Response of humification degree to monsoon climate during the Holocene from the Hongyuan peat bog, eastern Tibetan Plateau

The humification degree of peat has been used to indicate climate variations in Europe, with a dominant maritime climate. However, little research has been done so far in Asia, with a monsoon climate. Here for the first time, the absorbance value time series of the alkali-extraction of Hongyuan peat from the eastern Tibetan Plateau is determined. This is used as the proxy indicator for the humification degree of peat, and we compare it with the δ13C time series of the Carex mulieensis cellulose in the peat which has been used as a proxy indicator for the Indian Ocean summer monsoon during the Holocene. Our data show that the humification degree of peat can sensitively reflect the strength variation of the Indian Ocean summer monsoon. Both on orbital and millennial timescales, higher humification degree corresponds with stronger monsoon activity, and lower humification degree corresponds with weaker monsoon activity. The proxy-climate significance of the humification degree of the peat in the eastern Tibetan Plateau region seems to differ from that in the European continent. This difference could be attributed to the influences of local biogeochemical processes caused by the monsoon climate, including the varying combination of moisture and temperature, the alternating drying–rewetting variation, and the freeze–thaw effect.