Specific climatic signals recorded in earlywood and latewood δ18O of tree rings in southwestern China

Earlywood and latewood form during different parts of the growing season and therefore capture climate of distinct time intervals. Here we present a comparison of earlywood and latewood δ18O in tree rings from the Yulong Snowy Mountains of southwestern China, covering the period from 1902 to 2005. Earlywood and latewood δ18O exhibit different long-term behaviour obviously during the past century. Climate–response analysis indicates that the dominant parameters for earlywood δ18O are temperature and relative humidity during the early part of the monsoon season (May to July); however, for latewood, it is the moisture condition (precipitation and relative humidity) from August to October. Sea-surface temperatures over the Indian Ocean and the Pacific Ocean have imprinted their different influences on the earlywood and latewood δ18O. The δ18O of source water were reconstructed from the earlywood and latewood δ18O. We found that the source of the water synthesised into earlywood was mainly contributed by current precipitation, while for latewood it is more complicated. The signals from the Indian Summer Monsoon and the East Asian Summer Monsoon are temporally superimposed (though differently) on the source water of earlywood and latewood, as well as the El Ni o–Southern Oscillation events.