Sea of Japan

The seawater has an elevated concentration of dissolved oxygen that results in high biological productivity. Therefore, fishing is the dominant economic activity in the region. The intensity of shipments across the sea has been moderate owing to political issues, but it is steadily increasing as a result of the growth of East Asian economies.

History

For centuries, the sea had protected Japan from land invasions, particularly by the Mongols. It had long been navigated by Asian and, from the 18th century, by European ships. Russian expeditions of 1733–1743 mapped Sakhalin and the Japanese islands. In the 1780s, the Frenchman Jean-François de Galaup, comte de Lapérouse, traveled northward across the sea through the strait later named after him. In 1796, a British naval officer, William Robert Broughton, explored the Strait of Tartary, the eastern coast of the Russian Far East and the Korean Peninsula.


In 1803–1806, the Russian navigator Adam Johann von Krusenstern while sailing across the globe in the ship Nadezhda also explored, in passing, the Sea of Japan and the eastern shores of Japanese islands. In 1849, another Russian explorer Gennady Nevelskoy discovered the strait between the continent and Sakhalin and mapped the northern part of the Strait of Tartary. Russian expeditions were made in 1853–1854 and 1886–1889 to measure the surface temperatures and record the tides. They also documented the cyclonal character of the sea currents.


Other notable expeditions of the 19th century include the American North Pacific Exploring and Surveying Expedition (1853–1856) and British Challenger expedition (1872–1876). The aquatic life was described by V. K. Brazhnikov in 1899–1902 and P. Yu. Schmidt in 1903–1904. The Japanese scientific studies of the sea began only in 1915 and became systematic since the 1920s.^[13][14]


American, Canadian and French whaleships cruised for whales in the sea between 1847 and 1892.^[15] Most entered the sea via Korea Strait^[16] and left via La Pérouse Strait,^[17] but some entered and exited via Tsugaru Strait.^[18] They primarily targeted right whales,^[19] but began catching humpbacks as right whale catches declined.^[20] They also made attempts to catch blue^[21] and fin whales,^[22] but these species invariably sank after being killed. Right whales were caught from March to September,^[23] with peak catches in May and June.^[24] During the peak years of 1848 and 1849 a total of over 170 vessels (over 60 in 1848, and over 110 in 1849) cruised in the Sea of Japan,^[25] with significantly lesser numbers in following years.^[26]

The Sea of Japan was landlocked when the land bridge of East Asia existed.^[27] The Japan Arc started to form in the Early Miocene.^[28] In the Early Miocene the Japan Sea started to open, and the northern and southern parts of the Japanese archipelago separated from each other.^[28] During the Miocene, the Sea of Japan expanded.^[28]


The north part of the Japanese archipelago was further fragmented later until orogenesis of the north-eastern Japanese archipelago began in the later Late Miocene.^[28] The south part of the Japanese archipelago remained as a relatively large landmass.^[28] The land area had expanded northward in the Late Miocene.^[28] The orogenesis of high mountain ranges in north-eastern Japan started in Late Miocene and lasted in Pliocene also.^[28] The eastern margin of the sea may host an incipient subduction zone responsible for large earthquakes in 1940, 1964, 1983 and 1993.^[29]


Nowadays the Sea of Japan is bounded by the Russian mainland and Sakhalin island to the north, the Korean Peninsula to the west, and the Japanese islands of Hokkaidō, Honshū and Kyūshū to the east and south. It is connected to other seas by five straits: the Strait of Tartary between the Asian mainland and Sakhalin; La Pérouse Strait between Sakhalin and Hokkaidō; the Tsugaru Strait between Hokkaidō and Honshū; the Kanmon Straits between Honshū and Kyūshū; and the Korea Strait between the Korean Peninsula and Kyūshū.


