Pollen-recorded bioclimatic variations of the last similar to 2000 years retrieved from Bayan Nuur in the western Mongolian Plateau

摘要

The palaeoclimatic variations during the past 2000 years in western Mongolia were reconstructed using a high-resolution pollen sequence obtained from Bayan Nuur. The pollen-based mean annual precipitation (MAP) from Bayan Nuur and the tree ring-based temperature anomalies from the nearby Altai Mountains exhibit a 'warm-dry' Roman Warm Period (RWP; 1900 to 1500 cal. a BP), a 'cool-wet' Dark Age Cold Period (DACP; 1500 to 1150 cal. a BP), a 'warm-dry' Medieval Warm Period (MWP; 1150 to 800 cal. a BP) and a 'cool-wet' Little Ice Age (LIA; 800 to 100 cal. a BP). Nevertheless, the Current Warm Period (CWP; since 100 cal. a BP) is an exception that fits a 'warm-wet' mode. A more detailed comparison between the pollen-based MAP curve and the North Atlantic Oscillation (NAO) index curve suggests that the higher-precipitation episodes generally corresponded with more negative NAO episodes. The chronological correspondence between the higher-precipitation episodes and the more negative NAO episodes means that more Atlantic storm tracks originated from the southern part of the North Atlantic Ocean and also from the Mediterranean Sea during negative NAO episodes. It implies that the precipitation variations during the past two millennia have been modulated primarily by NAO variations and negatively phased NAO settings contributed to more winter precipitation in Bayan Nuur basin.