Holocene Tephrostratigraphy in the East Sea/Japan Sea: Implications for Eruptive History of Ulleungdo Volcano and Potential for Hemispheric Synchronization of Sedimentary Archives

Active volcanoes in East Asia pose potential threats to the surrounding areas. The eruptive history of many of the Japanese volcanoes are well understood, but their dispersal pathways are often based on visible tephra. Additionally, other important volcanoes in the region still require a deeper understanding of their eruptive potential. Here, we explore the Holocene cryptotephra record preserved in a marine core 13PT‐P4 in the southwestern East Sea, in order to better reconstruct past eruptive events and their dispersal. Six widespread tephra layers are identified and correlated to their source volcanoes in S Korea (Ulleungdo), China/N Korea (Changbaishan) and Japan (Kikai), with their dispersal ranges updated. Our results rank the 13PT‐P4 sequence the most intensively tephra‐constrained Holocene record in the East Sea, which permits synchronization of this mid‐latitude archive with records in the Arctic and tropical regions. Terrestrially based tephra ages are used to constrain the marine reservoir effect and the age‐depth model of the record. The average reservoir age in the region is estimated to be 1150 ± 30 14C yr at ca. 7.3–5.6 cal ka BP and 1565 ± 30 14C yr at ca. 1.0 cal ka BP. These observed changes in reservoir age could indicate active upwelling at a regional scale. Additionally, we provide a detailed age estimate and glass geochemistry for a previously poorly understood eruption (U‐1) from the Ulleungdo volcano, thus refining its Holocene eruptive history. The U‐1 eruption is dated to 3354‐3080 cal yr BP (95.4%), and has glass composition that is distinct from other Ulleungdo tephras. Plain Language Summary Explosive volcanic eruptions are one of the most important natural hazards in East Asia. The study of eruptive history and volcanic ash dispersal are the key to understand the behavior of certain volcanoes over time and to better identify the level of risk from different volcanoes. We studied the microscopic volcanic ash layers preserved in a marine core from the southwestern East Sea. Geochemical and stratigraphic evidence allow us to pinpoint the source volcanoes and eruptive events for these ash layers. The results indicate that several ash layers in the region are more widely dispersed than what we have learned from visible ash studies. We provide chronological and geochemical data for a previously poorly understood eruption from Ulleungdo volcano, S Korea, thus refining its Holocene eruptive history. We use terrestrial ages of the ash l