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

Situated in the Salawusu River Valley, southeast of China&#39;s 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.</p

Age of the MGS5 segment of the Milanggouwan stratigraphical section and evolution of the desert environment on a kiloyear scale during the Last Interglacial in China's Salawusu River Valley: Evidence from Rb and Sr contents and ratios

The MGS5 segment of the Milanggouwan stratigraphical section in China&#39;s Salawusu River Valley records 8.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and paleosols. Based on a comprehensive analysis of the distribution of Rb and Sr within the segment and paleoecological evidence (fossils), it appears that the observed sedimentation cycles mainly resulted from fluctuations between dry-cold and warm-humid climates, which indicates that the MGS5 segment experienced at least eight cold-dry and nine warm-humid climatic fluctuations. Of these, 12 cold-warm climate fluctuations correspond to DO20-DO25 and stadia 21-26 recorded by the NGRIP ice cores. Another five cold-warm climatic fluctuations that occurred during MGS5e correspond to five substages (5e1-5e5) recorded by the GRIP ice cores from Greenland. This kind of high-frequency climatic fluctuation on a kiloyear scale was mainly subject to variations in the strength of the East Asian winter and summer monsoons.</p

Climate fluctuation on a kiloyear scale during the Late Last Glacial in Mu Us Desert, China: evidence from Rb and Sr contents and ratios

The MGS2 segment of the Milanggouwan stratigraphical section in China&#39;s Salawusu River Valley records 5.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and palaeosols. The high Rb and Sr contents and low Rb/Sr ratios in the fluviolacustrine facies indicate the presence of a warm and humid climate, and vice versa for a dry and cold climate. Rb and Sr appeared to have 5.5 element cycles that are consistent with the sedimentation changes, and each cycle lasts about 2 ka on average. This study suggests that the observed cycles mainly resulted from variations in the strength of the East Asian winter and summer monsoons, and the MGS2 segment experienced six cold-dry winter monsoons and five warm-humid summer monsoons during the OIS2. In addition, the millennial-scale monsoonal climate fluctuations revealed by the element cycles corresponded well with the Dansgaard-Oeschger cycles recorded in the Greenland ice cores and Heinrich events in the North Atlantic marine sediments. Therefore, the monsoonal climate fluctuations revealed by the Rb and Sr in the MGS2 segment were likely triggered by global climate change.</p