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

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.

Oxygen isotopes of the Japanese stalagmites as global and local paleoclimate proxies

“…The most likely interpretation is that the surface water of the Japan Sea was depleted in 18 O during the glacial period because the sea was in an isolated setting owning to the lowered sea‐level (e.g., Oba et al, 1991). Lowered salinity at the surface of the Japan Sea has been suggested by the glacial sediment, in which foraminiferal tests recorded abnormally low δ 18 O. Amekawa et al (2021) estimated that the amplitude of the δ 18 O decrease in surface water was ~3‰.…”

“…A similar δ 18 O pattern was observed in the lower part of a stalagmite (at intervals of 64-35 ka) from the Ohtaki Cave (Figure 1), Gifu Prefecture (Figure 5b). (Shen et al, 2010), (b) Hulu cave (Wang et al, 2001), and (c) Fukugakuchi cave (Amekawa et al, 2021;Sone et al, 2013). Locations of the caves are shown in Figure 1.…”

“…We used the method of Amekawa et al (2021), which is described in Figure S1 in detail. Using this method, an appropriate number of rainfall events were randomly selected from the actual dataset until the total amount of rainfall reached the range of the actual meteorological data.…”

“…This cave, in Itoigawa City is located in a heavy snowfall area, where the amount of winter snowfall far exceeds that of summer rainfall. Figure 4c shows two δ 18 O profiles from the Holocene FG01 (Sone et al, 2013, 2015) and the latest Pleistocene FG02 (Amekawa et al, 2021). The δ 18 O of FG01 varies mainly in a range of −8.5‰ to −7.0‰ (Sone et al, 2013); its profile resembles that of the intensity of the East Asian winter monsoon (EAWM) reported from the loess‐paleosol sequences of western China (Maher & Mengyu, 2006) and lake sediments of southern China (Yancheva et al, 2007).…”

“…Latest Pleistocene to Holocene records of stalagmite δ 18 O from three caves in east Asia: (a) Maborishi cave (Shen et al, 2010), (b) Hulu cave (Wang et al, 2001), and (c) Fukugakuchi cave (Amekawa et al, 2021; Sone et al, 2013). Locations of the caves are shown in Figure 1.…”