Two modes of climatic control in the Holocene stalagmite record from the Japan Sea side of the Japanese islands

摘要

The Holocene stalagmite FG01 collected at the Fukugaguchi Cave in Itoigawa, central Japan provides a unique high-resolution record of the East Asian winter monsoon. Because of the climate conditions on the Japan Sea side of the Japanese islands, the volume of precipitation during the winter is strongly reflected in the stalagmite O-18 signal. Examination of the carbon isotopes and the Mg/Ca ratio of FG01 provided additional information on the Holocene climate in Itoigawa, which is characterized by two different modes separated at 6.4 ka. Dripwater composition and the correlation between the C-13 and Mg/Ca data of FG01 indicate the importance of prior calcite precipitation (PCP), a process that selectively eliminated C-12 and calcium ions from infiltrating water from CO2 degassing and calcite precipitation. In an earlier period (10.0-6.4 ka), an increase in soil pCO(2) associated with warming and wetting climate trends was a critical factor that enhanced PCP, and resulted in an increasing trend in the Mg/Ca and C-13 data and a negative correlation between the C-13 and O-18 profiles. A distinct peak in the C-13 age profile at 6.8 ka could be a response to an increase of approximately 10% in C4 plants in the recharge area. At 6.4 ka, the climate mode changed to another, and correlation between O-18 and C-13 became positive. In addition, a millennial-scale variation in O-18 and pulsed changes in C-13 and Mg/Ca became distinct. Assuming that O-18 and PCP were controlled by moisture in the later period, the volume of precipitation was high during 6.0-5.2, 4.4-4.0, and 3.0-2.0 ka. In contrast, the driest interval in Itoigawa was during 0.2-0.4 ka, and broadly corresponds to the Little Ice Age.