Holocene terrestrialization process on the Sanjiang Plain (China) and its significance to the East Asian summer monsoon circulation.

A wide-spread terrestrialization process has been reported occurring across the Sanjiang Plain in the Holocene Epoch, while little is known for its detailed process and links to regional climate variation. Here, we present high-resolution palynological and lithological data of a peatland's sedimentary profile in the central Sanjiang Plain. The study aims to reconstruct the local terrestrialization process and discuss its significance to the Holocene East Asian summer monsoon (EASM) evolution. The results indicate that a paleolake surrounded by broadleaved forests developed during ~7.4-4.5 ka BP, corresponding to a wet and warm stage with strengthened EASM. Thereafter, a wetland dominated by Cyperaceae and Poaceae was initiated with the terrestrialization process. This process lasted until 3.9 ka BP when a lithological mud-to-peat transition occurred indicating a peatland began to develop after the extinction of the paleolake. Considering the prevalent EASM climate on the modern Sanjiang Plain, this paleolake-to-peatland transition during 4.5-3.9 ka BP was attributed to the mid-Holocene EASM retreat in addition to the paleolake's autogenic infilling process. During the peatland developing stage, four dry intervals with weakened EASM occurred in 3.9-3.2 ka BP, 2.0-1.3 ka BP, 1.0-0.5 ka BP, and 0.1-0.0 ka BP. They were alternated with three wet stages of the strengthened EASM during 3.2-2.0 ka BP, 1.3-1.0 ka BP, and 0.5-0.1 ka BP. Our findings are supported by a series of paleoclimatic records across the monsoonal regions of China. We suggest that the EASM evolution associated with the tropical ocean-atmosphere interactions was initially modulated by the solar output variation.