Shuhuan Du

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.

Carbonate formation mechanism in paleosol sediments of the Bohai Sea coastal zone, China

The Bohai Sea coastal zone of China consists of the Pacific Ocean to the east and Eurasia to the west; hence, this region is influenced by both the ocean and continental landmasses. The carbonate formation mechanism of eolian sediment within this area is poorly understood. The loess-paleosol sediments of the Miaodao stratigraphical section (MDS) contain a record of carbonate changes in this region during the last interglacial period. New insights into regional carbonate formation mechanisms since the last interglacial period were obtained by analyzing the ages of various sedimentary facies in combination with proxy paleoclimatic indices (including average grain size, standard deviation, CaCO3 content, and clay minerals), as well as via foraminiferal analysis. The results led to three principal findings: (1) The carbonate content change in the MDS was neither controlled by grain size nor affected by minerals. The carbonate change controlled by precipitate leaching in the Loess Plateau region cannot explain the eolian sediments within the Bohai Sea coastal zone. (2) Various subsections contain obvious carbonate content changes caused by foraminiferal deposits atop the eolian sediments, which were deposited by storm surges during a high sea-level period. This increased the carbonate content in the eolian sediments and restricted the carbonate content in the Bohai Sea coastal zone. (3) Newly detected foraminifera of the last interglacial period on the eolian sediment of the MDS were the main source of carbonate content, providing a new understanding of the carbonate formation mechanism in eolian sediments different from that of the Loess Plateau.

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.