Atmospheric circulation, hydroclimate change, and peat accumulation over the last 250 years inferred from a Sphagnum peatland in the southern 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 macrofossil data and paired δ¹³C and δ¹⁸O 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 elucidate past shifts in moisture sources. δ¹³C values reflect peatland surface moisture, as dry conditions with less water film effects would increase isotopic discrimination against ¹³C and result in lower δ¹³C values. Our results from a 250-year peat record show a decrease of ~3‰ in δ¹³C from -25 to -28‰—with corresponding increase in dry-adapted moss Polytrichum—suggesting a drying trend since about 1980 AD. Also, the down-core δ¹⁸O and δ¹³C data show a positive correlation (r = 0.65, p < 0.001), in contrast with evaporative enrichment of δ¹⁸O being the dominant effect. We argue that δ¹⁸O values reflect the input of moisture derived from the Yellow Sea—that has higher δ¹⁸O 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 δ¹⁸O values in summer precipitation, dry conditions, and negative shifts in δ¹³C, and vice versa. Furthermore, carbon accumulation rates show a major decrease after the 1980s—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.