Oxygen isotopes of the Japanese stalagmites as global and local paleoclimate proxies

Stalagmite oxygen isotopes (& delta;O-18) have been used to reconstruct terrestrial paleoclimates during the late Pleistocene and Holocene. However, the interpretation of the & delta;O-18 is not straightforward when determining the factor controlling & delta;O-18; temperature or water & delta;O-18. In addition, the water & delta;O-18 changes with rainfall intensity (amount effect), rainfall seasonality, and some other factors. Here, we first review the hydrochemical processes and behaviors of the oxygen isotopes and the other proxies in a cave system, which are fundamental for interpretating the paleoclimatic signals. We then introduce the oxygen isotope records of Japanese caves. Some of the Japanese stalagmites demonstrated a & delta;O-18 profile that represented a similar pattern to the Chinese stalagmite records, but had relatively small & delta;O-18 amplitudes, which can be explained mainly by temperature changes rather than the amount effect. This demands a reversal of the relationship between climate and rainwater & delta;O-18 across the Japanese Islands. Using & delta;O-18 data for rainwater samples from four sites in Japan (in Niigata, Fukuoka, Gifu and Mie Prefectures), we presents the results of model calculations to verify how the rainfall intensity and the seasonality relate with the & delta;O-18 of rainwater. A significant correlation coefficient was observed in Niigata, where the rainfall & delta;O-18 decreases with an increase in the annual amount of rainfall, and with a decrease in the winter rainfall. Similar trends were observed in Fukuoka, whereas while the results of Gifu and Mie exhibited no significant trends. Temperature change was would be the main factor controlling the stalagmite & delta;O-18 at the latter two sites. For a better understanding of the stalagmite & delta;O-18 records, the measurement of fluid inclusions and carbonate clumped isotopes can be used to evaluate the effect of temperature on the stalagmite & delta;O-18, as well as to reconstruct the water & delta;O-18. We predict that the O-17 excess in stalagmites reconstructs the seasonal shift in the vapor sources.