Asian Summer Monsoon-Related Relative Humidity Recorded by Tree Ring δ~(18)O During Last 205 Years

摘要

To deeply understand the Asian summer monsoon (ASM) strength variation in its fringe region,we established a 205-year stable oxygen isotope (δ~(18)O) chronology based on four individual Pinus tabulaeformis Carr. from Ordos Plateau, China. First, we found that δ~(18)O in tree rings inherits the signals of summer (June to August) monsoonal precipitation δ~(18)O (δ~(18)O_P). Second, relative humidity (RH) was observed to have a large effect on the δ~(18)O of pine trees. The tree ring δ~(18)O series significantly correlates with the observed local RH from June to August (RH_(JJA)) with r = -0.65 (N = 56, p < 0.001). The RH over Ordos Plateau is greatly influenced by ASM-related precipitation. As such, it could well reflect the variations of ASM intensity. Thus, we reconstructed the RH_(JJA) over Ordos, the center of the ASM fringe region (ASMFR), for the last two centuries. Our reconstructed RH_(JJA) series has a large geographical and spatial representativeness, which is well compared with other precipitation reconstructions in ASMFR and jointly reflects ASM variations in the past. The RH_(JJA) reconstruction showed that the 1870s-1890s were the wettest years in the entire reconstruction, while the middle-late 1920s were the driest. From 1930 to 2012,the RHof the study area continuously decreased. We found significantly negative correlations betweenRH_(JJA) and the Central Pacific sea surface temperature. This finding means that if the El Ni?o-Southern Oscillation of the Central Pacific continues to increase in the future, the aridification in the ASMFR will be intensified.