Multi-proxy Reconstruction of Holocene Tsunami Events (TE2 and TE3) in a Coastal Lagoon, East Sea: Evidence for High-Energy Inundation and Volcanic-related Hazards

This study reconstructs the provenance and physical intensity of paleo-tsunami events by integrating organic microfossils, palynofacies, geochemical (coreXRF), and microbial eDNA analyses from core 20HH01, retrieved from Lagoon Hyangho on the eastern coast of Korea. While previous research identified Tsunami Event 1 (TE1, ca. 8.3 ka) linked to Ulleung Island’s volcanism, this study focuses on Tsunami Event 2 (TE2, ca. 6.5–7.8 ka) and Event 3 (TE3, ca. 0.3–2.5 ka), which exhibit distinct paleoenvironmental proxies.

TE2 is interpreted as one of the highest-energy tsunami inundation events recorded in the East Sea coastal region. This interval is characterized by a pronounced increase (>50%) in marine palynomorphs, including dinoflagellate cysts (Spiniferites spp.) and foraminiferal organic linings. Palynofacies analysis reveals poorly sorted, lath-shaped phytoclasts with low roundness, indicating rapid, high-energy landward sediment transport. A marked decline in pollen concentration is interpreted as a dilution effect caused by the rapid deposition of coarse sediments rather than regional vegetation collapse.

For TE3, we propose a novel geochemical and microbial linkage to volcanic activity at Mt. Baekdu. The sediment layer corresponding to the 946 CE “Millennium Eruption” exhibits a distinct enrichment in gallium (Ga) and elevated Ga/K ratios (exceeding 1.5 times background levels), coincident with the detection of the deep-sea hydrothermal bacterium Sulfurimonas f. These observations suggest a potential hazard cascade in which seismic disturbances associated with the Baekdu eruption may have triggered submarine mass failures and subsequent tsunami generation, while concurrently dispersing Ga-rich tephra across the East Sea.

Overall, this study highlights the value of coastal lagoon sediments as high-resolution archives of regional geohazards. The integration of microbial tracers and geochemical fingerprints, particularly Ga-based proxies, provides a robust framework for deciphering the origins and mechanisms of enigmatic paleo-tsunami events.