## 5 Discussion  
In this study, we characterized the B-KY1 tephra between the Toya (ca. 106 ka) and Aso-1 (ca. 255 ka) tephras in the ODP 794A core, which was collected from the Japan Basin of the East Sea/Japan Sea. Stratigraphically, the B-KY1 tephra is located between underlying DLM and overlying LBM (Figure 4C), in exactly the same stratigraphic position as the B-KY1 tephra that was first identified in the 20 EEZ-1 core from the Kita-Yamato Trough (Figure 9). A pale brown B-KY1 tephra in the ODP 794A core showed a wide range of SiO\({}_{2}\) (66.59-75.36 wt.%), Al\({}_{2}\)O\({}_{3}\) (9.17-15.76 wt.%), CaO (0.21-1.09 wt.%), Na\({}_{2}\)O (4.23-5.47 wt.%), and K\({}_{2}\)O content (4.18-5.35 wt.%), and high FeO\({}^{\star}\) content (5.20-6.05 wt.%). In the B-KY1 tephra, high SiO\({}_{2}\) content was correlated with less Al\({}_{2}\)O\({}_{3}\), CaO, and Na\({}_{2}\)O, and slightly more FeO\({}^{\star}\) (Figure 7C). The elevated FeO\({}^{\star}\) content remains open to interpretation. However, the geochemical characters of B-KY1 tephra in the ODP 794A core distinguished it from Aso-4 (88 ka; Figure 5D), Toya, and Aso-1 tephras, which erupted from Japanese volcanoes (Figure 6). The B-KY1 tephras from the ODP 794A and 20 EEZ-1 cores showed different textural characteristics (Table 1). To the south of Baekdusan, mixtures of coarse-grained pumice shards and bubble-wall shards were transported to the 20 EEZ-1 coreing site of the Kita-Yamato Trough. In the B-KY1 tephra layer of the ODP 794A core, relatively fine-grained bubble-wall shards were dominantly transported to the north of Baekdusan, perhaps reflecting changing wind patterns during the late Middle Pleistocene B-KY1 Baekdusan volcanic eruption. Shifts in wind direction can influence the distribution of tephra during its long-range transportation by explosive volcanic eruption [44]. Density separation due to greater distance from Baekdusan may also have contributed to the distribution pattern of B-KY1 tephra in the East Sea. Previous studies have concluded that explosive volcanic eruptions of Baekdusan are  
Figure 8: Major element variation diagram of B-KY1 tephra in the ODP 794A core and other Baekdusan tephra samples (Data from [2, 16, 17, 18, 20, 23]). (**A**): Ca versus FeO\({}^{\star}\), (**B**): Al\({}_{2}\)O\({}_{3}\) versus FeO\({}^{\star}\) (Peralikine classification diagram adapted from [41]). caused by comendite or comendite trachyte magma [1; 2; 8; 18], whereas B-KY1 tephra in the ODP 794A core originated from comendite, comendite trachyte, and pantelleritic magmas (Figure 8B). The high SiO\({}_{2}\) content (>72 wt.%) of B-KY1 tephra in the ODP 794A core was correlated with lower Al\({}_{2}\)O\({}_{3}\) content (9.17-11.86 wt.%), indicating the presence of pantelleritic magma. However, B-KY1 tephra in the 20 EEZ-1 core was composed of comendite and comenditic trachyte magma, without pantelleritic magma (Figure 8B). This wide range of magma types may be the results of a compositionally zoned magma chamber [44; 45] or magma mixing/mingling [44; 46; 47]. Pumices in the Upper Pollara eruption in Italy showed a heterogeneous SiO\({}_{2}\) composition (61-76 wt.%) due to mixing/mingling of andesite and rhyolite [46]. Even magma mixing between two andesite magmas can cause light and dark volcanic glass, the former having greater SiO\({}_{2}\), K\({}_{2}\)O, and FeO* content, and less CaO and Al\({}_{2}\)O\({}_{3}\)[47]. Recently, zircon isochron ages from Holocene pyroclastic deposits on Baekdusan suggested the occurrence of episodic magma generation at 110-130 ka and > 230 ka [11; 27; 28]. This indicates subsequent mixing of comendite and comenditic trachyte magma with injected pantelleritic magma during the late Middle Pleistocene Baekdusan volcanic eruption. In the present study, we compared sedimentary facies against eusstatic sea level fluctuation records to refine the eruption age of B-KY1 tephra. X-radiographs of DLMs in the 20 EEZ-1 core reflect  
Figure 9: Improved eruption age estimate (ca.