East Asian monsoon climates and Gobi dynamics in marine isotope stages 4 and 3

Abstract

Several thick last glacial loess sequences in the western part of the Chinese Loess Plateau and an eolian–colluvial sequence in the central Mongolian Plateau are used to understand how the summer and winter monsoons responded to global forcing factors during marine isotope stages (MIS) 4 and 3. The magnetic susceptibility data are compared with other climatic proxy data to improve the well-publicized reconstruction of the past monsoons. This study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages, which were characterised by cold and wet climates in the western part of Chinese Loess Plateau. After forest–steppe in MIS 5, coniferous forest emerged at the MIS 5/MIS 4 transition in cold and moist conditions. These imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior, and that the Mongolian High became dominant when the northern insolation entered a stadial state (MIS 4). Coniferous forest dominated MIS 4, but thereafter deteriorated to a steppe towards the end of the MIS 4, probably because the lower latitude oceans failed to supply water vapour to the interiors. A coniferous forest emerged again at the MIS 3/MIS 2 transition after forest–steppe in MIS 3. Consequently, the southern boundary of the Gobi Desert retreated northwards during the coniferous tree-dominated periods between 73 and 60 ka and between 27 and 19 ka, and expanded to maxima between 60 and 50 ka and between 19 and 10 ka. The extent of the Gobi Desert was considerably smaller for several times (around 47 ka and 41 ka, and 27+ ka) during MIS 3 than during the Holocene, and the northern boundary retreated 5 times (around 20 ka, 24 ka, 29 ka, 31 ka, and 34 ka) in just the later part of MIS 3.