segment experienced at least five and a half climate cycles (five cold–dry climates and six warm–humid climates) during 35,000–25,000 a BP. Of these, the warm climate fluctuations correspond well to the Dansgaard-Oeschger events (D/O3-D/O8) recorded in the Greenland Ice Core Project (GRIP). Moreover, the cold period 28D (30,600 ± 2,900 a BP) correlates well with the Heinrich Event H3 (approximately between 29,000 and 31,000 a BP). These results suggest that the driving forces of the East Asian monsoon in China’s deserts are probably as the same as the Dansgaard-Oeschger events and Heinrich oscillations in the Northern Hemisphere during that period. This study reveals the East Asian monsoonal climatic fluctuations on millennial scale in China’s deserts during 35,000–25,000 a BP.

Grain-size characteristics and climate variability in TMS5e sequence of Tumen section in southern Tengger Desert, northwestern China

The TMS5e sequence from the Tumen section, at the southern edge of Tengger Desert in the northwestern China, is synchronous with Marine Isotope Stage 5e (MIS5e). It consists of 16 layers of aeolian dune sands, 11 layers of lacustrine loess-like facies, and 5 layers of lacustrine facies. The results of grain-size analysis shows that the palaeo-mobile dune sands, palaeo-fixed to semi-fixed dune sands and loess-like sandy loams are mainly composed of sands, ranging from 70% to 96%; their silt contents ranged from 4% to 20%, and their clay contents ranged from 1% to 5%; the climate under which the aeolian dune sands were deposited is similar to that under which modern mobile dune sands form, which is caused by the dominance of the cold, dry East Asian winter monsoon. In contrast, the lacustrine loess-like facies and lacustrine facies had a lower sand contents than those of the three aeolian dune sands, but have higher silt and clay contents, most of their sand content ranged from 30% to 60%, their silt contents ranged from 35% to 55%, and their clay contents ranged from 6% to 20%. The lacustrine loess-like facies and lacustrine facies formed under the influence of the warm, humid East Asian summer monsoon based on their similarity with modern sediments. The grain-size indicator Mz (mean grain diameter) and the SC/D value in the TMS5e sequence indicate climatic instability at the southern edge of the Tengger Desert during MIS5e, with at least 14 fluctuations between a warm, humid climate and a cold, dry climate, divided into five stages: TMS5e5 (139 kyr to 129.3 kyr B.P.), TMS5e4 (129.3 kyr to 124 kyr B.P.), TMS5e3 (124 kyr to 119.5 kyr B.P.), TMS5e2 (119.5 kyr to 116.5 kyr B.P.), and TMS5e1 (116.5 kyr to 113.7 kyr B.P.). These correspond roughly to MIS5e5, MIS5e4, MIS5e3, MIS5e2, and MIS5e1, respectively, in the GRIP ice core data.

Millennial-Scale Climate Variations During the MIS3 in the North Piedmontof the Kunlun Mountains, China

According to the analyses of grain size and major element distribution in the Aqiang loess section AQS3 in the north piedmont of the Kunlun Mountains in China, the peaks and valleys in the loess and loess-like sandy sedimentary facies displayed clear variations in their mean particle diameter, standard deviation, SiO2, Al2O3, TOFE (Fe2O3+FeO), and (Al2O3+TOFE)/SiO2 ratio. Both grain size and major element distributions showed 19 cycles of alternation among the sedimentary facies. Results suggested that the observed cycles mainly resulted from fluctuations between the coldarid and warm-humid climates. Most warm periods in the AQS3 corresponded well to the D/O events recorded by the ice-core oxygen isotope in the GRIP during the MIS3. This study suggests that high-frequency climatic fluctuations on millennial scale occur in the north piedmont of the Kunlun Mountains, and they are regional responses to global climate changes during the MIS3.

The climate change during early Holocene recorded by trace elements of Shenmu section, Mu Us Desert

Through nine trace elements of the Shenmu section, Mu Us Desert is analyzed for the climate changes during Early Holocene. Except Sr, a migration process of P, Mn, Cr, Rb, Nb, Cu, Zn, and V is found in the dune sands, indicating the accumulation processes of the Asian winter monsoon-driven wind erosion and transport and deposition under the cold climatic phase. And accumulation of these elements in different layers of paleo sol dune sands is related to regional geomorphology and element properties. 8.5 winter-summer monsoon cycles in the early Holocene are observed. The duration time and climate of the stronger winter monsoon phases can be compared with the cold climate in the North Atlantic and other parts of China. The result of Red fit 3.8 power spectra shows 310a, 210a, 90a, and 70a centennial cycles for the element, which are consistent with the solar oscillation cycles. These suggest that the external solar activities of the Earth may have great influences on driving the winter and summer monsoon cycles during early Holocene.

Climate changes at millennium scale in East Asian monsoon during OIS3a in Badain Jaran Desert, China

The CGS3a from the Chagelebulu section locates southeast of China’s Badain Jaran Desert. This area includes 5.5 sedimentary cycles that consist of lacustrine facies and eolian dune sands or loess during the OIS3a. Based on analyses of contents of Rb and Sr and ratios of Rb/Sr in the CGS3a, along with particle Mz (Φ) and σ, the values of contents of Rb and Sr and ratios of Rb/Sr in the dune sands or loess are lower than those in the lacustrine facies, showing 5.5 fluctuations, which are similar to the sedimentary cycles in the CGS3a segment. Therefore, the CGS3a segment reveals 5.5 warm–wet and cold–arid climate cycles that are controlled by the East Asian winter and summer monsoons in the OIS3a. This trend suggests climate changes at the millennium scale in the East Asian monsoon in the desert areas of China during the OIS3a period. Among those changes, the cold periods correspond well to the Heinrich Events, and warm periods are consistent with the Dansgaard–Oeschger events in the Greenland ice-core project. The millennium-scale climate variation in the East Asian monsoon is the actual regional response to the global climate variations during the OIS3a period.