The Korea Strait is composed of the Western Channel and the Tsushima Strait, on either side of Tsushima Island. The straits were formed in recent geologic periods. The oldest of them are the Tsugaru and Tsushima straits. Their formation had interrupted the migration of elephants into the Japanese islands at the end of the Neogene Period (about 2.6 million years ago). The most recent is La Perouse Strait, which formed about 60,000 to 11,000 years ago closing the path used by mammoths which had earlier moved to northern Hokkaidō.^[13] All the straits are rather shallow, with a minimal depth of the order of 100 meters or less. This hinders water exchange, thereby isolating the water and aquatic life of the Sea of Japan from the neighboring seas and oceans.^[30]


The sea has a surface area of about 1,050,000 km² (410,000 sq mi), a mean depth of 1,752 m (5,748 ft) and a maximum depth of 4,568 m (14,987 ft). It has a carrot-like shape, with the major axis extending from south-west to north-east and a wide southern part narrowing toward the north. The coastal length is about 7,600 km (4,700 mi) with the largest part (3,240 km or 2,010 mi) belonging to Russia. The sea extends from north to south for more than 2,255 km (1,401 mi) and has a maximum width of about 1,070 km (660 mi).^[14]


It has three major basins: the Yamato Basin in the south-east, the Japan Basin in the north and the Tsushima Basin (Ulleung Basin) in the south-west.^[13] The Japan Basin is of oceanic origin and is the deepest part of the sea, whereas the Tsushima Basin is the shallowest with the depths below 2,300 m (7,500 ft).^[14] On the eastern shores, the continental shelves of the sea are wide, but on the western shores, particularly along the Korean coast, they are narrow, averaging about 30 km (19 mi).^[30]


There are three distinct continental shelves in the northern part (above 44° N). They form a staircase-like structure with the steps slightly inclined southwards and submerged to the depths of 900–1,400 (3,000–4,600), 1,700–2,000 (5,600–6,600) and 2,300–2,600 m (7,500–8,500 ft). The last step sharply drops to the depths of about 3,500 m (11,500 ft) toward the central (deepest) part of the sea. The bottom of this part is relatively flat, but has a few plateaus. In addition, an underwater ridge rising up to 3,500 m (11,500 ft) runs from north to south through the middle of the central part.^[30]


The Japanese coastal area of the sea consists of Okujiri Ridge, Sado Ridge, Hakusan Banks, Wakasa Ridge and Oki Ridge. Yamato Ridge is of continental origin and is composed of granite, rhyolite, andesite and basalt. It has an uneven bottom covered with boulders of volcanic rock. Most other areas of the sea are of oceanic origin. Seabed down to 300 m (980 ft) is of continental nature and is covered with a mixture of mud, sand, gravel and fragments of rock. The depths between 300 and 800 m (980 and 2,620 ft) are covered in hemipelagic sediments (i.e., of semi-oceanic origin); these sediments are composed of blue mud rich in organic matter. Pelagic sediments of red mud dominate the deeper regions.^[13]


There are no large islands in the sea. Most of the smaller ones are near the eastern coast, except for Ulleungdo (South Korea). The most significant islands are Moneron, Rebun, Rishiri, Okushiri, Ōshima, Sado, Okinoshima, Ulleungdo, Askold, Russky and Putyatin. The shorelines are relatively straight and lack large bays and capes; the coastal shapes are simplest in Sakhalin and are more winding in the Japanese islands.


The largest bays are Peter the Great Gulf, Sovetskaya Gavan; Vladimira Bay, Olga; Posyet Bay in Russia; East Korea Bay in North Korea; and Ishikari (Hokkaidō), Toyama (Honshū), and Wakasa (Honshū) Bays in Japan. Prominent capes include Lazareva, Peschanyi (sandy), Povorotny, Gromova, Pogibi, Tyk, and Korsakova in Russia; Crillon on Sakhalin; Sōya, Nosappu, Tappi, Nyuda, Rebun, Rishiri, Okushiri, Daso and Oki in Japan;^[30][14] and Musu Dan in North Korea.


As world sea level dropped during the ice cap advances of the last Ice Age, the exit straits of the Sea of Japan one by one dried and closed. There is controversy as to whether or not in each ice cap advance the world sea level fell low enough for the deepest, the western channel of the Korea Strait, to dry and close, turning the Sea of Japan into a huge cold inland lake with a surface layer of fresh water, freezing over in the winters.^[31]