Evaluation of the ability of the Chinese stalagmite δ18O to record the variation in atmospheric circulation during the second half of the 20th century
The Chinese stalagmite δ18O (δ18Ocs) has provoked debate worldwide over the past few years due to its lack of quantitative calibration, leading us to questions of whether δ18Ocs records a local or large-scale signal and whether δ18Ocs records the signal of a single remote water vapor source or multiple water vapor sources. In this study, we observe all of the δ18Ocs trends within the instrumental period to verify whether they possess a common trend, which could be used as a basis to determine whether the trends reflect the large-scale signal together or whether each trend reflects the local signal. The results show that most of the δ18Ocs experienced a linear increase from 1960 to 1994, which may indicate that the δ18Ocs could record a trend occurring in large-scale atmosphere circulations. We then quantitatively describe the proportion of water vapor transport (WVT) from different source regions. Using the NCEP/NCAR (National Centers for Environmental Protection/National Center for Atmospheric Research) reanalysis data from 1960 to 1994, the ratios of the intensities of three WVTs from the Bay of Bengal, the South China Sea, and the western North Pacific during the summer are calculated. We define RSCS/BOB as the ratio of the WVT intensities from the South China Sea to those from the Bay of Bengal, RWNP/BOB as the ratio of the WVT intensities from the western North Pacific to those from the Bay of Bengal, and RWNP/SCS as the ratio of the WVT intensities from the western North Pacific to those from the South China Sea. The significant decadal increase occurs in the time series of RWNP/BOB and RWNP/SCS, most likely resulting from the strengthening of the WVT from the western North Pacific in the late 1970s due to the western Pacific subtropical high that extended westward. Further analysis indicates that when the equatorial central and eastern Pacific is in the El Niño phase, the sea surface temperature (SST) in the tropical Indian Ocean, the Bay of Bengal, and the South China Sea is high, and the SST at the middle latitudes in the North Pacific is low, then the RWNP/BOB and RWNP/SCS values tend to be high. After the late 1970s, the equatorial central and eastern Pacific have often been in the El Niño phase. Therefore, we confirm that the δ18Ocs primarily records the variation in atmospheric circulation during the second half of the 20th century.