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A comprehensive and integrative view of East Asian monsoon evolution during the Holocene is still under debate, and additional high-resolution proxy records from climatically sensitive locations are requisite to solve this complex issue. In this paper, we present three well-dated mud/peat cores from a paleo-pingo depression in the Sanjiang Plain, a climatically sensitive region to monsoon variation, to reveal the paleoenvironmental history of the wetland and discuss the regional impacts from monsoon evolution. A paleolake developed in the study area before 5.5 ka BP, and a peatland initiated thereafter consequent upon the gradual shrinking of the paleolake. This transition lasted until 4.5 ka BP, when the paleolake changed entirely to a wetland. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest that the lake-to-wetland transition from 5.5 to 4.5 ka BP indicates a rapid decline of the East Asian summer monsoon in addition to autogenic basin infilling processes. Such a remarkable monsoon weakening event has been documented across northern China, and we associate this with ocean–atmosphere interactions throughout low-latitude regions. [ABSTRACT FROM AUTHOR]

The Sanjiang Plain (SJP) wetland is the largest freshwater marshland in China. Peatlands were initiated early and are widely distributed across the SJP and form a large carbon (C) pool. Consequently, there is a growing interest in understanding past, present, and future peatland dynamics. Most studies on peatland dynamics have been carried out on boreal and subarctic region; however, there are limited data about peatland dynamics on temperate region, such as SJP wetland, which is sensitive to climate change and human disturbance. Here, we presented a data synthesis of basal peat ages, peatland area, and peat C accumulation rate in the SJP to examine Holocene peatland dynamics and climate sensitivity, along with total C storage and their future fate. We show that peatland initiation in the SJP started in the early Holocene, but the most intense period of peatland initiation occurred during the late Holocene, when the climate was colder and drier than the early and mid-Holocene. And the C accumulation rate also continued to increase during the late Holocene. Our results suggest that insolation and monsoon intensity as well as the local topographic characteristics and hydrology during the late Holocene in the SJP might have played an important role in causing the highest rates of peatland initiation and C accumulation. Based on the Second National Wetland Resources Survey data, we estimated that the total peatland covered an area of about 10,520 km2 on the SJP and currently stores ~0.26 Pg C. However, human activities, together with the widespread warming on the SJP over the past 60 years, not only reduce the area of wetlands but also have switched it from being a net C sink to a significant C source. [ABSTRACT FROM AUTHOR]