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The density of maar lake type peatlands in the Changbai Mountain areas, northeast (NE) China is among the highest in the world. These deposition systems include both peat and limnic deposits, providing valuable sites to study their evolutionary history shaped by their sensitivity to climate-forced state shifts. To investigate the maar lake-mire shift in response to hydroclimatic variability, we examined developmental history of the Jinchuan peatland based on sedimentary facies, grain-size, physical and chemical properites, plant macrofossils and peat basal age. The results indicate that the Jinchuan peatland mainly originated from paludification in a maar lake from approximately 7000 cal. BP. Its water level continuously increased since the Middle Holocene, reaching the peak during the period of 5000–4000 cal. yr BP. The outward expansions of Jinchuan peatland suggest a climate–driven model based on which water level variability superimposes the underlying basin morphology. The hydroclimatic variability and peatland development history can be divided into three periods. From 12 to 7 ka cal. BP, the increasing East Asian summer monsoon (EASM) was the major water vapor source of Jinchuan peatland. The strong evaporation effects induced by the strong Winter Asian winter monsoon (WAWM) and the maximum sea surface temperatures (SSTs) of Japan Sea might have changed the Jinchuan maar lake into dry upland. From 7 to 4 ka cal. BP, the maximum EASM and increasing Westerly jet (WJ) provided water vapor for the peatland. The decreasing EAWM and SSTs of Japan Sea resulted in decreased evaporation effects. The moisture and water level in Jinchuan peatland gradually increased. The peat covered 68.97% of the area during this period. Since 4 ka cal. BP, the decreased EASM and the maximum WJ provided water vapor for the Jinchuan peatland. The weak EAWM and the lower SSTs of Japan Sea induced lower evaporation effects. The moisture and water level in the peatland reached the maximum. Subsequently, peat area further expanded and covered the remaining 31.03% area. This study reveals a remarkable link between the maar lake-mire shift and hydroclimatic variability, which is significant for future prediction of maar lake-mire ecosystem shifts under global climate change. Image 1 • Jinchuan peatland developed from approximately 7 ka cal. BP to present. • Maar lake-mire transition was related to the climate-driven water level variability. • East Asian summer monsoon was the major water vapor source of NE China. • Evaporation effects are more important than precipitation in controlling the moisture changes in NE China. [ABSTRACT FROM AUTHOR]

Peatlands are one of the most significant carbon reservoirs in the terrestrial ecosystem. Understanding past peatland carbon accumulation processes and their responses to varying external and internal forcing factors would help reveal the general development patterns of peatland ecosystems and provide useful insights into projecting the fate of carbon reservoirs into the future. In this paper, the basal ages of 17 peat cores were used to explore the lateral expansion processes of the Laolike peatland, northeast China. Two cores were selected to calculate carbon accumulation rates (CAR) and reconstruct moisture/precipitation records based on δ13C and grain size analyses. The basal ages show that the peatland was initiated at 12.1 cal kyr BP, then laterally expanded with its fastest rate occurring during the early Holocene, and reached its largest area around 6 cal kyr BP. The time-weighted mean CAR in the Laolike peatland ranged from 31.1 to 52.9 g C/m2/yr (with an average of 42 g C/m2/yr) during the Holocene. The peatland experienced a high CAR of 52.5 g C/m2/yr from 11.7 to 5 cal kyr BP, followed by a low CAR of 35.1 g C/m2/yr after 5 cal kyr BP. Both lateral expansion and vertical accretion are consistent with the summer insolation, climate seasonality, and the strength of the East Asia summer monsoon (EASM) over multi-millennium timescales, where the CAR correlated well with δ13C and grain size, implying moisture/precipitation might be the primary factors controlling carbon accumulation over millennium timescales. Local conditions, such as topography and hydrology, also played an important role in the process of peatland initiation and lateral expansion, as well as the discrepant CAR within the peatland. This study reveals the roles of climate and local conditions in peatland initiation, expansion, and CAR during the Holocene. In addition, we provide a window for a better understanding of the driving factors of peatland development in the temperate zones of the Northern Hemisphere. • Climate conditions are the primary control on the lateral expansion and vertical accretion of Laolike peatland over multi-millennium timescales. • Moisture/precipitation affects carbon accumulation of Laolike peatland over millennium timescales. • Local conditions play an important role in the lateral expansion and the internal differences of carbon accumulation rate. [ABSTRACT FROM AUTHOR]