Satellite Altimetry Reveals Spatially Heterogeneous Sea-Level Rise, Mesoscale Variability, and Increasingly Frequent Extremes in the East Sea (Sea of Japan), 1993–2024: Dokdo in Regional Context

Abstract

The East Sea (Sea of Japan) is a semi-enclosed marginal sea with an energetic mesoscale eddy field along the Tsushima Warm Current and its subpolar front. Unlike prior point reconstructions of Dokdo sea level, we use 0.125° gridded satellite altimetry (DUACS, 1993–2024) to map the spatial structure of the basin’s rise, its variability, and its extremes. The basin-mean rise is 4.1 ± 0.5 mm yr−1, heterogeneous (1.6–6.6 mm yr−1) yet significant across essentially the entire basin, and fastest along the East Korea Warm Current and in the Ulleung Basin at Dokdo. With the trend removed, the leading mode of variability is basin-coherent, concentrated over the southern eddy-energy maximum, and only weakly related to remote climate modes or local wind stress (R2 ≤ 0.08). Extreme high sea-level days, counted against a fixed 1993–2002 95th-percentile threshold, rose roughly sevenfold (4.9 ± 1.0 days yr−1), an increase driven by the rising mean rather than by a broadening of the daily distribution, though the multiplication factor is sensitive to the threshold definition (three- to twenty-eight-fold) and reflects open-water exceedance rather than coastal flooding frequency. The altimetry agrees with open-water tide gauges (mean r = 0.83) and an in situ Dokdo bottom-pressure record (r = 0.88), and a steric/non-steric decomposition shows that Dokdo’s coherence with the basin is dynamic rather than thermal. These results reframe Dokdo sea level as an expression of regional warm-current and eddy dynamics relevant to coastal-hazard exposure.