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Striations, which are jet-like structures comprising alternating ridges and furrows within large-scale circulations, are widely studied in the open ocean, although it is unclear whether they exist in marginal or semiclosed seas. Based on an appropriate choice of averaging time scale and cutoff wavelength, our analysis reveals striations in marginal seas, including the South China Sea (SCS), Sea of Japan, and Gulf of Mexico, and in the Mediterranean Sea (MS). Compared with the open ocean, these striations have a narrower bandwidth (about 60 km in marginal seas and 100 km in the MS), fewer zonal orientations, stronger baroclinic structure, and deeper intensification. Striations in the open ocean are usually barotropic; however, within the South China Sea and MS, they are baroclinic in the upper 1,000 m and intensified at depths greater than 3,000 m.

Plain Language Summary Striped structures are common in the universe, especially in a rotating fluid from atomic to planetary scales. Examples include zonal flow in plasma, the jet stream in Earth's atmosphere, and cloud bands on Jupiter. Comprising quasi-parallel symmetrical bands, these stripes are a kind of organized structure in complex multiscale and chaotic turbulent flows. In this study, we focus on flow stripes in the ocean that comprise striations; that is, two adjacent flows moving in opposite directions. We consider smaller sea basins such as the South China Sea, the Sea of Japan, the Gulf of Mexico, and the Mediterranean Sea. Compared with the open ocean, we find that striations in these basins are narrower and more complex in their directions. This result can help us understand the diverse structures of ocean striations.