A snapshot of the climate in the Middle Pleistocene inferred from a stalagmite from central Japan

Stalagmites are useful archives in reconstructing paleoclimates: most paleoclimate studies used stalagmites that are distributed in specific locations and ages. We examined a stalagmite (GYM-1) collected from Nara Prefecture, central Japan, where limestone areas are limited. Applying 238U-234U method, the ages of GYM-1 were determined as 744 +/- 70 to 677 +/- 74 ka (based only on analytical uncertainties, 1 sigma). Even assuming a 10% uncertainty in the initial activity of 234U/238U, (234U/238U)0, this age could be still older than 460 ka. Temperatures calculated based on delta D in the fluid inclusions and delta 18O in the calcium carbonate ranged from 9.0 to 11.9 degrees C (10.8 +/- 0.9 degrees C on average) or from 6.0 to 9.1 degrees C (7.9 +/- 0.9 degrees C on average) depending on the equation. The estimated temperature suggests that GYM-1 formed during an interglacial period of the Middle Pleistocene. Synchronous behavior of isotopic values with lamination likely reflects seasonal temperature in a highly ventilated cave system.