Moisture changes in Northeast China since the last deglaciation: Spatiotemporal out-of-phase patterns and possible forcing mechanisms

There is a strong chance that the 21 st century warming will cause differences in precipitation distribution over the globe. Northeast (NE) China is a unique area whose atmospheric circulation is still a controversial subject and is likely to be strongly impacted by global warming. Thus, a good understanding of the past variations in effective moisture in NE China will be benefit for the prediction of future hydrological changes. In this study, we use basal peat ages and published paleoclimate records to evaluate the spatial and temporal patterns and possible forcing mechanisms for the moisture changes in NE China over the past 16,000 years. Basal peat ages suggest that the moisture conditions in different regions of NE China show as a spatiotemporal out-phase pattern. In addition, the paleoclimate records of 17 sites also indicate that NE China experienced a spatiotemporal out-phase pattern of moisture changes along northwest-southeast direction since the last deglaciation. The moisture in southern NE China experienced increasing trend during the period of 16-8 cal ka BP, with the maximum moisture occurring 8-3 cal ka BP and decreasing trend after 3 cal ka BP. The moisture pattern in western NE China is similar to that in southern NE China. It experienced increasing trend during the period of 16-8 cal ka BP, the maximum moisture during the period 8-4 cal ka BP and decreasing trend from 4 cal ka BP to present. The moisture in eastern NE China experienced wet conditions from 16 cal ka BP to 4 cal ka BP, and decreasing trend after 4 cal ka BP. In central NE China, two relatively wet periods occurred during the periods of 13-8 cal ka BP and 6-3 cal ka BP, respectively. In addition, two wet periods occurred during the periods of 14-11 cal ka BP and 7-1 cal ka BP in northern NE China, respectively. The moisture patterns between NE China and other regions of China are also compared in this study. We propose that the possible forcing mechanisms for the moisture changes in NE China were different for each 4000 year interval. During the period of 16-12 cal ka BP, the weak East Asian summer monsoon (EASM) and strong Northeast monsoon (NEM) were the major water vapor sources of NE China. During the period of 12-8 cal ka BP, the increasing EASM and strong NEM were still the major water vapor sources of NE China. During the period of 8-4 cal ka BP, the strongest EASM was the major water vapor sources of the whole NE China. Furthermore, the increasing Westerlies slightly penetrated into northern NE China during this period. From 4 cal ka BP to present, the decreasing EASM provided precipitation for the most regions of NE China. The Westerlies reached the maximum and further penetrated into the whole northern NE China during this period.