Atmospheric Circulation,Hydroclimate Change,and Peat Accumulation Over The Last 250 Years Inferred From A Sphagnum Peatland In The Middle Greater Khingan Mountains Of Northeast China

Northeast China—located near the northern limit of the influence by the East Asian summer monsoon—receives most moisture through the westerly airflow,but variations in moisture contributions from the Yellow Sea in the western Pacific Ocean determine its hydroclimate during summer monsoon season.The proportion of moisture from the Yellow Sea is strongly modulated by the location and intensity of the Western Pacific Subtropical High(WPSH).However,it is still unclear how sensitive regional hydroclimate to WPSH-modulated change in moisture sources and its impact on peatland carbon accumulation.Here,we used peat accumulation,macrofossil data and paired?¹³C and?¹⁸O isotope analysis of Sphagnum moss cellulose from a well-dated bog from a steep mountain slope in the Greater Khingan Mountains(?47?N)to reconstruct peatland moisture changes and carbon accumulation and to elucidate past shifts in moisture sources.The main conclusions are as follow:(1)The recent rate of carbon accumulation(RERCA)in Motianling peatland was calculated to be 45-500 g C m^-2 year^-1,and the time-weighted average was 137 g C m^-2year^-1.The carbon accumulation rates show a major decrease after the 1987s—despite that more recent peat tends to have higher apparent accumulation rates—suggesting a sensitive response of this steep-slope mountain peatland to shift in regional hydroclimate in monsoon-margin region of Northeast China.(2)The peat input rate and peat decomposition rate of MTL18-C1 and MTL19-C1 peat cores in Motianling Mountain were analyzed by using the Clymo model.The peatland input rate is:362-415 g m^-2year^-1,peat decomposition rate is 0.009-0.0045 year^-1.Compared with other peatlands in high-latitudes regions,lower decomposition in Motianling peatland may be due to low temperature,at the same time increasing the possibility for organic matter preservation and peat accumulation.(3)We present a 250-year-resolution Motianling peat?-cellulose oxygen isotopic(?¹⁸O)and carbon isotopic(?¹³ C)record from a 125 cm-long peat cores(MTL19-C1)at the Motianling in the Great Khingan Mountain.The chronology of the record has been well-constrained by11 AMS¹⁴C dates of MTL19-C1.Our results from a 250-year peat record show a decrease in?¹³C—with corresponding increase in dry-adapted moss Polytrichum—suggesting a drying trend since about 1987-2019 AD?1920-1945 AD and 1830-1840 AD.By comparing with the index data of Hulunbuir area,it is found that evaporation effect has an important influence on the regional hydroclimate in Northeast China.(4)The down-core?¹⁸O and?¹³C data show a positive correlation(r=0.65,p<0.001),in contrast with evaporative enrichment of?¹⁸O being the dominant effect.We argue that?¹⁸O values reflect the input of moisture derived from the Yellow Sea—that has higher?¹⁸O values than that from the westerlies—as modulated by the WPSH.When the WPSH extends westward,it blocks moisture transport from the Yellow Sea to North China,causing low?¹⁸O values in summer precipitation,dry conditions,and negative shifts in?¹³C,and vice versa.The results show that the time when the water vapor from the Yellow Sea is more in the middle of the Great Khingan Mountains:1800-1830AD,1890-1920 AD,1960-1987 AD;Less water vapor from the Yellow Sea occurs in the middle of the Great Khingan Mountains:1750-1800 AD,1830-1890 AD,1920-1960 AD,1987-2019 AD.