Holocene Temperature Trend Inferred From Oxygen and Carbonate Clumped Isotope Profiles of a Stalagmite Collected From a Maritime Area of Central Honshu, Japan

The Holocene has been extensively researched concerning past climates, and various proxy records have provided information on temperature changes during this period. Many studies have found a period of elevated temperatures during the Middle Holocene, known as the Holocene Thermal Maximum (HTM). However, the exact timing of this warm period varies depending on the region. Here, we investigate a stalagmite collected from Kiriana Cave, which covers two intervals: 13.7–12.4 and 10.4–1.16 thousand years ago (ka before 1950 AD). In previous studies at this cave site, the meteoric water δ¹⁸O is not sensitive to the precipitation amount and the seasonality of precipitation but follows the seawater δ¹⁸O. By using these assumptions of the meteoric water δ¹⁸O, the paleo-temperature was quantitatively reconstructed from the stalagmite δ¹⁸O and the carbonate clumped isotopes. These paleoclimatic proxies indicated that the temperature at the cave site significantly changed during the Holocene. Based on the records of the stalagmite δ¹⁸O, the HTM occurred between 10.9 and 6.7 ka, reaching its peak temperature (15.0°C) around 7.0 ka. At this time, temperatures were approximately 3°C warmer than present. The timing of the warm interval aligns closely with marine temperature records but is notably earlier than terrestrial records from Europe and North America. Cooling began at 6.5 ka, and the decreased temperature stabilized in an interval between 6.0 and 4.5 ka. The temperature decreased further to the lowest value (~10.0°C) at 3.0 ka. After this cooling maximum, the climate gradually became warm until the stalagmite stopped growing at 1.16 ka. Our Holocene temperature reconstruction is consistent with the temperature and palaeoceanographic records obtained from reef corals and marine sediments in and around the Japanese Islands in terms of the amplitude of change, warm middle Holocene, and cool late Holocene.