Unusual changes in East Asian winter monsoon during MIS ۸ as recorded in Chinese loess and the implications for ice age dynamics

One of the basic shapes of the marine ۱۸O records of the last million years is “saw-toothed” form, characterized by the gradual cooling to full glacial conditions and then terminated by very rapid deglacial transitions. Understanding such a basic shape is crucial to improve our knowledge of global glacier dynamics. In this study, we present high-resolution grain-size and magnetic susceptibility records of East Asian monsoon from three typical loess-paleososl sections in central and western Loess Plateau, and make an integrated study on global terrestrial and marine records, to understand the regional and global implications of abnormal MIS ۸-۷ monsoonal climate. The result show grain-size records of East Asian winter monsoon (EAWM) from all the three sections exhibit a weakening trend through MIS ۸, interrupted by a low-amplitude strengthening in a very short interval corresponding to MIS ۸.۲. It is well known that variations in Northern Hemisphere ice sheets influence the Siberian High (an atmospheric pressure system), so variations in the EAWM can serve as a useful proxy of Arctic climate variability. We argue that the weakening trend of EAWM through MIS ۸ reflect trend of shrinkage of Arctic toward the termination, contrast with the trend indicated by the ۱۸O. To confirm this, we make an integrated study on the global paleoclimate records. The results show that there are numerus limes of evidence distributed from high-northern latitudes to middle-southern latitude to support our inference. We also find that it is the Antarctic Bottom Water (AABW) sourced from the sinking water around the Antarctica that leads to “abnormal changes” in deep water of the global ocean. In other words, the changes in ۱۸O during the MIS ۸ wasserious overprinted by signals of the deep-sea temperature. Our above explanations are supported by alignment of obliquity and local precessional summer insolation maxima in both Polar regions. Our results highlight the complexity of global paleoclimate reference curve of benthic ۱۸O, and need a multidisciplinary study on MIS ۸ to understand the high-latitude forcing from both Polar Regions and how they interact in modulating the buildup of the ice sheets and the deglacials.

کلیدواژه ها:

East Asian winter monsoon ، MIS ۸ ، Galcial climate trend ، Sourthern forcing ، Saw-toothed form