West Sea
Overview
West Sea (Seohae, 서해) is a sea area located west of the Korean Peninsula, called the Yellow Sea (Hwanghae, 황해) in China. To the north it connects with Bohai Bay, enclosed by the Liaodong Peninsula and Shandong Peninsula, and to the south it is separated from the East China Sea by a line connecting the southern tip of Jeju Island and the Yangtze River estuary. It is a broad continental-shelf sea with an average depth of only 40–50 m; its tidal range is among the world's largest, and it is rich in tidal flats and fishery resources, and is a place where the political, economic, and military interests of South Korea, China, and North Korea intersect.
Main Content
Geography and Topography
The West Sea is a semi-enclosed sea surrounded by land, with an area of about 380,000 km². The seabed has a widely developed continental shelf, making the topography gentle, and even the maximum depth is only around 100 m in the area south of Jeju. The west coast of the Korean Peninsula is a ria coast with severe indentation and many bays, and large and small islands and peninsulas such as Ganghwado, Anmyeondo, Byeonsan Peninsula, and Jindo are connected. Because of the large tidal range, extensive tidal flats have developed, and the tidal flats on the west coast of Korea are counted as one of the world's five major tidal flats. In 2021, 'Getbol, Korean Tidal Flats' was inscribed as a UNESCO World Natural Heritage site.
Tides and Currents
The West Sea is one of the sea areas with the largest tidal range in the world. In the waters off Incheon, the tidal range exceeds 9 m during spring tides, and tidal currents are fast. Water temperature varies greatly by season, rising from 3–5°C in winter to over 25°C in summer. Several water masses, including the Yellow Sea Warm Current, Chinese coastal water, and Yellow Sea Bottom Cold Water, interact, and sea fog frequently occurs in spring and summer, becoming a risk factor for ship navigation.
Ecosystem and Fishery Resources
Tidal mixing is active, so nutrients are abundant and productivity is high. Croaker, hairtail, blue crab, octopus, Manila clam, and shrimp are caught, and laver, wakame, and oyster aquaculture are active. Cheonsu Bay, the Geum River estuary, and Suncheon Bay are migratory bird habitats where endangered species such as the black-faced spoonbill and Eurasian spoonbill live. Tidal flats serve as a treasure trove of benthic organisms and a key buffer zone for coastal ecosystems.
History and Culture
Since ancient times, it has been a maritime transport route linking the Chinese mainland and the Korean Peninsula. Cheonghaejin of Jang Bogo during Unified Silla and the grain-tax transport routes used the West Sea, and during the Imjin War it was the stage of the naval battles of Myeongnyang and Uldolmok. After Incheon opened as a port in 1883, modern port cities grew. Intangible heritage such as fishing village culture based on tidal flats and croaker fishing, boat songs, and rites for abundant catches also remains throughout the West Coast.
Economy and Sea Routes
Incheon Port, Pyeongtaek–Dangjin Port, Gunsan Port, and Mokpo Port are close to ports along the Chinese coast and serve as major corridors for container, automobile, and petrochemical cargo. Large bridges such as the Seohae Bridge and Incheon Bridge cross the sea, and large-scale offshore wind farms are being promoted in areas such as Sinan and Buan.
Maritime Jurisdiction and Issues
Tension over the Northern Limit Line (NLL) in the West Sea has continued between South and North Korea. Military clashes have been repeated, including the 1999 and 2002 Yeonpyeong naval battles, the 2009 Daecheong naval battle, the 2010 sinking of the Cheonan and the shelling of Yeonpyeong Island. Between South Korea and China, negotiations on delimiting the boundary of the exclusive economic zone (EEZ) have continued since 2015 but have not been concluded, and conflicts remain over Ieodo (Socotra Rock) and the provisional measures area. Illegal fishing by Chinese fishing vessels and clashes during enforcement have long been pending issues.
Recent Developments
In 2024–2025 as well, the South Korea–China EEZ boundary delimitation negotiations continue working-level consultations without clear progress. In the process of enforcing illegal fishing, collisions and accidents involving fishing vessels have repeatedly occurred, and stronger responses by maritime police and fisheries guidance ships are being discussed. Large-scale offshore wind projects in the West Sea EEZ (such as the Sinan Ui and Anma complexes) are in a phase of slowed progress due to conflicts with fishermen's fishing areas and grid connection problems. With inter-Korean relations strained, discussions on establishing a peace zone in the West Sea have effectively stopped, and tensions near the NLL continue. Meanwhile, as water temperatures rise due to climate change, the appearance of subtropical fish species and ecological changes in tidal flats have been observed, and the designation of the West Coast tidal flats as a national marine ecological park and strengthening of the World Heritage management system have also emerged as major agenda items.
Related Topics
- [[Yellow Sea]]
- [[Tidal flat]]
- [[Northern Limit Line]]
- [[South Korea–China Fisheries Agreement]]
- [[Ieodo]]