Establishment of the East Sea (Japan Sea) Time-series station: an integrated physical–biogeochemical observatory for a climate-sensitive marginal sea

Long-term ocean time-series stations have significantly advanced our understanding of ocean–climate interactions, yet marginal seas remain underrepresented in global observing networks. The East Sea (Japan Sea) provides a valuable natural laboratory, characterized by rapid ventilation, oxygen-rich deep waters, and sensitivity to climate forcing. Recent evidence of weakening deep-water formation and a decline in the uptake of anthropogenic CO2 in the East Sea underscores the need for sustained, basin-scale observations to assess changes in ventilation, carbon sequestration, and nutrient cycling. Here, we present the establishment of the East Sea Time-series (EaST) station in the Ulleung Basin, with routine seasonal operations beginning in February 2026. The EaST program conducts seasonal measurements of hydrographic, chemical, and biological parameters from surface to deep waters, following international GO-SHIP and OceanSITES standards. All datasets are quality-controlled, archived, and disseminated through the Korea Oceanographic Data Center (KODC). EaST provides a sustained, multidisciplinary time-series framework in the East Sea . By establishing a long-term physical–biogeochemical baseline, the station facilitates sustained monitoring of climate-driven changes in marginal seas and supports integration of regional observations into global ocean observing frameworks.