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

Abstract

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 δ18OSW, 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.