Mid-Holocene pine forest expansion caused by the weakening of the East Asian winter monsoon and linked to climate change in the North Atlantic region

The East Asian winter monsoon (EAWM) system is one of the most active components of the global winter atmospheric circulation, and it has a major impact on the Eurasian climate in winter. However, relatively few proxy indicators are available to reconstruct the past evolution of the EAWM. Based on the physiology and modern distribution of the temperate forest and boreal forest in Northeast Asia, we found that the northern boundary of temperate pine forest is sensitive to winter temperature and thus it can be used as a proxy for EAWM intensity. A Holocene pollen record from Lake Woniupaozi in Northeast China shows that an expansion of temperate pine forest since -6.0 ka cal BP was linked to a weakening of the EAWM. This pattern is consistent with other paleoclimatic records from Northeast Asia and elsewhere, including the North Atlantic region, Middle East, Arabian Sea, and the Tibetan Plateau/Southwest China, which suggests a major climatic transition in the mid-Holocene. The mechanism responsible for this teleconnection may have been the continuous melting of the Laurentide ice which lowered the SST in the North Atlantic and maintained the North Atlantic Oscillation (NAO) in a positive winter phase. This influence was subsequently transmitted from the North Atlantic region to Eurasia via the winter southern Eurasian (SEA) teleconnection.