Stalagmite evidence for East Asian winter monsoon variability and 18O-depleted surface water in the Japan Sea during the last glacial period

Shota Amekawa,Akihiro Kano,Tsai-Luen Yu,Chuan-Chou Shen,Masako Hori,Kenji Kashiwagi,Hirokazu Kato,Tomomi Sone,Tomoyo Okumura

doi:10.1186/s40645-021-00409-8

Abstract

In the East Asian monsoon area, stalagmites generally record lower and higher oxygen isotope (δ18O) levels during warm humid interglacial and cold dry glacial periods, respectively. Here, we report unusually low stalagmite δ18O from the last glacial period (ca. 32.2–22.3 ka) in Fukugaguchi Cave, Niigata Prefecture, Japan, where a major moisture source is the East Asian winter monsoon (EAWM) that carries vapor from the warm surface of the Japan Sea. The δ18O profile of this stalagmite may imply millennial-scale changes, and high δ18O intervals that are related to Dansgaard–Oeschger (D–O) interstadials. More importantly, the stalagmite exhibits low overall δ18O values; the mean δ18O (− 8.87‰) is distinctly lower than the mid-Holocene mean of another stalagmite from the same cave (4.2–8.2 ka, − 7.64‰). An interpretation assuming a more intense EAWM and greater vapor transportation during the last glacial period, compared with the mid-Holocene, contradicts the limited inflow of the Tsushima Warm Current into the Japan Sea because of lowered sea level. Additionally, our model calculation using δ18O data from meteoric water indicated that the amount effect of winter meteoric water was insignificant (1.2‰/1000 mm). Low stalagmite δ18O for the last glacial period in Fukugaguchi Cave most likely resulted from 18O-depleted surface water, which developed in the isolated Japan Sea. The estimated amplitude of the δ18O decrease in surface water was ~ 3‰ at most, consistent with the abnormally low values for foraminifera (by ~ 2.5‰) in sediment during the last glacial period, shown by samples collected from the Japan Sea. This is the first terrestrial evidence of 18O depletion in Japan Sea surface water during the last glacial period.

Highlights

High-resolution isotopic records of well-dated stalagmites have been used as paleoclimatic archives in a terrestrial setting (e.g., Cheng et al 2016)
5 Conclusions Stalagmite FG02 during the last glacial period (32.3– 22.3 ka) in Fukugaguchi Cave on the Japan Sea side of the Japanese islands shows unique δ18OC trends, which have not been previously described in other caves in East Asia
An important finding of this study was that the glacial FG02 had distinctively lower δ18OC than the Holocene stalagmite from the same cave (FG01)

Summary

Introduction

High-resolution isotopic records of well-dated stalagmites have been used as paleoclimatic archives in a terrestrial setting (e.g., Cheng et al 2016). The oxygen isotope (δ18O) records of stalagmites can provide important insight into the precipitation dynamics of the Late Pleistocene and Holocene epochs. The link between climate and δ18OC has been mostly attributed to variability in the δ18O values of local meteoric water. Amekawa et al Progress in Earth and Planetary Science (2021) 8:18 from the amount effect on meteoric water δ18O (δ18OW) from the intensified East Asian summer monsoon (EASM), which controls the climate in Asia (Cheng et al 2009; Wang et al 2001, 2008). Δ18OC is seemingly synchronized with climatic changes in the North Atlantic Ocean during the late Quaternary (Cheng et al 2016; Sun et al 2012; Wang et al 2001, 2008; Zhao et al 2018). Regarding the warming transition associated with deglaciation from the last glacial period to the mid-Holocene, the stalagmites generally exhibit distinct reductions in δ18OC values, again ascribed to the intensification of the EASM

Methods

Results

Discussion

Conclusion