A Possible Interpretation For Chinese Stalagmite δ¹⁸O Records From The Observed Meteorological Data

Variability in oxygen isotope ratios collected from speleothems in the caves located in southern China is often interpreted as a proxy for variability of summer precipitation (the ratio of summer to winter precipitation), or the summer water vapor source. Some researchers argue that the winter temperature change also has strong impact on caveδ18O. Here we use the observed meteorological data and the contemporary stalagmiteδ18O records to test whether the decadal-centennial variability ofδ18O cave over southern China can be related to changes in climate. Recently published stalagmiteδ18O records from Heshang cave and Dongge cave in southern China all display gradually enriched trends during the last 50 years. During the period examined, the amount of summer precipitation and the ratios of summer to annual precipitation exhibit positive trends over the region where the caves are located. If the same seasonal moisture sources and transport pathways have prevailed in the past 50 years, a positive liner trend of the amount of summer rainfall (the ratio of summer to annual precipitation) should lead to a negative liner trend of stalagmiteδ18O values. And the results of correlation analysis between monthly summer precipitationδ18O data from seven GNIP stations indicate that most of the region's precipitation is from southwesterly water vapor fluxes for 1986-1992. The annual summer transport of water vapor to southern China is evaluated using the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis for 1951-2000. Results indicate that the same seasonal moisture sources and transport pathways have prevailed over southern China during the last 50 years. Thus, neither the change of the amount of summer precipitation, nor the variability of summer water vapor source plays an important role on the long-term increasing trend of precipitationδ18O data during the last 50 years. We calculated the linear trend through the last 50 years of temperature data for eight stations near the two caves. The results show generally positive trends (+0.03℃per decadal to+0.15℃per decadal), which may induce a positive trend in precipitation of+0.012%o per decadal to+0.105%o per decadal, consistent with the trend in stalagmiteδ18O records during the last 50 years. The enriched trend recorded in stalagmite records from southern China during the last 50 years, also expressed by the other Chinese and Oman stalagmite records, may be controlled by global warming.