The Mid-Holocene climatic transition and the orbital modulation of the solar insolation

In this study,the dust flux and the content of trace metallic elements(Ti,Ni,and V) in a peat sequence from the Hongyuan Swamp(32°46.7’N,102°31.0’E) are used to reconstruct variations in the intensity of the winter monsoon during the Holocene.This record,when compared with the summer monsoon proxy from the same core,can help elucidate the phase relationship between these two systems.The proxy-based reconstructions show different patterns of the winter and summer monsoons before and after 5.5 cal ka BP.Generally,two monsoons varied reciprocally before 5.5 cal ka BP;however,after 5.5 cal ka BP,these two systems exhibit synchronous changes.Moreover,the frequency and amplitude of the variations in these two monsoons are different before and after5.5 cal ka BR The rate of changes in the solar insolation during the Holocene matches well with these monsoon records,implying that the Mid-Holocene transition may have resulted from orbital forcing.