“Influences of temperature and the meteoric water δ¹⁸O value on a stalagmite record in the last deglacial to middle Holocene period from southwestern Japan”

Our understanding of stalagmite δ¹⁸O paleoclimate records would be significantly improved by determining the relative influence of the two factors, temperature and water δ¹⁸O. Here we apply carbonate clumped isotope thermometry to a well-dated (18.1–4.5 ka) stalagmite, Hiro-1 from Maboroshi Cave in Hiroshima Prefecture, southwestern Japan. The Δ₄₇ values from 50 stalagmite layers, calibrated using Δ₄₇-temperature relationships observed in modern stream tufa from Japan (Kato et al., 2019) yield estimates of paleo-temperature and water δ¹⁸O variability. Several layers affected by significant prior calcite precipitation under a dry climate display strong kinetic isotope influences: positive δ¹⁸O and negative Δ₄₇ deviations. Except for these layers, Hiro-1 Δ₄₇ records temperature changes that are broadly consistent with climatic stages after the last glacial maximum (LGM) to the mid-Holocene, although the significant Bølling-Allerød warming does not appear in Δ₄₇ values. The estimated temperature difference between the period after the LGM (18.0–16.0 ka) and mid-Holocene (7.7–4.9 ka) was 8.3 °C. Using Δ₄₇-temperature, stalagmite δ¹⁸O values, and change in seawater δ¹⁸O_SW, the comprehensive isotopic depletion from vapor source (seawater) to meteoric water was reconstructed. We obtained larger ¹⁸O-depletion (−9.5 to −10.0‰) in the pre-Holocene section than in the middle Holocene section (around −8.5‰). The larger ¹⁸O-depletion of the pre-Holocene period was ascribed to a larger fractionation during vapor generation under a lower temperature, change in seasonality of precipitation, or a longer vapor trajectory due to the subaerially exposed Seto Inland Sea. Unlike Chinese stalagmites, δ¹⁸O record of Hiro-1 stalagmite appear largely unaffected by rainfall amount.