The Asian monsoon system,composed of the Indian and East Asian mosoon subsystems,is a dynamic component of the modern and paleoclimate system.Studies of different influence extent of solar radiation and coupled atmosphere-ocean system to Asian monsoon subsystems still remain complex.Some stuidies indicated the inverse phase variations between the Indian and East Asian mosoon,which is different to most of monsoon proxies results.Understanding the interactions among them and their sensitivity to internal feedback mechanisms requires high resolution proxies of monsoon climate. Qingtian Cave(110°22′E,31°30′N,1 630m above sea level) is located almost at 10 km NW apart Muyu Town,Shengnongjia Natural Reserve,Hubei Province.Here,most of peaks are higher than 1500 m and generally become lower from SW to NE.Mean annual precipitation and temperature are 1 500-2 000mm at 1 500-2 000 m above sea level and 15.5℃ in the cave(measured in Sep.2004).Two samples for ICP-MS dating were conducted in the Isotope Laboratory of Geology and Geophysics Department,Minnesota University,USA.The reported error is in 2σ.A total of 183 samples for δ18O measurements have been analyzed with on-line automated carbonate preparation system(KIEL CARBONATE DEVICE) linked to Finnigan MAT-253 ratio mass spectrometer at Isotope Laboratory of College of Geography Science,Nanjing Normal University.Reference standards have been used to ensure a precision better than 0.06‰ and results were reported to PDB standard. A 3-year-resolution stalagmite oxygen-isotope record from Qingtian Cave has been established based on 230Th dates and results of annual band-counting.The variation of oxygen isotope ratios with time,with amplitude as large as 1.8‰ in δ18O,reflects changes in the amount of monsoon precipitation for the period from 6.7 to 6.1 ka B.P.This high temporal resolution δ18O series enables us to reconstruct decadal-centennial scale variation of East Asian monsoon intensity persisting about 580 years in Mid-Holocene. Comparison of the stalagmite δ18O time series between QT9 from Qingtian Cave and Q5 from Oman,shows the close relationship on multi-decadal to centennial variations in monsoon precipitation,indicating that the East Asian monsoon intensity is in phase with Indian monsoon.This observation suggests that Indian and East Asian monsoons,two sub-systems of Asian Monsoon system,are controlled by common forcing mechanisms.Consequently,these two climate subsystems may be influenced by large scale water transporting from Indian and Pacific Ocean,reflecting the integrated Asian land,ocean and atmosphere interacting system.A comparison between the stalagmite δ18O record and tree-ring 14C provides strong evidence for solar forcing of East Asian monsoons on centennial even multi-decadal time-scales.Results of spectrum analysis of the stalagmite δ18O indicate statistically significant periodicities centered at 163,81,16 and 11 years.The 163-year cycle is close to the 148 years periodicity of the tree-ring 14C records,while 81 and 11 years are similar to Gleissberg and Sunspot periodicities respectively.This statistic analysis further reinforces our interpretation for the solar forcing of Asian monsoon.
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